IGCSE Coordinated Science:Identification of Ion and Gases Identification of Ion and Gases 1. Use the following tests to identify: Aqueous cations: ● Ammonium, copper(II), iron(II), iron(III) and zinc by means of aqueous sodium hydroxide and aqueous ammonia as appropriate. Cation Test What happens if cation is present? Ammonium (NH4+) Add dilute sodium hydroxide, and then heat gently. Damp red litmus paper turns blue and ammoniagas is released. Copper (II) Add dilute sodium hydroxide OR ammonia solution Pale blue precipitate forms.However, as you add more ammonia, the solution dissolves, leading to a deep blue solution. Iron (II) Add dilute sodium hydroxide OR ammonia solution. Pale green precipitate forms. Iron (III) Add dilute sodium hydroxide OR ammonia solution. Red-brown precipitate forms. Zinc Add dilute sodium hydroxide OR ammonia solution White precipitate forms. Anions: ● Carbonate by means of dilute acid and then limewater, ● Chloride by means of aqueous silver nitrate under acidic conditions, ● Nitrate by reduction with aluminium, ● Sulfate by means of aqueous barium ions under acidic conditions, Anion Test What happens is
anion is present? Carbonate Add dilute hydrochloric acid Anion is present if bubbles give off gas that turns limewater milky Chloride 1. Add same amount of nitric acid as the chloride 2. Add silver nitrate solution Chloride ions will forma white precipitate. Nitrate Add sodium hydroxide.Afterwards, addsome pieces of aluminum Nitrate ions are present if ammonia gas is given off. Sulfate Add same amount of dilute hydrochloric acid.Next, add Barium Nitrate solution. White precipitate will form if Sulfate ions are present. Gases: ● Ammonia by means of damp red litmus paper, ● Carbon dioxide by means of limewater, ● Chlorine by means of damp litmus paper, ● Hydrogen by means of a lighted splint, ● Oxygen by means of a glowing splint. Gas Test What happens if gas is present? Ammonia, NH3 Use damp red litmus paper Indicator turns blue Carbon Dioxide, CO2 Bubble the suspected Carbon Dioxide samplethrough limewater. Limewater becomes cloudy or milky. Chlorine, Cl2 Hold damp litmus paper in the gas. Paper turns white. Hydrogen, H2 Put the gas in the tube and hold a lighted splint into the tube. Gas burns with a squeaky pop
Oxygen, O2 Collect the gas in a testtube and hold a glowing splint next to it. Splint relights.