Tests for Gases
Year 10 (IGCSE) 🧪 Acids, Bases & Salts Identify H₂, O₂, CO₂, NH₃ and Cl₂ using standard laboratory tests.
💨 Gas Tests Summary
| Gas | Test | Positive result |
|---|---|---|
| H₂ | Lit splint | Squeaky pop |
| O₂ | Glowing splint | Relights |
| CO₂ | Bubble through limewater | Turns milky |
| NH₃ | Damp red litmus | Turns blue |
| Cl₂ | Damp litmus | Bleaches (turns white) |
| SO₂ | Acidified KMnO₄ | Purple → colourless |
🔬 Reactions Behind the Tests
CO₂ + limewater: CO₂ + Ca(OH)₂ → CaCO₃↓ + H₂O (white CaCO₃ makes it milky)
NH₃ in water: NH₃ + H₂O → NH₄⁺ + OH⁻ (alkaline → blue litmus)
Cl₂ bleaching: Cl₂ + H₂O → HCl + HClO. HClO oxidises and bleaches dye.
NH₃ in water: NH₃ + H₂O → NH₄⁺ + OH⁻ (alkaline → blue litmus)
Cl₂ bleaching: Cl₂ + H₂O → HCl + HClO. HClO oxidises and bleaches dye.
⚗️ Gas Collection Methods
Downward displacement of air: for gases denser than air (Cl₂, CO₂).
Upward displacement of air: for gases lighter than air (H₂, NH₃).
Over water: for insoluble gases (H₂, O₂). Not for NH₃ or HCl (very soluble).
Upward displacement of air: for gases lighter than air (H₂, NH₃).
Over water: for insoluble gases (H₂, O₂). Not for NH₃ or HCl (very soluble).
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Interactive Demonstration — Tests for Gases
Click a gas to see how to test for it and the expected result.
🔥
H₂
🌬️
O₂
🧪
CO₂
🟡
Cl₂
💨
NH₃
😷
SO₂
Click a gas to see its test.
💨 Gas Test Guide
Calculate the volume of gas at RTP from moles.