Chapter 16, Problem 64A

Interpretation Introduction

Interpretation : The three colligative properties are to be identified and the reason for their occurrence is to be explained.

Concept Introduction : Colligative properties are the properties of a solution that depends on the number of solute.

Explanation of Solution

Colligative properties are the properties of a solution that depends on the concentration of the solute and temperature only.

The three colligative properties are:

• Elevation in Boiling point
• Depression in freezing point
• Relative lowering of vapor pressure

Colligative properties are the properties of a solution that depends on the number of solute and temperature only.

The three colligative properties are:

• Elevation in Boiling point: The elevation in the boiling point of a solution is a colligative property in which, on the addition of a non-volatile solute to a volatile solvent the boiling point of the solution increases as, it represents the temperature at which the vapor pressure of the solution is equal to the atmospheric pressure.

The expression for elevation in boiling point is as follows:

  $\Delta T_b=k_{b}m$

Here, $\Delta T_b$ is the change in boiling point, $k_b$ is the molal elevation constant, and m is the molality.

Depression in freezing point: The depression in the freezing point of a solution is a colligative property in which, on the addition of a non-volatile solute to a volatile solvent the freezing of the solution decreases.

The expression for depression in the freezing point is as follows:

  $\Delta T_f=k_{f}m$

Here, $\Delta T_f$ is the change in freezing point, $k_f$ is the molal depression constant, and m is the molality.

Relative lowering of vapor pressure: The vapor pressure of the volatile solvents gets reduced or lowered with the addition of a non-volatile solute.

The expression for the relative lowering of vapor pressure is as follows:

  $\mathrm{Re}lative\text{ loweing of vapour pressure}=\frac{P°-P}{P°}$

Here, $P°$ is the vapor pressure of pure solvent and $P$ is the vapor pressure of the solution.

Conclusion

Colligative properties are the properties of a solution that depends on the concentration of the solute and temperature only.

The three colligative properties are:

• Elevation in Boiling point
• Depression in freezing point
• Relative lowering of vapor pressure