Chapter 13, Problem 102AP

Interpretation Introduction

Interpretation:

The conclusion of the chemist, whether the compound is cocaine or not, is to be explained.

Concept introduction:

Molality ($m$

) is calculated by dividing the moles of the solute by Kg of solvent.

Freezing point depression is a colligative property observed in solutions that results from the introduction of solute molecules to a solvent.

The freezing points of solutions are lower than that of the pure solvent and are directly proportional to the molality of the solute.

$T_{\text{f}}$ is defined as the freezing point of a solution which is less than the pure solvent. The change in freezing point is represented by $\Delta T_{\text{f}}$.

$\Delta T_f=T_f(solvent)-T_f(solution)=K_f\times m$

where $\Delta T_f$ is the freezing point depression, $T_f(solvent)$ is the freezing point of the solution, $T_f(solution)$ is the freezing point of the solvent, $K_f$ is the freezing point depression constant, and $m$ is the molality