Chemical Tests

How do you test for carbonates?

• add dilute nitric acid

  • if CO₃^2- ions are present, bubbles are produced

  • Na₂CO₃ (aq) + 2HNO₃ (aq) → 2NaNO₃ (aq) + CO₂ (g) + H₂O (l)

• if bubbles are present, bubble the gas through limewater

  • a white precipitate will form if carbon dioxide is present

  • CO₂ (g) + Ca(OH)₂ (aq) → CaCO₃ (s) + H₂O (l)

How do you test for sulfates?

• aqueous barium ions are added to an unknown solution

• usually barium nitrate or barium chloride

  • use barium nitrate if going to do a halide test afterwards

• Ba²⁺ (aq) + SO₄^2- (aq) → BaSO₄ (s)

• if positive, a white precipitate will form

How do you test for halides?

• add aqueous silver nitrate to an aqueous halide solution

  • silver chloride will turn white

  • silver bromide will turn cream

  • silver iodide will turn yellow

  • Ag⁺(aq) + X^- (aq) → AgX(s)

• add aqueous ammonia to test solubility

• Cl^- - soluble in dilute ammonia

• Br^- - soluble in concentrated ammonia

• I^- - insoluble in concentrated ammonia

What is the correct sequence for tests?

• carbonate test

• sulfate test

• halide test

How do you test for ammonium?

• aqueous sodium hydroxide is added to a solution

• ammonia gas is produced if ammonium ions are present

• mixture is warmed

• test with damp litmus paper

• ammonia will turn it blue

How do you test for alcohols?

• primary and secondary only

• add K₂Cr₂O₇/H⁺

• colour change from orange to green