Question

$K_p$ for the reaction $CuS{O}_4.3H_2{O}_{\left(s\right)}+2H_2{O}_{\left(g\right)}\to CuS{O}_4.5H_2{O}_{\left(s\right)}is1.0\times {10}^{4}at{m}^{-2}$ at certain temperature. What lowest relative humidity of air can be achieved using $CuS{O}_4.3H_{2}O$ as drying agent at that temperature ? Aqueous tension at the given temperature = 16 torr

• A. 20%
• B. 30%
• C. 47.5%
• D. 50%

Answer 1

The correct option is C

47.5%

$K_p=1.0\times {10}^4=\frac{1}{p_{H_{2}O}^2}$
$\Rightarrow p{H}_{2}O=1.0\times {10}^{-2}atm=760\times 1.0\times {10}^{-2}=7.6torr$
Relative humidity of air that can be achieved
$=\frac{7.6}{16}\times 100=47.5\%$