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
Each common gas has a specific test with a characteristic positive result.
| Gas | Test | Positive result |
|---|---|---|
| H₂ (hydrogen) | Bring a lit splint to the gas | Lit splint gives a squeaky pop |
| O₂ (oxygen) | Insert a glowing splint | Glowing splint relights |
| CO₂ (carbon dioxide) | Bubble the gas through limewater | Limewater turns milky |
| Cl₂ (chlorine) | Expose damp blue litmus paper | Litmus paper bleached white |
| NH₃ (ammonia) | Expose damp red litmus paper | Litmus paper turns blue |
| H₂O (water vapour) | Add the gas to anhydrous copper sulfate | Anhydrous copper sulfate turns white to blue |
Flame tests
Method: Clean a nichrome wire loop, dip in dilute HCl, dip in sample, then place in a Bunsen flame.
| Cation | Li⁺ | Na⁺ | K⁺ | Ca²⁺ | Cu²⁺ | Ba²⁺ |
|---|---|---|---|---|---|---|
| Flame colour | Crimson | Yellow | Lilac | Orange-red | Green | Apple green |
Colours can be weak or masked by other ions. Clean the wire loop thoroughly between tests.
Cation tests with NaOH (aq)
Method: Add a few drops of NaOH(aq) to the solution.
| Cation | Observation (precipitate colour) | In excess NaOH |
|---|---|---|
| Al³⁺ | White precipitate | Dissolves |
| Ca²⁺ | White precipitate | Insoluble |
| Mg²⁺ | White precipitate | Insoluble |
| Cu²⁺ | Blue precipitate | Insoluble |
| Fe³⁺ | Brown precipitate | Insoluble |
| Fe²⁺ | Green precipitate | Insoluble |
| Zn²⁺ | White precipitate | Dissolves |
Al³⁺ and Zn²⁺ both give a white precipitate that dissolves in excess NaOH - they form soluble hydroxide complexes.
Anion tests
Halide tests
Method: Acidify with dilute HNO₃, then add AgNO₃(aq).
- Cl⁻ (chloride) - white precipitate forms; soluble in dilute NH₃
- Br⁻ (bromide) - cream precipitate forms; soluble in concentrated NH₃
- I⁻ (iodide) - yellow precipitate forms; insoluble in NH₃
Sulfate test
Method: Acidify with dilute HCl, then add BaCl₂(aq).
- SO₄²⁻ (sulfate) - white precipitate forms.
Nitrate test
Method: Add NaOH(aq) and aluminium powder, then warm gently.
- NO₃⁻ (nitrate) - ammonia gas is given off; pungent smell of ammonia; damp red litmus paper turns blue.
Carbonate test
Method: Add dilute acid (e.g. HCl).
- CO₃²⁻ (carbonate) - carbon dioxide gas given off; effervescence (bubbling); limewater turns milky.