Question

A solution is obtained by dissolving $0.2$ moles of urea in a litre of water. Another solution is obtained by dissolving $0.4$ moles of cane-sugar in a litre of water at the same temperature. The lowering of vapour pressure to the first solution is:

(Assume total moles of both solution is same)

• A. same as that of the second solution
• B. half to that of the second solution
• C. double to that of the second solution
• D. none of the above

Answer 1

The correct option is B half to that of the second solution

$\Delta P_1=X_{solute}{P}_{solvent}^o$
$\Delta P_1=\frac{n_{area}}{totalmoles}{P}_{water}^o$
$\Rightarrow \frac{0.2}{totalmoles}{P}_{water}^o$
$\Delta P_2=\frac{n_{canesugar}}{totalmoles}{P}_{water}^o$
$\Rightarrow \frac{0.4}{totalmoles}{P}_{water}^o$
$\frac{\Delta P_1}{\Delta P_2}=\frac{1}{2}$
$\Delta P_1=\frac{1}{2}\Delta P_2$