Question

$31g$ of ethylene glycol $\left(C_2{H}_6{O}_2\right)$ is mixed with $500g$ of solvent $(K_f$ of the solvent is $2Kkgmo{l}^{-1}$ ). What is the freezing point of the solution (in $K$ )? (Freezing point of solvent $=273K)$

• A. 272
• B. 271
• C. 270
• D. 274
• E. 275

Answer 1

Answer: (B)

Given, $W_B=$ mass of solute (ethylene glycol) $=31g$

$W_A=$ mass of solvent $=500g$

$M_B=$ Ethylene glycol $\left(C_2{H}_6{O}_2\right)$

$=(2\times 12+6+2\times 16)=62g$

$K_f=2Kkgmo{l}^{-1}$

$\Delta T_f=K_f\frac{W_B}{M_B}\times \frac{1000}{W_A}$

$\Delta T_f=\frac{2\times 31\times 1000}{62\times 500}=2K$

$\because \Delta T_f=T_f^{\circ }-T_f$

$T_f=T_f^{\circ }-2$

$(\because$ Depression in freezing point $=2K)$

$\therefore T_f=273-2=271K$