The chemical formula for the ionic compound aluminum sulfite is Al2(SO3)3. Explain why there are 2 cations for every 3 anions in this compound.

Explanation:

While trying to write the chemical formula for a compound (a neutral molecule), one must identify and exchange the charge of the cation with that of the anion to become the subscript of one other. For example

Aluminium oxide has Aluminium (Al) and oxygen (O); since Al has a charge of 3+ (the cation) and O has a charge of 2- (the anion), the compound would have it's charges as Al³⁺O²⁻ and when the charges are exchanged to there subscripts, it would form Al₂O₃; thus there would be two cations of aluminium for every three anions of oxygen in order to have a neutral molecule.

This same explanation can be given to Aluminium sulfite. Aluminium sulfite has Aluminium (Al) and sulfite (SO₃). Al has a charge of 3+ (cation) while sulfite has a charge of 2- (anion), with the compound having it's charges as Al³⁺(SO₃)²⁻ and when the charges are exchanged to there subscripts, it would form Al₂(SO₃)₃ and would thus have 2 cations of aluminium (Al³⁺) for every 3 anions of sulfite (SO₃³⁻) in order to have a neutral molecule.