water
Suppose that you wanted to know how many hydrogen atoms were in a mole of water molecules. First, you would need to know the chemical formula for water, which is H 2 O. There are two atoms of hydrogen in each molecule of water. How many atoms of hydrogen would there be in two water molecules? There would be 2 2 = 4 hydrogen atoms. How about in a dozen? In that case a dozen is 12 so 12 2 = 24 hydrogen atoms in a dozen water molecules. To get the answers, 4 and 24 you had to multiply the given number of molecules by two atoms of hydrogen per molecule. So to find the number of hydrogen atoms in a mole of water molecules, the problem could be solved using conversion factors.