Question

Why is the atomic mass of chlorine taken as 35.5? [2 MARKS]

Answer 1

Logic : 1 Mark
Process : 1 Mark

Chlorine exists as two isotopes, Cl-35 and Cl-37. Cl-35 is 75% abundant whereas Cl-37 makes up the remaining chlorine. When we consider the atomic mass of Cl, we take the average mass of Cl atoms.

Average wt. = 0.75 x 35 + 0.25 x 37 = 35.5