Rubidium possesses two stable forms and has an average mass of 85.5. 85Rb has a mass of 84.9 and a percent abundance of 72.2%. What is the mass of the other form of Rb?
A) 86.1 u
B) 85.7 u
C) 88.3 u
D) 87.1 u
E) 89.4 u

Question

Quizplus · Accepted Answer

Let x be the mass of the other form of Rb.

The average mass of Rb is given by:

(0.722)(84.9 u) + (1 - 0.722)(x) = 85.5 u

Solving for x, we get:

x = (85.5 - 0.722(84.9)) / (1 - 0.722) = 87.1 u

Therefore, the mass of the other form of Rb is 87.1 u, which corresponds to choice D.

Rubidium Possesses Two Stable Forms and Has an Average Mass