Question

The increase in boiling point of a solution containing $0.6g$ urea in $200g$ water is ${0.50}^{\circ }C$. Find the molal elevation constant.

• A. $10Kkgmo{l}^{-1}$
• B. $10Kgmo{l}^{-1}$
• C. $10Kkgmol$
• D. $1.0Kkgmo{l}^{-1}$

Answer 1

The correct option is A $10Kkgmo{l}^{-1}$

Molality, $m=\frac{\text{no. of moles of solute}}{\text{weight of solution is kg}}$

$m=\frac{1000\times W_1}{m_1\times W_2}$

$m=\frac{1000\times 0.6}{60\times 200}$

$m=0.05m$

$[\because$ Molecular weight of $N{H}_{2}CON{H}_2=60]$

Given, $△T_b=0.50$

Now,

$△T_b=K_b\times m$

or $0.50=K_b\times 0.05$

$\therefore K_b=10Kkgmo{l}^{-1}$.