Metallic ions (Cations)

Metallic ions can be classified as colourless and coloured ions.

Colourless metallic ions

The most commonly used colourless ions are zinc (Zn2+), calcium (Ca2+) Aluminum (AL3+) lead (Pb2+)

Test Observation Inference
Unknown solution +NaOH

in drop(aq) In excess

White precipitates formed. Zn2+ AL3+ Ca2+ Pb2+ present
White precipitates dissolves Zn2+ AL3+ Pb2+ present
Unknown solution +NaOH

in drop(aq) In excess

White precipitates formed. Zn2+ AL3+ Pb22+ present
White precipitates dissolves Zn2+ is confirmed.

NB – Ca2+ remains insoluble in excess of NaOH(aq) and does not react with NH3(aq)

Also, AL3+ and Pb2+ are insoluble in excess NH3(aq) but Zn2+ dissolve in excess of NH3(aq)

Coloured Metallic ions

Iron has two ions, which are Fe3+ and Fe2+ Copper (Cu2+) ions

Reading Ions Observation
NaOH(ag) Fe2+ Dirty green gelatinous precipitate which remain insoluble in excess of NaOH(aq)
Fe3+ Reddish – brown gelatinous precipitate which remains insoluble in excess of NaOH(aq)
Cu2+ Blue gelatinous precipitate is formed, which is insoluble in excess of NaOH(aq)
NH3(ag) Fe2+ Dirty green gelatinous precipitate which remain insoluble in excess NH3(ag)
Fe3+ Reddish – brown gelatinous precipitate which remains insoluble in excess
Cu2+ Blue gelatinous precipitate is formed, which is insoluble in excess of aqueous ammonia to deep blue solution. (confirmatory test)
Potassium Fe3+ Light blue precipitate
Hexacyano-

Ferrate (II)

Fe3+ Deep blue precipitate
Potassium Fe2+ Deep blue precipitate
Hexacyano-

Ferrate (III)

Fe3+ Brown colouration
Potassium Fe2+ No action
Thiocyanate

Solution

Fe3+ Blood-red colouration

NB- Copper salt has a bluish-green colour when viewed on a non-luminous flame.

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