Bromine has two naturally occurring isotopes. ⁷⁹Br has a mass of 78.9 amu and accounts for 50.3% of bromine atoms. If the atomic mass of bromine is 79.9 amu, what is the mass of an atom of the second bromine isotope? A)77.9 amu B)80.0 amu C)80.1 amu D)80.9 amu E)88.9 amu

Question

Quizplus · Accepted Answer

Let x be the mass of the second bromine isotope.

We know that the average atomic mass of bromine is 79.9 amu, and that one isotope (with a mass of 78.9 amu) accounts for 50.3% of bromine atoms.

Using this information, we can set up the following equation:

(0.503)(78.9 amu) + (0.497)x = 79.9 amu

Solving for x, we get:

x = (79.9 amu - (0.503)(78.9 amu))/0.497

x = 80.9 amu

Therefore, the mass of an atom of the second bromine isotope is 80.9 amu. The correct answer is D.

Bromine Has Two Naturally Occurring Isotopes