IGCSE Chemistry 2026 – 400 Free Practice Questions to Pass the Exam

To find the relative atomic mass of bromine given the isotopic composition, one must consider the mass and abundance of each isotope. Bromine has two major isotopes: bromine-79, which has a mass of approximately 79 amu (atomic mass units), and bromine-81, with a mass of approximately 81 amu.

In this case, bromine-79 accounts for 50.7% of the naturally occurring bromine, and bromine-81 makes up the remaining 49.3%. The calculation for the relative atomic mass involves taking a weighted average of the isotopes based on their relative abundances.

The calculation can be performed as follows:

1. Calculate the contribution of bromine-79:

\[

79 \times 0.507 = 40.053

\]

2. Calculate the contribution of bromine-81:

\[

81 \times 0.493 = 39.873

\]

3. Combine these contributions to find the relative atomic mass:

\[

40.053 + 39.873 = 79.926

\]

Rounding this value gives approximately 79.93, which aligns closely