Question

Bromine has two isotopes, 79Br and 81Br, with masses (78.9183 and 80.9163 amu) and abundances (50.69% and 49.31%, respectively). What is the average atomic mass of bromine?

a) 79.904 amu

b) 79.845 amu

c) 80.423 amu

d) 80.001 amu

Answer 1

The average atomic mass of bromine is calculated by converting the percent abundances to decimal form, multiplying each isotope's mass by its respective abundance, and adding together these weighted masses. The correct average atomic mass for bromine, based on the given data, is approximately 79.904 amu.

The correct answer is A.

Step-by-step explanation:

To calculate the average atomic mass of bromine, we need to use the given masses and abundances of its isotopes, 79Br and 81Br. The following steps outline how to determine the average atomic mass:

1. Convert the percent abundances of each isotope to decimal form by dividing by 100.
2. Multiply the exact mass of each isotope by its corresponding abundance (in decimal form) to find the weighted mass contribution of each isotope.
3. Add together the weighted mass contributions of both isotopes to obtain the total average atomic mass of bromine.

Here is the calculation:

• 79Br: 78.9183 amu x 0.5069 = 39.99 amu (approx)
• 81Br: 80.9163 amu x 0.4931 = 39.91 amu (approx)
• Total average atomic mass = 39.99 amu + 39.91 amu = 79.90 amu (approximately)

Therefore, the correct answer is (a) 79.904 amu, which is the average atomic mass of bromine based on the given isotopic masses and abundances.