General Chemistry/Molar Concepts

From Wikibooks, open books for an open world
< General Chemistry
Jump to: navigation, search

A mole is a conversion factor to convert from amu (atomic mass units) to grams and back. Specifically, a mole is 6.02214 x 10^{23} particles. So, to find the mass of one mole of carbon(12.01 amu) we would use the following equation: 
amu = (grams)(6.02 * 10^{23})

This number is known as Avogadro's number.


Why moles?[edit]

Because atoms and molecules are so small, the molar concept provides us with a way to deal with substances in the laboratory; to measure their properties and observe changes in their characteristics.

For example, a molecule of water is infintesimally small and weighs 18 amu. It consists of two hydrogen atoms and one oxygen atom. However, Avogadro's number of water molecules weighs 18 grams, and has a volume of 18 milliliters. It contains two moles of hydrogen atoms and one mole of oxygen atoms. The molar weight of an element or molecule is also known as the gram formula weight, or simply the atomic weight expressed in grams. Just remember that Avogadro's number is just that -- a number; one can have a mole of anything. A mole of oranges is 6.02 * 10^{23}oranges. (Although this quantity of oranges would surely be larger than our entire planet!)