2003-01-04

molarity

HINT: It is not "toothiness".

Molarity is the number of moles of a solute per liter of solution.

A mole of a substance is N grams of the substance, where N is the atomic or molecular weight of the substance. For example, Carbon 12 has an atomic weight of 12 (it has 6 protons and 6 neutrons in its nucleus). Therefore one mole of Carbon 12 is 12 grams of it.

It turns out that whatever the substance, the same number of atoms (or molecules) results in one mole of the substance. This idea is due to Amadeo Avogadro (1776-1856), a pioneer in the field of stoichiometry (the study of quantitative relationships among chemical substances in reactions) and chemistry in general. Although the specific number was determined first by Johann Joseph Loschmidt in 1865, and later by Jean Perrin and others, the number (approximately 6.02 x 10^23) is called Avogadro's Number.

A silly mnemonic I learned in High School for remembering Avogadro's name is "I'm a day old avocado".

A related word is molality, which is the number of moles of solute per kilogram of solvent.

See bogon (Gregor's Word of the Week for 2002-12-14) for another entry related to 'mole'.

More information at Cancer Web's On-line Medical Dictionary.

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