Chapter 6, Problem 4A

Interpretation Introduction

Interpretation: The reason of using the average atomic mass of an element while performing calculation needs to be explained.

Concept Introduction: The molecular mass of compound is the sum of atomic mass of all the atoms present in the given chemical compound. The atomic mass of an element is the sum of mass of sub-atomic particles.

There are different isotopes for an element which are found in different abundance.

Answer to Problem 4A

The average atomic mass of an element is used for performing calculation because different isotopes of an element have different abundance.

Explanation of Solution

An element can have more than one isotope. Here isotopes are the element with same atomic number and different mass number or atomic mass.

Since all elements are found in different abundance in nature therefore the average atomic mass must be used in different calculations. The mathematical expression of average atomic mass is:

  $\text{Average atomic mass = }\frac{\text{(abundance \%of isotope1}\times \text{mass of isotope 1) +(abundance \%of isotope2}\times \text{mass of isotope 2)+}\mathrm{....}}{\text{100}}$

Conclusion

  $\text{Average atomic mass = }\frac{\text{(abundance \%of isotope1}\times \text{mass of isotope 1) +(abundance \%of isotope2}\times \text{mass of isotope 2)+}\mathrm{....}}{\text{100}}$