Question

If $CuS{O}_{4\left(s\right)}$ . $5H_2{O}_{\left(s\right)}$ $\leftrightharpoons$$CuS{o}_4$ . $H_2{O}_{\left(s\right)}$ + $2H_{2}O$(g)$K_p$ = 1.0 x ${10}^{-4}$ atm2 at ${250}^{\circ }$. The efflorescent nature of CuSO4 . 5H2O can be noticed when vapour pressure of H2O in atmosphere is:

• A. > 7.6 mm
• B. <7.6 mm
• C. = 7.6 mm
• D. depends on nature of substance

Answer 1

The correct option is B

<7.6 mm

$CuS{O}_{4\left(s\right)}$ . $5H_2{O}_{\left(s\right)}$ $\leftrightharpoons$$CuS{o}_4$ . $H_2{O}_{\left(s\right)}$ $K_p$= ${(P_{H_{2}O)}}^2$; 1.0 $\times$ ${10}^{-4}$= ${\left(P_{H_{2}O}\right)}^2$l $P_{H_{2}O}$ = 0.01 atm = 7.6 mm of Hg. If $P_{H_{2}O}$ of the system is greater than that of saturated vapour pressure of the atmosphere, the subtance become efforescent.