Question

Under what pressure conditions is $Cu{SO}_4.5H_{2}O$ efflorescent at 25C? How good a drying agent is $Cu{SO}_4.3H_{2}O$ at the same temperature? Given
$Cu{SO}_4.5H_{2}O\left(s\right)\rightleftharpoons Cu{SO}_4.3H_{2}O\left(s\right)+2H_{2}O\left(v\right)$
$K_P=1.086\times {10}^{-4}{atm}^2$ at 25C. Vapour pressureof water at 25C is 23.8 mm of Hg.

• A. $Cu{SO}_4.5H_{2}O\left(s\right)$ will efflorescent but on the contrary $Cu{SO}_4.3H_{2}O$ will not absorb moisture from the atmosphere under given conditions.
• B. $Cu{SO}_4.5H_{2}O\left(s\right)$ will not act as efflorescent but on the contrary $Cu{SO}_4.3H_{2}O$ will absorb moisture from the atmosphere under given conditions.
• C. $Cu{SO}_4.5H_{2}O\left(s\right)$ will not act as efflorescent and $Cu{SO}_4.3H_{2}O$ will not absorb moisture from the atmosphere under given conditions.
• D. $Cu{SO}_4.5H_{2}O\left(s\right)$ will efflorescent but on the contrary $Cu{SO}_4.3H_{2}O$ will absorb moisture from the. atmosphere under given conditions.

Answer 1

The correct option is B $Cu{SO}_4.5H_{2}O\left(s\right)$ will not act as efflorescent but on the contrary $Cu{SO}_4.3H_{2}O$ will absorb moisture from the atmosphere under given conditions.

An efflorescent salt is one that loses $H_{2}O$ to atmosphere.
For the reaction
$Cu{SO}_4.5H_{2}O\left(s\right)\rightleftharpoons Cu{SO}_4.3H_{2}O\left(s\right)+2H_{2}O\left(v\right)$
$K_P=1.086\times {10}^{-4}{atm}^2$
Given at 25C, (i.e., 23.8) which is greater than 7.92 mm and thus, reaction will proceed in the backward direction, i.e.,
$Cu{SO}_4.3H_{2}O\left(s\right)+2H_{2}O\left(v\right)\rightleftharpoons Cu{SO}_4.5H_{2}O\left(s\right)$
Thus, $Cu{SO}_4.5H_{2}O\left(s\right)$ will not act as efflorescent but on the contrary $Cu{SO}_4.3H_{2}O$ will absorb moisture from the. atmosphere under given conditions.