Question

a sample of rhenium contains the following relative abundances of its isotopes.

isotope	relative abundance
$_{75}^{187}$re	62.60%

what is the average relative atomic mass of the rhenium in the sample?

Explanation:

Step1: Calculate contribution of \(^{185}\text{Re}\)

Multiply mass of \(^{185}\text{Re}\) (185) by its abundance (37.40% = 0.3740).
\(185 \times 0.3740 = 69.19\)

Step2: Calculate contribution of \(^{187}\text{Re}\)

Multiply mass of \(^{187}\text{Re}\) (187) by its abundance (62.60% = 0.6260).
\(187 \times 0.6260 = 117.062\)

Step3: Sum the contributions

Add the two contributions to get the average atomic mass.
\(69.19 + 117.062 = 186.252\)

Answer:

\(186.25\) (or \(186.252\) depending on precision)