The answer is in thermodynamics and kinetics. These two are arguably the most important concepts to grasp in chemistry.

But sometimes, even after several years of basic chemistry education, it is not easy to form a clear picture on how they govern reactivity!

Tutorial Review: Contents and Introduction

In this tutorial, we will try to introduce and summarize what these two concepts are, and their implications in chemical reactivity. This is obviously an introduction, intended for chemistry students of all levels.

For sure, there are more comprehensive explanations out there, and if you want one, go grab any of the best-known general chemistry books, or a more specific organic chemistry textbook. However, we have found that there are not many short explanations out there available for the general scientific public. This is somehow worrying, since, without a basic understanding of thermodynamics and kinetics, there is no way to understand the basic principles of reactivity. And without understanding reactivity, you are missing out on the most important part of chemistry.

But if you really want to dive on physical chemistry concepts as such, unfortunately you will find that most books can be impenetrable without a basic understanding of maths, physics and chemistry itself.

This is what we want to fix with this short tutorial. To give you a general overview on why chemical compounds react. We want to break the gate-keeping that has always been going on with physical organic chemistry!

As mentioned, this is intended to be brief. We will start off with the basic definitions, and hopefully make you go all the way through to understanding free-energy profiles of catalytic reactions.

Interested yet? Keep reading!

• A quick disclaimer: Since my background is in organic chemistry, I will base the explanations on simple organic chemical reactions, but most of the general principles apply to any kind of chemical reactivity.
• For most energy diagrams, the energy values are orientative, made up in order to explain the concepts.

Thermodynamics: The Energetic Stability of Molecules

Thermodynamics is the branch of physics that deals with heat, work and temperature, and their relation to energy, radiation, and physical properties of matter.

That is the definition of thermodynamics. As you can see, it is an incredibly broad concept. Let’s forget about it for now. How does thermodynamics dictate why do chemicals react?

Well, imagine every different molecule having an associated value for energy.

Some molecules will have larger energies and some others lower energies. Then consider that every chemical system has the tendency to go towards the point of lowest energy possible, in effect, the most stable point. This means that a molecule with high energy (less stable) will have a tendency (or “will want to react”) to transform into another molecule with lower energy (more stable).

Why is that? Because the process of going from a high energy state to a lower energy state releases energy, or heat, in what is called an exothermic process. This is what we call a thermodynamically-favored process, and it is basically what the laws of thermodynamics are telling us.

Thermodynamic Stability in Energy Diagrams

This is easier than it might sound. The image below illustrates what you just read. Molecule A can react in two ways: Absorbing heat it can be transformed into 1. Alternatively, it can evolve into 2 by releasing energy, in a thermodynamically-favorable manner. Of course, if these were the only two possible scenarios, all molecules of A would react to give 2, and stay there forever. But the picture is usually not that simple, and we will come back to this later.

You might be looking at the picture above and still not get what we mean by higher or lower energy. Let me redraw it in a way you will probably have seen elsewhere, or been taught in school/college:

The scheme above resembles what you are always taught in introductory organic chemistry courses: more substituted isomers of alkenes are more stable (A and 2 vs. 1) and trans isomers are more stable than cis isomers (2 vs A).

What does this means? It means that, given the appropriate circumstances or conditions, both 1 and A would like to react to give 2. But we now that less stable alkenes such as 1 are perfectly inert, and can be handled and stored without worries. So, what is the deal here?

The answer is kinetics and activation barriers.

Kinetics: The Barriers of Chemical Reactivity

Before diving into kinetics, let me present another quick example of a thermodynamically-favorable process. An energy diagram of an Sn2 substitution reaction in this case.

As you can see, if we set the zero in energy for a hydroxyde anion plus a chloromethane molecule (in energy diagrams you always set an energy for the whole system, not individual molecules), the total energy of the products of the corresponding Sn2 reaction (tert-butyl alcohol and a chloride anion) will be lower (about 20 kcal/mol lower!).

What does this mean? That the reaction is thermodynamically favorable, and in principle it will not take place the other way around.

But does this mean that, mixing hydroxide with chloromethane at any temperature will lead to the immediate formation of tert-butyl alcohol and chloride? Of course not! The rate at which the reaction proceeds will depend directly on the temperature, and if the temperature is low enough, the reaction will not take place at all, even though the process is thermodynamically favorable.

Why is that? Kinetics is the answer.

What Are Chemical Reaction Kinetics?

Chemical or reaction kinetics is the branch of physical chemistry that studies the rates (or speeds) of chemical reactions.

In summary, thermodynamics determines in what direction a chemical reaction proceeds, and kinetics determines the speed or rate at which that process occurs.

Of course, in the last scheme of the previous section, there was something missing. In a chemical reaction, reactant A does not simply transform into product B. Reactions take place through what we call transition states.

Transition states are intermediate structures between reactants and products of a chemical reaction step. They are usually higher in energy (less stable) than both the reactants and the products, and the energy difference between the reactants and the transition states, also known as activation energy, is the barrier necessary to overcome for a thermodynamically-favorable reaction to take place.

Why Do Chemicals React? Thermodynamics and Kinetics Combined

See below a now complete version of the free-energy diagram of the Sn2 substitution reaction. As you can see, the process is thermodynamically favorable, but a barrier or activation energy of 23.0 kcal/mol has to be overcome in order to reach the products.

The larger the activation energy, the lower the speed or rate of a reaction at any given temperature. Usually, we set a limit of barriers of around 25 kcal/mol for reactions to proceed at a significant rate (this is, in several hours or days) at 25 ºC. Easy enough to remember.

Stability vs Inertness

No matter how thermodynamically favorable a process is, if the barriers to reach the corresponding transition are too high (say, higher than 30-40 kcal/mol), that chemical reaction is not going to take place under regular conditions.

This allows us to make a clarification between stability and inertness as properties of chemicals.

Stability is a thermodynamic concept, while inertness is a kinetic concept.

• A compound is stable, if it is relatively low in energy (compared to the molecules to which it may interconvert into). The opposite would be unstable, high in energy.

• On the other hand, we say that a compound is kinetically inert if in order to react it has to overcome large activation barriers.

A compound can be both unstable and inert. That is why we can handle and store thermodynamically unstable primary alkenes such as 1-propene without them isomerizing to more-stable secondary alkenes such as cis- or trans-2-propene (see the first two schemes).

But we can trick kinetics! Catalysts can be used to lower the activation energy of chemical transformations, allowing them to proceed more rapidly, or simply to proceed at all!

• Note: Theoretically, no matter how high the activation energy of a process might be, we say that it is always taking place at a certain rate. However, if the energy barriers are higher than, say, 50 kcal/mol, the rate or speed of the reaction would be so low that it would take many many years before we can detect a significant conversion.

Catalysis: Lowering the Barrier!

Now that we know why chemicals react, let me explain how we chemists try to override the system and make activation barriers lower.

A catalyst is a chemical entity (a molecule, a salt, a coordination complex…) which speeds up a chemical reaction. It also can unlock new reactivity pathways and make reactions work that would not be possible otherwise.

Let’s take a specific classical example. The electrophilic aromatic substitution of benzene with molecular bromine (Br–Br). This reaction is traditionally carried out using a Lewis acid as catalyst, such as iron tribromide.

But let us imagine first a catalyst-free version of the process, which I am certain can occur if you mix together benzene and bromine, and heat it up enough.

How Thermal, Catalyst-Free Reactions Occur

The first step of this reaction is the formation of the well-known Wheland intermediate. An intermediate (not to be confused with a transition state, which rather connects intermediates together) is a reactive chemical species which is formed in one of the steps in the middle of a chemical reaction of A leading to B, as intermediate point. For benzene to be transformed into bromobenzene, it has to pass through this intermediate species. Intermediates can rarely be isolated, since they usually are both thermodynamically unstable and kinetically reactive.

In any case, the reactants have to overcome a high activation barrier of 30 kcal/mol. Once the temperature is enough for this to take place, the rest of the process has lower activation barriers, and takes place downhill to give reaction products in an overall thermodynamically favorable process (exothermic by -11 kcal/mol).

But we can speed things up with a catalyst!

Lewis Acid-Catalyzed Electrophilic Aromatic Substitutions

By adding a catalyst to the mixture, we can access new transitions states, which are more stable, and hence lower in energy. And what happens when the transition state of the rate-limiting step of a reaction is lower in energy? That the activation barrier of the whole process is much lower!

This is basically the role of FeBr₃ (the catalyst) of this reaction: stabilizes transition states and intermediates. Now the activation barrier to reach the first transition state is much lower (20 vs 30 kcal/mol), allowing the reaction to take place under mild conditions.

Also, note that FeBr₃ is recovered unreacted with the products. This is another feature of catalysts: they can be recovered and re-enter another reaction cycle. This is why they are often employed in sub-stoichiometric amounts (this is, less than one mole of catalyst is enough to drive full conversion of one mole of starting material).

But as we have already mentioned, thanks to catalysis we not only can lower activation barriers that would need totally unpractical temperatures. We can also unlock reactions that would take hundreds of years to complete by themselves. We can also achieve completely new selectivities, and develop new chemical processes.

I work in catalysis myself, and I can tell you this is one of the most important, exciting and active fields of chemistry.

This is the end of this tutorial review, and I hope it has helped you to get a clearer picture of why chemical reactions take place and what leads chemicals to react. We certainly covered concepts you have to master if you are learning chemistry at any level!

The post Why Do Chemicals React? Kinetics and Thermodynamics appeared first on Chemistry Hall.

What Is the Swern Oxidation?

The Swern oxidation is the oxidation of a primary or secondary alcohol to an aldehyde or a ketone, respectively, by the combination of oxalyl chloride and dimethylsulfoxide followed by triethylamine.

Discovery and Applications

The Swern oxidation was first discovered by Daniel Swern and Kanji Omura in 1978. From this point, this methodology evolved into one of the most used strategies to oxidize both secondary and primary alcohols to ketones or aldehydes, respectively.

In this reaction, dimethylsulfoxide (DMSO) acts as the effective oxidizing agent, getting reduced to dimethylsulfide (DMS) as a consequence. However, DMSO by itself is not reactive enough to take part in this redox process, it needs to be activated by oxalyl chloride, (CO)₂Cl₂. This results in the formation of an adduct that can evolve into the corresponding ketone or aldehyde by action of a base (generally triethylamine), upon release of CO, CO₂, and dimethylsulfide (SMe₂), through a beautiful mechanism that is a must know for any student of organic chemistry.

This reaction has distinctive features that make it extremely popular among synthetic chemists.

Advantages and Drawbacks

One of the best features of this oxidation method is that it does not further oxidizes aldehydes to carboxylic acids, so a single 2-electron oxidation of primary alcohols can be achieved. This is often not the case with, for instance, metal-based oxidations, such as the use of potassium permanganate. Other alternatives that stop at the aldehydes, such as DMP, are usually much more expensive than the simple reagents required for the Swern.

This reaction often proceeds smoothly at very low temperatures. The usual procedure is run at -78 ºC, which means that the reaction conditions are extremely mild, this usually leads to very selective procedures that usually don’t harm other functional groups of complex molecules. On the other hand, this can also be considered a small inconvenience, since it requires setting up an acetone-dry ice bath (-78 ºC) or the use of a cryocooler instrument.

There are not many disadvantages for this reaction, as evidenced by how it has withstood the test of time, but the more characteristic one is on of the side products: dimethylsulfide is a nasty smelly gas! Make sure to run the reaction in a well-ventilated fumehood.

The Mechanism of the Swern Oxidation

The mechanism of this oxidation starts by the activation of the oxidant (DMSO) by oxalyl chloride. This generates an adduct upon release of a chloride anion. This chloride anion acts then as nucleophile towards the electrophilic sulfur atom, which makes the intermediate collapse. This results in the release of a molecule of CO₂ and a molecule of CO. This results in the formation of Me₂Cl₂S, and highly activated oxidizing agent.

This Me₂Cl₂S intermediate can react with primary and secondary alcohols to give the adduct shown below. Then, this adduct can be deprotonated by an organic base (triethylamine) to give a sulfur ylide, upon release of triethylammonium chloride.

Finally, this ylide intermediate evolves through a 5-membered cyclic transition state to release dimethylsulfide (DMS) and the resulting oxidized product (an aldehyde or ketone).

How Do You Run a Swern Oxidation in the Lab?

As someone who has run this oxidation at work many times myself, here is a general illustration of the practical procedure for this reaction.

Finally you can further purify the product if it is required by flash column chromatography, and you are all done1

The post The Swern Oxidation: Mechanism and Features appeared first on Chemistry Hall.

However, there are instances when they can cause nuisances in the household, interfering with our daily activities. They might start to cause stress and pain. 

The only time that spiders show their aggressive nature is when they are provoked or agitated.  This usually happens when we attempt to get rid of them. They retaliate in return. When they do this, they resort to biting and secrete spider venom into the skin. 

If you enjoyed our last journey covering the differences between bee and wasp venom, join us for a new venomous journey, and the biochemistry behind it!

Are Spider Venoms Usually Very Dangerous?

The spider venom is a mix of a lot of chemicals. Usually, spider bites are not as deadly as people think.  The composition of their venom is often only enough to paralyze small animals.

So the short answer is no, besides some species that can be very dangerous or even deadly, in most cases, there is no reason to panic if bitten by a spider.

However, there are spider species like the black widow spider (Latrodectus) and the brown recluse spider (or brown fiddler) that causes more than just skin allergies. Their venom is composed of more fatal components. Those can lead to necrosis, severe skin infections, or worse. So let’s discuss what it comprises so we know how to deal with it. 

What Are the Components of a Spider Venom?

The venom is released through the spider’s fangs called “Chelicerae” as they bite. These are usually composed of the following substances. 

• Venomous Peptides: A variety of peptides (small-chain proteins) are the major components of the spider venom, some of these are venomous and in a dose high enough to harm humans, in some cases.  These peptidic toxins can serve many purposes. Among these, paralyzing small animals, or help the spider in the digestion process.
• Enzymatic and Non-Enzymatic Proteins: These, on the other hand, have a high molecular weight that usually act as agents to help spread the venom throughout the body of the bitten creature.
• Small Molecules: Different mixtures and concentrations of active small molecules can bee found in venom. The most notable ones act as neurotoxins or necrotic agents. Other active compounds like serotonin can also be found in spider venom. 
• Other Components: Spider venom has other more common substances like salts, biogenic amines, and carbohydrates.  All of these contribute to might contribute to producing pain, or have other functions.

Most people develop an allergic reaction to many of these chemicals because they are foreign agents. Plus, these can dissolve tissues and cause pain.  Depending on the components of the venom, it can either be categorized as a cytotoxin- or neurotoxin-based venom.  So what is the difference? 

Spider Venom: Is it Cytotoxins or Neurotoxins?

Two types of spider venom are found as harmful and dangerous to people. This includes venom composed mainly of cytotoxins and venom that consists of neurotoxins. The difference between these two types is obviously the nature of the main chemical components found within them and the physical damage that they cause to humans.

Cytotoxins

Cytotoxins are substances that have a toxic effect on cells.

Cytotoxins have enzymes and linear peptides that damage the cells and tissues of the prey. Insects that are charged with this venom are liquefied for the easy ingestion of the spider. In the case of humans, cytotoxins create blisters, inflammation, or lesions on the skin surrounding the bite (necrotic bite). Loxoscelism is the condition where necrosis of the skin and the spread of red blood cells occur. Other symptoms of this condition include fever, headache, and vomiting. Some of the spiders that secrete cytotoxins dangerous to humans include the recluse spider and the South African sand spider.

Neurotoxins

Neurotoxins have a toxic effect on cells, but only a specific type of cells: neurons. They are destructive to nerve tissue.

Neurotoxins present in spider venom usually are proteins, disulfide-containing peptides, or polyamines. These chemicals paralyze and then kill the prey. They attack and immobilize the nervous system. Animals can die because of neurotoxins but rarely does it happen to humans. Only in extreme situations neurotoxins from spider venom kill people. 

The condition known as Latrodectism is caused by neurotoxic venom that can cause muscle cramps, pain in the abdomen or chest, vomiting, and sweating. Out of the two kinds of venom, this is the most dangerous of all. The black widow spider or red back spider, the Brazilian wandering spider, and the Australian funnel web spider all have neurotoxins that can potentially harm humans. 

What to Do When Bitten by a Spider

Generally, spiders are harmless, but being bitten by a spider is a whole different story. The type of spider should be considered when treating a spider bite. And in extreme cases, the spider should be captured to identify the venom for the proper medical attention. This is many times not possible, so it always helps to have in mind the clearest description possible of how the spider looks like. As we said, almost always, spiders will only attack and bite when disturbed, so there should be not such thing as getting bitten while sleep without realizing.

The first aid treatment to a spider bite is to wash the affected area with soap and water. When the bite is painful and inflamed, a cold compress on the wound can be helpful. Antihistamines and analgesics can be used to reduce pain and swelling. 

Immediate medical attention is needed as soon as symptoms are detected, especially if the bite of the spider has neurotoxins or necrotic substances. The bite of the Australian funnel web, the red back spider, and the Brazilian wandering spider can be fatal to humans.

In any case, what you should not do is panicking. In most cases you are going to be perfectly fine even without serious treatment. But better be safe than sorry and if you spot any serious symptom, go get it checked out.

About the author

Jenelly Laroco is a writer for Go-Forth Pest Control. She writes about pests and how to get rid of them safely but effectively using environmentaly-friendly methods. 

The post Neurotoxin vs. Cytotoxin: The Difference between Spider Venoms appeared first on Chemistry Hall.

Indeed, oxygen is one of the most abundant chemical elements on the planet, and it has been baffling scientists since its official discovery in 1773 by Carl Wilhelm Scheele and Joseph Priestley, independently. You will know why I said official when we get to the some facts about oxygen later.

Associated with the chalcogen group, molecular oxygen, dioxygen, or O2, is an extremely volatile covalent compound.

As obvious as it may seem, the discovery of oxygen was key for the development of chemical science: In fact, the process of abstracting electrons from a molecule, known as the chemical process of oxidation, takes its name from this element. This is due to the fact that elemental oxygen has the capacity of forming “oxides” with most chemical elements.

Technically, it is also the third most abundant element in the universe, trailing behind hydrogen and helium, respectively. 

Hence, in this article, you will learn several facts about this fascinating chemical element. We want to get into its photochemical properties (i.e. its color). But also, you will hopefully discover new things to add up to your knowledge. Let’s get started. 

General Properties of Oxygen

First off, we will take a look into molecular oxygen’s physical and chemical properties.

Oxygen is a colorless and tasteless gas at normal circumstances. This chemical compound is virtually odorless. People have stated, however, that it is actually possible to distinguish between air or pure oxygen. If the odor of oxygen does exist, we may not smell it because of olfactory fatigue.

Os we already mentioned, the most common form of that the element oxygen takes is that of molecular oxygen, dioxygen, or simply O2.

Dioxygen molecules, which are found in gas form under standard conditions, are composed by two atoms of oxygen which are bound through a covalent bond to one another.

However, oxygen is not always in a gas form.

Like most chemical compounds, under certain conditions, which we are about to discuss, it can also transition to different states of matter.

Liquid Oxygen

Liquid oxygen is the condensed form of dioxygen. Nowadays, liquid oxygen is used in many industries such as submarine, and aerospace, or in medicine.

In 1877, liquid oxygen was first discovered by Louis Paul Cailletet (France) and Raoul Pictet (Switzerland). This was after Michael Faraday had liquefied most gases known by 1845, but failed to do so with 6 of them which were known as “permanent gases” at the time. Oxygen was one of those gases.

Slightly denser than water in a liquid state, liquid O2 has a density of precisely 1.141 g/cm3. At its freezing point of 54.36 K (−361.82 °F or −218.79 °C), it becomes a solid.

Furthermore, liquefied oxygen is paramagnetic, a special type of magnetism. Paramagnetic materials (such as liquid oxygen) become weakly attracted to an external magnetic field. Check out the experiment on this video:

Oxygen is also an oxidizing agent as it can readily oxidize organic or inorganic (such as metals) materials. It is in fact used as oxidizing agent in liquid-fueled rockets, since its invention in 1926 by Robert Goddard.

Solid Oxygen

Under standard atmospheric pressure, and at temperatures below 54.36 K (−361.82 °F, −218.79 °C), dioxygen transitions from gas to solid, forming a spin-lattice crystal. Also in this state, diatomic oxygen is one of the few small molecules that carry a magnetic dipole moment.

Color and Properties of Oxygen in Different States

Now the question is:

What is the color of oxygen? Well, gaseous oxygen is colorless. However, when in liquid form, it comes in a shade of pale sky-blue.

The color of solid oxygen, on the other hand, ranges from light blue, pink-to-faint blue, faint-blue, orange, dark-red-to-black, and metallic in six of its different possible phases.

You basically can have solid dioxygen in 6 different phases. And each of them display a particular color.

Why Is Liquid Oxygen Blue?

Similarly to what happens to water (which is also blue, by the way!), the energetic transitions of the electrons in oxygen (which are also the cause of its para magnetism) absorb light on the red spectrum. So red light is absorbed to some extent, giving the substance its complementary color: blue.

If you want more info, this paper in the Journal of Chemical Education gets you covered.

Other Facts About Oxygen

Oxygen is a fascinating chemical element. Apart from its physical and chemical properties, it also has a fascinating history. Add more to your new knowledge and digest some of the following facts below.

If you are hungry for even more, make sure to check our explanations to 100 chemistry facts!

Who Discovered Oxygen?

The question of “who” only brings confusion as sources may vary.

The earliest mention of oxygen is in Michael Sendivogius’s 1604 study. A Polish philosopher, physician, and alchemist, he motioned that air contains a substance called ‘cibus vitae,’ which translates as the food of life.

However, most scholars say that the real discoverer of oxygen is Carl Wilhelm Scheele, a Swedish pharmacist. Between the years 1771 and 72, Scheele experimented with various metal salts, including several nitrates. Scheele discovered the release of a then-unknown combustible agent.

Scheele wrote in his manuscript, Treatise on Air and Fire, his observations about a so-called ‘fire gas’ that is released from heating nitrates. He submitted his findings in 1775 and had them published two years later.

During that same time, though, Joseph Priestley, an aptly named British clergyman, observed that mercuric oxide in a glass tube released a gas he called ‘dephlogisticated air’ after sunlight exposure. He further noted that candles burned brighter in ‘dephlogisticated air’ and that a mouse lived longer even after being exposed to it. He also tried breathing it in and noted that it was like breathing regular air. Priestley published these findings in his 1775 paper called An Account of Further Discoveries in Air.

On a different note, Antoine Lavoisier, also made claims that he independently discovered this substance. Both Lavoisier and Priestley exchanged correspondence and shared ideas. However, the former denied having received any letter from Carl Wilhelm Scheele.

Where Did Oxygen Originate on Earth?

Oxygen comes in third as the most abundant element across the whole universe. However this only accounts for about 1% of oxygen, since the two main constituents, hydrogen and helium, account for 75% and 23% of the entire universe, respectively.

But it was relatively scarce during the formation of Earth.

Accordingly to theories, early forms of cyanobacteria have produced oxygen and added it into the atmosphere of our then-prehistoric planet. Like plants of today, these organisms used photosynthesis as a form of sustenance. For millions of years, they took in carbon dioxide and released oxygen — a grand event dubbed as the Great Oxidation Event.  

What Is the Effect of O2 in the Blood?

Oxygen is crucial to our bodily functions. Without it, we would not last long. Oxygen is not only the basic source of energy that fuels the activity of all cells in our body, but also has several other secondary functions such as serving as a buffering agent – keeping our pH levels in check.

The average blood O2 level is around 75-100 mm Hg or millimeters of mercury. When it drops below normal, we may experience shortness of breath. Likewise, our blood will become acidic because of an increase in blood carbon dioxide or CO2.

Now, what if blood O2 increases? We will experience hyperoxia, which, when aggravated, may lead to oxygen toxicity. This condition may also cause severe damage to your body.

Why Do We Turn Blue When Blood O2 Decreases?

Bright red is the color of oxygenated blood because of the protein, hemoglobin. However, when a person experiences hypoxia, hemoglobin will not bind with the red blood cells, resulting in a darker hue, making us appear as bluish.

Basically, oxygen forms a coordination complex with the ‘heme’ group on hemoglobin. This complex is red-colored, whereas free hemoglobin is actually blue.

Why Are Oxygen Atoms Usually Depicted in Red Color?

If you are familiar with molecular models (and you should!), for sure you know that oxygen atoms are usually red-colored.

Considering that these colors (CPK coloring system) are usually inspired by the color of the elements themselves (hydrogen is white since its always colorless, carbon is black because of charcoal, sulfur powder is yellow…) his seems counter-intuitive after everything we have just explained.

The inspiration for traditionally coloring oxygen atoms in red is not that clear. It probably has to do with oxygen being required for combustion (and fire is red), or due to the previous fact that we covered: oxygen makes hemoglobin look bright red!

To Sum Up

And that concludes our discussion on this element.

So what is the color of oxygen, you say? Well, the answer is: it depends on its physical and chemical state. It is colorless when in gas form; pale or sky blue when in liquid, and shades of blue, red, and black-metallic when in solid state.

The post What Is the Color of Oxygen: Properties and Exciting Facts appeared first on Chemistry Hall.

Well, the chemical difference is not the one you hear on the news which distinguishes “organic” vegetables from “non-organic” ones. Guess what, both are made up of organic and inorganic compounds.

Let’s say that the “agriculture industry” definition is not the same as the chemical definition. In chemistry, there is a major difference, which is well defined.

Telling the difference between organic and inorganic compounds is one of the main things you need to make clear while learning chemistry. If you are interested, learn more about thermodynamics and kinetics, another two of thee most important concepts in chemistry.

In this article we will explain it in detail, so at the end you will be able to differentiate both of types of chemicals without any difficulty. We will try to solve all your doubts about this eternal chemistry question!

In the early days, scientists separated organic and inorganic compounds on the fact that the first group was considered as a result of the activity of living beings, whereas the second group belonged to the processes unrelated to any way of life. Now there are much clearer definitions.

Introduction

About 200 years ago, at the transition between alchemy and chemistry, chemists classified the chemical compounds into two main groups.

1. Organic Compounds

An easy, layman-friendly definition for organic compounds is that those are the ones which are derived from living things such as plants and animals are known as organic compounds like sugars, lipids, proteins, nucleic acids, etc.

More strictly speaking, we consider a compound to be organic if it is made of carbon atoms which participate in covalent bonds. Generally (but not always), organic compounds also present covalent C–H bonds.

2. Inorganic Compounds

An easy definition for an outsider, is that those compounds which are obtained from non-living things or mineral sources are known as inorganic compounds like NaCl (table salt) and NaHCO₃, (baking soda), etc.

Defining inorganic compounds is pretty easy after having defined organic compounds. As a rule, every chemical that does not fall into the category of “organic”, is considered an inorganic compound.

The Vital Force Theory and the First Chemical Total Synthesis

Let’s go back in time once again, to the very early days of chemistry. The theory known as the “vital force theory” might ring a bell to you if you are familiar with the history of chemistry.

This theory was proposed by Swedish chemist Berzelius in 1815. This theory states that organic compounds can’t be synthesized in a laboratory. Early chemists believed that organic compounds could only be obtained from living organisms, through “vital forces”. That is why this theory is referred to as “vital force theory”.

In 1828, Friedrich Wohler, a German chemist, synthesized urea in the laboratory. This accounts for the first chemical total synthesis of a natural organic compound ever!

This accomplishment showed that it was possible to synthesize an organic compound (urea), starting from an inorganic compound (ammonium cyanate), in the laboratory: treating silver cyanate with ammonium chloride afforded a crystalline compound that was found to be identical to urea isolated from urine.

This chemical transformation invalidated the vital force theory, and soon after this, chemists began to make organic compounds in the laboratory. Hence the modern definition of organic compounds was introduced in the scientific world. This also marks the very beginning of organic chemistry as a discipline.

The Modern Definitions

Organic Compounds

The compounds which contain carbon atoms as main constituent, which are bonded together through covalent bonds, are called organic compounds. Most organic compounds also contain hydrogen. Other common elements present in organic compounds are oxygen, nitrogen, sulphur, halogens, or phosphorous. But those are not the only ones.

In most cases, all atoms of the different elements are held together through covalent bonds. Some exceptions would be, for example, organic carboxylates, or ammonium salts. But you could argue that those are “inorganic salts of organic compounds”.

Some compounds that might sound “non-organic as hell” such as polymers (a fancy name for plastics), are actually long-chained organic compounds. An example is polystyrene. It’s backbone is basically all covalent C–C and C–H bonds.

Bear in mind that “organic compound” does not imply “biochemical compound”. On the other hand, the backbone of biochemistry is mostly organic compounds (although metals are extremely important in biological systems such as iron in hemoglobin).

Inorganic compounds

Take every organic compound out. You are left with inorganic compounds. If it doesn’t fall into the definition of organic, it is inorganic.

In general, the compounds which do not have C–C or C–H covalent bonds are called inorganic compounds.

There are many compounds that only have covalent bonds, they have carbon atoms, but are not organic compounds. Examples of this type of inorganic compounds include carbon monoxide, carbon dioxide, inorganic carbonates, carbides, etc. Notably, allotropes of carbon such as graphite, graphene or diamond, contain only carbon atoms, but are considered inorganic compounds.

As you can see, sometimes the definition is not so well established. In fact, I couldn’t really find a clear definition for both provided by IUPAC. This illustrates the fact that defining the line between inorganic and organic chemicals.

Some interesting examples of this middle ground are organometallic compounds. These are made up of an organic component, generally bound to an inorganic component through a carbon–metal bond. These are really fun and are one of the most widely explored research topics in modern chemistry!

Major Differences Between Organic and Inorganic Compounds

We will try to sumarize in a quick comparison table the key differences between organic and inorganic compounds.

However, bear in mind that in most cases these are just generalizations and won’t be true for any scenario, and definitely will have exceptions.

And as you can probably guess, the examples for both types of both types can go on forever.

Examples of Organic Compounds

Time to dive into learning organic chemistry! These are just some natural and non-natural examples of organic compounds.

Carbohydrates

These are commonly known as sugars. In terms of functional groups, these are aldehydes or ketones having additional hydroxyl groups. Carbohydrates are a simple way to illustrate organic compounds, since they are just chains of C–C and C–H covalent bonds in the company of some of the most typical organic functional groups (alcohols and carbonyls). Examples of carbohydrates are glucose, fructose, sucrose, etc.

Proteins

Proteins are made up of chains of amino acids joined together to form peptides. Proteins are actually polymers, which can be made up of a single chain of many amino acids, or of several chains that are packed together by non-covalent interactions. Since they are made of amino acids, they contain carbon, hydrogen, oxygen, and also nitrogen atoms, everything held together by covalent bonds, and also non-covalent interactions. A classical example of proteins are enzymes.

Organic Solvents

Organic solvents are organic compounds which are commonly used to dissolve chemicals in the lab, mainly for setting up chemical reactions. “Like dissolves like” they say, so these solvents are a must for carrying out organic reactions. They are usually simple organic compounds made of carbon, hydrogen, and also oxygen or nitrogen, sometimes sulphur. They are usually liquids at room temperature and have boiling points ranging from 40 ºC to 200 ºC. Common examples are hexane, cyclohexane (CyH), acetone, tetrahydrofuran (THF), toluene (PhMe), ethanol (EtOH), methanol (MeOH), benzene (PhH), dimethylsulfoxide (DMSO) or dimethylformamide (DMF).

Whatever Organic Compound that You Can Imagine Making on an Organic Chemistry Lab

The only limit for organic compounds is the imagination of the chemist. Theres is most likely an infinite number of combinations in which you can arrange carbon and hydrogen atoms to form organic compounds. Not to mention other elements.

That’s something I just made up in less than 1 minute in ChemDraw, and it seems like a totally reasonable organic compound.

Examples of Inorganic Compounds

Getting ready to study the realm of inorganic chemistry? These are just some common examples of inorganic molecules.

NaCl – Sodium Chloride or Table Salt

The salt you use for cooking is mostly sodium chloride, NaCl, and this is the most classical example of an inorganic compound. Specifically, it’s an ionic compound composed of an equal number of sodium(I) cations and chloride anions, arranged though a symmetrical three-dimensional network.

Carbon dioxide

Carbon dioxide is another example of inorganic compound with a chemical formula CO₂.  Despite of the presence of carbon atom, CO₂ is considered an inorganic compounds because containing carbon and covalent bonds doesn’t directly make a compound organic. You need a C–H bond or an equivalent.

For example, carbon tetrachloride, CCl4, is considered an organic compound, because instead of C–H covalent bonds it has C–Cl bonds, which are electronically equivalent. The bonding model in carbon dioxide, carbon monoxide, and other small inorganic compounds is quite different.

Diamond and Graphite

Allotropes of carbon such as graphite, graphene or diamond are classified as inorganic compounds, even when they have

Example of an Organometallic Compound

Right in the middle of organic and inorganic compounds, we can find organometallic compounds, which are characterized by having a carbon–metal bond (which in many cases is a “hybrid” between a covalent and an ionic bond).

An example of this are Grignard reagents (such as phenyl magnesium bromide) or organolithium compounds (such as butyl lithium).

To Sum Up

I hope we managed to explain clearly the basic differences between organic and inorganic compounds.

Organic compounds always contain carbon atoms, and almost always hydrogen atoms, all of them held together by covalent forces.

Inorganic compounds are just the rest!

The post What Is the Difference Between Organic and Inorganic Compounds? appeared first on Chemistry Hall.

Especially in the most recent years, many conference lectures by the best research group leaders on chemistry are being recorded and posted publicly online, so everybody can enjoy them and learn about chemistry. All around the globe. Without the need to travel long distances.

Simply thinking about it is amazing! Who could have though that this would be possible >30 years ago. At that time, the possibility of even checking research papers online, did not exist. We did research without the aid of databases on the library.

Now you can access all research that has ever been published online. But not only that, you can also “assist to conferences virtually” from anywhere.

However, not only modern chemistry has been recorded. One of the greatest examples out there of online chemistry talks are the Woodward’s legendary lectures.

Woodward’s Organic Chemistry Lectures

R. B. Woodward won the Nobel prize in chemistry in 1965 for his achievements in the art and science of organic synthesis. In my opinion, he is the greatest organic chemist of all time. He could’ve gotten two more Nobel prizes if he didn’t die so young (1979, at 62), probably due to his contributions to the chemistry of metallocenes and to the Woodward-Hoffmann rules, among many others.

Anyway, he’s been known for giving epic hours-long lectures, explaining the details of his total synthesis. And some of these were filmed at the time! And now, thanks to the internet, are available to watch on YouTube. This is one example:

You can look for a couple more that are around the internet. Even if you are a young chemistry student, if you are interested in organic chemistry, you should take a look. Classical organic reactions that are employed in these >50 years old synthesis are the ones that are usually taught in undergraduate organic chemistry courses.

In any case, watching the master of organic chemistry is an incredible source of inspiration for any aspiring chemist.

The Best Conference Chemistry Lectures Online

As we already mentioned, more and more, we get big conference lectures tape recorded and posted online. These are some of the most enjoyable ones that we have found.

Baran’s Electrifying Chemistry

First off, you can watch and hour-long presentation on synthetic organic electrochemistry by Phil S. Baran, from Scripps Research.

In this lecture, he covers the main reasons behind how using electricity as oxidant/reductant, instead of a chemical reagent is the greenest possible approach for carrying out redox transformations.

New chemical reactivity is being unlocked month after month taking advantage of synthetic electrochemistry. Here, Baran summarizes how he and his research group are pursuing this field of chemistry. He also presents new IKA equipment for carrying out electrochemical transformations in a reproducible manner.

2018 Nobel Prize Frances Arnold

Frances Arnold, from Caltech, won the 2018 Nobel Prize in chemistry for her contributions to the field of directed evolution of enzymes. This lecture is from one year before, in a symposium called “Tailored Biology”.

Her ground-breaking research has to do with modifying enzymes, to make them catalyze chemical transformations that they would not promote naturally, or at least not as selectively.

John Goodenough’s Nobel Prize Press Conference

John Goodenough, a chemistry professor at the University of Texas (Austin), and he is the oldest Nobel laureate of all time!

Prof. Goodenough got his Nobel Prize in chemistry in 2019, as a recognition of his contributions on the development of lithium-ion rechargeable batteries. What’s to say about this discovery? All of us use rechargeable batteries on a daily basis, all the time. We cannot imagine a world without them right now. And one of the main responsible people for these advances is this man. Here’s his Nobel press conference:

The Magic of Chemistry by David Leigh

In 2016, the Nobel prize in chemistry was awarded jointly to Ben Feringa, Fraser Stoddart, and Jean-Pierre Sauvage. They got it for their work on molecular machines, an exploding and revolutionary field within supramolecular chemistry.

Arguably, the fourth key player on this field is David Leigh. He also works on molecular machines. But his lectures are best-known for his personal touch. He is also a professional magician, and brings magic tricks to the chemistry lectures. Apart from presenting some amazing research, the magic makes these lectures some of the best in the world. And you can enjoy and watch one of these online chemistry lectures right now.

The Best Educational Chemistry Lectures

Besides top-tier ground-breaking research conference lectures, you can also enjoy and learn form some more educational resources.

Some More Magical Chemistry

Some of the most both educational and entertaining videos that you can find online on chemistry are the ones by Andrew Szydlo.

He goes though color and phase changes, and he leads students through the world of “playing tricks” with molecules. This might seem like a long video, but I assure you, if you decide to start to watch it, make sure that you don’t have anything to do for the following hour-and-a-half!

Walter Lewin’s Physics Lectures

So we are past chemistry for this video. But I bring it to your attention for two reasons:

• Chemistry and physics are heavily packed together.
• The lectures by MIT professor Walter Lewin are just fantastic, the best educational videos I have ever watched online.

To be fair, when I started studying some physics in college, I didn’t enjoy them that much. That was until I found Lewin’s lectures online. This made love physics almost as much as chemistry.

MIT Lectures from Your Couch

Who said that not anyone in the world can take chemistry lectures from MIT? Now it is completely possible with this and other courses on chemistry offered by this prestigious institution.

Here, this solid state chemistry course is a brilliant example of some of the best online chemistry lectures from a purely educational point of view.

General Chemistry Online Lecture Series (UCI)

This is another example, this time brought to you by the OpenCourseWare of UC Irvine. This is one of the best educational series of lectures on general chemistry that you can watch online.

Periodic Videos!

Finally, we could not end this post with a mention to the Periodic Videos YouTube channel. Here, Sir Martyn Poliakoff and the rest of his team at the University of Nottingham, tackle the most exciting chemistry facts, experiments and questions. Here, every experiment that you alway wanted to perform, but couldn’t, is answered in these videos.

As the title of the site claims, they have covered the entire periodic table, with at least one video on each of the elements. Go on now and check the one for your favorite element!

Closing Up

As you can see, there is plenty of online chemistry lectures that you can explore throughout the internet. These are just some examples, but go ahead and find some more that fit your interests!

Finally, make sure to share your favorite chemistry lectures in the comment sections with us!

The post Watch The Best Online Chemistry Lectures From Your Coach appeared first on Chemistry Hall.

Perhaps some would argue that this Chemistry area is not as “cool” as others, but I am sure that those who agree with me will find plenty of reasons to support the beauty of analytical chemistry.

But in any case, it’s something really necessary, and for making the process of learning it easier, getting your hands on the best analytical chemistry textbook that you can find its key.

But… What Do Analytical Chemists Do?

Now I might have caught a bit your attention on the subject, but, what is exactly analytical chemistry? A dictionary definition would say:

“Analytical chemistry is a scientific discipline which develops and applies methods, instruments, and strategies to obtain information on the composition and nature of matter in space and time”.

Kellner, R. Analytical Chemistry 1994, 66, 99A–101A

Fancy, but maybe not very insightful for a beginner. Analytical chemistry deals essentially with three aspects: measurement, analysis, and information. That’s it! In analytical chemistry you measure (quantity, concentration, etc.) a chemical/biochemical substance, you analyze the results, and then you obtain useful information that can be used to solve a technical (or social) problem.

This process seems simple, but the importance can be huge. A good example is residual pesticides found in food, which must comply with stringent regulations that define acceptable limits (although some substances are totally forbidden) for their presence in food. Analytical chemists work all the time on problems like this, and we are grateful for that!

Not only that, chemist from other disciplines (physical, organic, inorganic) base their daily research and rely on results obtained from analytical techniques (such as GCMS or LCMS analysis).

More interested in analytical chemistry now? Great! the next step is to open a book and start reading. As in all fields of science, we always start from the basics before achieving mastery. Of course, with a good analytical chemistry book, the path is going to be even better, particularly if some of you have already experienced some problems learning analytical chemistry. 

Furthermore, if you are a professor looking to find the very best book to base your lectures on, we’ve got you covered too.

What is the Best Analytical Chemistry Textbook?

But, which book do we choose? What is the best analytical chemistry textbook? Don’t worry, in this review, we will help you to find exactly the textbook you need.

For starters, we are going to make it easy for you and disclose our preference as top pick, which is Quantitative Chemical Analysis by Daniel C. Harris. Even thought Skoog’s comes as second runner up, Harris’ is simply as good as it gets regarding analytical chemistry texts for college.

Harris Quantitative Chemical Analysis

We will now quickly summarize all the reviewed texts, and then go deep exploring the pros and cons of each of then on the specific reviews.

Quick Reference Table: Top 5 Analytical Chemistry Books

Complete Review of All Books

Harris Quantitative Chemical Analysis

Considered the gold standard for analytical chemistry, the Quantitative Chemical Analysis book by Daniel C. Harris (and Charles A. Lucy in the latest version) has been in the bookstores since 1982.

Harris Quantitative Chemical Analysis

A must-to-read book for anyone interested (grad or undergrad) in analytical chemistry, this book is easy to understand and contains several examples and problems that will make learning analytical chemistry a much friendlier experience. 

It will provide you with sound principles of analytical chemistry and will teach “How” and “Why” analytical chemistry should be applied in real-life situations.  You will also find this book very useful for learning instrumental analysis, being a great balance between readability for non-Chemistry majors and in-depth content for more advanced readers.

Being a very comprehensive book, you will find information from the basic statistics, through acid-base equilibria, titrations, to electrochemistry, spectroscopy, and chromatography. The use of suitable software is also encouraged and exemplified in most, if not all, topics. 

This book is written in a quite straightforward style that makes its content easy to follow and understand. Concepts are presented right away and succinctly explained. If you want direct answers to your questions, this is the book of choice.

Skoog Fundamentals of Analytical Chemistry

A book with a good price/quality ratio, although it is more suitable for readers already familiar with analytical chemistry topics. Written by Douglas A. Skoog, Donald M. West, F. James Holler, and Stanley R. Crouch, it is a readable and engaging book with well-explained examples that is a safe bet to learn the principles of analytical chemistry and much more.

Skoog Fundamentals of Analytical Chemistry

Being a very comprehensive book, it is also reinforced by multiple high-quality images and case studies that properly demonstrate the principles, importance, and applicability of analytical chemistry. Several questions and problems are also presented for readers to practice.

Interesting topics such as kinetics methods of analysis and supercritical fluid separations, which are not common among analytical chemistry textbooks, are also covered in this book. This is one of my favorite books in analytical chemistry, and for sure, the book I recommend on every chemist shelf.

Analytical Chemistry (Christian)

This book, authored by Gary D. Christian, Purnendu K. Dasgupta, and Kevin A. Schug, is already in the 7^th edition.

Analytical Chemistry (Christian)

Particularly designed for undergraduate students in fields related to chemistry, it contains the necessary techniques and principles related to quantitative and instrumental analysis. The book has a modern approach with a clear methodology and explanations. It is also very versatile, being useful as an introductory text for first courses in analytical chemistry or as a reference guide for practicing analytical chemists.

Nevertheless, the style of this book might result more difficult to follow, so some base of chemistry is advisable before start reading and practicing. Not a first-choice book for people from other fields adventuring into analytical chemistry for the first time.

Worth to mention: an entire section of the book is devoted to genomics and proteomics, making it very useful for analytical chemistry in biological applications.

Analytical Chemistry and Quantitative Analysis

David Hage and James Carr created a book with a contemporary approach, presenting practice and applications of today’s analytical chemistry.

Analytical Chemistry and Quantitative Analysis

Applications span from forensics to environmental analysis and pharmaceutical sciences, although other interesting topics are also approached. Ideal as an undergraduate quantitative analysis book, as well as an introductory book to the area.

Easy to follow, this book somewhat combines the material from the more comprehensive “Quantitative Chemical Analysis” and “Fundamentals of Analytical Chemistry” and put it in a clearer version.

Principles and Practice of Analytical Chemistry

The book, created by F.W. Fifield and David Kealey, is already in the 5^th edition. Recognized as a complete and useful reference manual, is another example of a particularly valuable analytical chemistry book for undergraduate students.

Principles and Practice of Analytical Chemistry

Coming at a much more affordable price is also very encouraging, particularly if you are seeking a quick reference book of principles and techniques for practical applications. Not as comprehensive as other books, it is a concise presentation of up-to-date information regarding modern molecular spectrometry, atomic spectrometry, and separation techniques.

The focus is more practical in comparison to other books, including chapters devoted to automation as well as the role of computers and microprocessors in analytical chemistry. Thermal and radiochemical techniques are also included in this book, reinforcing its value as a reference book for analytical chemists that are already working in the area. 

Closing Up and Final Thoughts

There are different great books to learn analytical chemistry from out there. There are many different options for each taste. Here we presented the best five in our opinion.

However, if you want a safe choice with which you can never go wrong, don’t think twice a go for Harris’ Quantitative Chemical Analysis. The second runner up would be Skoog’s.

No matter which one you choose, always keep in mind that with a good textbook and with a touch of perseverance, you will find yourself mastering analytical chemistry faster than you think.

Finally, I would like to remind you that if you are going through the awesome process of learning chemistry, we have you covered with reviews for the best textbook on the other major subjects of this science: Check them here for organic, inorganic, physical and general chemistry!

As always, please, let us know in the comments if you find any discrepancy, or if you want to suggest an alternative textbook for discussion. (Since we only include here the books that we have available for review ourselves).

The post The Best Analytical Chemistry Textbook appeared first on Chemistry Hall.

Through chemistry history, different materials have been employed to build these containers, although it is generally acknowledged that glass is the material of choice for most applications. From simple test tubes to the more complex micro-Kjeldahl distillation units, glass is used in most, if not all for some fields, chemical experiments performed in a laboratory.

Whether you are an experienced researcher or a curious student trying to unveil the fascinating world of chemistry, I am sure you will find in this article several interesting details that you could have missed and could be very useful once you are in front of you laboratory bench. Remember, small details make big differences!, particularly in experimental Chemistry.

Considering this, in the following paragraphs, you will find a description and useful information about the most common laboratory glassware found in any laboratory. All of them come with pictures so you can esily identify those weird pieces of glassware sitting around in the lab.

Enjoy!

• Erlenmeyer flask: It has a cone shape and a cylindrical neck, being also flat by the base. It serves to contain substances or heat them, although the shape of this flask also helps to prevent liquid spillage and facilitates swirling motion to perform titrations, or other procedures. The narrow opening of this flask also prevents dust contamination and minimizes losses by evaporation.

• Volumetric flask: A flat bottom glass container with an elongated and narrow neck that presents a line that exactly defines the volume of any liquid substance. It is generally employed to prepare solutions.

• Beaker: A cylindrical container with a flat bottom and a wide opening. It consists of presents graduations that can often be used as a measurement reference. It is commonly used to contain substances as well as to heat them.

• Measuring cylinder: It is a cylindrical and graduated glass tube that is employed to measure precisely the volume of liquid substances.

• Test Tube: These are a small cylindrical glass tube with one end open and the other closed and rounded. It is used to prepare small reactions or tests in it. They are also commonly used to collect fractions in column chromatography.

• Büchner flask: Volumetrically graduated glass container. It has a small side tube coming out of the neck which can be connected to other equipment, generally a vacuum pump. Widely employed to perform vacuum filtrations along with a Büchner funnel.

• Round-Bottom Flask: This is probably one of the most common types of chemistry flasks. Ball-like container with a wide base and narrow neck that has a stopper. It is used when the substances contained must be stirred, avoiding spillage and evaporation of gases. It can possess one, two, or three necks. They are the bread and butter for setting up chemical reactions.

• Burette: Graduated container, usually made of glass. It is a long tube of small diameter with a stopcock that allows the liquid to drip. It is used to transfer exact amounts of liquids. The most common application of this are titrations.

• Desiccator: Not really a reaction container, but you do store chemicals in it. It is a glass container with a lid that allows a tight seal. It is used to remove moisture from solid substances. Silica gel (desiccant) is placed at the bottom, while the substance to be dried is placed on a plate a few centimeters above.

• Crystallizer: A low container with a flat base. It is used in the laboratory to crystallize the solute from a solution by evaporating the solvent.

• Fleaker flask: Sometimes used to heat liquids, not a very common piece of material. It resembles an Erlenmeyer flask and a beaker. Its body is cylindrical and culminates in a neck that curves before opening into a rounded opening.

• Two-necked flasks. These are round bottom flasks with multiple (2-3) necks or entrances. One is usually employed to take chemicals in or out for the reaction. The others can have multiple uses. They can be connected to a condenser to perform reactions under reflux conditions. You can attach a dropping funnel. You can also attach a connection with a source of an inert gas to work in a closed system under argon or nitrogen, for air-sensitive reactions.

• Kohlrausch volumetric flask: They are used for sugar determination, according to the Kohlrausch method.

• Kjeldahl flask: It is used for the determination of organic nitrogen. Guess how: the Kjedahl method.

• Iodine flask: It is used to make iodine determinations in quantitative analysis of substances by electron exchange (oxidization-reduction) titrations that involve the use of iodine (or any other volatile chemical, for that matter). It’s quite similar to an Erlenmeyer flask (but significantly more expensive!), but is equipped with a stopper joint in order to avoid partial losses of iodine through evaporation, which would lead to errors on the quantifications.

• Saybolt flask: Used for viscosity determination.

• Fernbach flask: It is a narrow neck flask. Its shape provides a large cultivation area suitable for growing microorganisms, in liquid nutrient media. It allows faster growth, due to better ventilation.

• Mojonnier flask: It is used in fat determination, which is extracted with a mixture of ethyl ether and petroleum ether in a Mojonnier flask, the extracted fat is placed at a constant weight and expressed as a percentage of fat by weight.

• Le Chatelier flask: It is used to determine the density of things. Generally applied to determining density of stuff such as hydraulic cement, granulated blast furnace slag and fly ash for concrete, filler aggregates, and lime.

• Schlenk flask: The corner stone of working under strictly anhydrous conditions. This flask is a reaction vessel designed to perform chemical reactions which are sensitive to air. There are many variations for this, but usually it has two different necks or connections, one designed to put in the chemical reagents, and another one that is simply a connection to a Schlenk line, or source of an inert gas such as argon or nitrogen.

• Straus flask: They differ mainly from other Schlenk flasks by their neck structure. Two necks emerge from a round bottom flask, one larger than the other. The largest neck ends in a frosted glass joint and is permanently distributed by the blown glass with direct access to the flask. The smaller neck includes the thread required for a Teflon cap to be screwed perpendicular to the flask. The two necks are joined through a glass tube. The frosted glass gasket can be connected to a manifold directly or through an adapter and a hose. A typical use for these is storing anhydrous solvents with molecular sieves.

• Collector or Receiver Flask: It is a glass jar, with a very short neck, spherical body, and frosted mouth. It is designed as a piece of glass in rotary evaporators, to collect distillations of reactions with reflux. It is usually made of borosilicate glass.

• Florentine Flask: It is a glass flask, with a long neck and spherical body. It is designed for uniform heating and is produced with different thicknesses of glass for different uses. It is usually made of borosilicate glass.

• Pear-shaped flask: It is designed for uniform heating and is produced with different thicknesses of glass for different uses. It is usually made of glass.

The biggest advantage of classic round bottomed flasks, is that its rounded base makes it easy to stir or remove its contents without being able to spill any substance out of its container as a precaution.

Pear-shaped flasks are used for evaporating solutions to dryness post-synthesis using a rotary evaporator, the ’rounded V’ shape of the flasks enables solid materials to be scraped out more efficiently than from a round-bottomed flask. Also, collecting liquids using a syringe, it’s easier with the pear-shape!

• Laboratory bottles: Made of borosilicate glass, they can withstand high temperatures and are of high chemical resistance. They are used basically to store chemicals and solutions, such as brine or ammonium chloride solutions for aqueous reaction work-ups.

• Dropper bottles with pipette: Contains substances. It has a dropper and for that reason, it allows dosing substances, such as organic solvents, in small quantities.

• Winkler oxygen bottles: It is made of clear glass, has a frosted cap and the exact volume is engraved on the bottle. It is used for the determination of dissolvable oxygen in the water.

• Big reaction vessels resistant to high temperatures or pressures. These reactors usually consist of two parts: a cylinder where the reaction mixture has to be introduced and a cap or head where there are usually different valves or connections necessary to carry out the reaction, to be able to control or monitor safety elements. In some cases, it has a heating jacket that plays the role of keeping the fluid at a constant temperature, either high or low.

• Microwave vials: Reaction vials that can be sealed with a cap, snd can resist high pressures. They are used to heat up reactions at temperatures higher than the boiling point of the employed solvent. This happens usually when heating using a microwave reactor.

• HPLC vials: These vial have a cap with a septum that can be pierced by needles, such as the ones from an HPLC or GCMS autosampler, so they are used to inject samples on instruments such as those. You can also set up small-scale chemical reactions on those if you have a stirring bar small enough!

As you can see, the list is long, and there is virtually a flask for every task you can possibly imagine. By the way, thanks to wikimedia for some of the pictures here.

Of course, you don’t really need everything if you want to set up of own home chemistry lab, but it is always good to know about them all!

The post Types of Chemistry Flasks: A Complete Guide appeared first on Chemistry Hall.

Some other students find are more intimidated by organic chemistry. However, most chemistry students are not incredibly fluent in maths, so all those physical chemistry equations can seem a bit overwhelming.

Physical chemistry isn’t the easiest subject to learn; it might frustrate you at times. Very basic and important concepts such as thermodynamics and kinetics are often overlooked in basic chemistry courses. However, if you have the right tools, in this case, the right books, you will have no problem whatsoever studying and passing exams. 

For this review, we will look at some of the best physical chemistry textbooks. For better or worse, it doesn’t seem to be a huge variety to choose from, in contrast with what happens with organic chemistry or general chemistry textbooks. So this comparison review will be quite concise, focused on the three most recommended physical chemistry reference books.

In any case, it does not matter if you are a college professor with a physical chemistry course to teach, or a student who is looking for a solid book to study from, either way, you are covered.

Our Top Pick: Which Book Is the Absolute Best?

After having used all the reviewed books, it didn’t take us long to choose McQuarrie’s Physical Chemistry: A Molecular Approach as the absolute best way to study, learn or teach physical chemistry.

Physical Chemistry: A Molecular Approach

McQuarrie is definitely the king. The red book, even being still on it’s first edition, is undefeated as the best book to learn physical chem. I know many students that had another books defined as course assignment text, but turned to McQuarrie’s to really be able to grasp everything and ace the courses.

McQuarrie’s is just the way to go in most situations, you cannot go wrong with it.

The Best Physical Chemistry Books Reviewed

And now we jump right into the entire reviews!

1. Physical Chemistry: A Molecular Approach

Authored by Donald A. McQuarrie and John D. Simon, this chemistry book is, without a doubt, the most logical and best physical chemistry book you will find anywhere. If you are a beginner, and you plan on getting your feet wet in physical chemistry, this book is an excellent choice.

Physical Chemistry: A Molecular Approach

The book is logically organized, and its concepts are clear and very easy to follow. The math, which is also clear and easy to follow, comes before the physical chemistry chapters. For beginners, I find this helpful because rather than assuming you learned the math elsewhere, the book explains it to you. And there are adequate mathematical reviews at the end of each math section that you can go over. 

For more advanced students or courses, you aren’t left out. This book is the go-to textbook in the area of Thermodynamics and Quantum. I have never seen quantum chemistry explained in any other book as beautifully and enjoyably.

There are many problems on each chapter. You can grab a copy of the problems and solutions manual for McQuarrie here. Many say it is a must if you are interested in focusing on solving problems (which are the main part of courses and exams), or if you are an instructor.

What Makes McQuarrie’s Physical Chemistry the Best?

After explaining the mathematical equations in the math chapters, the book then introduces the fundamentals of quantum theory with explanations. And then base everything else on a microscopic, atomic/molecular standpoint. And this is revolutionary because it helps students to see the subject in a unified and logical fashion, not leaving them confused. As you are probably aware, quantum chemistry and thermodynamics cover many concepts which are difficult to grasp. But not so much with this book. It takes an approach which I feel is the easiest way to learn these concepts.

All in all, I’d say that this book is a must-have physical chemistry textbook that most students of chemistry or college professors and should have on their book shelf. 

I’ve even hear a story of a non-chemist science enthusiast that grabbed a copy of this book and found it to be highly entertaining and instructive! It leaves you with a great feeling on how chemistry works from a (sub)atomic point of view.

To finish, the only drawback is the fact that the book hasn’t been updated since first release, so the figures can be a bit ugly and sometimes not easy to understand.

2. Atkin’s Physical Chemistry

Next runner up is Physical Chemistry by Peter Atkins, Julio de Paula and James Keeler. Now, here’s an updated and nicely illustrated textbook.

It comes in two volumes. The first one covers thermodynamics and kinetics. On my case, I studied quantum at college before thermodynamics and kinetics, so it seemed to me a bit counterintuitive. But I guess the two-volumes distribution was established for exactly this kind of situations.

This is nice, so you only have to buy and handle a 450 pages book for your thermodynamics and kinetics courses.

Atkins’ Physical Chemistry Volume 1: Thermodynamics and Kinetics

The second volume covers quantum chemistry and spectroscopy. It goes on for a little less than 400 pages, and focuses on the physical chemistry itself, not too much in the math behind. it gives just enough to be understandable with a solid base. But you’d better be equipped with that skillset!

Atkins’ Physical Chemistry Volume 2: Quantum Chemistry, Spectroscopy, and Statistical Thermodynamics

Atkins’ books excel in probably being a bit easier to read than McQuarrie’s. It reads pretty much like a novel, and the well illustrated modern figures definitely help. Besides, the book was updated in 2018 with its 11th edition. These are probably the facts that make Atkins’ the most ubiquitous textbook as part university courses syllabus. It’s a great primary resource.

It goes less in depth than McQuarrie’s, but it is arguably easier to read and a bit less dry.

The corresponding Student Solutions Manual also makes Atkin’s text complete.

3. Levine’s Physical Chemistry

I would say that Physical Chemistry by Ira N. Levine is the third most widely used physical chemistry book over the world. This book aims at making the learning process as easy as possible.

Levine’s Physical Chemistry

It comes with stepwise derivations and all maths quite carefully explained. Does a better job than Atkins’ but still not at the level of McQuarrie’s.

This book is on its 6th edition, but this update was released in 2008. It is written on a more formal or more dry manner than Atkins’, but this also makes it pretty specific and concise most of the times.

However, I would not recommend this text over the other two. It does a good job, but Atkins’ and McQuarrie’s do it better.

Closing Up

In summary, whatever textbook you select for guarding you from mighty physical chemistry, be aware that these courses can be a real challenge.

Just put enough time into studying and you will be fine. Also, make sure to have a decent base on maths (especially calculus) before taking physical chem courses. If you put time, have a good base, and one of these great textbooks, you will do fine.

In terms of comparison, we have already stated how McQuarrie’s Physical Chemistry: A Molecular Approach is the winner of the race. It is simply the best book for learning the subject from scratch, since even the math is explained carefully. It is particularly wonderful for quantum mechanics and statistical mechanics.

Even if your course ask you to follow Atkin’s or Levine’s, McQuarrie’s makes up for the best supplement.

On the other hand, Atkins’ can be arguably considered as the best “starting point” book out of the three. That is probably why it is the most recommended one for university courses.

This is all from our side. Make sure to check our general guide for learning chemistry. You can find there plenty of other resources that we have published or updated recently.

And also, please, if you have any comment or suggestion, or another book that you would like to see reviewed, go ahead and hit the comments section!

The post What Is The Best Physical Chemistry Textbook? appeared first on Chemistry Hall.

This said not all people actually have the luck of being able to study through college without working on a part-time job. This highly depends on the country you are living in, or on the wealth of your family.

I was one of those lucky guys. This approach lets you focus on simply getting your degree(s), which is nice. But there’s always the downside of not having any real work experience. That’s why you should start looking into building a career. Especially when you are close to graduation.

In this post I wanted to share the story on how I got my first research internship. And how this led me to another one, and then to my PhD without even having to interview.

Disclaimer: My career is purely academic, but I will try and finish the article with several tips that can help you land into your first job, either in industry or academia.

Getting Your First Working Experience

Getting research or industrial experience is key for building up a career in chemistry. This is clear. But is not equally easy in every part of the world.

But in any case, working as an undergraduate in something related to chemistry, will definitely help you. Always. It’s not just about having something to put in your CV. It will help you greatly in your transition from being a student to working full time.

If you can combine studying chemistry with working on you first chemistry job, you are off to a great start of your career!

I am aware that doing undergrad internships is quite common in the US. I worked here and know many people that studied chemistry here at the US, but I grew up in Europe. As a matter of fact, having some sort of experience is usually a requirement for most gradate programs.

But the world is quite big, and it doesn’t work like that everywhere.

How Did I Land into my First Job Experience

I grew up in Europe, and did my undergraduate studies in a very small university. Education was great, but job opportunities are pretty poor to say the least. Most people graduate without any job experience, which is average for people here.

However, if you plan to build your career outside, having no experience at all can be a problem. Both for getting industry positions or joining academic graduate programs.

Here undergraduate chemistry studies take 4 years. So during my third year, I decided to make a move which defined entirely my career. I wanted to check out how a research chemistry job looked like.

For this purpose, I applied to an internship program offered by my university. Only two positions were available each year for the entire university, and I got one of those.

But still, those positions are not great at all, because they are kind of “rotations” in which you spend one or two weeks (no more than 10 h) in each of the 8-10 different labs on the department. This is simply not enough to get a flavour of what doing research in that lab looks like. Not even close.

So I decided to approach the head of one of the organic chemistry labs. I simply showed my genuine in their chemistry. I loved o-chem, so I figured doing research in organic chemistry would be great!

As a matter of fact, I was right. I got to work only in that lab, and I immediately fell in love with research. I my first lab a lot! My first chemistry job and the gate to open up my passion for research.

Bonus tip: Always be learning new things! An example of where you can do this is on this post reviewing some of the best online chemistry lectures. Also, keeping up to date on new methods of science communication and outreach can always be a plus.

Approach Professors: They Love Seeing Students Interested in their Chemistry!

I talked with many chemistry students who tell me that it doesn’t feel right to them approaching professors and ask them to join their labs. If you feel the same way, I would like to encourage you not to be scared!

Almost every professor who works in research love what they do, and also love sharing it with others! Even if you don’t quite understand what their research is about, just go and ask!

Many research groups have a website set up in which they have, not only a complete list of publications, but also a fairly accesible summary of what their research is all about. To go even further, if you enjoy what they teach, you will most likely enjoy what they do too.

On my case, I simple knew the professor that taught one of my favorite chemistry courses had a research group. I showed my interest and that was pretty much it.

I got a full paid internship on his lab, where I was given the opportunity to start a brand-new project for myself, in collaboration with a 4th year grad student. This student taught me enough to continue the project by myself over a bit more than 1 year.

After this time, I was fluent on a synthesis research lab, got the maximum grade on my undergrad dissertation, and got a first author publication. And I can tell you that this doesn’t happen to >95% of the people that graduate there. Not even close. And the key was just going ahead and showing interest!

Where Do You Go From Your First Chemistry Job?

In my case, I applied for another internship in a different European research group. In this case, one of the biggest European groups in organic chemistry. Thanks to my first experience on my university, I got the second internship, that directly led me to joining a graduate program over there. Not even an interview required. Just a bit experience, which showed that I dared to go a bit further ahead than my peers was enough.

Then I worked too in the US, mainly in an academic environment, but also in close collaboration with industry. From a position like this, with you PhD under your arms, you are in a pretty great position to move towards any industrial or academic job you want to pursue. Chemjobber here does an amazing job on gathering and publishing job opportunities and analyzing the job market in chemistry.

Getting The Technical Details Right

I might have made it sound easier than it is, since I didn’t comment on any technical issue, such as CV or email writing. When you are getting started, or if you know the guy you want to work with, the approach process is definitely easier.

But for any further application, you obviously need to know a bit how to write a CV or a cover email. Or how to tackle interviews.

Writing Your First Chemistry CV

If this is your very first CV, and have an average almost-zero experience, I wouldn’t go further than writing one page.

The structure that I like is as follows:

1. Essential data: First state your name and essential data. Nationality, place of birth, current address, phone number and email (which is just your name, with a gmail or university domain). Depending on the place, you might have to include age (date of birth), or in some countries, your picture (definitely not in the US or UK).
2. Two lines description: Then I usually follow with a two-three lines description of who you are or what are you aspiring to do. For example “XXX YYY, chemistry undergraduate student looking forward to developing a career in process chemistry. Looking for an entry job or internship in industry”.
3. Education: Unless you have strong and related working experience, education comes on the top. If you are already an undergraduate in college, I would not include any education data below high-school. Even high-school, I wouldn’t include it you don’t have anything to highlight there. If you got any prize, or had some experience, or joined anything such as a science club, make sure to add it. Anything that shows your interest on what you do/study, will be positive. About grades: If yours is above average, by all means add it. If it’s below average, not be scared not to include it. If they want to know, they can ask, but no need to show something bad for no reason.
4. Working experience/history: Try to fill all the gaps possible. It’s understandable that you have spent student holidays just as holidays, but once you graduate from college, blank gaps of more than a couple of months raise red flags to employees.
5. Language proficiency: This is usually most important for non-English native people, since English is the universal language of science. State clearly your English proficiency if you are not a native. And of course, if you can speak other languages, it’s always a great bonus, especially if you want to join an international working environment.
6. Prizes and other achievements: If you participated or joined the chemistry olympiad, or organized events on your science club at high school, you can add it to your CV.
7. Other skills and hobbies: You could add skills such as having a driving license, or playing a musical instrument. Or being a part-time high level athlete. Don’t bother including interests such as “reading”, “listening to music”, “traveling”, or “watching TV shows”. Everybody does this and no employer cares.

Don’t go crazy with colors. Black and white works just fine. A simple design such as this one, is more than enough. Just make it as easy to read as possible.

Cover Letters/Emails and Interviews

Your CV can go almost identical for any position that you want to apply to, but your cover email/letter needs to be tailored.

You can extract the main ideas for writing an email for your first chemistry job from the first sections of this article. Just show interest about the job, and include a couple of highlights from your CV.

As for interviews, they can vary largely between country to country, lab to lab, and company to company. I’m not going to go into details. You can go and check some great advice in this Reddit post.

Closing Up: Share Your Experience with Us!

If you are a chemistry student looking for your first job, I really hope you found this post useful.

On the other hand, if you are already past this point, please, we invite you to share your experience in the comments, so other people can learn from it!

The post How I Got My First Chemistry Job (And How You Can Do It Too) appeared first on Chemistry Hall.

There is so much to this science that it can be hard to even know where to start! That’s why we put together this guide with recommendations for how to learn chemistry, plus tons of useful resources no matter what your level is.

What exactly is this guide?

Obviously you won’t learn chemistry reading this blog post by itself. This is more of a pedagogical article. However, we will point you towards tons of resources for learning this science, no matter if you are just a chemistry enthusiast or a college student.

This is a general introduction for approaching chemistry, from any level.

There is a very specific way of thinking that helps tackling the problems that chemistry has to offer. We will base our guide upon that cornerstone.

And you will find out what this theme is pretty soon if you keep reading.

An Introduction to Chemistry

But first, a quick introduction to the study of chemistry, what it is, and why you should make the effort to learn this awesome science.

What Is Chemistry?

Chemistry can be defined as the study of matter and the changes it undergoes. You’ll sometimes hear it called the central science because it is the connection between physics and all the other sciences, starting with biology. All that makes it sound abstract and esoteric, but really, chemistry is all around us. It wouldn’t be a stretch to say that it governs every aspect of your life.

Are you sitting inside? You’re surrounded by building materials that are structurally sound because of how chemistry holds them together. Reading this outside? Every living plant you see is consuming CO2 and releasing oxygen in the process of photosynthesis. The food you eat, the products you use to clean your house, the fuel you put in your car, the very air you breathe—it’s all chemistry.

What’s really incredible about chemistry is the seemingly infinite variety of stuff around us and the fact that it’s all just combinations of around 100 chemical elements. In reality, most of what we interact with in everyday life is made up of far fewer. When two or more of these elements are combined in a compound, the properties of the compound can be amazingly unlike the constituent elements. Would you guess that the table salt in your kitchen is made up of a chemical weapon and a metal that causes an explosion when it touches water?

What is Chemistry Used for?

It should come as no surprise, then, that chemistry is used for just about anything you can imagine. Life itself relies on chemistry, but humans have been harnessing it for our own benefit for thousands of years, knowingly or not. From our first combustion reaction (making fire) to the latest cutting-edge medical technology, this science has changed our lives in ways that are mind-blowing.

Long before we knew any scientific concepts that we take for granted today, we were performing basic chemistry. Some of the most important examples from the ancient world are processes that we still use today, such metallurgy and extracting compounds from natural sources, e.g. plants.

Many people consider alchemy to be the forerunner of modern chemistry. This is debatable, but regardless, the discipline that tirelessly sought a way to turn lead into gold fell out of favor among intellectuals right about the time when something closer to modern chemistry was beginning to catch on. The earliest publications in chemistry as a proper science date to the 16^th and early 17^th centuries.

Now, a few hundred years later, the field has positively exploded, with numerous subdisciplines. Today, we say that the five major branches of chemistry are general chemistry, organic chemistry, inorganic chemistry, biochemistry, and analytical chemistry. But there are tons of more niche areas of chemistry, too, like physical, materials, and nuclear chemistry, neurochemistry, chemical engineering, medicinal chemistry and pharmacology… The list goes on and on because chemistry is used for everything!

Why Should I Learn Chemistry?

So, aside from the fact that it is used for practically everything in life, why should you learn chemistry? There are tons of reasons!

Even if you don’t plan on a career in science, you’ll pick up a lot of useful skills and knowledge when you learn chemistry. Studying science helps you understand important issues, like climate change or food additives, more objectively. Chemistry is also great for developing problem solving skills.

More specifically, knowledge of chemistry unlocks some of life’s most profound mysteries… like how to make sure your baked goods come out moist and fluffy! Seriously though, it can make many routine tasks—like cooking—easier, and more importantly, it can help keep you safe. Knowing which cleaning products are okay to be used together and which should never be mixed is possible with chemistry, as is understanding how certain medicines work in your body, and much more.

This video sums it up really well:

Besides, chemistry is not a profession which seems to be going anywhere soon. Careers and jobs in chemistry, especially in research, are usually pretty fun, and creativity-driven.

Now that you’re convinced that you want to learn chemistry, how do you do it?

How to Learn Chemistry

I talked with many people that have studied chemistry, like myself, and everyone seems to have learnt this science very similarly.

There is a way of reasoning and thinking about chemistry which is common in chemical education.

Chemistry is an empirical science, so it is based on explaining observations, and taking what you extract from those observations to extrapolate and make predictions about other phenomena.

You can explain extremely simple chemistry questions, such as differentiating organic and inorganic compounds, to very complex scenarios with this same methodology.

This way of reasoning is, in my opinion, the best way to tackle chemistry problems. This goes from a kid learning basic science to a professional chemistry PhD working on ground-breaking research.

How to Rationalize, Explain and Extrapolate

To illustrate this, we will use a simple example:

First an observation: We observe that water freezes at a certain temperature (0 ºC at atmospheric pressure).

Then, rationalization/explanation: Thanks to previous knowledge, we can explain this observation in simple terms saying that at lower temperatures, molecules vibrate less, and can pack in a more efficient manner. The way water molecules can pack below 0 ºC, gives it a solid state structure.

We can generalize this to any other substance: Depending on how strong are intermolecular interactions between each molecule of a given substance, they will be able to pack in a solid state form more easily (at higher temperature).

Then we extrapolate to other systems/molecules: intermolecular forces between hexane molecules are much weaker (dispersion forces) than between water molecules (hydrogen bond). This will make it harder to pack them in a solid state structure, thus making its melting point much lower (-95 ºC, to be exact).

And this turns out to be true, as we can easily validate by determining (or consulting) the melting point of hexane.

And this can be made as simple as that or as complex as you would like your model to be.

This way of thinking fits perfectly with chemistry. That’s why I highly recommend it.

If you already took chemistry courses, you are probably familiar with this reasoning process, even if you didn’t really notice.

Where to Find Any Resource for Learning Chemistry

So you are already packed with a clear thinking process that you can adopt for tackling chemistry.

What do you need now?

Of course, you need information. Information is everything. You need books, resources and materials to study.

Well, we have good news for you! We live in the age of information technologies, and you can find literally everything anywhere. You can order a textbook from almost anywhere, and even find electronic versions of those books. You can find scientific research articles from home. You can visit Wikipedia and take a quick look about any subject you want. You can Google whatever you want and find tons of resources to learn from…

One might say, that there’s too much information out there! More than you can handle!

But I really don’t think there’s such a thing as ‘too much information’. Not if you are good at searching through it, and filtering what’s important. And this is a basic yet overlooked skill in our age. Focus on learning how to process, select and filter! And this not only applies to chemistry, but to every subject out there.

To be completely honest, even in 2020, I don’t think there is a better way to learn a natural science such as chemistry than starting from a good textbook.

Not get me wrong, there is plenty of info about chemistry. Heck, probably most of the university level course materials can be found in Google.

However, there is nothing like the great and didactical organization of a textbook. You can get one for your level, and when you are done going through most of it, you will be a master on that level. Of course, I encourage you to expand every topic that is not clear enough, or not covered deeply enough. For this purpose, or for a quick outlook, the internet is amazing.

There are plenty of different textbooks for any level. Which one is the best for me? What are my options? This is what we will cover next.

We strongly recommend you to navigate this site through the links on each section to check specific details and thorough comparison data.

The Best Books to Learn Chemistry at Any Level

No matter what your interest or level in this subject may be, there’s a great book out there to help you learn chemistry. This section won’t be too extensive, but you can find detailed write-ups on all of the books below in other posts.

Kids and Casual Learners

Our recent post on the best chemistry-themed gifts included three books that are a great fit for older kids or adults who have a casual interest in the central science.

Elements: A Visual Exploration of Every Known Atom in the Universe is visually stunning and chock full of cool information. It contains gorgeous photos and fun facts, and it would be an excellent introduction for people who are curious to learn about the chemical elements that make up our universe.

Ask a Science Teacher: 250 Answers to Questions You’ve Always Had About How Everyday Stuff Really Works is a book that is less focused on chemistry specifically, but which has still got tons of fascinating explanations in plain English. It’s a great book to show all the practical ways in which science affects us every day.

Chemistry for Everyone: A Helpful Primer for High School or College Chemistry is exactly what it sounds like. It’s definitely the most educational of the books in this section, although it is not intended to replace a complete chemistry course. We would recommend picking this up before taking your first chem class so that you have an idea of what to expect.

High School

We have two favorites when it comes to books for high school chemistry students. You can read more in our post on these and other high school chem textbooks, but here are our top picks in a nutshell:

Chemistry: Concepts and Problems: A Self-Teaching Guide is, of course designed for self-taught students. This makes it ideal if you end up in a class with a “teacher who doesn’t teach”, as students often report. It’s based on the programmed learning method for maximum learning effectiveness.

Chemistry for Dummies tracks a typical introductory chemistry course, making it suitable for high school and college intro to chem classes. No matter what your current level is, you can learn chemistry with this book.

We also published a separate review for the best chemistry books for self-study, which can be suitable for anyone, but especially to people at the high-school level.

University Level

At the university level, there are several types of chemistry courses you could be taking, each with its own separate textbook. Or, if you’re curious to learn chemistry but don’t need the credit to graduate, you could use one of these books to teach yourself!

If you’re learning General Chemistry, we’ve got a whole post dedicated to the best books for this class. But in the interest of time, our two top picks are Brown’s Chemistry: The Central Science and Tro’s Chemistry: A Molecular Approach. Both are top-notch textbooks, with the second one being a bit more expensive but also more accessible for most students, especially visual learners.

For people with a serious interest in learning chemistry, the next course is usually Organic Chemistry, or o-chem. Your professor has likely listed a book on their syllabus, but in our opinion, the best textbook to learn organic chemistry is Clayden’s Organic Chemistry. According to research, students value clarity above all else in textbooks, and this one is very easy to follow with plenty of practice problems. We also try to publish resources in which reaction mechanisms are well explained, here is an example with the Swern oxidation!

Your o-chem professor will probably also require or suggest you get a molecular modeling kit. This is highly recommended, even if it isn’t mandatory in your class. But remember, it doesn’t do any good to buy a kit if you don’t use it, so make sure you take full advantage of all the concepts it can help you understand.

By the time you get to Inorganic Chemistry, you’ve likely made a major commitment to studying chemistry. There are several inorganic chemistry textbooks that can help you learn more effectively, but our preference is Housecroft & Sharpe’s Inorganic Chemistry. It’s got just the right balance of detail and being easy to understand with very instructive graphics.

Two other main fields of chemistry are not forgotten. Here you can go and check for the best physical chemistry textbooks and the best analytical chemistry books.

Other important subfields such as biochemistry and electrochemistry are not left behind.

Also, it is mandatory that you start learning how to properly take notes in the form of a laboratory notebook, and writing good lab reports.

Online Resources

Apart from books, the second best resource for finding resources is clearly the internet. But what sites should I visit?

Of course, there are many university websites with plenty of information, but the easiest and quickest way find something, is of course, a search engine such as Google. But make sure to check what kind of site are you visiting, and if the information they provide is reliable. Many times, your query will take you to university sites that you can trust. But as we advised before, learning how to filter information is key!

As for other great websites to look for information, some of them are:

Wikipedia: Some criticize that anyone can edit it and write any information. This is true, but it is also true that it undergoes continuos review by experts, and inaccurate or undocumented information rarely goes unnoticed. The info sources or citations are usually great and often refer to original research.

Youtube: Just the same as Google, just search anything you want and you will most likely find a channel explaining everything about it to you! An example for Organic Chemistry is presented by Crash Course here.

As an example of this, we have collected some of the best chemistry lectures and conference talks in another article.

SciFinder and Reaxys: Professional scientific databases. They are paid tools, but if you study or work in a research institution, you will most likely have access to a subscription. These are great for looking through original research, and if you are serious about doing a career on chemistry, you’d better get used to playing with them!

Libretexts: Great repository for completely open access books online, which might not be accessible anywhere else. Lot’s of chemistry material there to find!

This list could go on forever, for example, our own place, Chemistry Hall, has plenty of resources to discover. But we really want to remark how important is to master search engine searches to look for exactly what you are looking for.

We will now finish with an important section for students: tips on taking on some of the most popular standarized chemistry exams in the US.

Taking Standardized Chemistry Exams

The single best thing you can do to prepare for most standardized exams is to take practice tests that are as similar to the real thing as possible. In addition to that, check out these tips for some of the major standardized chemistry exams.

Tips for AP Chemistry Exams

The AP chem exam is a college credit exam for high school students, so it literally pays to be prepared for this one. Your first step should be to buy one of the best AP chemistry review books, preferably one with lots of practice test so that you’ll feel comfortable with the structure of the exam and the formats of the different types of questions.

When taking your practice exams, make sure you do it under simulated testing conditions. Most of all, that means that you need to time yourself. Another important thing to keep in mind is that the topics that are covered on the exam are changed from time to time, so if you buy a review book, make sure it’s the most recent edition.

Similarly, make sure you get the latest version of exam logistics, such as when you will be allowed to use a calculator, the provided equation sheet, etc. And if your handwriting looks like chicken scratch, remember that your free response questions are being graded by humans, and doing your best to keep things legible could save you some points by making your grader’s life easier.

Tips for the SAT Chemistry Subject Test

Many colleges and universities do not require SAT II exams, i.e. subject tests, but they can be useful to present yourself as a better applicant. Usually, students are advised to take one science SAT subject exam and one humanities, and the SAT Chemistry Exam is one of the most popular science tests.

It should come as no surprise that your first step to success is to buy a chemistry SAT subject textbook. But it’s also important to realize that not all review books are created equal. There is one specific type of question on the SAT Chemistry Exam that is quite different from what most students are used to. They are called “relationship analysis”, and they can be confusing at first, so you need to make sure that your practice exams contain this type of problem.

When taking practice tests, always do it as close to real-life testing conditions as possible. That means setting a timer and being aware in advance of the things that are and aren’t allowed on exam day. For example, you are NOT permitted a calculator on the chemistry SAT II. If your algebra and basic math skills aren’t strong, it’s best to start working on them as far in advance of exam day as you can.

You will, however, be given a very basic periodic table of the elements. It wouldn’t be a bad idea to review periodic trends, groups, series, etc. and make a “brain dump” of all this information as soon as you are allowed to begin the test.

Tips for ACS Exams

Some college professors opt to give the American Chemical Society general chemistry or organic chemistry exam as their course final in lieu of preparing their own. This sounds like a terrifying prospect to lots of students, but it can actually be a blessing because you will be able to prepare yourself for it with more confidence.

Since the ACS exam is standardized, you can know in advance exactly what topics will be covered, the sorts of questions they tend to ask, etc. You can find official study guides and practice tests online, along with the rules for the test, provided materials, and so on.

We recommend that you start prepping well in advance so that you can space out the material and take your time with everything. Remember that active forms of studying, like doing practice problems or trying to explain concepts to someone else, are much more effective than just reading and rereading notes.

The ACS finals are cumulative, which means they are more about breadth than depth in terms of material. You can choose to go back to the beginning of your course work and study chronologically, or take a more tailored approach and first focus on material that you have a good, but not great, understanding of, before continuing on to any parts that make you feel hopelessly lost.

Tips for MCAT, PCAT, etc.

Pre-professional exams, like the MCAT and PCAT, are designed to measure your knowledge and aptitude in multiple subjects. On the MCAT, one section is called Chemical and Physical Foundations of Biological Systems, while the comparable section on the PCAT is Chemical Processes (there is a separate section for biology).

The names of these sections give you a clue as to what you are expected to know on each exam. Understandably, there is a greater focus on chemistry in this section for pharmacy students and more of a biology focus for med school.

The two exams have totally different structures and rules, so you need to get all that information as soon as you can so that you know how to study and prepare. For example, the PCAT is now given on the computer at a testing center with a calculator built into the exam in the chemistry section and others. However, calculators are not allowed on the MCAT chemistry section, so part of your test prep may include practicing doing calculations by hand.

As with other exams, you’ll greatly improve your chances of getting into med school or pharmacy school if you make use of a good review book with plenty of practice problems.

Time to Learn Chemistry!

If you follow this guide and make use of the resources at your disposal, you’ll be well on your way to learning chemistry. Now, all you need is to dedicate some time to daily study—consistency will make the difference in how far you go!

The post How To Learn Chemistry at Any Level appeared first on Chemistry Hall.

If you want to become a synthetic chemist, or you are planning to ace an experimental course on organic chemistry, TLC is something you really need to master.

So, what is this tutorial about? What am I going to learn if I continue reading?

Well, I am a synthetic organic chemist with years of experience in the lab, and I have run thousands of TLC and flash columns in any solvent combination that you can imagine. I also enjoy sharing and reading lab tricks with colleagues, or even online. You could say that there are very few things that I still don’t know about this technique.

What I decided to do, is to put together all my knowledge in this tutorial article, so you can start reading without knowing what a TLC is, and finish up by being able to separate and identify (almost) anything you want in an organic chemistry lab!

This guide is for many different levels.

I can tell you that even if you have never been in a chemistry lab before, you will be prepared to do a thin layer chromatography just by continuing to read the first sections.

On the other hand, I can also promise you that even if you have PhD in organic synthesis, there is still some tricks or hacks to learn in this guide.

Considering this, you can navigate this tutorial page by using the index shown right below. Happy TLCing everyone!

What is Thin Layer Chromatography?

You might be familiar with what chromatography is, but maybe you din’t know that, as a matter of fact, the name “chromatography” comes from some early experiments on thin layer chromatography.

The word chromatography comes from the Greek chroma, “color”, and graphein, “to write”. It was a technique to separate substances that had different colors.

Basically, a chromatography is any lab technique in which we separate different chemical components of a mixture by their affinity to a stationary phase (usually silica gel in TLC) and to a mobile phase (the solvent or mixture of solvents). They don’t necessary have to be colored compounds, since there are many other ways to detect or identify them.

Initial experiments on TLC allowed separating pigments of plant’s extracts. These pigments (such as chlorophyl) have different colors, and elute at different rates through the stationary phase, so they can be separated and easily visualized:

Chromatography can get very complex, with complicated and expensive instruments such as GC-MS or HPLC, but the most basic, most important and oldest technique is thin layer chromatography, or TLC.

In TLC, we use a stationary phase (most frequently silica gel) which is deposited over a glass or aluminum support. We then can spot mixtures of compounds over the same line. Then we elute the TLC with an organic solvent, and the different compounds will move upwards at different rates, allowing the separation of the different components.

What Is Thin Layer Chromatography Used for?

Thin Layer Chromatography is a cheap, quick and easy technique to separate components of a mixture. It is used by synthetic chemists to monitor chemical reactions and purifications.

And How Does a TLC Work?

Well, a TLC plate is an aluminum plate coated by a “thin layer” of a stationary phase, which is usually (>95% of the time in organic synthesis) silica gel.

Around 1 cm above the bottom of the plate, you can spot a solution of a mixture of compounds of different polarity.

Then, you “elute” the plate. you basically put it vertically inside a closed chamber which contains an amount of an appropriate solvent mixture. The solvent flows slowly up the plate through capillary action.

The stationary phase, silica gel contains Si–O–H bonds that bind to the different compounds of the mixtures in a variable manner depending on the polarity of the compounds. Also, depending on the nature of the solvent used (more polar or less polar), it will pull upwards some compounds faster than others.

In general, more polar compounds will “climb” slower up through the TLC plate, and less polar ones will fly upwards.

Then you just need to check how many and where in the TLC plate each spot is. Each spot corresponds to a different chemical compound on the mixture.

Usually you will need a UV (Ultraviolet) lamp to visualize the different spots, but if the compounds are strongly colored, as in the picture above, you can easily see the different components of the mixture.

How Do You Run a TLC? Step by Step Guide

1. Cut Your Plate

First you need to cut a piece of TLC plate of the appropriate size. What is the appropriate size? It depends on the purpose of the TLC, and how many spots you need to separate. If you just want to take a look on how many compounds you have in a mixture, one spot is enough.

TLC plates are generally made of aluminum coated by the stationary phase, and can be cut with scissors. Sometimes, the supporting material is glass and you will need a glass cutter to do the job.

Usually, a thin layer chromatography plate is around 5–7 cm high, and a line is drawn around 0.5–1.0 cm from the bottom. That is the line in which you will spot your mixtures to separate. It is important that you spot the mixtures above the solvent level on your elution chamber!

Also, remember to leave some separation between each spot at the bottom spotting line (so they don’t mix to each other!) and also leave a similar separation (of around half a centimeter) from each edge of the TLC plate.

2. Spot Your TLC

Then is time to prepare the samples of the mixtures to separate, and spot them on the TLC plate.

For simplicity, let’s start off with just a single spot, in which we will put a solution of a mixture of several compounds.

First we need to prepare a solution of our mixture. The usual average concentration of these solutions is a few miligrams of mixture/compound in around 0.5–1 mL of solvent. Those few miligrams are totally approximate. Just add a spatula or Pasteur pipette tip and dissolve it in a bit of solvent!

Once you got the solutions prepared (in this case, just the one!), it’s time to spot it on the bottom line of the TLC. You need to use a capillary tube (see the corresponding section for details). Take up some mixture solution with the capillary tube and press it lightly into the corresponding marked spot (use ALWAYS a pencil to mark in a TLC! Pen ink will elute with organic solvents, pencil graphite will not!) at the line around 0.5–1 cm above the bottom of the TLC.

Try to spot your mixtures as tightly as possible. Make very small spots of sample. Very wide spots will make the different compounds overlap leading to a not so nice separations. Maybe even some compounds will be hidden since those will be basically co-eluting with other massive spots. Generally speaking, more diluted and smaller spots are they way to go.

3. Elute the TLC Plate

Then is time to elute the plate. For this you need an elution chamber. There are commercial options, as the one in the picture below, specific for that purpose.

But you can use any glass container that you can cap, actually. A beaker works. A a clean jam jar will also do the job!

Then you need to fill it with about 0.5 cm height of the desired solvent system.

There is no absolute best starting point for selecting a solvent system. However, a extremely quick summary would be:

• If you are working with absolutely apolar organic molecules (no polar functional groups, only C and H), such as naphthalene, start with pure pentane or hexane.
• If you want to separate a compound with one or two mildly polar functional groups (ether, ketone, ester…), go for a 4:1 hexane/EtOAc mixture.
• If your molecule has one or two very polar groups (alcohol, amine, etc), go for 1:1 hexane/EtOAc.
• If your molecule is much more polar than that (e.g. a sugar, an amino acid…), swap hexane for DCM, and keep EtOAc as polar component. Use a 1:1 ratio for starters.
• If your compounds are so polar that do not move at all from the baseline with DCM/EtOAc, go for 9:1 DCM/MeOH or even 9:1 EtOAc/MeOH.
• If none of this works, you are looking at a extremely polar compound and you might want to consider using reverse phase (an apolar stationary phase, instead of silica gel)

If you want more details about choosing a solvent system, check the corresponding section below!

This being said, it is important that the solvent level is below the initial point where you spot your samples! Otherwise, they will get diluted and you will not get a clean separation.

Once the chamber is ready, just put in the TLC inside, vertically, and wait for the solvent to go up by capillary action. Take out the TLC plate when the solvent level is around 90% form the top (don’t let it drown!)

Before the plate dries, mark the eluent front (the line on the plate the solvent level has reached). You will need this to determine the retention factor (Rf) of each spot/compound.

Then, dry off the plate (with compressed air, blowing air, or just waiting…)

4. Visualize the TLC: Check Out the Results!

Finally, visualization. This is a matter of finding the right way to visualize the spots corresponding to each compound in the mixture you just separated.

If they are strongly colored (as in the picture above), you are good! You don’t need anything else, just look directly at the plate.

Most of the times, organic compounds will not be visible, but they will absorb UV radiation. So you just use a UV lamp. Finally, there are a lot of staining solutions that can be used to develop the plates and easily tell where each compound appears. Scroll down to the corresponding section to known more about visualization.

5. Determine the Retention Factor of the Different Compounds

What is Retention Factor?

In thin layer chromatography, retention factor (Rf) is the distance that a compound travels through the stationary phase (TLC plate) between the origin spot and the distance the solvent front moved above the origin.

To calculate the value of the Rf, you just have to apply this simple formula:

Rf(spot) = (distance the spot has moved)/(distance solvent front moved)

A visual example:

After eluting a mixture of benzaldehyde and benzyl alcohol in a TLC plate using 7:3 pentane/diethyl ether as a solvent, the two compounds travel a certain distance.

Benzaldehyde is less polar than the corresponding alcohol, so it is easily identifiable as the top spot.

After measuring the distance that both of the spots traveled, we can determine the retention factor for each compound in that solvent mixture. Simply divide the distance that one spot has traveled by the total distance the solvent has moved from the origin spot line.

For example, for benzaldehyde, it moved 3.2 cm from the origin. The solvent from has moved a total of 5 cm. So we can say and report the Rf of benzaldehyde in 7:3 pentane/diethyl ether to be 3.2/5 = 0.64.

Please, keep in mind that retention factors depend greatly on the solvent system used and on the stationary phase of the TLC. If you modify any of those, Rf will change. That’s why when reporting retention factor values, it is essential to specify those parameters for each compound.

6. Re-run the TLC with a Better Solvent System if the First Attempt Was not Successful

Finally, something that is very common while working with new compounds: Many times the first choice of solvent system will not be the appropriate, and maybe all the compounds of the mixture eluted together to the top of the TLC, or just didn’t move from the base spot, or maybe they are somewhere between, but still the separation is not perfect.

In any of these cases, you just have to keep tweaking the solvent system until you find the most suitable for your mixture!

It is not uncommon to run 3-4 TLC plates of a reaction crude (even for experienced chemists) before starting a flash column chromatography purification.

And that is pretty much what you really need to know to perform a TLC experiment. The only thing left is knowing which solvent system you need to separate your mixture appropriately, and to know what are the real-life applications of TLC.

Was anything not clear?

Don’t worry, a video is worth a thousand words! Check out this video guide for TLC:

A Quick Infographic Guide for Thin Layer Chromatography

After lining up the entire procedure for running a TLC, I want to cut to a quick reference graphical guide that we prepared.

It is the most visual way to sum up TLC technique that we could think of, and here it is for you:

Please, feel free to link, share and use this infographic as you please!

From this point, the introduction is finished.

We will get first into the main basic uses of TLC. Then we will move onto more details into each component of the technique. Then we will cover more advanced uses and techniques, such as prep TLC, 2D TLC, or flash chromatography.

And then we will finish with some mind-blowing tips and tricks and TLC troubleshooting.

Keep reading!

Thin Layer Chromatography for Reaction Monitoring

The main use of TLC is monitoring chemical reactions.

In a chemical transformation, you usually have a starting material (SM) that will get consumed to give rise to a product. In most cases, this product will have a different polarity than the SM. This means that they will have different retention factor in TLC, and you will be able to separate them by TLC.

You generally want a solvent mixture that gives both compounds a retention factor between 0.2 and 0.8. But of course, the main idea is that you can see both spots resolved, not together, so you can see if you still have SM in your reaction mixture or if it is all consumed. This would mean that the reaction is finished in most of the cases.

The trick is to make three spots on the TLC, one with the SM, another one with the reaction mixture (RM), and another one in the middle (co-spot or cross-spot) in which you put both a solution of the SM and the reaction mixture. This way you can clearly visualize, after elution, that your SM actually reacted to form a new product. This is particularly important if both SM and product have very similar Rf, and it is difficult to see if you actually have a new product or just SM in the reaction mixture.

As you can see in the diagrams below, it is very easy to see whether a reaction didn’t work at all (yet), if a product is being formed, but the reaction is not finished, or if all SM has been consumed and there are only products on the RM.

Furthermore, if you happen to have a sample of the reaction product that you want to obtain (because maybe you had run the same reaction before, or because it is a commercially available product), you can add another spot for the product, and another for a co-spot of both product and reaction mixture. This way you can confirm that the desired product has been formed.

TLC for Column Chromatography Purification

The second most typical scenario in which you are gonna have to use thin layer chromatography is while working on a flash column chromatography purification.

What Is Column Chromatography?

Column chromatography is a method for separating and isolating chemical compounds in the lab on a preparative scale, depending on its relative polarity.

The basis are exactly the same than for TLC. We have a glass column filled with a stationary phase (also usually silica gel).

On top of the stationary phase, we put the mixture of compounds that we want to separate. When we are trying to isolate one product from a reaction mixture, we call this mixture “crude product”.

Then, we pass solvent through the column, from the top to bottom, sometimes aided by applying pressure (this is what we call “flash column chromatography”). This makes the different compounds of the mixture elute through the stationary phase at different rates.

Then, the different fractions that come out of the bottom of the column are collected in different test tubes. If the separation was performed correctly, we will have each compound of the mixture in different test tubes. The we can just get rid of the solvent by evaporation and we will have our product pure.

The rate of elution for each compound depends on its retention factor (i.e. its polarity) in that particular solvent system. This means, they will come out of the column in the same relative rate rate as their spots eluted in a TLC.

How Do We Use TLC for Column Chromatography?

Well, first of all, before running a flash column chromatography, we need to select what is the appropriate solvent system for the purification. We do this by using TLC.

Ideally, the product(s) that we want to isolate, should have an Rf (retention factor) of around 0.4 in a given eluent (mixture of solvents) to allow for a smooth column purification.

The following image on the left illustrates how an ideal TLC for purification should look like. As you can see, two products are clearly visible and separated. So the solvent mixture that yields this result on TLC, will be a great choice for running the big scale column chromatography purification.

The images on the right, illustrate how this separation does proceed using that same solvent system. As you can see on the far right, the first compound leaves the column completely separated from the other one. It can be collected, and concentrated in vacuum, getting your product completely pure and dry!

TLCing the Fractions from Column Chromatography

But after running the column chromatography, you usually end up with dozens of tubes filled with eluent with the different compounds dissolved. Now we have to use TLC again!

As you can see, we spotted all the fractions/test tubes on the TLC, and eluted in the same solvent system. As you can see, we have two different products (spots) that came out of the column pretty close.

From fraction 5 to 10, we only have compound one, pure. We can mix these fractions, concentrate them, and we will have pure compound 1.

Fractions 11 and 12, have a mixture of the two compounds. Usually we throw away this kind of mixed fractions (unless we don’t actually care about the impurity, maybe it just doesn’t affect the next step of our synthesis!).

Fractions 13 and 14 have pure compound 2. If we also need this compound, we will just concentrate them together as well.

As you can see, TLC is extremely important for both reaction monitoring and product purification, the two cornerstones of any synthesis laboratory.

Checking What’s on Each Fraction with Other Techinques

Sometimes TLC is just not enough and you don’t know what compound/product is in each of the different fractions that came out of your flash column. Evaporating everything and taking an NMR is really time consuming, so you might want to go for an alternative technique if it’s available to you.

If you have access to a GC-MS (gas chromatography-mass spectrometer) or LC-MS (liquid chromatography-mass spectrometer), you can analyze quickly all the different fractions, and know the molecular mass of the compound(s) present on each of them.

Another cool instrument is the TLC-MS. This technique is usually much less available in chemistry labs than GC-MS or LC-MS, but if you can use it is great. Basically this machine automatically scraps off individual spots on an eluted TLC, and makes an MS analysis, so you can check the molecular masses present on of each spot of the TLC in usually less than a minute.

A Comment on Retention Factors and Flash Column

Using an eluent which gives an Rf of 0.4 for your compound is the usual rule of thumb, but it has of course many exceptions. If you have two compounds that are very close together in Rf, this might not be enough. Having two compounds show as two separate spots in TLC doesn’t mean that they will come out separately from flash column.

Column bands are like much much wider TLC spots, especially as we scale up the purification. Imagine that typical TLC that you overload with sample and you get two big unresolved overlapping spots. That is a closer picture to what is actually happening in your column chromatography.

For this reason, sometimes an Rf of 0.4 will not do the trick. If spots are separated by less than 0.15 Rf, you will usually need to be a bit more conservative and choose an eluent in which they have a retention factor of around 0.3, or even a bit less. Another cool trick to enhance this kind of purification is using thicker columns, this helps a lot with separation. Using longer columns doesn’t usually help, since you are just thickening the bands and making them overlap more!

On the flip side of the coin, sometimes your compound of interest just flies on TLC using certain solvent mixture, giving an Rf of 0.7-0.9. This might allow for extremely easy and fast separations in a couple of the first tubes/fractions.

In Depth Guide: Materials for Thin Layer Chromatography

Making Capillary Tubes

You will have to spot reaction mixtures, or reference samples in your TLC using capillary tubes.

You can either buy them, or make them yourself. This depends on your lab’s budget, but I don’t think there is much harm in buying some good capillary tubes. The commercial ones I use on a daily basis, usually last for months before breaking, if you are careful enough.

But you can make thin capillary tubes out of thicker glass tubes, you just need to heat them up and then pulling. For this, you can either use thicker capillary tubes or glass Pasteur pipettes.

Explaining the method for heating and pulling will sound more complicated than it actually is, just take a look at this short but on-point video:

As you can see is not terribly complicated, and it can even be a nice experiment for undergraduate labs. Just be careful with the flame (or other heating source that you use! Avoid using open flames in the lab if you have alternatives).

Elution Chambers for TLC

So, there are actual chambers designed for running TLC, and they are just great, such as these from Fischer:

But that doesn’t mean you need one of those fancy pieces of glasswares to run a TLC. The beauty and simplicity of this technique is that you can use it in basically any situation!

A typical temporary solution, if you are in a rush, is just using a beaker covered with something (like a watch glass, or even aluminum foil), so the solvent doesn’t evaporate and allows for a nice saturated atmosphere

It is worth mentioning here that this is another key for a good eluent chamber: You need the atmosphere as saturated as possible. This way, the solvent doesn’t evaporate on its way up through the plate, which would cause an uneven movement of the eluent front. This can be detrimental for the separation, so always ensure that your chamber is a reasonably closed system.

As you can see in the picture above, you can also put a piece of filter paper inside the chamber a while before eluting your TLC.

Why? The solvent will ascend through the filter paper as well (by the same principle than through the TLC), helping a lot in saturating the atmosphere inside the chamber with the eluent. This will make the eluent go up the TLC plate in a much more even manner.

Also, be patient, leave the eluent in the chamber with the filter paper for a while before eluting you plate!

Finally, the more practical low-cost alternative, in my opinion, is just using a glass tar with a screw cap, like the ones you get you jam, or other edible stuff in!

I survived through my undergrad labs and also through my first research experience only by using these “ghetto-chambers” on a daily basis!

Alternative Stationary Phases

As we were saying, more than 95% of the cases you will perform a TLC in plates coated by silica gel as stationary phase.

But there are very specific cases in which different stationary phase may be considered.

Silica gel (SiO2) is slightly acidic, so certain compounds are quite sensitive to these acidic conditions. In those cases, you can first try to neutralize the silica gel adding a basic solvent to your eluent (typical conditions are adding 2-5% of triethylamine to your solvent mixture).

Many times this does the trick, but in other cases is not enough. For those cases, there are alternative stationary phases such as neutral alumina (Al2O3). Maybe your target compound does survive in alumina and you can use it for both TLC and flash column chromatography purification.

Another alternative stationary phase is reverse phase.

Typical silica gel stationary phases are very polar, and you elute the plate with a solvent systems that is (much) less polar than SiO2. This works wonders form most typical organic compounds.

However, if you are working with extremely polar molecules, you will find that they get stuck into the SiO2 like crazy and no matter how polar you make your eluent, they simply won’t move.

For these cases, we can use reverse phase chromatography, in which the stationary phase is apolar (it will retain polar compounds much less), and you will use polar solvents, such as MeOH, as eluent. Very polar compounds, such as oligopeptides, can literally fly on reverse phase.

But these alternative stationary phases have some drawbacks:

• They are not the standard method, and many times you won’t find TLC plates of alumina or reverse phase around in the lab.
• Correlating with being less available: they are more expensive than silica gel.
• In general, separation and resolution are worse. Also visualization can be more difficult in certain plates.

But sometimes (although very few times, we have to say) they are the only way to go, so keep in mind that these alternatives exist!

Finally, I have to mention that simple filter paper can be used as stationary phase. Separations are going to be bad, and you will get poor visualization. But if you have colored compounds, you can still see some separation. As a matter of fact, my first TLC experiment was just spotting a solution of spinach extract on filtering paper, and eluting it with acetone.

Visualizing Agents: Which One is Best?

There is no use in running a TLC if you cannot see the spots of the different compounds on your mixture. That’s why having access to the appropriate visualization technique is a must.

Visible or UV Light

Sometimes your compounds absorb visible light very strongly, and you don’t need visualizing agent at all. You can see the spots right as they elute up the plate!

This is common with highly conjugated compounds (such as polyaromatics, or polyenes), and with organometallic compounds, such as ferrocene derivatives. These compounds are great because you can basically run TLCs and column chromatography purifications knowing at all times where your compounds are on the silica!

However, most organic compounds do not absorb visible light strongly enough. So you have to use a visualizing agent.

The most common one is just using an ultraviolet lamp. TLC stationary phases are prepared to make your compounds visible in certain UV wavelengths. Most organic compounds, which have a minimum of conjugation will be observable in this manner.

But there are some compounds which don’t even absorb light on the wavelengths typically used in TLC UV lamps. Those are generally highly aliphatic compounds with little functional groups.

For these cases, we use staining agents.

Staining Solutions

Staining agents for TLC are basically solutions of one or more compounds in which we can dip the plates after elution. They will react with your products and help visualizing easily all the different spots/compounds present.

It is worth keeping in mind that, even if your target compound(s) absorbs strongly UV (or even visible) light, it is recommended to stain the plate anyway, if you can. This is because there might be other components of the mixture present as impurities which you cannot observe correctly under typical UV-Vis conditions.

So remember, even if your compound is visible at first sight, check also under UV light. And even if you can see everything under UV light, developing the plate with a general-purpose staining agent will almost never be overkill.

Now follows a list of the most typical staining agents, and how to prepare them. There are many others, some incredibly specific for certain types of compounds. But for the reasons, above, I’d always go with a general-purpose stain. And one of these will work for >95% of organic compounds, so pick your favorite, and go!

Acidic Vanillin

Many people use this vanillin solutions. It is really easy to prepare, and after heating, it is really sensitive to most functional groups.

The coolest thing is that many times, small changes in functionalities on organic compounds lead to a change in the color of the TLC plate after vanillin staining and heating. This is really great if your starting material and product have a very close Rf. You can still differentiate them by the color!

Specifically, it shows brightly most compounds with polar functional groups. It might not be great for highly apolar compounds, such as simple alkenes or aromatics.

The recipe for this stain is really easy: Weigh 10-15 g of vanillin, dissolve it 250 mL of ethanol, and add 2.5 mL of concentrated sulfuric acid. Stir and you are good to go! To use it just dip your eluted TLC plate, and heat up with a heating gun.

Phosphomolybdic Acid (PMA)

This is another great general purpose stain. It is my personal favorite, and it does color almost anything you can find in an organic chemistry lab. From polyaromatics to alcohols, going through alkenes, or simpler aliphatic compounds.

It gives you different blue-green shades, so it might not be the best for identifying different compounds with similar Rf, but for first choice, it will do great.

This staining solution is also extremely easy to prepare. You just need to dissolve around 5 g of phosphomolybdic acid (buy the lesser quality one for this purpose!) for each 500 mL of ethanol, and it’s done!

Potassium Permanganate (Basic KMnO4)

This is the most classical one, probably the cheaper option, and it is also quite general. Basically it turns your TLC plate purple, and every compound that can potentially be oxidized will show up as a yellow spot. This guy makes no distinction, and TLCs don’t look very pretty, but sometimes it does the trick.

The usual recipe is a bit more complex here, but nothing that you won’t find around in any lab. You basically need to dissolve 1.5 g of potassium permanganate and 10 g of potassium carbonate in 200 mL of water. To this mixture, add in 1 mL of 10% aqueous NaOH, and stir. Just be careful not to stain yourself with the mixture! You don’t want your skin to get oxidized (i.e. dark brown for a couple of days-weeks…)!

Cerium Ammonium Molybdate/Sulfate/Nitrate (CAM/CAS/CAN…)

This stain is also known as Hanessian’s Stain, or simply “blue stain” (for obvious reasons), and it is another multi-purpose beast.

It is a water based stain which makes your spots turn blue over a cool pale yellow background, after heating. If you heat too much, the background will also turn blue and the plate won’t look so nice, so be careful!

I have seen people use two different recipes. Both work more or less the same, it just depends in which cerium reagent you find around/is cheaper for you.

Dissolve 5 g of ammonium molybdate and 1 g of cerium sulfate (OR 2 g of cerium ammonium sulfate) into 100 mL of water. To this mixture, add 10 mL of concentrated sulfuric acid, and stir!

Other Staining Agents

There are many other staining agents, but they are usually more specific for certain types of compounds, and not the best ones to prepare or use routinely in the lab.

• Iodine vapor chamber: Fill a more or less sealed jar with a small spoon of iodine crystals. Cover it with silica gel. Put the dry eluted TLC plate in this developing chamber, and wait for the brown spots to appear. This is not the most sensitive stain, but the good thing is that you can use the same plate and develop it right after with a different stain.
• Ninhydrin: A solution of 10 g of ninhydrin in 250 mL of EtOH. It is great for amines, especially primary ones. Those will show up as green spots even before heating.
• Dinitrophenylhydrazine (DNP): Dissolve 1 g of DNP in 250 mL of aqueous HCl 2 M. This stain is extremely selective for aldehydes and ketones. Those spots will turn orange immediately at room temperature.
• Anisaldehyde: Dissolve 4 mL of anisaldehyde in 200 mL of EtOH. Then, add 3 mL of glacial acetic acid and finally 10 mL of concentrated sulfuric acid. The result is a stain very similar to vanillin. Maybe less selective and less easy to prepare, but sometimes, it makes for a wider variety of colors after development, allowing to distinguish very close spots on the plate.

Solvent Polarity: Reference Guide

To anyone with a couple of years of experience in the lab, choosing the solvent combination for running a TLC or a column comes really easy. Or at least a good starting point.

But for beginners, it can be really overwhelming. After all, there are a lot of different functional groups, and A LOT of different combinations. Not to mention the endless solvent combinations that you could imagine.

That is the reason why it is extremely difficult to find a good guide out there to choosing the eluent for chromatography.

A Solvent Polarity Guide for Thin Layer Chromatography

We wanted to get as close as possible to the best guide. And we came up with the following infographic for choosing solvents for TLC.

Keep in mind that of course this is an orientation and approximation, and there will always be compounds that behave weirdly. But we think that it will do the trick to for most situations, at least as a first shoot for a new reaction that you are running.

As you can see, we have broken down organic compounds depending on their functional groups, and added a value in the form of a % of polar solvent that you would need to your eluent mixture in order to get the compound with that group to go up the plate significantly.

We have limited it to classical mixtures of apolar solvent (hexane, pentane or cyclohexane) and polar solvent (ethyl acetate or diethyl ether), as a combination of these solvents will be usually enough to deal with most organic compounds.

Again, this is an approximation, and the values are not always additive. For example, an alcohol elutes with a 7:3 hexane/EtOAc. But if you have 3 alcohols, it is not certain that 1:9 will work. Maybe 1:1 is enough. Or maybe not even 1:9, maybe you even need to add methanol. There is no universal rule, that’s why guides such as this one are not very abundant.

As you can imagine, the most polar group itself will often dictate the polarity of the entire molecule.

Relative polarities of “minor” groups are important. Take a molecule which has an amide (6:4 hexane/EtOAc), but also a methoxy group (2-3% extra polarity). Then you change that methoxy group for an alcohol. Alcohol adds an extra 30-35% of polar solvent, so your reaction product spot will appear below the one for your starting substrate!

Which One of the Most Common Solvents is Better?

For practical purposes, solvents such as pentane, hexane, heptane or cyclohexane are similar, polarity-wise.

However, there are several considerations that might make you go for one or another.

Hexane/EtOAc is usually the standard mixture for organic separations. However, hexane is known to be a neurotoxic compound, that’s why many people swap from hexane to cyclohexane or heptane.

The only problem with those two solvents is that are less volatile, and more difficult to get rid of. If you need a more volatile alternative, use pentane. This should be used in cases where your target compound is relatively volatile and you cannot put it under high vacuum to remove the solvent completely.

In the polar component side, ethyl acetate and diethyl ether can be the main options. Diethyl ether is more volatile, so it should generally be avoided if possible, unless it gives you a much better separation or your target product is also volatile.

Also, when pairing solvent mixtures, try to go for solvents with similar volatility, so you don’t get faster evaporation of one of the components of the mixture than the other. This can potentially lead to reproducibility issues.

“Sticky” Compounds with Acid or Basic Sites

As an exception, you might want to consider as additives (up to 5-10%) of your mixtures other solvents such as MeOH (for extremely polar compounds), triethylamine (for compounds with basic sites) and acetic acid (for compounds with acid sites).

Compounds with basic or acidic sites, such as amines, amides (basic) or carboxylic acids (acid), can sometimes stick to the silica gel of the stationary phase a little bit too much.

This results on very wide spots on TLC, and as a consequence, very broad bands in your flash column chromatography purifications. Band/spot broadening often complicates purification, since your target compound might overlap with a byproduct or impurity that you want to get rid of.

Many times this has a simple solution: add to your solvent mixture 2-5% of triethylamine for basic compounds. This deactivates de acidic sites of the silica: Si–O–H bonds. These bonds, or extra protons, are responsible of basic compounds sticking to the silica gel, and making broader bands/spots. By adding Et3N to your eluent, you remove all of them and your compound will elute freely!

Similarly, acidic compounds such as carboxylic acids can react with Si–O bonds in silica gel to give Si–O–H, which really makes them stick to the stationary phase. You just need to add acetic acid as an additive, saturating Si–O sites into Si–O–H. This will make acidic compounds much more mobile through the TLC plate or column.

Preparative TLC

We have already covered flash column chromatography in a previous section. Running purifications is one of the main applications of thin layer chromatography.

But we can actually apply TLC to run preparative-scale purification. Not just to check how the different compounds/spots on a mixture separate, but to separate our reaction mixtures themselves, and isolate miligrams of pure products!

How Does Prep TLC Work?

Well, preparative TLC is just a regular thin layer chromatography separation, but with a bigger plate!

There are commercial TLC plates made specifically for prep TLC. They are usually made of glass coated with a thicker layer of silica gel. Then, instead of a single point spot, you apply the solution of your mixture (in roughly 0.5-1 mL of a volatile solvent such as DCM) along a line, parallel to the bottom (around 3-4 cm above the bottom).

For applying this solution, I usually use a 1 mL syringe with the thinest needle I can find. It has to be uniform and you need to be careful not to scrap the silica!

After drying it, you elute the plate in the appropriate solvent system (carefully chosen by classical TLC), and the different compounds will get separated. You obviously will need a bigger chamber. Typical prep TLC plates are around 30×30 cm.

Afterwards, you just need to scrap off separately the bands that you are interested in. For this, visualize the plate under UV light, and mark with a pencil the bands you are interested in.

Then, scrap off the band, and just pass a polar solvent such as DCM through the silica gel with your product, so it gets dissolved. Filter it off to get rid of the SiO2.

Then, just remove the solvent and there you go, pure product!

Preparative Thin Layer Chromatography: When Should I Use It?

So what are the advantages of preparative TLC?

• Allows you to separate compounds that are extremely similar in polarity. Often times, you can separate a little bit two compounds by TLC but they wont come separately after column chromatography. This is the perfect scenario to run prep TLC!
• You elute the plate several times with lower polarity solvent. If you need to perform a very careful separation, just use an eluent in which your compounds have a retention factor of around 0.10. Then, dry the plate, and elute it again. Repeat this process until your bands are well resolved.
• It’s handier than column chromatography. You just spot your compound, put the plate in the elution chamber and wait until the solvent goes up. Then dry and repeat until the level of separation pleases you. In the meantime, you can do anything else!
• It’s great to separate compound when you have only a few miligrams. Doing flash column of 10 mg of target product can be painful. This is not a problem with prep TLC.
• Sometimes you can use the same 30×30 to elute several mixtures. You can cut the glass plate on half to use different eluents, or just mark it in half with a pencil and deposit each solution in each of the halves, along the same parallel line.

But of course, there are drawbacks:

• It is not really scalable. I have separated up to 100-150 mg of compound using 2000 microns silica gel prep plates. But you cannot really go further than that in a practical manner. Preparative TLC is great for purifying the products of a reaction scope, or for the final steps of your total synthesis, but you cannot get grams of pure material with it.
• If your compound does not absorb UV or visible light, you will have a hard time knowing where it is on the plate. You can always “paint” a vertical line with a staining agent on one edge, and then heat. But I would only use this as a last resort measure.
• It is more expensive than flash column chromatography. No more to add to this, regular silica gel will always be cheaper than a commercial prep TLC plate. And making them yourself is really time consuming.

All this being said, I will leave you with a short time-lapse video of how does running preparative thin layer chromatography go:

Reporting Thin Layer Chromatography Data

TLC is a simple yet widely used technique. So in most reports and journals, you should provide information about TLC data for experimental procedures.

The very minimum is stating in which solvent mixture you have run the purification of each compound.

The best way, is reporting retention factors (Rf) of your product in a certain solvent mixture.

For example, you report a procedure to make benzaldehyde. You should mention that the product was purified by X chromatographic technique, using pentane/diethyl ether 1:1 as eluent, in which the product has a Rf of 0.75.

Tips and Tricks for Thin Layer Chromatography

We will finish by gathering some tricks, tips and lab hacks for TLC. You will definitely find something useful here!

2D TLC: Checking Compound Stability

Two-dimensional thin layer chromatography or 2D TLC got me through my first year of grad school, when I had to work with a great deal of compounds that could potentially decompose during purification on silica gel.

How to run a two-dimensional TLC

1. Get a square TLC: Cut a TLC plate with the shape of a square, around 7×7 cm is fine.
2. Spot the sample in one corner: Spot the solution of your sample in one of the corners of the square, leaving around 0.5-1 cm from each of the two borders.
3. Elute the plate in one direction: Use an eluent that gives roughly an Rf of 0.5 for your compound, and elute the plate as usual in one direction.
4. Elute the plate in another direction: Dry your plate, and rotate it 90 degrees, so the lane of all the spots is at the bottom. Elute it again on this direction.
5. Analyze the results: Any compound that is stable in silica gel, will appear somewhere in the diagonal of the square plate. Any compound that appears below the diagonal is decomposing.

Sand Bed for Your Elution Chamber

We have covered this sand bed for TLC in our lab hacks post.

If you have trouble leaving your plates standing vertically on your elution chamber, of if you want to run many plates on the same eluent at the same time… Get a big enough chamber, and make a bed with sea sand at the bottom (about 2 cm is enough)

Then, put your eluent in the chamber covering just a bit above the sea sand, and stick all the TLCs you need on the sand! They will not fall, and you can elute many of them parallel to each other.

Frequently Asked Questions (FAQ)

Closing Up and Conclusions

We really hope this comprehensive guide can help you master this wonderful technique.

Also, thanks to Lisa Nichols for borrowing some of her images from: Organic Chemistry Laboratory Techniques, Nichols, 2017.

Top sum up, o matter if you are new to synthetic chemistry or an experienced researcher, we hope you have learnt something from it!

Also we would love to hear from you and read your feedback and questions!

So please, head right into the comment section, and ask whatever you want. Remember that there are no stupid questions.

Any criticism and suggestion to improve the guide further will be highly appreciated. If you think that something is missing, or not well explained, go for it.

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