Chemistry · 12.5 Identification of anions & gases · Paper 5/6
Anion & Gas Tests. Confirm it.
Run the standard bench tests for the common anions (carbonate, halides, sulfate, sulfite, nitrate) and identify gases with litmus, limewater, splints and acidified potassium manganate(VII). Apply the right reagent and read the result.
0620 Topic 12.5 — Anions & gases
AgNO₃ · Ba(NO₃)₂ · limewater
Paper 5/6 — Practical
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📊 Reference: tests & results (0620)
📋 Method & tips
- Carbonate: add dilute acid → effervescence; bubble the gas through limewater → turns milky (CO₂).
- Halides: acidify with dilute nitric acid, then add silver nitrate → Cl⁻ white, Br⁻ cream, I⁻ yellow precipitate.
- Sulfate: acidify with dilute nitric acid, then add barium nitrate → white precipitate.
- Sulfite: add acidified potassium manganate(VII) → purple decolourises to colourless.
- Nitrate: add NaOH and aluminium foil and warm → ammonia (damp red litmus turns blue).
- The nitric acid removes carbonate ions first, so they cannot give a false positive for the halide/sulfate test.
🎯 Syllabus reference (0620)
- 12.5 — describe tests to identify carbonate, chloride, bromide, iodide, nitrate, sulfate and sulfite anions, and the gases NH₃, CO₂, Cl₂, H₂, O₂ and SO₂.