Question

The solubility (S) of a solute in water varies with temperature as given by $S=Ae^{- \Delta H / R T},\Delta H$ being the enthalpy of solution. For a given solute, variation of lnS with temperature is as shown in figure. The solute is expected to be

• A. $\text{CaO}$
• B. $MgSO_{4}$
• C. $CuSO_{4}$
• D. $CuSO_{4}.5H_{2}O$

Answer 1

Answer: (D)

$\text{lnS} \, \text{=} \, \text{lnA} - \frac{\text{ΔH}}{\text{RT}}$
$\text{Slope} \, \text{=} \, \frac{- \text{ΔH}}{\text{RT}}$
$\text{lnS} \, \text{vs} \, \frac{\text{1}}{\text{T}}$ graph with negative slope.
So, $\Delta H>0$
Salts with water of crystallisation.
i.e., $CuSO_{4}.5H_{2}O$ .