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Analysis of Iron(II) Sulphide (FeS)

Qualitative analysis

How to do salt analysis · Viva · Quiz

Aim

To analyse the given inorganic salt for one acidic and one basic radical.

Preliminary Test

  • Colour: Pale green
  • Odour: Rotten eggs
  • State: Crystalline solid
  • Solubility: Insoluble in water

Test of Anion (S²⁻)

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 (Fe²⁺)

ExperimentObservationInference
Salt solution + NaOH solutionDirty green precipitateFe²⁺ may be present
Confirmatory Test
Potassium Ferricyanide Test
Add potassium ferricyanide solution		Dark blue precipitate (Turnbull's blue)Presence of Fe²⁺ is confirmed

Result

The given salt contains Fe²⁺ as the cation (basic radical) and S²⁻ as the anion (acidic radical). The salt is Iron(II) Sulphide (FeS).

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.