Question

A solution of 0.450 gm of Urea (mol.wt.60) in 22.5 gm of water showed ${0.170}^{\circ }C$ of elevation in boiling point. Calculate the molal elevation constant of water:-

• A. ${0.17}^{\circ }Ckg/mol$
• B. ${0.45}^{\circ }Ckg/mol$
  
• C. ${0.51}^{\circ }Ckg/mol$
  
• D. ${0.30}^{\circ }Ckg/mol$

Answer 1

The correct option is C ${0.51}^{\circ }Ckg/mol$


$\begin{array}{cc}& \\ \text{wt.of solute w=0.450 gm}& \text{molal elevation}\\ \text{wt.of solvent W=22.5 gm}& \text{constant}{K}_b=?\\ \text{mol.wt. of solute = m=60}& \end{array}$

Boiling point elevation $\Delta T_b={0.170}^{\circ }c$

Subtituting these values in the equation:-
$K_b=\frac{m\times W\times \Delta T_b}{1000\times w}$

$={0.51}^{\circ }Ckg/mol$