How will the vapor pressure of an aqueous solution of sodium chloride compare to that of pure water?

Question

A.
The solution's vapor pressure will be higher.
B.
The solution's vapor pressure will be lower.
C.
The solution's vapor pressure will be the same.
D.
The solution's vapor pressure will be twice as great.
E.
There is not enough information given to answer the question.

Answer 1

The correct answer is B. The solution's vapor pressure will be lower.

When a non-volatile solute, such as sodium chloride (NaCl), is dissolved in a solvent like water, it leads to a reduction in the vapor pressure of the solvent compared to that of pure water. This phenomenon is explained by Raoult's Law, which states that the vapor pressure of a solvent in a solution is proportional to the mole fraction of the solvent in the solution. Since the presence of sodium chloride reduces the mole fraction of water, the vapor pressure of the solution will be lower than that of pure water.