A solute added to a solvent raises the boiling point of the solution because
A) the solute particles lower the solvent's vapor pressure, thus requiring a higher temperature to cause boiling.
B) the temperature to cause boiling must be great enough to boil not only the solvent but also the solute.
C) the solute increases the volume of the solution, and an increase in volume requires an increase in the temperature to reach the boiling point (derived from PV = nRT).
D) the solute particles raise the solvent's vapor pressure, thus requiring a higher temperature to cause boiling.
E) Two of the above are correct.

Question

Quizplus · Accepted Answer

When a solute is added to a solvent, it forms a solution with a lower vapor pressure than the pure solvent. This is because the solute particles occupy some of the surface area of the liquid, reducing the number of solvent molecules that can escape into the gas phase. Thus, to reach the same vapor pressure as the pure solvent, the solution must be heated to a higher temperature, which raises its boiling point. Option B is incorrect because the boiling point is determined by the vapor pressure of the liquid, not the presence of the solute. Option C does not accurately reflect the relationship between volume and boiling point. Option D is also incorrect because the solute particles lower the vapor pressure of the solvent, not raise it.

A Solute Added to a Solvent Raises the Boiling Point