Question

What is the mass of water in 0.01132 moles of MgSO4.7H2O ?

Answer 1

The percentage of water is

$$\omega=\dfrac{7(2·1+16)}{24+32+16·4+7(2·1+16)}=0.5122.$$

How many moles is water:

$$n_1=n\omega=5.798·10^{-3}\text{ mol}.\\ m=Mn_1=18·5.798·10^{-3}=0.104\text{ g}.$$