Chapter 10.1, Problem 7SP

Interpretation Introduction

Interpretation: The molar mass of ${\text{PCl}}_{\text{3}}$ should be calculated.

Concept Introduction: The mass in grams of one mole of the compound is said to be its molar mass.

Answer to Problem 7SP

The molar mass of ${\text{PCl}}_{\text{3}}$ is $\text{137}\text{.35 g/mol}$ .

Explanation of Solution

To determine the molar mass of ${\text{PCl}}_{\text{3}}$ , the sum of the masses of P and Cl elements are added up.

The moles of P and Cl are converted to grams of P and Cl as:

  $\begin{array}{l}\text{1 mol P }\times \frac{31\text{ g P}}{1\text{ mol P}}\text{ = 31 g P}\\ \text{3 mol Cl }\times \frac{35.45\text{ g Cl}}{1\text{ mol Cl}}\text{ = 106}\text{.35 g Cl}\end{array}$

The mass of 1 mol of ${\text{PCl}}_{\text{3}}$ is:

  $\begin{array}{l}{\text{mass of 1 mol PCl}}_3\text{ = 31 g P + 106}\text{.35 g Cl}=\text{ 137}\text{.35 g}\\ {\text{molar mass of PCl}}_3=\text{ 137}\text{.35 g/mol}\end{array}$

Hence, the molar mass of ${\text{PCl}}_{\text{3}}$ is $\text{137}\text{.35 g/mol}$ .