Under what pressure conditions `CuSO_(4).5H_(2)O` be efforescent at `25^(@)C`. How good a drying agent is `CuSO_(4).3H_(2)O` at the same temperature? Given
`CuSO_(4).5H_(2)O(s) hArr CuSO_(4).3H_(2)O(s)+2H_(2)O(v)`
`K_(p)=1.086xx10^(-4) atm^(2)` at `25^(@)C`. Vapour pressure of water at `25^(@)C` is `23.8` mm of Hg.

Explanation

An efflorescent salt is one that loses water to the atmosphere
`K_(p)=p_(H_(2)O)^(2)=1.086 xx 10^(-4)`
`p_(H_(2)O)=1.042 xx 10^(-2) "atm"=7.94mm`