Qualitative analysis of iron (II) and iron (III) ions

Qualitative analysis of Fe²⁺ salt

Common iron II salts include

•  Ferrous sulphate: FeSO₄.7H₂O
•  Ammonium ferrous sulphate (NH₄)₂Fe(SO₄)₂.6H₂O

•  Ferrous oxalate. FeC₂O₄

Qualitative analysis of Fe²⁺ salt

Addition of dilute sodium hydroxide or ammonia solution

Observation

A dirty green precipitate insoluble in excess turn brown on standing.

Fe²⁺(aq) + 2OH^–(aq) → Fe(OH)₂(s)

 

Confirming presence of Iron II ions

Forms a deep blue solution with potassium hexacyanoferrate III.

Qualitative analysis of Fe³⁺ salt

Addition of dilute sodium hydroxide or ammonia solution

Observation

Brown ppt precipitate insoluble in excess turn brown on standing.

Fe³⁺(aq) + 3OH^–(aq) → Fe(OH)₃(s)

 

Confirming presence of Iron III ions

Forms a deep blue solution with potassium hexacyanoferrate II.

Forms a red solution with ammonium thiocyanate solution.

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