Question

Multiple choice-- 16 pts!

Two moles of aluminum chloride are dissolved in two liters of water.
How does the vapor pressure of the water change?

It increases because aluminum and chloride ions displace water molecules, which escape into the gas phase.

It first decreases as aluminum chloride attracts the water molecules, but it then increases as dissolving completes and starts to push water molecules out.

It decreases because nonvolatile aluminum and chloride ions now occupy some of the volume of the system.

Answer 1

Answer: It decreases because nonvolatile aluminum and chloride ions now occupy some of the volume of the system.

Step-by-step explanation:

Vapor pressure of a liquid is defined as the pressure exerted by the vapors in equilibrium with the liquid/solution at a particular temperature.

So, when a non-volatile solute is added to a solvent then its molecules align at the surface of liquid. As a result, less number of solvent molecules will escape from the solution. Thus, there will be decrease in vapors and thus the vapor pressure decrease.

The relative lowering of vapor pressure is directly proportional to the amount of dissolved solute.