Question

Chlorine has two stable isotopes: Cl-35 and Cl-37 with atomic masses 34.96 and 36.95, respectively. If the average mass of chlorine is 35.43, calculate the percentage abundance.

Answer 1

Let x = fraction of Cl-35

Let y = fraction of Cl-37

x + y = 1

So, y = 1 - x

Given, atomic mass of Cl-35 = 34.96; atomic mass ofCl-37 = 36.95; average mass of chlorine = 35.43

34.96 $\times$ x + 36.95 $\times$ y = 35.43

34.96 $\times$ x + 36.95 $\times$ (1 - x) = 35.43 (since, y = 1 - x)

Solving for x gives x = 0.7595

Solving for y gives y = 0.2405

Multiplying with 100 gives percentage abundance:

Percentage abundance of Cl-35 = 0.7595 $\times$ 100 = 75%

Percentage abundance of Cl-37 = 0.2405 $\times$ 100 = 24.05%