Question

Lithium has two isotopes with mass numbers 6 and 7. If the relative atomic mass of Lithium is 6.94, determine the percentage abundance of each isotope.

Answer 1

R.A.M = (Mass.no ×Abundance)
                 (Total abundance)
Let the abundance of Li-6 be x
Relative abundance of Li-7 will be 100−x.
∴ 6.94 = (6 × x)+ 7(100−x)
                       100
6x + 700 – 7x = 694
X = 6%
Li-6 has 6%, Li-7 has 94%