Regents Chemistry August 2022

34 Given information about the naturally occurring isotopes of bromine:

Which numerical setup can be used to determine the atomic mass of bromine?

(1) (78.92 u)(50.69) + (80.92 u)(49.31)

(2) (80.92 u)(50.69) + (78.92 u)(49.31)

(3) (78.92 u)(0.5069) + (80.92 u)(0.4931)

(4) (80.92 u)(0.5069) + (78.92 u)(0.4931)

**Explanation:** Atomic mass of an element is calculated by taking mass of each isotope and multiplying it by % abundance (in decimal form, divide by 100). First, we can divide % abundance by 100, so we would get 0.5069 and 0.4931. Then we multiple these abundances by the mass of the isotope they are paired with.

**Answer:** 3