This is stolen from wikipedia because I am lazy.

The mole (symbol: mol) is the SI base unit that measures an amount of substance. One mole contains Avogadro's number (approximately 6.022×1023) entities. A mole is much like "a dozen" in that both units can describe any set of elementary objects, although the mole's use is usually limited to measurement of subatomic, atomic, and molecular structures. This is all due to the fact that a mole represents an exceedingly large number of entities.

Utility of moles

The mole is useful in chemistry because it allows different substances to be measured in a comparable way. Using the same number of moles of two substances, both amounts have the same number of molecules or atoms. The mole makes it easier to interpret chemical equations in practical terms. Thus the equation:

2H2 + O2 → 2H2O

can be understood as "two moles of hydrogen plus one mole of oxygen yields two moles of water."

Moles are useful in chemical calculations, because they enable the calculation of yields and other values when dealing with particles of different mass.

Number of particles is a more useful unit in chemistry than mass or weight, because reactions take place between atoms (for example, two hydrogen atoms and one oxygen atom make one molecule of water) that have very different weights (one oxygen atom weighs almost 16 times as much as a hydrogen atom). However, the raw numbers of atoms in a reaction are not convenient, because they are very large; for example, just one mL of water contains over 3×1022 (or 30,000,000,000,000,000,000,000) molecules.

[edit] Example calculation

In this example, moles are used to calculate the mass of CO2 given off when 1 g of ethane is burned. The equation for this chemical reaction is:

7 O2 + 2 C2H6 → 4 CO2 + 6 H2O

that is,

7 molecules of oxygen react with 2 molecules of ethane to give 4 molecules of carbon dioxide and 6 molecules of water.

The first thing is to figure out how many molecules of ethane were burnt. We know that it was just enough to make 1 g, so we now need the molecular mass of ethane. This can be calculated : the mass in grams of one mole of a substance is by definition its atomic or molecular mass; The atomic mass of hydrogen is 1, and the atomic mass of carbon is 12, so the molecular mass of C2H6 is (2 × 12) + (6 × 1) = 30. One mole of ethane is 30 g. So 1 g of ethane is 1/30th of a mole; the amount burnt was 1/30th of a mole (remember that it is a number, quite like "half a dozen").

Now we can calculate the number of molecules of CO2 given off. Since for 2 molecules of ethane we obtain 4 molecules of CO2, we have 2 molecules of CO2 for each molecule of ethane. So, for 1/30th of a mole of ethane, 2 × 1/30th = 1/15th of a mole of CO2 were produced.

Next, we need the molecular mass of CO2. The atomic mass of carbon is 12 and that of oxygen is 16, so one mole of carbon dioxide is 12 + (2 × 16) = 44 g/mol.

Finally, the mass of CO2 is 1/15 mol × 44 g/mol = 2.93 g of carbon dioxide.

Notice that the number of moles does not need to balance on either side of the equation. This is because a mole does not count mass or the number of atoms involved, but the number of particles involved (each of them composed of a variable number of atoms). However, we could likewise calculate the mass of oxygen consumed, and the mass of water produced, and observe that the mass of products (carbon dioxide and water) is equal to the mass of dioxygen plus ethane:

* (7/2)(1/30th mol of dioxygen) (2 × 16 g/mol) = 7×16/30 g = 3.73 g
* (6/2)(1/30th mol of water)(2×1 + 16 g/mol) = 1.8 g
* 3.73 g + 1 g = 2.93 + 1.8 g

(Note: According to the mass-energy relationship, there is a very small difference between the mass of carbon, hydrogen and oxygen separated, on one side, and on the other side the mass of the molecules made of them; this has not been accounted for here.)

NOW GET TO WORK.

dear god, we're making an attempt to teach these people, firetime?

i thought the day would never come...woah, things are wiggling around infront of my screen that arent there, what the hell was in that water......any way, yeah, atleast we can hope they'll know something, and will stop asking constant stupid questions.....even if it is just basic shit tho, i doubt anyone on here read it(i didnt bother, 2 years of highschool chem, one of them in new zealand, i know this quite well, and if i didnt remember, i have loads of notes, i liked chem)

woot stoichiometry and other related chemical calculations!

wow i learned more from this then i did last year in chem, probably cus my teacher was an idiot and couldnt even work a bunsen burner and also taught religion.

but thank you firetime