Question

Two beakers containing solvent other having a mixture of a solvent with a non-volatile solutes are sealed in a container. The changes that will be seen over time are:

• A. The volume of the solution and the solvent does not change
• B. The volume of the solution increases and the volume of the solvent decreases
• C. The volume of the solution decreases and the volume of the solvent increases
• D. The volume of the solution does not change and the volume of the solvent decreases

Answer 1

The correct option is B

The volume of the solution increases and the volume of the solvent decreases

Explanation for the correct options:

b. The volume of the solution increases and the volume of the solvent decreases

• Let's say that the beaker $1$ hold the solvent and beaker $2$ the solution. Make the beaker I's and beaker II's respective vapour pressures $\left({\mathrm{P}}_{\mathrm{Solvent}}^{°}\right)$ and $\left({\mathrm{P}}_{\mathrm{Solution}}^{°}\right)$, respectively.
• Raoult's law states that the solvent's vapour pressure $\left({\mathrm{P}}_{\mathrm{Solvent}}^{°}\right)$ is higher than the solution's vapour pressure $\left({\mathrm{P}}_{\mathrm{Solution}}^{°}\right)$
• ${\mathrm{P}}_{\mathrm{Solvent}}^{°}>{\mathrm{P}}_{\mathrm{Solution}}^{°}$
• Pure solvent has higher vapour pressure and is highly volatile, the vapour molecules condense.
• The non-volatile solute solution will attempt to maintain an equilibrium with lower vapour pressure while the pure solvent solution attempts to maintain a greater vapour pressure in the sealed container, causing the solvent vapour molecules to condense in the non-volatile solute solution.
• When a non-volatile solute is combined with a volatile solvent, there is a decrease in vapour pressure.
• On the contrary, the vapour pressure will drop because particles from the vapour phase are condensing in beaker $2$.
• Evaporation will be encouraged more in order to make up for the decreased vapour pressure, as noted in the preceding paragraph because beaker $1$ achieves a higher vapour pressure at equilibrium.

Hence, option (B) is correct, in that the volume of the solution increases, and the volume of the solvent decreases.