Today's Blog is Brought to You by the Letter N and the Number 7

I recently was part of a conference where young girls in grade 6 are brought to the University to take part in science experiments. The lab that I personally teach with them is "Cryogenics". This lab is a lot of fun and involves investigating dry ice and liquid nitrogen. So today's blog is dedicated to the young lady who asked me about the discoverer of liquid nitrogen.

Nitrogen was discovered by Joseph Priestley (1733-1804) between 1773-1780. In this time he also discovered ammonia (a nitrogen based gas), carbon monoxide, sulfur dioxide, silicon tetrafluoride, and his most famous discovery: oxygen. On the periodic table, nitrogen is element 7, and is symbolised by the letter "N". Its boiling point is -196 C.

Nitrogen exists as a diatomic molecule, N2, making up over 75% of the Earth's atmosphere. The two atoms are held together by a triple bond that has a bond energy of over 800 kJ/mol. (This is A LOT, making this bond very favourable!)  In the form N2, nitrogen is completely inert; however, other molecules that contain nitrogen are not inert. Many explosive compounds contain nitrogen, the most notable being TNT: TriNitroToluene. Anything that has a high nitrogen content risks becoming explosive due to the extreme favourability in the formation of N2. 

The Haber Process: NH3 is ammonia and is an important fertilizer for crops (plants need nitrogen). However, very few plants actually have the ability to draw nitrogen from the air and convert it into a usable form. They require a symbiotic relationship with microorganisms in their roots to do this. This is called "nitrogen fixing". One of the most important discoveries in human history is the Haber Process.  While N2 may be inert, ammonia is not and in 1908 Fritz Haber worked out the necessary conditions for converting nitrogen from the air into ammonia. This process became instrumental to Germany's World War I effort because it allowed for the production of inexpensive explosives. Of course today this process is still used to generate ammonia and is celebrated for the feeding 1/3 of today's population with ammonia-fertilised crops. (Interesting Historical Side Note: Haber also worked with chlorine gas, and was instrumental in developing the practice of using this poisonous gas by German troops in the trenches during World War I. In 1933 this Jewish scientist, who had contributed to the German war effort considerably in WWI, was driven from his work by the Nazi regime.)

Back to nitrogen: liquid nitrogen was first obtained in 1895 with the invention of the liquifaction of air. This process also allowed for the separation of the components of air by distillation. Nitrogen is the most volatile (lowest boiling), boiling at -196 C. This is followed by oxygen at -186 C. And lastly, argon at -183 C. Liquid nitrogen is often used in flash freezing. Anything that has a high water content will freeze extremely quickly. In the lab I ran, I froze flowers, tomatoes, bananas, and latex gloves which the girls then smashed, much to their delight. (My favourite are always flowers as they shatter like light bulbs.) Being inert, liquid nitrogen is relatively safe and easy to work with. I actually freaked out some of the girls by showing that you can pour liquid nitrogen over the hand of a person (I had another lab helper not one of the kids do this) and it will not freeze them because the temperature of a person's hand at +37 C causes the liquid nitrogen to immediately evapourate into gas before touching the skin. Not unlike dropping water on a hot skillet. The big danger is with its ability to liquefy oxygen. This is a very reactive compound, to the point of scary! My favourite thing to do with liquid nitrogen is to make ice cream. If you ever have the chance to have liquid nitrogen ice cream, take it!

 
References:

Gray, T. The Elements 2009 Black Dog & Leventhal Publishers Inc., New York, NY.

Petrucci, R. H.; Harwood, W. S.; Herring, F. G. General Chemistry 2002 Prentice Hall Inc., Upper Saddle River, NJ.

Balchin, J. Quantum Leaps: 100 Scientists Who Changed the World 2010 Arcturus Publishin Limited, London. 

What's in a Chemical? Would a Rose Made of Any Other Smell as Sweet?

Hello followers. I apologise for the long delay since my last entry; as many chemists will understand, I had an exam to prepare for. An exam which is the most important of the Ph.D. path. So I can now get back to entertaining your chemistry questions (please keep them coming). During my hiatus, I also took in a chemistry conference in Hawaii. It was there that the inspiration for today's blog comes from. Here is a picture of a packet of sunscreen. If you notice, it says that it is "chemical free". So what is in this sunscreen? Let's take a look at the back of it: Active ingredients are zinc oxide and titanium dioxide. Those sound like chemicals to me.


Chemistry is the study of matter; therefore, anything that has matter is a chemical. Matter is comprised of atoms. Anything with atoms is a chemical. I am sure you can now see where I am going with this. This sunscreen is a chemical. This makes this packet blatant false advertising. If it isn't matter, then what is it? Energy?


This to me highlights one of the many negative public images that chemistry has and that chemists like me try to fight against. Just because something is a chemical, doesn't make it evil or dangerous! This actually goes hand-in-hand with the idea that just because a chemical is natural it is better. This one always makes me scratch my head as the most toxic things on this earth are nature made not man made. We have yet to even come close. Some chemicals are dangerous. Some cause cancer. Others can cause burns. Some will kill you. But you use chemicals everyday, and some are great. Some fight cancer. Can you imagine life without medicines? Those are chemicals. Imagine life without PLASTIC. Hell, imagine life without matter. Without chemicals there wouldn't be life.


Also, be careful when using things that say "natural, chemical-free". Often what these products are made of are botanicals (chemcials from plants). These are still chemicals and it is very easy to develop allergies to these chemicals, especially if you already have a sensitive skin. (This comes from a personal anecdote and the advice of a doctor.) 


Let's talk about matter for a bit. As I said, matter is comprised of atoms (side note: the concept of the atom was proposed by Democritus of Abera around 300 B.C. long before John Dalton in 1803 A.D.) When we talk about elements, we are talking about a substance that is comprised of only a single type of atom. Copernicium is the newest element: symbol Cn, number 112.  When we take about molecules (I, for example, am a small molecule synthetic chemist) we are taking about compounds comprised of more than one atom type. Example: Hydrogen is an element; it is comprised of only one type of atom. Water is a molecule; it is made of hydrogen atoms and oxygen atoms. Chemical changes or reactions refer to the conversion of one (or more) type of matter into another type of matter. For example: converting water into hydrogen gas and oxygen gas. Remember: matter cannot be created or destroyed, but merely change form.


I mentioned that I am a small molecule synthetic chemist. What this means is that my research is concerned with making small molecules. But what is meant by "small molecule" especially considering we are talking about atoms here. To measure molecules we talk about their atom/molecular weight and this is in the units grams per mole (g/mol). (The concept of the mole is a whole other entry so I will skip over that for now.) To get the molecular weight you simply add the atomic weights of all atoms in the molecule. Hydrogen is 1g/mol; oxygen is 16 g/mol; water, which has two hydrogen atoms and one oxygen atoms, is 18 g/mol. A "small molecule" is generally considered to be one under 700 g/mol. There is another type of molecule called "macromolecules". These are molecules whose molecular weight is well over 1000 g/mol. These are generally polymers. So things like DNA, proteins, and plastics are all macromolecules. You are one big, walking, talking collection of macromolecules!


Hopefully I have dispelled some previously negative views you had about what exactly chemicals are. Keep those chemistry questions coming friends!

References:

Petrucci, R. H.; Harwood, W. S.; Herring, F. G. General Chemistry 8th ed. 2002; Prentice Hall Inc. Upper Saddle River, N. J. 


Gray, T. The Elements 2009, Black Dog & Leventhal Publishers, Inc. New York, N. Y.

Elephant Toothpaste-A Way to Prank a Co-Worker?

Another fun reaction that is a favourite demo of chemists is termed "Elephant Toothpaste". This experiment is fairly simple. 

What you need:

A graduated cylinder

30% solution of hydrogen peroxide (note: household hydrogen peroxide is 3% solution)

Potassium Iodide-KI (either solid or saturated solution)

Dish soap

Food colouring (a minty green is where the "toothpaste" moniker comes from.)

The potassium iodide is used as a catalyst-it starts the reaction, but is not consumed in the reaction. The actual chemical reaction that happens is the break down of the hydrogen peroxide into water and oxygen very rapidly, accompanied by the production of heat. 

2 H2O2 ----> 2 H2O + O2

In the graduated cylinder, you mix the soap, the hydrogen peroxide, and the food colouring. Then very carefully add the potassium iodide. The oxygen gas produced causes the soap to foam up rapidly and make a huge mess to the delight of many (except those who have to clean it up). 

This particular reaction has obtained pop culture notoriety by being used on the Big Bang Theory as a method of revenge. Check it out: http://www.youtube.com/watch?v=-pUeOAit7zI 

The amount of foam produced on their kitchen counter is absolutely not exaggerated, which is what makes the demo so cool. 

There is one small thing in this scene, however, that bugs me every time I see it and therefore feel I should mention it now. Sheldon, while wearing latex gloves (which you should wear if you handle these chemicals-serious burns can arise from 30% H2O2. Just think about the sting 3% gives you.) picks up a glass of Mountain Dew and drinks it. This is just terrible and upsetting lab protocol. There is dangerous chemicals on those gloves and all around, and he's bringing them to his mouth! That is a great way to ingest something that may kill you rapidly. It makes me cringe to watch. I guess you shouldn't expect better from a physicist.   

A Chemist's April Fools' Joke: Nitrogen Triiodide

I was recently asked about interesting chemical reactions and so I started thinking about a few fun demonstrations that we like to do during National Chemistry Week, or at the University's Open House. Which brought me to nitrogen triiodide.

Nitrogen triiodide (NI3) is a contact explosive. There are many types of explosions and explosive materials, but I will focus on chemical explosives. An explosion is characterised by the rapid increase in volume and release of energy. This is also accompanied by the production of heat, light, sound, and pressure (the shock wave-this is the part of an explosion that does the damage). Generally explosions produce gasses, this is because the production of gasses is an extremely thermodynamically favourable (see blog entry A Diamond is Forever...Or Maybe Not) process. Explosions are detonated by the application of energy. In the case of a contact explosive, only very small amounts of energy need to be applied to the material. This energy can be in the form of heat, light, sound, or physical pressure. 

Nitrogen triiodide is very sensitive as it produces nitrogen gas and iodine, which are way more stable compounds and therefore results in a huge release of energy. It also produces a sound reminiscent of a gunshot. It does, however, leave purple stains due to the iodine. This compound is actually so sensitive that brushing it lightly with a feather can cause an explosion. The sound produced by the explosion can actually cause subsequent explosions of the compound to occur. I think the following video shows it best:

http://www.youtube.com/watch?v=2KlAf936E90 

A great practical joke is to place this on the underside of toilet seats or in the key holes of doors. Small amounts of course. Just to scare people. (Please note: the author of this blog is not recommending that you try this at home.) 

Ask a Chemist!

Hello loyal followers! This is just a request for more questions. I am putting the plea out there. I want to make sure that your questions get answered so please make sure that you are leaving your questions in the comments. To keep this blog going I need your science questions!

Thanks!

Careful of the Icy Patch!

In the winter time, as hardy Canadians, we pour salt onto the icy patches on the sidewalks to keep people from slipping and preventing litigation. But ever wondered why salt? What does the salt do? Well I shall explain this by introducing the concept of "colligative properties".

A colligative property is one where by introducing an impurity of some sort (this is often called the solute) the properties of the solution are changed. What makes a colligative property different from other chemical properties is that a colligative property is only dependent on the number of added impurity molecules, not the type of molecule.

The important colligative property that we need here in Canada during the winter time is: Freezing Point Depression. When you add an impurity, such as salt or sand or antifreeze (ethylene glycol) to a solution of water (or that icy patch on your front walk) the result is that the freezing point of the water becomes lower. This means that even though it is -15 C outside, the ice on your walkway stays liquid. And because freezing point depression is a colligative property, it doesn't make a difference what kind of additive you put on the icy patch. All will cause the freezing point to become depressed. The amount that the freezing point lowers is solely dependent on the amount added, not what is added. 

Freezing point depression is used in undergraduate chemistry labs the world over as a means to determine the purity of the products that they were supposed to isolate. If they have a pure compound then the freezing point should be nice and sharp, and agree with literature standards. If they have an impure compound then their freezing point will be much lower than the standards.  

Another example of a colligative property is Boiling Point Elevation. When you are making pasta and you add a little salt to the water, this does not make the water boil sooner (contrary to what my ninth grade science teacher taught me) it actually raises the temperature that the water boils at. 

Reference:
Laidler, K. J.; Meiser, J. H.; Sanctuary, B. C. Physical Chemistry 4th ed. 2003; Houghton Mifflin Company, Boston, MA.

A Diamond is Forever...Or Maybe Not

"A diamond is forever" is a phrase synonymous with one of the most successful advertising campaigns in history. This has been the slogan De Beers has used since 1948 to promote the sale of diamonds to couples world wide. It even inspired an adventure of Ian Flemming's 007. De Beers also has told us that diamonds are rare and exceptionally beautiful, neither of which is true. This leads to the question: are diamonds actually forever? Or is this another myth? Are diamonds a stable chemical compound?

Stability: in chemistry stability has a very specific definition. It is determined by the free energy of the product compared with the reactant of a reaction. This is a thermodynamic property. If the free energy of the product is less than the free energy of the reactant, in other words the free energy is a negative value, then the product is considered stable. Now taking a look at two allotopes of carbon (an allotrope is different structural form of the same element): graphite and diamond, we see that by converting diamond into graphite, the free energy is -2.9 KJ/mol. This means that diamonds are higher in energy than graphite, and also means that diamonds are unstable compounds. Hmm starting to look like a diamond is NOT forever.

However, since billions of dollars are tied up in the diamond industry, this must mean that they do not rapidly turn into graphite. This brings us to the concept of lability.

Lability: in chemistry lability describes the speed at which are reaction occurs. This is governed by the activation energy of the reaction. This is a kinetic property. The larger the activation energy, the more energy needed to be put into a reaction to drive it to completion. This is usually accomplished by adding heat to the reaction. In the case of diamonds, there is an extremely large activation energy.  Because of this, diamonds will not be converted into graphite without the addition of an IMMENSE amount of heat. 

So while diamonds are not stable, they are also not labile. This means that De Beers can get away with the slogan "a diamond is forever," even if it is not chemically true because on the time scale of the human lifespan we will never see the conversion to graphite. 

Another example of this that may be important to know during the holiday baking season is table sugar, aka sucrose! Sucrose, by the definitions above, is unstable because upon heating it has free energy of -5650 KJ/mol! But again, sucrose is also not labile and therefore requires the addition of heat. But the activation energy is not nearly as high as it is for diamonds, which is why sugar is so easy to burn: it doesn't require too much heat and causes the release of over 5000 KJ of energy. Keep that in mind before you ever try to microwave icing (I am looking at you Bridget).

References:

Petrucci, R. H.; Harwood, W. S.; Herring, F. G. General Chemistry 8th ed. 2002, Prentice Hall Inc. Upper Saddle River, NJ.

Campbell, G. Blood Diamonds 2004, Basic Books, Cambridge, MA.

Gray, T. The Elements 2009, Black Dog & Leventhal Publishers Inc. New York, NY.