Chapter 4.3, Problem 25SP

Interpretation Introduction

Interpretation : The atomic mass of bromine is to be calculated.

Concept Introduction : The weighted average mass of the atoms in a naturally occurring sample of an element is the atomic mass.

Answer to Problem 25SP

The atomic mass of bromine is $79.9062\text{amu}$ .

Explanation of Solution

Given information:

The relative abundance of bromine of atomic mass $\text{78}\text{.92 amu}$ is $50.69\%$ .

The relative abundance of bromine of atomic mass $\text{80}\text{.92 amu}$ is $49.31\%$ .

The weighted average mass of the atoms in a naturally occurring sample of an element is the atomic mass.

For the calculation of atomic mass, multiply each isotope's mass by its natural abundance, represented as a decimal, and add on the products.

The relative abundance of bromine of atomic mass $\text{78}\text{.92 amu}$ is given as:

  $\begin{array}{c}50.69\%=\frac{50.69}{100}\\ =0.5069\end{array}$

The relative abundance of bromine of atomic mass $\text{80}\text{.92 amu}$ is given as:

  $\begin{array}{c}49.31\%=\frac{49.31}{100}\\ =0.4931\end{array}$

The atomic mass of bromineis calculated as follows:

  $\begin{array}{c}\text{atomic}\text{mass}\text{=}\text{78}\text{.92 amu}\times 0.5069\text{ amu}+\text{80}\text{.92 amu}\times 0.4931\\ =40.0045\text{amu}+39.9017\text{amu}\\ \text{=}79.9062\text{amu}\end{array}$

The atomic mass of bromine is $79.9062\text{amu}$ .