Sunday, October 23, 2011

Happy Mole Day!

The Speed of Light = 670,616,629 mph: It's not just a good idea, it's the law!
Unless you're a very early riser you have already missed the celebration of Mole Day at 6:02 am on Oct 23. What the heck?

Mole Day is an unofficial chemistry holiday celebrated on a date that relates to Avogadro's number, which is approximately 6.02 x 1023. Avogadro's number is the number of particles in a mole of a substance.

Mole Day traces its origins to an article that appeared in The Science Teacher magazine in the early 1980s about a high school chemistry teacher's reasons for celebrating the day. The idea for Mole Day took root and the National Mole Day Foundation was formed in 1991. The American Chemical Society plans National Chemistry Week so that Mole Day falls within chemistry week each year.

So what exactly is a mole? (Not the one's digging holes in our yard.)  A mole is a quantity of any substance where the number of particles match the number of atoms in 12 grams of pure carbon-12, approximately 602,000,000,000,000,000,000,000 atoms. What so special about Avogadro's number of 6.02 x 1023? It's just the right amount so that the mass of one mole of a substance, expressed in grams, is exactly equal to the substance's mean molecular weight. For example, the mean molecular weight of water is about 18.016, so one mole of water is about 18.016 grams. This property considerably simplifies many chemical and physical computations.

For example: mix 4 moles of Hydrogen gas (H) with 1 mole of  oxygen gas (O2) to get exactly 2 moles of water H2O. This would mean 4 * 1.008 grams of H and 32 grams of O2 (atomic weight of O is 16) to get 36.032 grams of water (2 * 18.016).

Bottom Line

Too much math? I'll digress with a story about the fuzzy moles. We have a cat who loves to sit next to mole and chipmunk tunnels and play wack-a-mole. My wife recently saw him playing with a chipmunk by repeatedly tossing it into the air.

Update  10/26

The General Conference on Weights and Measures (CGPM) in Paris, France, has unanimously agreed on a proposal that would lead to reform of the mole, kilogram, kelvin and ampere, according to the international system of units (SI).

The first sign that the SI was flawed was noticed in 1949 in a check on a lump of metal kept inside a vault at the International Bureau of Weights and Measures (BIPM) in Paris. By definition, it is the only object in existence with a mass of exactly 1 kilogram – one of the seven SI base units – so metrologists were unsettled to discover that this mass had changed.

For the kilogram, the proposal is to use the Planck constant, which relates the energy of electromagnetic radiation to its frequency. The Planck constant can also be used to define the Avogadro constant, the number of atoms in 12 grams of carbon-12, which in turn can be used to obtain the mole.

The decision will not be binding without another vote in four years' time.

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