An atom of aluminium has an atomic mass of 27 - Edexcel - GCSE Chemistry Combined Science - Question 3 - 2022 - Paper 1

First, calculate the number of moles of aluminium and bromine in the sample:

For aluminium:

$\text{Moles of Al} = \frac{1.35g}{27.0g/mol} = 0.05 \text{ moles}$

For bromine:

$\text{Moles of Br} = \frac{12.00g}{80.0g/mol} = 0.15 \text{ moles}$

Next, find the simplest mole ratio by dividing by the smallest number of moles:

• Moles of Al ratio: $\frac{0.05}{0.05} = 1$
• Moles of Br ratio: $\frac{0.15}{0.05} = 3$

Thus, the empirical formula for aluminium bromide is:

• Empirical formula: AlBr$_3$