Project Of Christopher Boo

Chemistry Level 2

There are two rubidium isotopes occurring in nature: $\text{Rb}^{85}$ , which has a molar mass of $84.91$ , and $\text{Rb}^{87}$ , whose molar mass is $86.92$ . The atomic mass of rubidium is $85.47$ . What is the percentage of $\text{Rb}^{87}$ out of the total existing $\text{Rb}?$

20.1 % 27.9 % 56.0 % 72.1 %

1 solution

Tong Choo
Jan 27, 2014

Let the fraction of rubidium-87 be x. Therefore, the fraction of rubidium-85 = 1 - x

x * 86.92 + (1 - x) * 84.91 = 85.47

Solving, you get x = 0.279. Therefore, percentage of rubidium-87 = 27.9%

Project Of Christopher Boo

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