Chemical analysis/group 7

• Test for Halide Ions

  To test for halide ions you add dilute nitric acid and silver nitrate
• Halide precipitate colours after silver nitrate

  Chloride ion - White precipitate

  Bromide ion - Cream prcipitate

  Iodide ion - Yellow precipitate
• Further halide testing with ammonia

  Chloride ion - white precipitate dissolves in dilute ammonia

  Bromide ion - cream precipitate dissolves in concentrated ammonia

  Iodide ion - Insolube so doesn't dissolve
• Halide displacment reactions

  Chlorine displacing Bromine - solution is orange

  Chlorine displacing Iodine - solution is brown and purplue

  Bromine displacing Iodine - solution is brown and purple
• What do you add to the halogen solution in a displacment reaction

  You add an organic substance e.g cyclohexane
• Colour of Halogens at RT

  Florine - Yellow gas

  Chlorine - Green gas

  Bromine - Red/brown liquid

  Iodine - Grey solid
• Disproportionation reaction

  A reaction where an element is simultaneously oxidised and reduced
• Water sterilisation with halogens

  Adding chlorine to water will kill bacteria and is used is swimming pools and drinking water
• Advantages of chlorinating water

  Kills harmful bacteria

  Is long lasting

  Reduces algae growth
• Disadvantages of chlorinating water

  Chlorine is a toxic gas

  It causes chemical burns

  Can react with organic compounds and cause cancer through radical substitution
• Test for ammonium

  First, you add sodium hydroxide and gently heat

  If ammonium is present damp litmus paper turns blue
• Test for hydroxides

  You use damp litmus paper and it turns from blue to red
• Test for carbonates

  First you add hydrochloric acid. This should form CO2 gas. You bubble the product into limewater and it should go cloudy
• Test for Sulfates

  First you add hydrochloric acid, next you add barium chloride and if the result is positive, a white precipitate should form