Phenol associates in benzene to a certain extent for a dimer. A s… - Vidyadip

MCQ

Phenol associates in benzene to a certain extent for a dimer. A solution containing $20 \times 10^{-3}\,kg$ of phenol in $1\,kg$ of benzene has its freezing point decreased by $0.69\,kelvin$ . ........ $(\%)$ percentage degree of association of phenol. ( $K_f$ for benzene $= 5.12\,K\,kg\,mol^{-1}$ )

✓
$60$
B
$85$
C
$73.3$
D
$90.3$

✓

Answer

Correct option: A.

$60$

a
$2A\, \to \,{A_2}$

$1 - \alpha $ $\frac{\alpha }{2}$

$1 - 0.8$ $\frac{{0.8}}{2}$

$i\, = 1 - 0.8\, + \,\frac{{0.8}}{2}\, = \,0.6$

$\Delta {T_f}\, = \,{K_f}\, \times \,\,i\,\, \times \,\,m$ $ = \,5\,\, \times \,0.6\,\, \times \,\frac{X}{{122}}\, \times \,\frac{{1000}}{{30}}\, = \,2$ (Since $\Delta {T_f}\, = \,2$ )

$\therefore \,X\, = \,2.44\,g$

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