Question

When 20 g of naphthoic acid ($C_{11}H_8O_2$) is dissolved in 50 g of benzene (K$_f = 1.72 K kg mol^{-1}$), a freezing point depression of 2 K is observed. The van-t Hoff factor (i) is

• A. 0.5
• B. 1
• C. 2
• D. 3

Answer 1

Answer: (A)

0.5

Answer 2

Molality$=\bigg(\frac{20}{172}\bigg) \times \frac{1000}{50} =2.325 m$ $\Rightarrow \, \, \, \, \, \, \, \, \, -\Delta T_f =2 = iK_f.m$ $\Rightarrow \, \, \, \, \, \, \, \, i=\frac{2}{1.72 \times 2.325}=0.5$