The Language of Chemistry — Question 27

Aluminium is trivalent cation with a valency of 3 → Al³⁺

Sulphate is divalent anion with a valency of 2 → SO₄^2-

Formula:

$\text{Al}^{3+} \space \text{SO}_4^{2-} \\[1em] \overset{3}{\text{Al}} \space {\swarrow}\mathllap{\searrow} \space \overset{2}{\text{SO}_4} \Rightarrow \underset{2}{\text{Al}} \space {\swarrow}\mathllap{\searrow} \space \underset{3}{\text{SO}_4} \\[1em] \text{Al}_2(\text{SO}_4)_3$

Hence, the formula is : Al₂(SO₄)₃