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Analysis of Cations - Analysis of Group-IV Cations

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Estimated time: 3 minutes
CBSE: Class 12

Key Points: Analysis of Group IV Cations

Analysis of Group IV Cations (Zn²⁺, Mn²⁺, Ni²⁺, Co²⁺):

  • Group reagent: H₂S in presence of NH₄OH
  • Precipitate colours: ZnS (white), MnS (buff/dirty pink), NiS (black), CoS (black)

Test for Zn²⁺ ion:

  • ZnCl₂ + 2NaOH → Zn(OH)₂↓ (white ppt.) → soluble in excess NaOH → Na₂ZnO₂ (confirms Zn²⁺)
  • Pass H₂S → white ZnS ppt. forms
  • K₄[Fe(CN)₆] after neutralisation with NH₄OH → white or bluish white ppt. of zinc ferrocyanide

Test for Ni²⁺ ion:

  • NiS (black) dissolves in aqua regia: NiS + 4HNO₃ + 6HCl → NiCl₂ + NO + ...
  • Dimethylglyoxime (DMG) added after making alkaline with NH₄OH → brilliant red precipitate (Ni–DMG complex)

Test for Mn²⁺ ion:

  • Mn(OH)₂ (white ppt.) with NaOH
  • NaHCO₃ + heat → MnCO₃ → NaOH + Br₂ → boil → black ppt. of Mn₂O₃ (MnO₂)
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