How do you calculate the number of moles from the mass?

This is a generic answer with an example of how to solve this kind of problem. You can use the technique given here to find the answer to your particular problem. First you need to find the molecular weight of the compound. Once you've done that, then you simply divide the mass of the compound (in grams) by the molecular weight of the compound (in amu). The result is the number of moles. For example: Water (H2O) has a molecular weight of 2 * 1.0 (for the two hydrogens, 1 amu each) + 1 * 16.0 (for the oxygen, 16 amu) or 18.0 amu. So if I have 27.0 grams of water, then I have 27.0 / 18.0 = 1.5 moles of water.