Question

An element has two naturally-occurring isotopes. The mass numbers of these isotopes are 125 amu and 127 amu, with natural abundances of 45% and 55%, respectively. Calculate its average atomic mass. Report your answer to 1 decimal place

Answer 1

The average atomic mass is 126.1

Step-by-step explanation:

To obtain the atomic mass of the isotope we use this formula;

(% composition of isotope 1 * mass number) + (% composition of isotope 2 * mass number)

1. Equate the percentage composition with the mass number of each isotope

45/100 * 125 = 56.25

55/100 * 127 = 69.85

2. Add both answers together you get,

56.25 + 69.85 = 126.1.

The average atomic mass is therefore 126.1