Question

(a) Two stable isotopes of lithium and have respective abundances of 7.5% and 92.5%. These isotopes have masses 6.01512 u and 7.01600 u, respectively. Find the atomic mass of lithium.

(b) Boron has two stable isotopes, and. Their respective masses are 10.01294 u and 11.00931 u, and the atomic mass of boron is 10.811 u. Find the abundances of and .

Answer 1

(a) Mass of lithium isotope , m₁ = 6.01512 u

Mass of lithium isotope , m₂ = 7.01600 u

Abundance of , η₁= 7.5%

Abundance of , η₂= 92.5%

The atomic mass of lithium atom is given as:

(b) Mass of boron isotope , m₁ = 10.01294 u

Mass of boron isotope , m₂ = 11.00931 u

Abundance of , η₁ = x%

Abundance of , η₂= (100 − x)%

Atomic mass of boron, m = 10.811 u

The atomic mass of boron atom is given as:

And 100 − x = 80.11%

Hence, the abundance of is 19.89% and that of is 80.11%.