Identifying Ions Virtual Lab: Flame and Precipitate Tests

This identifying ions virtual lab matches the AQA GCSE Chemistry required practical on using chemical tests to identify the ions in unknown single ionic compounds. Students carry out flame tests and add sodium hydroxide drop by drop, then in excess, to find the metal ion. They 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. They record a results table, work out the formula of each unknown salt and get instant feedback, with no burner, concentrated acid or silver and barium waste.

Curriculum links

• AQA GCSE Chemistry 4.8.3 (identification of ions by chemical and spectroscopic means): flame tests, metal hydroxides, carbonates, halides and sulfates, and the required practical on identifying the ions in unknown single ionic compounds. This practical is in GCSE Chemistry only, not in Combined Science: Trilogy.
• Other courses: the same qualitative tests appear in IB Chemistry, A-level inorganic chemistry and many national curricula. AP Chemistry teachers can use the precipitate tests alongside net ionic equations (Unit 4).

Simulic is not affiliated with or endorsed by the College Board or AQA.

Before the lab (5 min)

Ask students to commit to a prediction, on paper or as question 1 of the class link:

"You add sodium hydroxide solution, first a few drops and then in excess, to aluminium chloride solution and to magnesium chloride solution. What will you see in each tube?"

Most students know that both give a white precipitate. Few predict the difference in excess. Don't correct them yet.

Method in the simulation

The simulation has two modes. In Known salts (practice) every salt is named, and the equations appear after each test. In Unknown salts the simulation picks random salts, and students identify them.

1. Set Mode to "Known salts (practice)". Choose Test: Sodium hydroxide. Run AlCl₃, MgCl₂, CuSO₄, FeSO₄ and FeCl₃: press Add a few drops of NaOH, then Add excess NaOH.
2. Choose Test: Flame test. Press Clean wire, then Dip wire in salt and Hold in flame for LiCl, NaCl, KCl, CaCl₂ and CuCl₂. Then try KCl straight after NaCl without cleaning the wire.
3. Run the carbonate, halide and sulfate tests on Na₂CO₃, NaCl, KBr, NaI and K₂SO₄. For the halides, also try Acidify with dilute HCl on NaI to see why nitric acid is used.
4. Switch Mode to "Unknown salts". For each unknown, run every test and choose what you saw in the buttons below the steps. The results table fills in.
5. Pick the cation, the anion and the formula of each unknown, then press Check my answers. New unknowns gives a fresh set.

Sample	Flame color	NaOH, a few drops	NaOH in excess	Dilute HCl, gas into limewater	HNO₃ then AgNO₃	HCl then BaCl₂	Formula
Unknown A
Unknown B
Unknown C

Expected results

These observations come from the simulation in Known salts mode:

Ion	Test	What students see
Li⁺, Na⁺, K⁺, Ca²⁺, Cu²⁺	flame	crimson, yellow, lilac, orange-red, green
Al³⁺	NaOH	white precipitate that dissolves in excess
Ca²⁺	NaOH	a small amount of white precipitate
Mg²⁺	NaOH	white precipitate that stays in excess
Cu²⁺	NaOH	blue precipitate
Fe²⁺	NaOH	green precipitate, slowly turning brown at the surface
Fe³⁺	NaOH	brown precipitate
CO₃²⁻	dilute HCl, then limewater	fizzing; limewater turns milky
Cl⁻, Br⁻, I⁻	HNO₃, then AgNO₃	white, cream, yellow precipitate
SO₄²⁻	HCl, then BaCl₂	white precipitate

Three method errors show up clearly:

• KCl tested after NaCl without cleaning the wire gives a mixed flame, and the sim warns about traces of the earlier salt. After cleaning, the flame is lilac.
• NaI acidified with HCl gives a pale, yellowish-white precipitate, because the added chloride ions precipitate as AgCl.
• Na₂CO₃ with BaCl₂ and no acid gives a white precipitate, a false positive for sulfate.

Questions for students

1. (Prediction, asked again after the lab) What happens when NaOH is added, then in excess, to AlCl₃ and to MgCl₂?
2. Why is the flame-test wire cleaned before every test?
3. What do you see when NaOH is added to FeSO₄, first a few drops and then in excess?
4. Which salt gives a lilac flame, no precipitate with NaOH, no fizzing with acid, a cream precipitate with acidified AgNO₃ and nothing with acidified BaCl₂?
5. Acidify NaI with dilute HCl before adding AgNO₃. What do you see, and why must nitric acid be used instead?

Answers for teachers: (1) Both give a white precipitate; only the aluminium one dissolves in excess. (2) To remove traces of the previous salt, which would mix with or hide the new flame color. (3) A green precipitate that stays in excess and slowly turns brown at the surface. (4) KBr. (5) A pale, yellowish-white precipitate. HCl adds chloride ions, which precipitate as white AgCl whatever the salt is and hide the yellow AgI. Nitric acid removes carbonate ions without adding halide ions.

Common misconceptions

• "A white precipitate with NaOH means aluminium." Ca²⁺ and Mg²⁺ give white precipitates too. Only the test with excess NaOH tells them apart.
• "Any acid will do before adding silver nitrate or barium chloride." HCl adds Cl⁻ and H₂SO₄ adds SO₄²⁻, so each one gives a false positive in one of the tests.
• "A yellow flame proves the salt is a sodium salt." A trace of sodium on a dirty wire is enough to turn the flame yellow.

Extension

• Cobalt-blue glass: in Known salts mode choose the NaCl + KCl mixture. The flame looks yellow. Tick Cobalt-blue glass: the glass absorbs the sodium yellow and the potassium color shows through.
• Halides in more depth: the halide ions simulation separates AgCl, AgBr and AgI with ammonia solution.

FAQ

Can students do the required practical without a lab?

They can practise every test and identify unknowns with instant feedback. Use it before the wet lab so students know the order of the steps, or instead of it when time is short.

Are the unknowns the same for every student?

No. Each student gets a random set, so classmates cannot copy each other's formulas. That is why the question set uses Known salts mode, where the answers are fixed.

How do I stop students using the equations as hints?

In Unknown salts mode the equations only appear after a correct answer or after Show answers. Untick "Describe observations in words" to make students read the picture instead of the text.

Related simulations and guides

Group 1/2 flame colors and water hardness treatment Halide ions – identification with AgNO₃

For more chemistry activities, see interactive chemistry lesson ideas. For writing your own questions on a simulation like this, see writing questions for virtual labs.