The table below shows the atomic masses and natural abundances of the two naturally occurring isotop

NY Regents Chemistry Exam Jan 2023

The table below shows the atomic masses and natural abundances of the two naturally occurring isotopes of rhenium.

Which numerical setup can be used to calculate the atomic mass of rhenium?

(1) (184.95 u)(37.40) + (186.96 u)(62.60) (2) (184.95 u)(0.3740) + (186.96 u)(0.6260) (3) ((184.95 u)(37.40) + (186.96 u)(62.60))/ 2 (4) ((184.95 u)(0.3740) + (186.96 u)(0.6260))/ 2

Solution: To calculate the average atomic mass of an element, we take the atomic mass of each isotope and multiply by percent abundance in the decimal form ( divide by 100).

Average atomic mass of rhenium = (184.95 u)(0.3740) + (186.96 u)(0.6260)

Choice 2 is the correct answer.