Identifying ions

• What is the aim of the procedure described?

  Identify ions in unknown salts
• What equipment is needed for identifying ions?

  • Distilled water
  • Test tubes
  • Wire loop
  • Bunsen burner
  • Heatproof mat
  • Tongs
  • Red litmus paper
  • Boiling tube
  • Bung and delivery tube
• What chemicals are required for the ion identification tests?

  • Unknown samples of salts
  • Hydrochloric acid
  • Dilute sodium hydroxide
  • Limewater
  • Barium chloride
  • Nitric acid
  • Silver nitrate
• What should be done before starting the tests for unknown salts?

  Dissolve the unknown solid in distilled water
• What are the steps in the flame test for identifying ions?

  1. Clean wire loop with HCl and blue flame
  2. Dip loop in unknown salt and hold in flame
  3. Record the flame color
  4. Repeat for other samples
• What should you do if a white precipitate forms in the hydroxide precipitates test?

  Add excess sodium hydroxide solution
• How can you test for ammonium ions?

  Add dilute sodium hydroxide and warm gently
• What indicates a positive test for ammonium ions?

  Gas turns damp red litmus paper blue
• What is the procedure to test for carbonate ions?

  Add dilute hydrochloric acid and observe
• What is a positive result for carbonate ions?

  Bubbles of gas and limewater turns cloudy
• How do you test for sulfate ions?

  Add hydrochloric acid and barium chloride
• What indicates a positive test for sulfate ions?

  A white precipitate forms
• What is the procedure to test for halide ions?

  Add nitric acid followed by silver nitrate
• What are the positive results for halide ions?

  Chloride: white, Bromide: cream, Iodide: yellow
• What are the key points to remember when testing for ions?

  • Distinguish Al​3+ ​from Ca​2+ ​using excess NaOH
  • Faint precipitates in dilute solutions may mislead
  • Acid prevents false positives for sulfate ions
  • Flame test not suitable for mixtures
• What safety precautions should be taken during the experiment?

  • Use dilute barium chloride only
  • Wear goggles and gloves with silver nitrate
  • Handle Bunsen burner safely
  • Treat all unknown samples as harmful
  • Ventilate the laboratory well
• What is the flame color for Lithium ions?

  Red
• What is the flame color for Sodium ions?

  Yellow
• What is the flame color for Potassium ions?

  Lilac
• What is the flame color for Calcium ions?

  Orange-red
• What is the flame color for Copper ions?

  Blue-green
• What color precipitate forms for Aluminium ions in the hydroxide precipitates test?

  White, dissolves in excess NaOH
• What color precipitate forms for Calcium ions in the hydroxide precipitates test?

  White, no change in excess NaOH
• What color precipitate forms for Copper ions in the hydroxide precipitates test?

  Blue
• What color precipitate forms for Iron(II) ions in the hydroxide precipitates test?

  Green
• What color precipitate forms for Iron(III) ions in the hydroxide precipitates test?

  Brown
• What is the positive test result for ammonium ions?

  Gas turns damp red litmus paper blue
• What is the positive test result for carbonate ions?

  Bubbles of gas and limewater turns cloudy
• What is the positive test result for sulfate ions?

  A white precipitate forms
• What are the positive test results for halide ions?

  • Chloride: white precipitate
  • Bromide: cream precipitate
  • Iodide: yellow precipitate