Question

For a dilute solution containing 2.5 g of a non-volatile non-electrolyte in 100 g of water, the elevation in boiling point at 1 atm pressure is $2^{o}C$. Assuming concentration of solute is much lower than the concentration of solvent, the vapour pressure (mm of Hg) of the solution is (take $K_b=0.76Kkg{\text{mol}}^{-1})$

• A. $740$
• B. $736$
• C. $724$
• D. $718$

Answer 1

The correct option is C $724$

$\Delta T_b=1\times K_b\times m$

$\Rightarrow 2=1\times 0.76\times m$

$\Rightarrow m=\frac{2}{0.76}=2.63$

$\Rightarrow \frac{760-P_s}{760}=2.63\times \frac{18}{1000}$

$\Rightarrow P_s=724mmHg$