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.

Today's Blog is Brought to You by the Letter K

K is for potassium. Potassium is element 19 on the periodic table and its symbol arises from Latin for potassium carbonate kalium. (Sodium metal, symbol Na comes from Latin for sodium carbonate natrium.) It has an atomic mass of 39.098 g/mol. It is an alkali metal and is therefore known for its explosive reaction with water. It is actually more reactive than sodium metal and results in pretty purple flames. The K 40 isotope (sorry, I can't seem to publish superscript so this is not the correct notation) is actually radioactive-that's right that banana you had on your Cheerios this morning was radioactive! Of course this is nothing to be concerned about since this stuff is everywhere and is postulated (by Isaac Asimov) to be a contributing factor to our evolution. Please note that only one hundredth of one percent of potassium atoms in the world are actually the radioactive K 40 (which can be figured out by examining the atomic mass; however, since I started this blog for my sister I should probably skip the math lesson.) 

But what I would like to talk about today is K+, the potassium ion. This little guy is very important to life. For plants it is essential for growth, which is why it is included in plant fertilizers. My research has so far has found that the exact role of potassium in plant growth has yet to be defined. It is associated with the movement of water, nutrients, and carbohydrates within the plant, all of these things tied inextricably to plant growth. Research has shown that potassium improves the efficiency of water use in the plant, therefore it is tied to plant stomata, which are the pores through which plants "breathe". It has been found to increase plants' resistance to disease and insects. It also results in early growth, increased production of proteins, and winter-hardy plants (important for Canadian crops). 

In animals, K+ is way cooler. It is involved in nerve transmission through out the body. Animal cell membranes have a Na+/K+ pump: this is the primary transporter on cell membranes. What happens is that the transporter pumps three ions of Na+ outside the cell, and then pumps two ions of K+ inside the cell. This results in a potential energy gradient across the cell membrane. When a nerve impulse is sent, it converts this potential energy into kinetic energy by allowing the ions to flow back down the gradient. (In other words, opposite to the process that established the gradient). When you are low on K+, then the gradient cannot be established, which means that no nerve signals can be sent, and your muscles, usually starting with your fingers, will start to freeze up. Now think about the most important muscle in your body. Hopefully you are thinking of your heart. Imagine what would happen if your heart muscle was low on potassium. It would freeze. This would result in death. So if you start to dip in K+ a great way to get some is by eating a banana. Bananas are very rich in potassium.

References:

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

Pratt, C. W.; Cornely, K. Essential Biochemistry 2004, Wiley & Sons Inc. Danvers, MA.

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

Potassium for Crop Production www.extension.umn.edu/distribution/cropsystems/dc6794.html accessed 11/14/2010.  

Ee is for Endothermic

I was walking through our undergraduate organic chemistry labs the other day and one student noticed that while she was evapourating solvent under vacuum that the flask got quite cold. She asked me why this was. Here is my answer.

Endothermic is the physical term used chemical processes that absorb heat from the environment to proceed. This is opposite to the term exothermic, which are chemical processes that give off heat to the environment as they proceed. In order to for molecules to change state from liquid to gas they require an input of energy. This energy comes from the surrounding environment. If heat leaves the environment and goes into the system you are observing (in this case the from the flask to the solvent), then the environment will become cooler. This is why sweat actually cools your body. As the sweat evapourates from your skin, it takes with it heat leaving you cooler. 

Endothermic reactions are also what take place in those cooling packs. The spontaneous reaction inside is endothermic, taking heat from the surrounding environment and the result is the pack is cold. Exothermic reactions are what are in heat packs. The reaction gives off heat, making the environment hot.  

In Your Cosmetics...What You Don't Know...Still Won't Kill You Pt. 2

This entry is designed to answer the question about chemicals in cosmetics. If you haven't yet read part 1, do so before reading this, because it gives context. What are the issues? Well I think the biggest issue that is leading to all this concern is the large information gap between the public and the scientists. There is a lot of misleading information out there, and from what I have garnered, the major lobby groups are making their cases based on a misreading of study presented in the Journal of Applied Toxicology. Here's the deal: just because something is "chemical" doesn't make it unsafe. As I have said in other entries, we are all chemicals, what eat are chemicals, our world is chemicals. 

So what has people concerned for their cosmetics? Preservatives. Those are the formaldehydes and parabens that are being referred to. They are added to cosmetic products to prevent bacterial growth, which could lead to infection as cosmetics and places in which they are stored (ie, your bathroom) are ideal microbe breeding grounds. Without preservatives, you would have to treat your personal care products like perishable food items, and the result would be contamination. A particular ingredient is made unsafe by the dose or exposure. I think caffeine highlights this nicely because many of don't function without a daily caffeine jolt from tea, coffee, or cola. But have you ever read an MSDS (material safety data sheet-just Google MSDS caffeine)? The LD50, which is the dose at which the compound resulted in the death of 50% of the test population, is 127 mg/Kg (for a rat). To put that in perspective, the LD50 of sodium cyandide is 6.4 mg/Kg, nicotine is 0.3 mg/Kg, ethanol (your vodka martini) is 1200 mg/Kg, and PCBs (which are banned) are 1295 mg/Kg. Formaldehyde (ingested) is 100 mg/Kg. That means that caffeine, which is ingested without compunction, is about the same toxicity as formaldehyde and that is if you ingest formaldehyde. The LD50 for skin absorption of formaldehyde is 270 mg/Kg. 

The public push is for "natural" products. But there is absolutely a danger in this. They are not necessarily safer because natural counterparts are not as well defined, therefore not as well legislated, and can contain many impurities that lead to allergic reactions. I actually have been having problems with eczema (stupid dry weather) and one of the things that the doctors have all told me is to avoid any lotions that contain natural botanicals because my skin is already over sensitive and those chemicals will spur an allergic reaction to make things worse. Also keep in mind that the most poisonous compounds that we know about are all nature made not human made. 

There is a really great article in C&EN Chemical & Engineering News that essentially describes all of this. I have linked it here. I hope you read it and enjoy it. http://pubs.acs.org/cen/coverstory/88/8820cover.html 

Things you should definitely stay away from are dollarstore made in China cosmetics that still contain lead and arsenic. No good will come of those ones. As for the others, read the actual scientific data that is published, not the data given out by those with an agenda.