Question

Ordinary chlorine gas has two isotopes: \[\ce{^35_17Cl}\] and \[\ce{^37_17Cl}\] in the ratio of 3 : 1. Calculate the relative atomic mass [atomic weight] of chlorine.

Answer 1

Ratio of isotopes of chlorine
\[\ce{^35_17Cl}\] and \[\ce{^37_17Cl}\] = 3 : 1
Ratio of atomic masses = 3 : 1
Total mass = (3 × 35) + (37 × 1)
= 105 + 37 = 142
Relative atomic mass of chlorine = `"Total mass"/(3+1)`
= `142/4=71/2=35.5`