Rubidium has two naturally occurring isotopes,⁸⁵Rb (84.912 amu)and ⁸⁷Rb (86.909 amu).Rubidium-85 is the more abundant isotope (72.17%).Calculate the average atomic mass of Rb.

Question

Quizplus · Accepted Answer

To calculate the average atomic mass, we need to take into account the abundance of each isotope.

Let's use x to represent the abundance of Rb-85, and (1-x) for Rb-87. We know that Rb-85 is 72.17% abundant, so:

x = 0.7217
(1-x) = 0.2783

Next, we can use the formula for average atomic mass:

average atomic mass = (mass of isotope 1 x abundance of isotope 1) + (mass of isotope 2 x abundance of isotope 2)

average atomic mass = (84.912 amu x 0.7217) + (86.909 amu x 0.2783)
average atomic mass = 61.2785 + 24.1570
average atomic mass = 85.4355 amu

Therefore, the best choice is B (85.47 amu).

Rubidium Has Two Naturally Occurring Isotopes,85Rb (84

Rubidium Has Two Naturally Occurring Isotopes,⁸⁵Rb (84