Question

rubidium is a soft silvery-white metal that has two common isotopes, 85Rb and 87Rb. If the abundance of 85Rb is 72.2% and the abundance of 87Rb is 27.8%, what is the average atomic mass of ribidium?

Answer 1

Average atomic mass of Rb = 85.6 amu.

Step-by-step explanation:

Abundance of Rb⁸⁵ = 72.2%

Abundance of Rb⁸⁷ = 27.8%

Average atomic mass = ?

Solution:

Average atomic mass of Rb= (abundance of 1st isotope × its atomic mass) +(abundance of 2nd isotope × its atomic mass) / 100

Average atomic mass of Rb = (85×72.2)+(87×27.8) /100

Average atomic mass of Rb = 6137 + 2418.6 / 100

Average atomic mass of Rb = 8555.6 / 100

Average atomic mass of Rb = 85.6 amu.