Relative atomic mass

3 marks · Normal

Bromine consists of two isotopes: and . The percentage abundances are 51% and 49% respectively. Calculate the relative atomic mass of bromine. Give your answer to 1 decimal place.

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79.98 (±0.1)

Also accept: 79.98; 80.0

Common mistakes: Forgetting to divide by 100; Using mass numbers as percentages

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Marking points

M1 · 1 mark · Multiplies each isotope's mass number by its percentage abundance.

M2 · 1 mark · Sums results and divides by 100.

A1 · 1 mark · Final correct answer to 1 decimal place: 79.98 or 80.0 allowed. (follow-through)

Worked solution