GCSE identification tests
Flame colours, precipitates and gas tests — the whole qualitative-analysis topic on one page, with the AQA observation wording. Flip on Test yourself to drill it.
Reading mode — every observation on show.
Flame tests (metal ions)
Clean a nichrome wire in acid, dip in the sample, hold in a blue Bunsen flame. A mixture can mask colours — that's why instruments are more reliable (see below).
| Ion / gas | Positive result |
|---|---|
| Lithium, Li⁺ | crimson red |
| Sodium, Na⁺ | yellow |
| Potassium, K⁺ | lilac |
| Calcium, Ca²⁺ | orange-red |
| Copper, Cu²⁺ | green |
Metal hydroxides (add sodium hydroxide)
| Ion / gas | Positive result |
|---|---|
| Aluminium, Al³⁺ | white ppt — dissolves in excess NaOH the white ppt that redissolves — distinguishes Al³⁺ from Ca²⁺/Mg²⁺ |
| Calcium, Ca²⁺ | white ppt — insoluble in excess |
| Magnesium, Mg²⁺ | white ppt — insoluble in excess |
| Copper(II), Cu²⁺ | blue ppt |
| Iron(II), Fe²⁺ | green ppt |
| Iron(III), Fe³⁺ | brown ppt |
Gas tests
| Ion / gas | Test | Positive result |
|---|---|---|
| Hydrogen, H₂ | lit splint | squeaky pop |
| Oxygen, O₂ | glowing splint | relights the splint |
| Carbon dioxide, CO₂ | bubble through limewater | limewater turns milky/cloudy |
| Chlorine, Cl₂ | damp litmus paper | bleaches it white |
| Ammonia, NH₃ | damp red litmus paper | turns it blue |
Negative ions (anions)
| Ion / gas | Test | Positive result |
|---|---|---|
| Carbonate, CO₃²⁻ | add dilute acid | fizzes; gas turns limewater milky (CO₂) |
| Sulfate, SO₄²⁻ | add dilute HCl, then barium chloride | white precipitate (BaSO₄) add HCl first to remove carbonates that would also give a ppt |
| Chloride, Cl⁻ | add dilute HNO₃, then silver nitrate | white precipitate (AgCl) |
| Bromide, Br⁻ | add dilute HNO₃, then silver nitrate | cream precipitate (AgBr) |
| Iodide, I⁻ | add dilute HNO₃, then silver nitrate | yellow precipitate (AgI) |
Instrumental methods
Machines like flame emission spectroscopy are more accurate, sensitive and rapid than flame tests, and can identify ions in a mixture. The output is a line spectrum; the pattern of lines identifies the metal ion and the intensity gives its concentration.
Drill it with flashcards
The AQA GCSE Chemistry deck tests these — and the rest of the spec — with spaced repetition.
AQA GCSE Chemistry flashcardsStruggling with identifying ions? The first tutoring lesson is free.
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