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Under what pressure conditions will CuSO_(4). 5H_(2)O become efflorescent at 25^(@)C ? Given CuSO_(4)*5H_(2)O(s) hArr CuSO_(4)* 3H_(2)O(s)+2H_(2)O"(vapour)", K_(p)=1.086xx10^(-4)"atm"^(2)" at "25^(@)C. Vapour pressure of water at 25^(@)C is 23.8 of Hg. |
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Answer» 3.64 mm HG For the reaction, `CuSO_(4)*5H_(2)O(s) hArr CuSO_(4)*3H_(2)O(s)+2H_(2)O`(vapour) `K_(p)=(P_(H_(2)O))^(2)=1.086xx10^(-4)"atm"^(2)` `(P_(H_(2)O))=1.042xx10^(-2)"atm"=8.92`mmHg `therefore ` Given `P_(H_(2)O)` at `25^(@)C` (i.e. 23.8) mmHg `gt` 7.92 mmHg and THUS, reaction will proceed in backward direction, i.e. `CuSO_(4)*3H_(2)O(s)+2H_(2)O"(vapour)" hArr CuSO_(4)*5H_(2)O(s)` Thus `CuSO_(4). 5H_(2)O` will not act as efflorescent but on the contrary `CuSO_(2).3H_(2)O` will absorb moisture from the atmosphere under given conditions. The salt `CuSO_(4).5H_(2)O` will effloresce only on a dry when the partial pressure of moisture in the air is LESS than 7.92 mm or if relative humidity of air at `25^(@)C=7.92//23.8=0.333 or 33.3%`. |
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