on this cheat sheet
Everything on the GCSE Chemistry Chemical Tests poster is written out below, section by section. Use it to search the sheet, copy parts into your own notes, or check a fact quickly.
Gas Tests
| Gas | Test | Positive result |
|---|---|---|
| Hydrogen (H₂) | Bring a lit splint to the gas | Squeaky pop |
| Oxygen (O₂) | Insert a glowing splint | Glowing splint relights |
| Carbon dioxide (CO₂) | Bubble through limewater | Limewater turns milky |
| Chlorine (Cl₂) | Damp blue litmus paper | Bleached white |
| Ammonia (NH₃) | Damp red litmus paper | Turns blue |
| Water vapour (H₂O) | Anhydrous copper sulfate | Turns from white to blue |
Flame Tests
Method
- Clean a nichrome wire loop.
- Dip in dilute HCl.
- Dip in the sample.
- Place in a Bunsen flame.
| Cation | Flame colour |
|---|---|
| Li⁺ | Crimson |
| Na⁺ | Yellow |
| K⁺ | Lilac |
| Ca²⁺ | Orange-red |
| Cu²⁺ | Green |
| Ba²⁺ | Apple green |
Colours can be weak or masked by other ions. Clean the wire loop thoroughly between tests.
Cation Tests with NaOH(aq)
Add a few drops of NaOH(aq) to the solution.
| Cation | Observation | In excess NaOH |
|---|---|---|
| Al³⁺ | White precipitate | Dissolves |
| Ca²⁺ | White precipitate | Insoluble |
| Mg²⁺ | White precipitate | Insoluble |
| Cu²⁺ | Blue precipitate | Insoluble |
| Fe²⁺ | Green precipitate | Insoluble |
| Fe³⁺ | Brown precipitate | Insoluble |
| Zn²⁺ | White precipitate | Dissolves |
Anion Tests
| Anion | Reagents and method | Positive result |
|---|---|---|
| Chloride (Cl⁻) | Acidify with dilute HNO₃, then add AgNO₃ | White precipitate (soluble in dilute NH₃) |
| Bromide (Br⁻) | Acidify with dilute HNO₃, then add AgNO₃ | Cream precipitate (soluble in concentrated NH₃) |
| Iodide (I⁻) | Acidify with dilute HNO₃, then add AgNO₃ | Yellow precipitate (insoluble in NH₃) |
| Sulfate (SO₄²⁻) | Acidify with dilute HCl, then add BaCl₂ | White precipitate |
| Nitrate (NO₃⁻) | Add NaOH(aq) and aluminium powder, warm gently | Ammonia gas – pungent smell, damp red litmus turns blue |
| Carbonate (CO₃²⁻) | Add dilute acid (e.g. HCl) | Effervescence; CO₂ turns limewater milky |