Chemical Tests

• What is the main aim of the practical described?

  To identify ions in unknown salts
• Why is it important to use appropriate apparatus and substances in the practical?

  To ensure safety and observe chemical changes
• What must be worn during the practical for safety?

  Eye protection
• What is the method for testing salts in the practical?

  • Carry out one or more tests on each salt
  • Dissolve solid salts in distilled water if needed
  • Record observations carefully
  • Repeat tests for unclear results
• What is the flame test used for?

  To identify metal ions present
• What are the flame test colors for common metal ions?

  • Lithium, Li+: Crimson
  • Sodium, Na+: Yellow
  • Potassium, K+: Lilac
  • Calcium, Ca2+: Orange-red
  • Copper, Cu2+: Green
• What do you add to test for hydroxide precipitates?

  A few drops of dilute sodium hydroxide
• What are the colors of hydroxide precipitates for different metal ions?

  • Aluminium, Al3+: White (dissolves in excess)
  • Calcium, Ca2+: White (no change)
  • Magnesium, Mg2+: White (no change)
  • Copper, Cu2+: Blue
  • Iron(II), Fe2+: Green
  • Iron(III), Fe3+: Brown
• How do you test for carbonate ions?

  Add dilute hydrochloric acid and observe bubbles
• What indicates the presence of carbonate ions?

  Bubbles and limewater turning milky
• What is the test for sulfate ions?

  Add hydrochloric acid and barium chloride
• What indicates the presence of sulfate ions?

  A white precipitate forms
• How do you test for halide ions?

  Add nitric acid and silver nitrate solution
• What are the precipitate colors for halide ions?

  • Chloride, Cl-: White
  • Bromide, Br-: Cream
  • Iodide, I-: Yellow
• How should results be recorded after tests?

  • Use a suitable table
  • Include salt, test, observation, and inference
• What inference can be made from a yellow flame color in a flame test?

  Presence of sodium ions
• Why might it be difficult to distinguish between dilute solutions of halide ions?

  Very faint precipitates make identification hard
• What are the hazards and precautions in the practical?

  Hazards:

  • Barium chloride: Harmful if inhaled
  • Silver nitrate: Causes serious eye irritation

  
  

  Precautions:

  • Use dilute solutions supplied by teacher
  • Wear eye protection and gloves
• What is a possible harm of barium chloride solid?

  Harmful if inhaled and toxic if swallowed
• What should be done to avoid skin contact with silver nitrate solution?

  Use dropper bottles or wear gloves