Question

What are the valencies of Sulfite, Bisulfite and Sulphate?

Answer 1

Hint : Valency describes the combining capacity of an element or compound. Chemical or molecular formula demonstrates the symbolic representation of compounds. The molecular formula for Sulfite, Bisulfite and Sulphate are $S{O_3}^{2-},HS{O_3}^{-}$ and $S{O_4}^{2-}$ , respectively.

Complete Step By Step Answer:
Sulfite, Bisulfite and Sulfite are the oxy-anions of sulphur and carry a negative charge. The molecular formula for Sulfite, Bisulfite and Sulphate are $S{O_3}^{2-},HS{O_3}^{-}$ and $S{O_4}^{2-}$ , respectively. Valency describes the combining capacity of a compound and the overall charge on the compound infers its valency. On the above basis, the valencies of Sulfite, Bisulfite and Sulphate are $2,1,$ and $2$ , respectively. It means that sulfite and sulphate can both gain two electrons each while Bisulfite can gain one electron in order to complete their respective octets.

Additional Information:
In sulphates, sulphur is present in higher oxidation state in comparison to sulfites. Sulphur is present in +6 oxidation state in sulphates, and in +4 oxidation state in sulfites. Therefore, sulfites act as a reducing agent since it can be easily oxidised into sulphates. For instance, sodium sulfite readily decolourises acidified potassium permanganate solution. While sulphate doesn’t act as reducing agent as it cannot further oxidises and thus doesn’t decolorize acidified potassium permanganate solution. Moreover, Sulfite is the conjugate base of the bisulfite.

Note :
It is important to note that the molecular formula for Sulfite, Bisulfite and Sulphate are $S{O_3}^{2-},HS{O_3}^{-}$ and $S{O_4}^{2-}$ , respectively. The overall charge on the compound infers its valency. Therefore, the valencies of Sulfite, Bisulfite and Sulphate are $2,1,$ and $2$ , respectively.