8.4 Identification of ions and gases Aqueous cations: Test Ion Result Add a few of dilute sodium Cu2+ Pale blue precipitate hydroxide solution. A precipitate will Fe2+ precipitate form. Fe3+ Red-Brown precipitate Al3+, Zn2+, White precipitate Ca2+ Divide the solutions into two equal Al3+ The precipitate dissolves again in volumes. To one, add double the sodium hydroxide solution giving volume of sodium hydroxide a colourless solution but not in solution. To the other, add double excess ammonia solution the volume of aqueous ammonia. Zn2+ Precipitate dissolves in both solutions, giving a colourless solution. Ca2+ Dissolves in neither. Take a small amount of the solid or NH4+ Ammonia gas given off (it has a solution. Add a little dilute sodium strong sharp smell and turns red hydroxide solution and heat gently. litmus blue) Anions: Test Ion Result Take a small amount of the Carbonate Carbon dioxide gas is solid/solution. Add a little produced so there are dilute hydrochloric acid. bubbles and limewater goes milky Take a small amount of the Chloride precipitate solution. Add an equal Iodide Yellow volume of dilute nitric acid. Then add silver nitrate solution. Silver halides are insoluble, so a precipitate forms. Take a small amount of the Nitrate Ammonia gas off solution. Add a little sodium hydroxide solution. Add aluminium foil and heat gently. Take a small amount of the Sulphate White precipitate (barium solution. Add an equal sulphate) volume of dilute hydrochloric acid. Then add barium nitrate solution.
8.4 Identification of ions and gases Aqueous cations: Test Ion Result Add a few of dilute sodium hydroxide solution. A precipitate will form. Cu2+ Pale blue precipitate Fe2+ precipitate Fe3+ Red-Brown precipitate Al3+, Zn2+, Ca2+ White precipitate Divide the solutions into two equal volumes. To one, add double the volume of sodium hydroxide solution. To the other, add double the volume of aqueous ammonia. Al3+ The precipitate dissolves again in sodium hydroxide solution giving a colourless solution but not in excess ammonia solution Zn2+ Precipitate dissolves in both solutions, giving a colourless solution. Ca2+ Dissolves in neither. Take a small amount of the solid or solution. Add a little dilute sodium hydroxide solution and heat gently. NH4+ Ammonia gas given off (it has a strong sharp smell and turns red litmus blue) Anions: Test Ion Result Take a small amount of the solid/solution. Add a little dilute hydrochloric acid. Carbonate Carbon dioxide gas is produced so there are bubbles and limewater goes milky Take a small amount of the solution. Add an equal volume of dilute nitric acid. Then add silver nitrate solution. Silver halides are insoluble, so a precipitate forms. Chloride precipitate Iodide Yellow Take a small amount of the solution. Add a little sodium hydroxide solution. Add aluminium foil and heat gently. Nitrate Ammonia gas off Take a small amount of the solution. Add an equal volume of dilute hydrochloric acid. Then add barium nitrate solution. Sulphate White precipitate (barium sulphate)
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