The atomic mass of rhenium is 186.2. Given that 37.1% of natural rhenium is rhenium-185, what is the other stable isotope?

Question

Quizplus · Accepted Answer

Let x be the percent abundance of the other stable isotope, rhenium-187. Since the sum of the percent abundances of all naturally occurring isotopes is 100%, we have:

x + 37.1% = 100%
x = 62.9%

Now we can calculate the atomic mass of the other stable isotope:

atomic mass of rhenium-187 = (187 amu)(62.9/100) = 117.6 amu

We know that the atomic mass of natural rhenium is 186.2 amu, so we can set up an equation to solve for the percent abundance of rhenium-187:

(37.1/100)(185 amu) + (62.9/100)(atomic mass of rhenium-187) = 186.2 amu

Simplifying this equation, we get:

68.535 + 0.629(atomic mass of rhenium-187) = 186.2

0.629(atomic mass of rhenium-187) = 117.665

atomic mass of rhenium-187 = 187.0 amu

Therefore, the other stable isotope of rhenium is rhenium-187.

The Atomic Mass of Rhenium Is 186