Happy Mole Day!

Happy Mole Day 2009!!!

So, unless you're familiar with a lot of chemistry, you're probably wondering what on earth I'm talking about. It's a "holiday," of sorts. October 23rd is recognized as mole day. This does not refer to the little furry animals, or to birthmarks. A mole is a unit of counting, like a dozen. In fact, you might say a mole is a chemist's dozen.

One mole of something is an Avogadro's number of individual parts. Avogadro's number is equal to 6.0221x10²³. This is a huge number on a macroscopic scale. However, we don't typically use Avogadro's number to count things like cars or people. We use it to count the number of molecules in a sample. So, say you have... a tank of helium, to fill your Mole Day balloons. There's 5 pounds (approximately 2268 grams) of helium in the tank. So, how many moles of helium do we have? And how many molecules is that?

Well, the molar mass (number of grams in a mole) for helium is 4.00 g/mole. So, we have:

2268 g x 1 mole/4.00 g = 567 moles
567 moles x N_a (this is the abbreviation for Avogadro's number) = 3.41x10²⁶ molecules of helium

That's a very large number of molecules. Yet, we only have 5 pounds of the gas. Avogadro's number, and the mole, help scientists to work with molecules on a scale we can comprehend. We can fill balloons with 5 pounds of helium. If we had to collect each of 3.41x10²⁶ molecules, we'd never finish filling even one. That's what makes the mole such an important concept.

And why today? Well... 10²³, 10/23. There's no better day to celebrate the mole.

For more on Mole Day, you can look at the National Mole Day Foundation site.