Question

The relative abundance of two rubidium isotopes of atomic weights 85 and 87 are 75% and 25% respectively. Find the average atomic weight of rubidium

Answer 1

Answer:

85.5

Explanation:

Atomic weight of first element = RA(1) = 85 (Given)

Atomic weight of second element = RA(2) = 87 (Given)

Relative abundance of RA(1) = 75% (Given)

Relative abundance of RA(2) = 25% (Given)

Therefore,

Average atomic weight = R.A(1) × at.mass(1) + R.A(2) × at.mass(2)/ R.A(1)+R.A(2)

Average atomic weight = 85 ×75 × 87 ×25 / 75+25

= 6375+2175/ 100

= 8550/ 100

= 85.5

Thus, the average atomic weight of rubidium is 85.5

Answer 2

Answer:

Explanation:

Atomic weight of first element = RA(1) = 85 (Given)

Atomic weight of second element = RA(2) = 87 (Given)

Relative abundance of RA(1) = 75% (Given)

Relative abundance of RA(2) = 25% (Given)

Therefore,

Average atomic weight = R.A(1) × at.mass(1) + R.A(2) × at.mass(2)/ R.A(1)+R.A(2)

Average atomic weight = 85 ×75 × 87 ×25 / 75+25

= 6375+2175/ 100

= 8550/ 100

= 85.5

Thus, the average atomic weight of rubidium is 85.5