Question

On a mission to a newly discovered planet, an astronaut finds chlorine abundances of 13.85 % for 35Cl and 86.15 % for 37Cl. What is the atomic mass of chlorine for this location?

Answer 1

Answer : The atomic mass of chlorine is, 36.723 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:

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

As we are given that,

Mass of 35-Cl isotope = 35 amu

Percentage abundance of 35-Cl isotope = 13.85 %

Fractional abundance of 35-Cl isotope = 0.1385

Mass of 37-Cl isotope = 37 amu

Percentage abundance of 37-Cl isotope = 86.15 %

Fractional abundance of 37-Cl isotope = 0.8615

Now put all the given values in above formula, we get:

$\text{Average atomic mass }=[(35\times 0.1385)+(37\times 0.8615)]$

$\text{Average atomic mass }=36.723amu$

Therefore, the atomic mass of chlorine is, 36.723 amu