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Confirmatory Tests for Cations

Both Al³⁺ ion and Pb²⁺ ion give the same observations when tested with sodium hydroxide solution, NaOH and ammonia solution, NH₃. Thus, a confirmatory test is required to differentiate between Pb²⁺ ion and Al³⁺ ion. Other than that, ions such as Fe²⁺, Fe³⁺ and NH₄⁺ too can be confirmed using specific reagents.

Potassium hexacyanoferate(II) solution, K₄Fe(CN)₆ is used to confirm the presence of iron(III) ion, Fe³⁺.

If this solution is added to an aqueous solution that contains iron(II) ion, Fe²⁺, a light blue precipitate is formed.

• Potassium hexacyanoferate(III) solution, K₃Fe(CN)₆ is used to confirm the presence of iron(II) ion, Fe²⁺.

If this solution is added to an aqueous solution containing iron(III), Fe³⁺, a greenish brown colour is obtained.