Test for Anions and Cations

Carbonate test (CO3 2-) (aq) ions

• Add weak or dilute acid to sample and bubble gas produced through limewater (fizzing)

• Limewater turns cloudy

• Adding nitric (dilute) acid, solution fizzes

• CO3 2- (aq) + 2H+ (aq) → CO2 (g) + H2O (l)

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

Sulfate test (SO4 2-) (aq) ions

• Add dilute acid (e.g HCl) to test tube with sample in

• Add barium chloride solution, BaCl2 (aq)

• Ba2+ + SO4 2- → BaSO4

• Forms white precipitate

• Use barium nitrate or barium sulfate → means sample is still able to do the chlorine halide test

Halide test

• Silver halide are insoluble

  → Ag+ (aq) + X- (aq) → AgX (s)

• React with silver nitrate (AgNO3 (aq)) + (HNO3 (aq))

  (pure ammonia dissolves bromide to show the difference between silver bromide and silver iodide)

  → iodide is insoluble

Halide precipitates

• Silver Chloride (Cl-)

  → White precipitate

• Silver Bromide (B-)

  → Cream precipitate

• Silver Iodide (I-)

  → Yellow precipitate

Ammonium test

• Add 10 drops sodium hydroxide (NaOH) to test tube with sample

• Gently heat test tube in a water bath

• Test fumes releases using damp, red litmus paper

  NH4 + (aq) + OH- (aq) → NH3 (g) + H2O (l)

• Heated together forms gas

• Litmus paper turns blue