4

• What is the focus of Required Practical 4 in AQA Chemistry A-level?

  Identifying cations and anions
• Which ions are tested for in the cation tests?

  Group 2 ions or NH​4​+
• What is the method for testing group 2 ions with sodium hydroxide?

  1. Add 10 drops of 0.1 moldm​-3 ​barium chloride to a clean test tube.
  2. Add 10 drops of 0.6 moldm​-3 ​sodium hydroxide and mix.
  3. Add sodium hydroxide dropwise until in excess.
  4. Dispose of contents in a bowl of water.
  5. Repeat with calcium bromide, magnesium chloride, and strontium chloride.
• What is the method for testing group 2 ions with dilute sulfuric acid?

  1. Add 10 drops of 0.1 moldm​-3 ​barium chloride to a clean test tube.
  2. Add 10 drops of 1.0 moldm​-3 ​sulfuric acid and mix.
  3. Add sulfuric acid dropwise until in excess.
  4. Dispose of contents in a bowl of water.
  5. Repeat with calcium bromide, magnesium chloride, and strontium chloride.
• What safety precautions should be taken when testing for group 2 ions?

  Wear gloves due to toxic barium salts
• What are the overall results for Group 2 ions when tested with sodium hydroxide?

  • Mg2+: White precipitate of Mg(OH)​2
  • Ca2+: White precipitate of Ca(OH)​2
  • Sr2+: Slight white precipitate
  • Ba2+: No change
  • Ammonium: No change
• What is the method for testing for ammonium ions?

  1. Add 10 drops of ammonium chloride to a clean test tube.
  2. Add sodium hydroxide and shake.
  3. Warm the mixture in a water bath.
  4. Test fumes with damp red litmus paper.
  5. Observe the litmus paper turning blue.
• What indicates the presence of ammonium ions in the test?

  Damp red litmus paper turns blue
• What are the tests for hydroxide ions?

  1. Test with red litmus paper or universal indicator.
  2. Observe that sodium hydroxide turns damp red litmus paper blue.
• What is the method for testing for carbonate ions?

  1. Add dilute hydrochloric acid to sodium carbonate solution.
  2. Use a delivery tube to transfer gas to calcium hydroxide solution.
  3. Shake the tube; limewater will go cloudy if carbonate ions are present.
• What is the equation for the reaction of sodium carbonate with hydrochloric acid?

  Na​2​CO​3​ + 2HCl → 2NaCl + H​2​O + CO​2
• What is the method for testing for sulfate ions?

  1. Add dilute hydrochloric acid and barium chloride to the solution.
  2. Observe the formation of a white precipitate of barium sulfate.
  3. Add dilute HCl; if precipitate does not dissolve, sulfate ions are present.
• What is the equation for the reaction of magnesium sulfate with barium chloride?

  MgSO​4​ + BaCl​2​ → BaSO​4​(s) + MgCl​2​(aq)
• What are the safety precautions when testing for sulfate ions?

  • Wear gloves and a lab coat.
  • Barium chloride is harmful.
• What is the method for testing for halide ions?

  1. Add dilute nitric acid to the solution.
  2. Add silver nitrate and record observations.
  3. Divide contents for further tests with ammonia solutions.
• What are the overall results for Group 7 ions when tested with silver nitrate?

  • KCl: White precipitate
  • KBr: Cream precipitate
  • KI: Yellow precipitate
• What are the safety precautions when testing for halide ions?

  • Use a fume cupboard.
  • Wear chemical splash-proof eye protection and gloves.
• What is the method for testing group 7 ions using solid salts?

  1. Add solid potassium chloride to a test tube.
  2. Add concentrated sulfuric acid and record observations.
  3. Test any gas evolved with litmus paper.
• What are the overall results for Group 7 ions when tested with concentrated sulfuric acid?

  • KCl: White, steamy fumes
  • KBr: Orange fumes
  • KI: Purple fumes and purple/black solid
• What is the safety precaution regarding concentrated sulfuric acid?

  It is corrosive and toxic
• What should be worn when handling concentrated ammonia?

  Chemical splash-proof eye protection and gloves
• What is the purpose of adding dilute nitric acid before silver nitrate in halide tests?

  To remove ions that may form different precipitates
• What is the role of barium chloride in sulfate ion testing?

  It forms a white precipitate of barium sulfate
• What is the expected result when testing for carbonate ions?

  Limewater goes cloudy
• What is the expected result when testing for hydroxide ions?

  Damp red litmus paper turns blue
• What is the expected result when testing for ammonium ions?

  Damp red litmus paper turns blue
• What is the expected result when testing for group 2 ions with sulfuric acid?

  White precipitate of barium sulfate