Chapter U4.76, Problem 1E

Interpretation Introduction

Interpretation:

The method to calculate the average atomic mass of an element needs to be explained.

Concept introduction:

Average atomic mass is the ratio of mass of an atom of the element to mass of 1 hydrogen atom or 1/12 th of a C¹² atom or 1/16 th of a O¹⁶ atom.

  $\mathrm{Average}atomicmass=\left[sumof\left(abundance\times atomicmassofallisotopes\right)\right]/100$

Answer to Problem 1E

Average atomic mass is calculated by considering all the isotopes of the elements. The abundance and mass are used to calculate the average atomic mass.

The unit is equal to that of atomic mass or amu.

Explanation of Solution

Average atomic mass is calculated in the following way. Example of Cl atom is taken to explain the caculation.

Cl has two isotopes Cl³⁵ and Cl 37. Abundances of 1st one is 75 % and 2^nd one is 25 %.

Average atomic mass can be calculated as follows:

  $\begin{array}{l}\mathrm{Average}atomicmass=\frac{\left(\%Cl-35\right)\left(35\right)+\left(\%Cl-37\right)\left(37\right)}{100}\\ =\frac{\left(35\times 75+25\times 37\right)}{100}\\ =\frac{2625+925}{100}\\ =35.5\end{array}$