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

If 37.1% of natural rhenium is rhenium-185, then 62.9% must be rhenium-187 (since these are the only two stable isotopes of rhenium). To calculate the weighted average atomic mass, we need to multiply the atomic masses of each isotope by its percentage abundance (expressed as a decimal) and add the results.

(0.371)(185) + (0.629)(187) = 68.635 + 117.523 = 186.158

This is very close to the given atomic mass of rhenium, which suggests that rhenium-185 and rhenium-187 are indeed the only two stable isotopes. The answer choice that corresponds to rhenium-187 is B.

The Atomic Mass of Rhenium Is 186