1. The problem statement, all variables and given/known data A percent yield lab says to add 5.00 g of CuCl2•2H2O(s) to 50 mL of dissolved water. Then, add 1.0 g of steel wool (100% iron) to the beaker. I am trying to find out how many moles of CuCl2 react here. I am confused about the dihydrate. 2. Relevant equations The reaction given in the lab is Fe(s) + CuCl2(aq) → FeCl2(aq) + Cu(s) 3. The attempt at a solution To find out how many moles of CuCl2•2H2O(s) I used, do I calcuate the molar mass including the dihydrate? Or do I use just the molar mass of CuCl2? I think I am supposed to include the dihydrate in the molar mass calculation, but I'm confused because the dihydrate doesn't appear in the reaction. It doesn't react with anything. So wouldn't I need to figure out how many moles of CuCl2 there were, not how many moles of CuCl2•2H2O(s)? Also, I know the CuCl2•2H2O(s) is the excess reactant, but to show that, I need to find out how many moles of it I have first.