A 1.547-g sample of blue copper(II) sulfate pentahydrate, CuSO4*5H2O, is heated. The white crystals of CuSO4 that are left behind have a mass of 0.989 g. How many moles of H2O were in the original sample?

Answer 1

1.547-0.989 0.558 g H2O
0.989 = g CuSO4

0.989/molar mass CuSO4 = moles CuSO4
0.558/molar mass H2O = moles H2O
Find the radio of water to 1 mole CuSO4. The easy way to do that is to divide the smaller moles by itself (thus getting 1.00 for CuSO4) and divide the other number by the same small number. Round to a whole number.