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Tests for ions
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Chemists identify unknown substances with simple tests for metal ions and non-metal ions. Separate Chemistry only.
Flame tests (metal ions)
Sodium hydroxide test
Add sodium hydroxide solution and look at the precipitate:
Cu2+: blue. Fe2+: green. Fe3+: brown. Al3+: white, dissolves in excess. Ca2+: white, does not dissolve.
Ammonium ions (NH4+): warming gives ammonia gas, which turns damp red litmus blue.
Cu2+: blue. Fe2+: green. Fe3+: brown. Al3+: white, dissolves in excess. Ca2+: white, does not dissolve.
Ammonium ions (NH4+): warming gives ammonia gas, which turns damp red litmus blue.
Non-metal ions
Carbonates: add acid, bubbles of CO2 turn limewater milky.
Sulfates: add hydrochloric acid then barium chloride: white precipitate.
Halides: add nitric acid then silver nitrate: chloride white, bromide cream, iodide yellow.
Sulfates: add hydrochloric acid then barium chloride: white precipitate.
Halides: add nitric acid then silver nitrate: chloride white, bromide cream, iodide yellow.
A compound gives a lilac flame and a cream precipitate with acidified silver nitrate. Identify it.
- Lilac flame: potassium.
- Cream precipitate: bromide.
Answer: Potassium bromide
Flame tests: Li red, Na yellow, K lilac, Ca orange-red, Cu blue-green. NaOH precipitates: Cu blue, Fe2+ green, Fe3+ brown. Halides with silver nitrate: white, cream, yellow. Sulfates: white with barium chloride.
The interactive lesson includes the diagrams for this topic.
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