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Experiment No. N

Analysis of Aluminium Sulphide ((Al)₂(S)₃)

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 + Dil. HCl + NH₄Cl solid + NH₄OHWhite gelatinous precipitateAl³⁺ may be present
Confirmatory Tests
Dissolve white precipitate in dilute HCl and divide into two partsTo the first part, add sodium hydroxide and warm. A white gelatinous precipitate dissolves in excess sodium hydroxide solutionAluminium is confirmed
Blue Lake Test
To the second part, add few drops of blue litmus solution and then NH₄OH dropwise along the sides of the test tube		A blue floating mass appears in colourless solutionPresence of Al³⁺ is confirmed

Result

The given salt contains Al³⁺ ions as cation and S²⁻ ions as anion. The salt is (Al)₂(S)₃.

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.