Anions

• They are negatively charged ions
• How to test for OH- ions?

  1. Using universal indicator or red litmus paper
  2. Positive result is a colour change to blue
• Test for carbonate ions

  1. Add a equal volume of dilute hydrochloric acid to solution
  2. Bubble gas into limewater
  3. Turns it cloudy and forms effervescence
• How to test for sulfate ions?

  • First add 5cm^3 of unknown solution containing sulfate ions in a test tube using measuring cylinder
  • Next acidify it with dilute hydrochloric acid to prevent the precipitation of other insoluble ions such as carbonate
  • Then add few drops of barium chloride solution
  • The positive result is white precipitate of barium sulfate forming
• What is the order of testing ions? (Carbonate, sulfate and halide)

  Carbonate ions --> Sulfate --> Halide
• Testing halides

  • Add nitric acid and acidified silver nitrate
  • Fluorine forms no precipitate
  • Chlorine forms a white precipitate
  • Bromine forms a cream precipitate
  • Iodine forms a yellow precipitate
  • Add dilute ammonia solution to dissolve the chlorine ppt
  • Add concentrated ammonia solution to dissolve the bromine ppt
• How to test for sulfate ions?

  • First add 5cm^3 of unknown solution containing sulfate ions in a test tube using measuring cylinder
  • Next acidify it with dilute hydrochloric acid to prevent the precipitation of other insoluble ions such as carbonate
  • Then add few drops of barium chloride solution
  • The positive result is white precipitate of barium sulfate forming