Question

$75.2g$ of $C_6{H}_{5}OH$ (Phenol) is dissolved is $960g$ of a solvent of $K_f=14Kkg{kg}^{-1}$. If the depression in the freezing point is $7K$, then find the percentage of phenol that dimerizes.

• A. $75$
• B. $80$
• C. $30$
• D. $40$

Answer 1

Answer: (A)

$75$

Please find the answer to your question

$2C_6{H}_{5}OH\rightleftharpoons (C_6{H}_{5}OH{)}_2$

Initial: $1$ $0$

At eqb $1-\alpha$ $\alpha /2$

Total number of moles at equilibrium $=1-\alpha +\alpha /2=1-\alpha /2$

$\Delta T_f=i{K}_{f}m$

⇒ $7=14\times 75.2/94\times (1-\alpha /2)$[weight of phenol = 75.2g mol. wt of phenol = 94]

∴$\alpha =0.75$

So the percentage of phenol that dimerises $=75$%