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Qualitative Analysis · Cation & Anion Tests

CBSE Class 12 · IGCSE 0620
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🧪 MrChemCoach | Qualitative Analysis Virtual Lab
CBSE Class 12 | IGCSE 0620
🧴 Reagents
Dilute HNO₃
Dilute HCl
AgNO₃ (aq)
Ba(NO₃)₂ (aq)
NaOH (aq)
NH₃ (aq)
NaOH + Al (warm)
KMnO₄ (acidified)
💡 Note: Always acidify with HNO₃ before testing for Halides or Sulfates to avoid interference.
🔬 Unknown Samples
📓 Coach's Notebook
Observations Log
Select a tube and add reagents…
🏆 Score: 0 / 0

What this experiment shows

Qualitative analysis is identifying what is in an unknown salt, and Cambridge tests it every year. The routine is fixed: sodium hydroxide and then aqueous ammonia for the metal ion, a flame test if it is a Group I or II metal, and then a separate test for the anion. The precipitate colours - and whether a precipitate redissolves in excess - are what separate the ions from one another.

Cu2+ + 2OH- → Cu(OH)2(s), pale blue

What you need

  • Sodium hydroxide solution and aqueous ammonia
  • Dilute nitric acid and silver nitrate
  • Dilute hydrochloric acid and barium chloride
  • Nichrome wire for flame tests
  • Limewater, and aluminium foil with sodium hydroxide for nitrate

How it is done

  1. Add sodium hydroxide a little at a time, then in excess, and note both stages.
  2. Repeat with aqueous ammonia, again to excess.
  3. For a flame test, clean the wire in acid, dip in the solid and hold it in a blue flame.
  4. For halides: acidify with nitric acid, then add silver nitrate.
  5. For sulfate: acidify with hydrochloric acid, then add barium chloride.

What you should see

  • Copper(II): pale blue precipitate, dissolving in excess ammonia to a deep blue solution.
  • Iron(II): green precipitate. Iron(III): red-brown precipitate.
  • Aluminium and zinc: white precipitate that dissolves in excess sodium hydroxide.
  • Chloride white, bromide cream, iodide yellow with silver nitrate.
  • Sulfate: white precipitate with barium chloride. Carbonate: fizzes with acid, gas turns limewater milky.

Where marks are lost

  • Not adding the reagent in excess. Aluminium and zinc are told apart at that step.
  • Skipping the acid before silver nitrate, so carbonate gives a false white precipitate.
  • Using hydrochloric acid before silver nitrate. It adds chloride ions of its own.
  • Writing "a precipitate" with no colour, or the wrong shade.

Questions students ask

How do I tell aluminium from zinc?
Both give a white precipitate with sodium hydroxide that dissolves in excess. Use ammonia: the zinc precipitate dissolves in excess ammonia, the aluminium one does not.
Why acidify before testing for a halide?
To destroy any carbonate present. Carbonate would give a white precipitate with silver nitrate and be mistaken for chloride.
What does a flame test tell you?
The metal ion. Lithium red, sodium yellow, potassium lilac, calcium orange-red, copper(II) blue-green.

Try these next

Written for Cambridge IGCSE Chemistry 0620 and CBSE Class 9-12 by Ajay Shekhawat, founder of MrChemCoach. Run the simulator above, then check yourself against the questions.