chemical tests

• Halide ions with aqueous silver nitrate:

  • chlorides-> white
  • bromides -> cream
  • iodides -> yellow

  Nitric acid is added to prevent the formation of silver precipitates, by reacting with the cation. Ammonia solution is then added.

  • chlorides -> soluble
  • bromides -> insoluble in dilute, soluble in concentrated
  • iodides -> insoluble
• Add PCl5 to substance, if there are steamy fumes, there is an -OH group.
• Fehling's solution changes from clear blue to opaque red when aldehydes are oxidised to carboxylic acids, so it is used as a test for the -CHO group.
• Tollen's reagent changes from clear to a silver mirror when aldehydes are oxidised to carboxylic acids, so it is used as a test for the -CHO group.
• Ammonium ions and sodium hydroxide solution form ammonia gas, which turns damp red litmus paper blue.