Chapter 4, Problem 53A

Interpretation Introduction

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

Concept Introduction : Atomic mass is the weighted average mass of the atoms in a sample of an element that is present in nature.

Answer to Problem 53A

The atomic mass of lithium is $6.9409\text{amu}$ .

Explanation of Solution

Given information:

The relative abundance of lithium of atomic mass $\text{6}\text{.015 amu}$ is $7.5\%$ .

The relative abundance of lithium of atomic mass $\text{7}\text{.016 amu}$ is $92.5\%$ .

Atomic mass is the weighted average mass of the atoms in a sample of an element that is present in nature.

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 lithium of atomic mass $\text{6}\text{.015 amu}$ is given as

  $\begin{array}{c}7.5\%=\frac{7.5}{100}\\ =0.075\end{array}$

The relative abundance of lithium of atomic mass $\text{7}\text{.016 amu}$ is given as

  $\begin{array}{c}92.5\%=\frac{92.5}{100}\\ =0.925\end{array}$

Calculate the atomic mass of lithiumas follows:

  $\begin{array}{c}\text{atomic}\text{mass}\text{=}\text{6}\text{.015 amu}\times 0.075\text{amu}+\text{7}\text{.016 amu}\times 0.925\text{amu}\\ =0.4511\text{amu}\text{+}6.4898\text{amu}\\ \text{=}6.9409\text{amu}\end{array}$

Thus, the atomic mass of lithium is $6.9409\text{amu}$ .