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Experiment No. N

Analysis of Lead(II) Sulphide (PbS)

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 HClWhite precipitatePb²⁺ may be present
Confirmatory Tests
Potassium Iodide Test
Dissolve one part of the hot precipitate in hot water and add potassium iodide solution		Yellow precipitate is formedPresence of Pb²⁺ is confirmed
Potassium Chromate Test
To the acidified solution obtained above, add potassium chromate solution		Yellow precipitate is formedPresence of Pb²⁺ is confirmed
Lead Sulphate Test
Dissolve lead sulphide precipitate in dilute HNO₃, then add a few drops of dilute H₂SO₄ and alcohol		White precipitate of lead sulphate is formedPresence of Pb²⁺ is confirmed

Result

The given salt contains Pb²⁺ ions as cation and S²⁻ ions as anion. The salt is PbS.

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.