Chapter 12, Problem 143CP

(a)

Interpretation Introduction

Interpretation: The number of moles of $\text{NaCl}$ should be calculated.

Concept Introduction: The freezing point is directly proportional to the molality of the solution.

  $\Delta T_f\propto m$

Or,

  $\Delta T_f=K_{f}m$

Here, $K_f$ is freezing point constant. This is constant for every substance.

The molality of solution can be calculated as follows:

  $m=\frac{n\left(\text{solute}\right)}{M\left(\text{solvent kg}\right)}$

Here, n is number of moles of solute and M is mass of solvent in kg.

(b)

Interpretation Introduction

Interpretation: The number of moles of ${\text{K}}_{\text{3}}{\text{PO}}_{\text{4}}$ should be calculated.

Concept Introduction: The freezing point is directly proportional to the molality of the solution.

  $\Delta T_f\propto m$

Or,

  $\Delta T_f=K_{f}m$

Here, $K_f$ is freezing point constant. This is constant for every substance.

The molality of solution can be calculated as follows:

  $m=\frac{n\left(\text{solute}\right)}{M\left(\text{solvent kg}\right)}$

Here, n is number of moles of solute and M is mass of solvent in kg.