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Analysis of Sodium Sulphite (Na₂SO₃)

Qualitative analysis

Aim

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

Preliminary Test

  • Colour: White
  • Odour: Odourless
  • State: Crystalline solid
  • Solubility: Soluble in water

Test of Anion (SO₃²⁻)

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 (Na⁺)

ExperimentObservationInference
Flame test in a clean non-luminous flameIntense yellow flameNa⁺ may be present
Confirmatory Test
Zinc Uranyl Acetate Test
Take a filtrate and add zinc uranyl acetate solution
Yellow crystalline precipitateNa⁺ is confirmed

Result

The given salt contains Na⁺ as the cation (basic radical) and SO₃²⁻ as the anion (acidic radical). The salt is Sodium Sulphite (Na₂SO₃).

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.