Ferric Sulphite

Ferric Sulphite is a rarely encountered iron(III) compound with the tentative chemical formula Fe2(SO3)3; however, iron(III) sulphite is not widely found or characterized due to its instability—most iron(III) salts of sulfur-based oxyanions exist either as sulphate (Fe2(SO4)3) or as mixed oxidation state species. Reliable sources and common laboratory catalogs often list ferric sulphate (Fe2(SO4)3) instead, which is a well-characterized, yellow-brown solid used in water treatment and as a coagulant.​

Ferric Sulphite: Chemical Highlights

Proposed formula: Fe2(SO3)3

Iron oxidation state: +3

Sulphite ion: SO3^2−

Appearance: Not well established; typically iron(III) sulphite would be unstable and decompose, possibly forming iron(III) oxides and sulfur dioxide.​

Ferric Sulphate (Reference Standard Compound)

Formula: Fe2(SO4)3

Molar mass: 399.88 g/mol

Appearance: Yellow-brown crystalline solid

Solubility: Soluble in water, insoluble in ethanol and acetone

Used for: Water purification, dyeing, as a coagulant, and in laboratory applications.​

For practical and catalog purposes, ferric sulphate (Fe2(SO4)3) is typically listed and supplied instead of ferric sulphite, as the latter has little commercial or laboratory use due to its marked instability and potential for decomposition.​