Question

A certain element consists of two stable isotopes. The first has atomic mass of 7.02 amu and a percent natural abundance of 92.6%. The second has an atomic mass of 6.02 amu and a percent natural abundance of 7.42%. What is the atomic weight of the element? in amu

Answer 1

Answer: The average atomic mass of the element is 6.95 amu

Explanation:

Average atomic mass of an element is defined as the sum of masses of each isotope each multiplied by their natural fractional abundance.

Formula used to calculate average atomic mass follows:

$\text{Average atomic mass }=\sum_{i=1}^n\text{(Atomic mass of an isotopes)}_i\times \text{(Fractional abundance})_i$ .....(1)

We are given:

Mass of isotope 1 = 7.02 amu

Percentage abundance of isotope 1 = 92.6 %

Fractional abundance of isotope 1 = 0.926

Mass of isotope 2 = 6.02 amu

Percentage abundance of isotope 2 = 7.42 %

Fractional abundance of isotope 2 = 0.0742

Putting values in equation 1, we get:

$\text{Average atomic mass of element}=[(7.02\times 0.926)+(6.02\times 0.0742)]$

$\text{Average atomic mass of element}=6.95amu$

Hence, the average atomic mass of the element is 6.95 amu