After the water is boiled off, the mass is 9.7 grams, so find the weight of the water.
12.98 - 9.7 = 3.28g H2O
Find how many moles of CuSO4 and H2O you have.
If there are about 18g per mole of H2O
3.28/18 = .1822 moles of H2O
If there are about 160g per mole of CuSO4
9.7/160 = .0606 moles of CuSO4
.1822/.0606 = 3
Ratio of H2O to CuSO4 = 1:3
Formula
CuSO4.3H2O
Full Name
Copper (II) Sulphate Trihydrate