Qualitative analysis

• what are the three tests for anions?

  carbonate test, sulphate test and halide test
• how to carry out the carbonate test and what are positive results?

  • add dilute nitric acid id substance is carbonate - CO2 will form
  • to test if gas formed is CO2 = bubble through limewater (Ca(OH)2)
  • if CO2 white precipitate of calcium carbonate forms and limewater turns milky
• How to carry out a sulfate test ?

  all sufates are soluble except BaSO4, therefore if barium ions ( as barium chloride or nitrate) are added it should react with sulfate ions and form insoluble white precipitate
• how to carry out a halide test and how to distinguish between the colour of precipitates?

  Add silver nitrate solution to the halide solution (silver halides are insoluble)

  • silver chloride - white - soluble in dilute NH3
  • silver bromide - cream - soluble in conc NH3
  • silver iodide - yellow insoluble in conc NH3

  add ammonia to test solubility and distinguish
• what sequels should the anion tests be carried out?

  carbonate, then sulfate then ammonia

  • neither sulfate or halides produce bubbles so carbonate test should be first
  • important to use barium sulfate if planning to do halide test afterwards as chloride will show up in halide test
• what is the test for ammonium ions?

  Add sodium hydroxide

  heat mixture- ammonia gas is released can be smelt or turns moist pH indicator paper blue