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?

Average atomic mass of Rb = 85.6 amu.

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.