write the formula unit mass of
[a] CUSO_{4}
[b] 5H_{2}O

CuSO_{4}
Mass no. of Cu = 63.54
mass no. of S = 32
mass no. of O = 16
CuSO_{4} = (63.54) + 32 + (4 X 16)
= 159.54 
5H_{2}O
mass of O = 16
mass of H = 1
5H_{2}O = 5 [( 1 X 2 ) + 16]
= 5 X 18
= 90