Chapter 9, Problem 9.1CP

Interpretation Introduction

Interpretation: The reason for the lesser magnitude of the boiling point elevation than that of the freezing point depression must be interpreted.

Concept introduction: Colligative properties are the properties that depend on the number of particles present in the solution. Elevation in boiling point, depression in freezing point, lowering in vapor pressure and osmotic pressure are some common examples of colligative properties.

Answer to Problem 9.1CP

The boiling point elevation is less than the freezing point depression because it depends on the ${\text{K}}_{\text{f}}$ and ${\text{K}}_{\text{b}}$ values of the solvent. For water and most of the solvents, the value of ${\text{K}}_{\text{f}}$ is greater than ${\text{K}}_{\text{b}}$ .

Explanation of Solution

The elevation in the boiling point can be expressed as:

  ${\text{ΔT}}_{\text{b}}{\text{=K}}_{\text{b}}\text{× m}$

Whereas, the depression in the freezing point is:

  ${\text{ΔT}}_{\text{f}}{\text{=K}}_f\text{× m}$

Since the value of ${\text{K}}_{\text{f}}$ is greater than ${\text{K}}_{\text{b}}$ , so, the elevation of the boiling point is lesser than the depression of the freezing point.

Conclusion

The elevation in the boiling point and depression in the freezing point varies with ${\text{K}}_{\text{f}}$ and ${\text{K}}_{\text{b}}$ values.