Chapter 16, Problem 74A

(a)

Interpretation Introduction

Interpretation: The freezing point of two solutions A and B falls down with an increase in the mole of solute, the slope of the two lines is to be explained.

Concept Introduction:

The temperature at which the liquid gets converted to a solid is called the freezing point of the solution.

Explanation of Solution

Freezing point of the solution decreases with the increasing number of solutes in the solvent because solutes decrease the vapor pressure of the solvent resulting in a lowering of the freezing point.

Therefore, from the above graph, the slopes fall between $\text{0}\text{to}\text{4}\text{moles}\text{of}\text{solute}$ the moles of solute.

(b)

Interpretation Introduction

Interpretation: The freezing point of solution B slope becomes constant when the mole of solute is increasing; the reason behind it is to be explained.

Concept Introduction:

Increase in the number of moles of solute decreases the freezing point but at a particular point, the freezing point remains constant when there is equilibrium.

Explanation of Solution

From the graph, solution B remains the same even after adding solute because there is an equilibrium between the liquid and the solid state.

It implies that the vapor pressure of both the liquid and the solid phases are equal.