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Experiment No. N

Analysis of Iron(III) Sulphide ((Fe)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 + NH₄OH solutionReddish-brown precipitateGroup-III cation may be present
Confirmatory Tests
Potassium Ferrocyanide Test
Dissolve the precipitate in dilute HCl, divide into two parts and add potassium ferrocyanide to one part		Blue/Prussian blue precipitateFe³⁺ is confirmed
Potassium Thiocyanate Test
To second part add potassium thiocyanate solution		Blood-red colouration is formedFe³⁺ is confirmed

Result

The given salt contains Fe³⁺ ions as cation and S²⁻ ions as anion. The salt is (Fe)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.