Single Choice

75.2 g of $$C_{6}H_{5}OH$$ (phenol) is dissolved in a solvent of $$K_{f}=14$$. If the depression in freezing point is 7 K then find the % of phenol that dimerises.

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Solution

The equilibrium for the association of phenol is as shown.
$$2C_{6}H_{5}OH\leftrightharpoons (C_{6}H_{5}OH)_{2}$$
The molar mass of phenol is 94.11 g/mol
75.2 g of phenol corresponds to $$\dfrac {75.2}{94.11} = 0.8$$ moles
Let $$\alpha$$ be the degree of association
The vant Hoff's factor i is $$(\frac{2-\alpha }{2})$$
The depression in the freezing point $$=7=14\times 0.8 (\frac{2-\alpha }{2})$$
$$\alpha =0.75 = 75$$%

SIMILAR QUESTIONS

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