Question

Mole fraction of a non-electrolyte in aqueous solution is 0.07. If $K_f$ is ${1.86}^{\circ }mo{l}^{-1}$ kg, depression in freezing point, $\Delta T_f$ is,

• A. ${0.26}^{\circ }$
• B. ${1.86}^{\circ }$
• C. ${0.13}^{\circ }$
• D. ${7.78}^{\circ }$

Answer 1

The correct option is D

${7.78}^{\circ }$

Given: $n_{solute}$ = 0.07
$K_f$ = 1.86

$\Delta T_f$ = $K_f$ m

$n_{solute}+n_{solvent}=1$

$\therefore n_{solute}=0.93$

$\Delta T_f=1.86\times \frac{0.07\times 1000}{0.93\times 18}={7.78}^{\circ }$