Question

Exactly $1g$ of urea dissolved in $75g$ of water gives a solution that boils at ${100.114}^{\circ }C$ at $760torr$. The molecular weight of urea is $60.1$. The boiling point elevation constant for water is :

• A. $1.02$
• B. $0.51$
• C. $3.06$
• D. $1.51$

Answer 1

The correct option is B $0.51$

Weight of solute $\left(w\right)=1g$
Weight of solvent $\left(W\right)=75g$
Boiling point of solution $={100.114}^{\circ }C$
Boiling point of solvent $={100}^{\circ }C$
$△T=100.114-100={0.114}^{\circ }C$
Molecular weight of solute $\left(m\right)=60.1$
Boiling point elevation constant $\left(K\right)=?$
$m=\frac{1000\times K\times w}{△T\times W}$
$K=\frac{m\times △T\times W}{100\times w}$
$=\frac{60.1\times 0.114\times 75}{1000\times 1}$
$=\frac{513.8}{1000}=0.513$