Question

1. rubidium 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 rubidium, rounded to two spaces after the decimal?

Explanation:

Step1: Identify atomic masses of isotopes

The atomic mass of $^{85}$Rb is approximately 85 u and of $^{87}$Rb is approximately 87 u.

Step2: Calculate contribution of $^{85}$Rb

The contribution of $^{85}$Rb to the average atomic mass is $85\times0.722 = 61.37$ u.

Step3: Calculate contribution of $^{87}$Rb

The contribution of $^{87}$Rb to the average atomic mass is $87\times0.278= 24.186$ u.

Step4: Find average atomic mass

The average atomic mass is $61.37 + 24.186=85.556\approx85.56$ u.

Answer:

85.56 u