The aluminum sulfate hydrate [Al2(SO4)3•xH2O]contains 8.10percent Al by mass.Calculate x that is,the number of water molecules associated with each Al2(SO4)unit

Question

Help cant get this right 

Answer 1

Al = 26.98 x 2 = 53.96 g

S = 32 x 3 = 96 g

O = 16 x 12 = 192

Molar Mass of Al₂(SO₄)₃ = 342 g/mole

H₂O = 18 g/mole

x/342 + x = 0.0810

x = 30 g H2O

moles H2O = 30g x 1mole/18 g = 1.7 molecules H2O/formula unit of salt