Chapter 4.3, Problem 24SP

Interpretation Introduction

Interpretation : The atomic mass of copper 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 24SP

The atomic mass of copper is $\text{63}\text{.546}\text{amu}$ .

Explanation of Solution

Given information:

The mass numbers of copper are 63 and 65.

The relative abundance of copper of atomic mass $\text{62}\text{.93 amu}$ is $69.2\%$ .

The relative abundance of copper of atomic mass $\text{64}\text{.93 amu}$ is $30.8\%$

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 copper of atomic mass $\text{62}\text{.93 amu}$ is given as:

  $\begin{array}{c}69.2\%=\frac{69.2}{100}\\ =0.692\end{array}$

The relative abundance of copper of atomic mass $\text{64}\text{.93 amu}$ is given as:

  $\begin{array}{c}30.8\%=\frac{30.8}{100}\\ =0.308\end{array}$

The atomic mass of copper is calculated as follows:

  $\begin{array}{c}\text{atomic}\text{mass}=\text{62}\text{.93 amu}\times 0.692+\text{64}\text{.93 amu}\times 0.308\\ =19.9984\text{amu}+43.5475\text{amu}\\ =\text{63}\text{.546}\text{amu}\end{array}$

The atomic mass of copper is $\text{63}\text{.546}\text{amu}$ .