Tests for Positive Ions (Cations)

Tests for Positive lons (Cations)

A. Test for Fe³⁺

• Ferric ions react with ammonium hydroxide to form a red-brown precipitate of ferric hydroxide.
• The chemical reaction is Fe³⁺ + 3OH⁻ → Fe(OH)₃↓ (red-brown ppt)
• This precipitate can be confirmed by adding 6M HCl, which causes the red-brown precipitate to dissolve.

Procedure

• Add 1 mL of 0.1 M FeCl₃ solution into a clean dry test tube.
• Add 0.5 mL of ammonium hydroxide and observe the formation of the red-brown precipitate.
• Add 0.5 mL of 6M HCl and shake to observe the disappearance of the red precipitate.

B. Test for Ca²⁺

• A calcium-containing solution reacts with ammonium oxalate in an alkaline medium to form a white precipitate of calcium oxalate.
• The chemical reaction is Ca(NO₃)₂ + (NH₄)₂C₂O₄ → CaC₂O₄↓ + 2NH₄NO₃
• Calcium oxalate is a white precipitate.

Procedure

• Add 1 mL of drops of 0.1M Ca(NO₃)₂ solution into a clean dry test tube.
• Add 0.5 mL of 6M ammonia and shake gently.
• Add 0.5 mL of (NH₄)₂C₂O₄ and observe the formation of the white calcium oxalate precipitate.