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Experiment No. N

Analysis of Zinc Sulphite (ZnSO₃)

Aim

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

Preliminary Test

  • Odor: Odorless
  • Texture: Crystalline
  • Color: White
  • Solubility: Soluble in water

Test of Anion

ExperimentObservationInference
Warm 1 mL of water extract or sodium carbonate extract with dilute H₂SO₄Colourless gas with pungent smell of burning sulphur is evolvedSO₃²⁻ may be present
Confirmatory Tests
Barium Chloride Test
Add barium chloride to water extract or sodium carbonate extract		White precipitate dissolves on adding dilute HCl and SO₂ is evolvedSO₃²⁻ is confirmed
KMnO₄ Decolourisation Test
Add dilute H₂SO₄ to the barium sulphite precipitate and then very dilute KMnO₄ solution		Colour of potassium permanganate solution is dischargedSO₃²⁻ is confirmed

Test of Cation

ExperimentObservationInference
Original solution + H₂S gas in presence of NH₄OHWhite precipitate is formedGroup IV cation may be present
Confirmatory Tests
Sodium Hydroxide Test
Add sodium hydroxide solution dropwise		White precipitate forms and dissolves in excess NaOH on heatingZn²⁺ is confirmed
Potassium Ferrocyanide Test
After neutralisation with NH₄OH, add potassium ferrocyanide solution		Bluish-white precipitateZn²⁺ is confirmed

Result

The given salt contains Zn²⁺ ions as cation and SO₃²⁻ ions as anion. The salt is ZnSO₃.

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.