Hello, Clarie,
The term mole is simply a shortcut phrase that is used to describe a very large number, 6.02x1023. When one says I have a mole of pennies, they are telling you they have 6.02x1023 pennies. Just as when one says a dozen eggs, rhey mean they have 12 eggs. Or a foot means 3 inches.
So why assign a silly name to such an odd number? Glad you asked!
The answer lies on the periodic table. Every element has an atomic mass noted under the element symbol. For carbon (C), that is 12.01 amu (atomic mass units), for sodium (Na), it is 23.0 amu.
BUT, these numbers can also be read in units of grams/mole. That means if you have 12.01 grams of carbon, you'll have 6.02x1023 individual atoms of that element! Same with sodium: 23.0 grams contains 1 mole of sodium atoms.
A balanced equation, such as:
2H2 + O2 = 2H2O
says that if we take two molecules of H2 and react it with one molecule of O2, we'll get two molecules of water. But how does anyone measure individual atoms or molecules efficiently? You can't count them individually-they are too small and it would take a very fine pair of tweezers, and a LOT of time. So the mole is used, instead. We can read the same equation as 2 moles of hydrogen eacts with 1 mole of oxygen to produces two moles of water. What this means is that we can know use grams to measure out a known count quantity of each element. This makes it easier to insure we have the numbers of molecules we need for a complete reaction. This also works for molecules - just add up the atomic masses of each atom in the molecule. One molecule of oxygen, for example, is 32 amu, or 32 grams/mole.
I hope this helps,
Bob
