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Experiment No. N

Analysis of Arsenic(III) Carbonate ((As)₂(CO₃)₃)

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
Take 0.1 g of salt, add 1–2 mL of dilute H₂SO₄Colourless odourless gas is evolved with brisk effervescence; lime water turns milkyCO₃²⁻ may be present
Confirmatory Tests
Lime Water Test
Pass the gas through lime water		Lime water turns milky; milkiness disappears on excess gasCO₃²⁻ is confirmed
Sodium Nitroprusside Test
Take 1 mL water extract or sodium carbonate extract, make it alkaline with dilute NH₄OH, then add a drop of sodium nitroprusside		Purple or violet colouration is producedCO₃²⁻ is confirmed

Test of Cation

ExperimentObservationInference
Original solution + H₂S gas in presence of dil. HCl and NH₄ClYellow precipitate is formedGroup-II-B (As³⁺) may be present
Confirmatory Test
Ammonium Molybdate Test
Treat the dissolved precipitate with concentrated nitric acid and ammonium molybdate solution		Canary yellow precipitate is formedPresence of As³⁺ is confirmed

Result

The given salt contains As³⁺ ions as cation and CO₃²⁻ ions as anion. The salt is (As)₂(CO₃)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.