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Chapter 12: Problem 43

How is vapor-pressure lowering related to a rise in the boiling point of a solution?

Short Answer

Expert verified
The vapor-pressure lowering of a solution due to the addition of non-volatile solute results in an increase in the boiling point of the solution. The phenomenon is related as both are colligative properties, dependent on the concentration of solute particles in the solution.

Step by step solution

01

Understanding vapor-pressure lowering

Raoult's law relates the vapor pressure of a solution to the mole fraction of the solvent. According to this law, the vapor pressure of the solvent in a solution is equal to the mole fraction of the solvent multiplied by the pure solvent's vapor pressure. When a non-volatile solute is added into a solvent, it decreases the number of solvent molecules on the surface, leading to a decrease in escaping tendency of solvent molecules, thus reducing its vapor pressure. This phenomenon is known as vapor pressure lowering.
02

Understanding boiling point elevation

Boiling point is the temperature at which the vapor pressure of a liquid becomes equal to the atmospheric pressure. The addition of a non-volatile solute causes a decrease in vapor pressure. To compensate for this decrease, the solution must be heated to a higher temperature to achieve an external pressure equal to the reduced vapor pressure of the solution. In other words, the boiling point of the solution is elevated relative to that of the pure solvent. This phenomenon is known as boiling point elevation.
03

Relating vapor-pressure lowering to boiling point elevation

Vapor-pressure lowering and boiling point elevation are directly related. When the vapor pressure of a solution is lowered due to the addition of a non-volatile solute, the boiling point of the solution is elevated. This is because a higher temperature is required for the vapor pressure of the solution to match atmospheric pressure and cause the liquid to boil.

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Most popular questions from this chapter

Write the equations relating boiling-point elevation and freezing-point depression to the concentration of the solution. Define all the terms, and give their units.

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