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Experiment No. N

Analysis of Calcium Sulphide (CaS)

Aim

To determine the presence of anion and cation in the given salt

Preliminary Test

  • Odor: Odor of rotten eggs
  • Texture: Crystalline
  • Color: White
  • Solubility: Soluble in water

Test of Anion

ExperimentObservationInference
Warm the salt with dilute H₂SO₄Colourless gas with smell of rotten eggs is evolvedS²⁻ may be present
Confirmatory Tests
Lead Acetate Test
Pass gas through filter paper dipped in lead acetate solution		Paper turns blackS²⁻ is confirmed
Sodium Nitroprusside Test
Make solution alkaline with NH₄OH (or sodium carbonate extract) and add sodium nitroprusside solution		Purple/violet colouration is producedS²⁻ is confirmed

Test of Cation

ExperimentObservationInference
Original solution + Dilute HClNo reactionGroup I cation is absent
Original solution + Dilute HCl + H₂S gas (with NH₄Cl)No reactionGroup II cation is absent
Original solution + Dilute HCl + NH₄Cl solid + NH₄OHNo reactionGroup III cation is absent
Original solution + NH₄Cl + NH₄OH + (NH₄)₂CO₃White precipitate is formedGroup V cation may be present
Confirmatory Test
Ammonium Oxalate Test
Dissolve white precipitate in dilute acetic acid and add ammonium oxalate solution		White precipitateCa²⁺ is confirmed

Result

The given salt contains Ca²⁺ ions as cation and S²⁻ ions as anion. The salt is CaS.

Precautions

  1. Handle the chemicals with care.
  2. Don't use excess of chemicals.
  3. Keep the mouth of the test tube away from the face.