Question

The boiling point and freezing point of a solvent A are ${90.0}^{0}C$ and ${3.5}^{0}C$ respectively. $K_f$ and $K_b$ values of the solvent are 17.5 and 5.0 K.kg/mol respectively. What is the boiling point of a solution of B in A if the solution freezes at ${2.8}^{0}C$?

• A. ${90.0}^{0}C$
• B. ${89.8}^0$
• C. ${90.2}^{0}C$
• D. ${90.7}^{0}C$

Answer 1

Answer: (C)

${90.2}^{0}C$

As we know

$\Delta T_b=k_{b}m$

$\Delta T_f=k_{f}m$

Given

boiling point = ${90}^{0}C$

freezing point = ${3.5}^{0}C$

$k_b=5K/m$

$k_f=17.5K/m$

Dividing both equations, we get

$\frac{T-90}{3.5-2.8}=\frac{5}{17.5}$

After calculating, we get :

$T={90.2}^{0}C$