Chapter 16.3, Problem 28LC

Interpretation Introduction

Interpretation: The three colligative properties of solutions are to be defined and described.

Concept introduction: Colligative properties are those properties of a solution that depend upon the number of solutes but not on the nature of the solute.

Answer to Problem 28LC

The three colligative properties of the solution are lowering of vapor pressure, depression in freezing point, and elevation in boiling point.

Explanation of Solution

The three colligative properties of the solution are as follows:

1. Lowering of vapor pressure: In a closed system, the vapors are in dynamic equilibrium with their liquid, and the pressure exerted by vapors on their liquid is known as vapor pressure. If a solute is non-volatile that means, the solute will remain in a liquid state and a very less number of solute particles will be in the vapor state. Hence, the pressure exerted by vapors will be lowered as compared to the vapor pressure of the pure solvent. This property is known as a lowering in vapor pressure.
2. Depression in freezing point: The freezing point is the measure of temperature when the liquid starts freezing. When water freezes, the molecules of water form a pattern but when the solute is added then, this pattern gets disrupted. To solidify the solution, more kinetic energy has to be withdrawn than the pure solvent. Hence, the freezing point is lowered than that of the pure solvent. This difference in freezing point is known as freezing point depression. This property is known as depression in freezing point.
3. Elevation in boiling point: The boiling point is the measure of temperature when the liquid starts converting to the vapor state. This happens when the atmospheric pressure and vapor pressure of the liquid become equal. A non-volatile solute decreases the vapor pressure. Hence, more kinetic energy needs to be given to increase the vapor pressure therefore, the boiling point of the solution becomes more than that of the pure solvent. This difference in boiling point is known as boiling point elevation and the phenomenon is called elevation in boiling point.

Conclusion

The three colligative properties of the solution are lowering of vapor pressure, depression in freezing point, and elevation in boiling point.