Identifying ions in salts – flame tests and precipitate tests
ChemistryInorganic ChemistryAges 17–18
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Sign in to playA virtual lab for identifying the ions in salts. Use flame tests for Li⁺, Na⁺, K⁺, Ca²⁺ and Cu²⁺; add sodium hydroxide drop by drop and then in excess for Al³⁺, Ca²⁺, Mg²⁺, Cu²⁺, Fe²⁺ and Fe³⁺; test for carbonate with dilute acid and limewater, for halides with nitric acid and silver nitrate, and for sulfate with hydrochloric acid and barium chloride. Record your observations, work out the formulas of randomly chosen unknown salts and check your answers to see the ionic equations. An extended bench adds NH₄⁺ (warm with NaOH), OH⁻ (red litmus) and the Group 2 ions Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ (dilute sulfuric acid), and a gas bench tests H₂, O₂, CO₂, Cl₂, NH₃ and SO₂ with splints, limewater, damp litmus and acidified KMnO₄.
Lesson: Chemical tests for ions (identifying ions in salts)
What it shows
Chemists identify ions and gases with simple tests. Li⁺, Na⁺, K⁺, Ca²⁺, Cu²⁺, Sr²⁺ and Ba²⁺ ions colour a flame. Many metal ions form insoluble hydroxides with sodium hydroxide, and ammonium ions give ammonia gas when warmed with it. Carbonates fizz with acid, halides give silver halide precipitates and sulfates give white barium sulfate, while dilute sulfuric acid separates the Group 2 ions. Hydrogen burns with a squeaky pop, oxygen relights a glowing splint, carbon dioxide turns limewater milky, ammonia turns damp red litmus blue, chlorine bleaches damp litmus and sulfur dioxide decolourises acidified potassium manganate(VII).
How to use
Choose a Bench, a Sample and a Test, then press the step buttons in order. Press Clean wire before each flame test. Record what you saw with the buttons below the steps; it goes into the results table. Identify each unknown, then press Check my answers; Show answers reveals the equations. On the Gas tests bench, untick Damp litmus paper to see why the litmus must be damp.
Parameters you can change
- Mode Unknown salts (random), Known salts (practice)
- Starting test Flame test, Sodium hydroxide (cations), Dilute acid and limewater (CO₃²⁻), Silver nitrate (halide ions), Barium chloride (SO₄²⁻)
- Number of unknowns 2–4 samples
- Describe observations in words
- View the flame through cobalt-blue glass
- Bench Ion tests, Ion tests + NH₄⁺, OH⁻, Group 2, Gas tests
Questions to explore
- Why must the solution be acidified with nitric acid, not hydrochloric acid, before adding silver nitrate?
- A solution gives a white precipitate with sodium hydroxide that dissolves in excess. Which metal ion is present?
- Why can a trace of sodium make it hard to see the lilac flame of potassium?
Teaching ideas
All guides- Identifying Ions Virtual Lab: Flame and Precipitate TestsAn identifying ions virtual lab for the GCSE required practical: flame tests, sodium hydroxide, carbonate, halide and sulfate tests on unknown salts.
- Gas Tests Virtual Lab: Identifying Six Common GasesA gas tests virtual lab: test hydrogen, oxygen, carbon dioxide, chlorine, ammonia and sulfur dioxide with splints, limewater, litmus and KMnO₄.
- Gravimetric Analysis Virtual Lab: Calcium in Hard WaterA gravimetric analysis virtual lab: precipitate calcium in hard water as CaCO₃, filter, wash and dry to constant mass, then find the hardness in mg per dm³.
