Chapter 16, Problem 66A

Interpretation Introduction

Interpretation: The reason of $1m$ solution of calcium nitrate having lower freezing point than $1m$ solution of sodium nitrate is to be explained.

Concept Introduction: Freezing point Depression is the term used to describe how adding solutes lowers the freezing point of solvents. It is a collective feature of solutions. Freezing point depression is given by:

  $\Delta t=i{K}_{f}m$

Here, $\Delta t$ is depression in freezing point, $i$ is van’t Hoff factor, $K_f$ depression in freezing point constant, and $m$ is molality.

Answer to Problem 66A

Calcium nitrate has a lower freezing point compared to $1m$ sodium nitrate.

Explanation of Solution

The van’t Hoff factor ‘ $i$ ’ depends upon the no. of solutes particles given by the dissolution of solute particles.

The chemical formula of sodium nitrate is ${\text{NaNO}}_{\text{3}}$ and the chemical formula of calcium nitrate is ${\text{Ca}}_{\text{2}}{\text{NO}}_{\text{3}}$ .

The van’t Hoff factor ‘ $i$ for ${\text{NaNO}}_{\text{3}}$ is 2 and the van’t Hoff factor ‘ $i$ for ${\text{Ca}}_{\text{2}}{\text{NO}}_{\text{3}}$ is 3. So, the depression in freezing point for ${\text{Ca}}_{\text{2}}{\text{NO}}_{\text{3}}$ will be more.

Thus, ${\text{Ca}}_{\text{2}}{\text{NO}}_{\text{3}}$ will have lower freezing point.

Conclusion

Therefore, $1m$ Calcium nitrate has a lower freezing point compared to $1m$ sodium nitrate.