Chlorine is 75.78% Cl-35 with a mass of 34.969 amu and 24.22% Cl-37 with a mass of 36.966 amu. Find the average atomic mass.

Solution

Chemistry · Medium

Problem

Chlorine is 75.78% Cl-35 with a mass of 34.969 amu and 24.22% Cl-37 with a mass of 36.966 amu. Find the average atomic mass.

Use a weighted average with the percent abundances as decimals.
average mass = (0.7578)(34.969 amu) + (0.2422)(36.966 amu)
average mass = 26.50 amu + 8.953 amu
average mass = 35.45 amu.

Result

35.45 amu