October 23, 2011 - National Mole Day

Avogadro's number, commonly used in chemistry, is 6.02 × 1023, and that is why we celebrate Avogadro's number from 6:02 in the morning until 6:02 in the evening on 10/23.

And, yes, we who celebrate such a chemical constant are geeks! Thanks for asking!

But...why is a day celebrating Avogadro's number called Mole Day?

Well, Avogadro's number has to with “moles,” which is an amount. For any sort of molecule, one mole is a mass in grams whose number is equal to the atomic mass of the molecule. A water molecule, as you may know, is H2O, and it has an atomic mass of 18. So one mole of water weighs 18 grams. But oxygen gas (two oxygen atoms) has an atomic mass of 32, and so one mole of oxygen gas weighs 32 grams.

In general, one mole of any substance contains Avogadro's Number of molecules or atoms of that substance. Another way of saying that is that 18 grams of water has 6.02 x 10^23 molecules of water, and 32 grams of oxygen gas has 6.02 x 10^23 molecules of oxygen gas.

On this day in chemistry history....

On October 23, 1803...
Chemist John Dalton read aloud to the Manchester Literary and Philosophical Society his essay about how water absorbs gases, and he gave atomic weights for 21 different elements and compounds. From this work on absorption of gases and atomic weights, Dalton came up with a much of the modern atomic theory eventually adopted by physics.

A very appropriate essay to have read on Mole Day!

To learn more about Mole Day, and to find links to a funny song and official website, check out last year's post!

By the way, did you notice...?

National Mole Day has nothing to do with moles-the-mammals-that-dig?

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