Chapter 16.4, Problem 43LC

Interpretation Introduction

Interpretation: To evaluate the freezing point depression and boiling point elevation related to molality.

Concept introduction: Molality is defined as the measurement of the Number of moles of solute present in 1kg of solvent.

Answer to Problem 43LC

Assuming the solute is molecular, not ionic so the magnitudes of freezing point depression and boiling point elevation of the solution are directly proportional to the molal concentration.

Explanation of Solution

Molality is defined as the measurement of the number of moles of solute present in 1kg of solvent.

  $m=\frac{n(moles)}{M(Kg)}$

Where,

• $n$ represents the moles of solvent.
• $M$ represents the Mass of the solution.

Boiling point of elevation

The boiling point of elevation is directly proportional to that of the molality of the solute particles, in a dilute solution with a non-volatile solute.

  $\Delta T_b=K_{b}m$ ;

Where,

• $\Delta T_b$ represents the amount through which the boiling point is raised.
• $m$ represents molality (the moles of solute particles).
• $K_f$ represents the molal boiling point elevation constant that depends on the solvent.

Freezing point depression The freezing point of depression is directly proportional to that of the molality of the solute particles, in a dilute solution.

  $\Delta T_f=-K_{f}m$ ;

Where,

• $\Delta T_f$ represents the amount through which the freezing point is lowered.
• $m$ represents molality (the moles of solute particles).
• $K_f$ represents the molal boiling point elevation constant that depends on the solvent.

So, we get that both boiling points of elevation and freezing points of depression are directly proportional to that the molality of the solution.

Conclusion

Assuming the solute is molecular, not ionic so the magnitudes of freezing point depression and boiling point elevation of the solution are directly proportional to the molal concentration.