Question

If hydrated magnesium sulphate on heating loses 57.2% of its mass. Calculate the number of water molecules of crystallisation in it.

Answer 1

Dear Student,

$$\begin{gathered} \mathrm{Let}\mathrm{us}\mathrm{consider}100\mathrm{g}\mathrm{of}\mathrm{hydrated}\mathrm{magnesium}\mathrm{sulphate}\mathrm{is}\mathrm{present}. \\ \mathrm{So},\mathrm{mass}\mathrm{of}\mathrm{water}\mathrm{lost}=57.2\mathrm{g} \\ 1\mathrm{molecule}\mathrm{of}\mathrm{water}=18\mathrm{g} \\ \mathrm{So},\mathrm{No}.\mathrm{of}\mathrm{molecules}\mathrm{of}\mathrm{water}=\frac{57.2}{18}\approx 3 \\ \mathrm{So},\mathrm{No}.\mathrm{of}\mathrm{water}\mathrm{molecules}\mathrm{of}\mathrm{crystallisation}\mathrm{in}\mathrm{it}\mathrm{are}3. \end{gathered}$$