Test for Anions

• Anions are negatively charged ions
• The test for carbonates:

  • carbonate + acid ---> salt + carbon dioxide + water
  • we can use this equation to know if we add HCl to a carbonate, carbon dioxide will be produced.
  • We can then perform the limewater test to see if it goes cloudy
• Test for sulfates:

  • If we add barium ions to sulfate ions they will create barium sulfate, this is a WHITE PRECIPITATE
  • Before we can add barium we must add dilute HCl to remove any carbonate or sulfite ions. (these ions are impurities and can also react with barium)
  • Then add barium chloride solution
  • Then we will see the white precipitate form
• Test for Halide ions (silver nitrate test):

  • Add dilute nitric acid to remove sulfite and carbonate impurities.
  • Then add silver nitrate. This will react with the halides to form a precipitate.
  • the colour depends on the ions
  • Chloride ion -> white
  • Bromide ion -> cream
  • Iodide ion -> yellow
• 1. React the substance with hydrochloric acid (HCl) to remove any carbonate ions.
  2. Add barium chloride solution.
  3. If sulfate ions are present, it will form a white precipitate of barium sulfate.
• 1. React the substance with hydrochloric acid (HCl).
  2. If the substance contains a carbonate ion, carbon dioxide gas will bubble out of the solution. 
  3. Collect the gas and bubble it through limewater.
  4. If the limewater turns cloudy, it confirms the gas is carbon dioxide.
  5. Confirmation that the gas is carbon dioxide is confirmation that the original substance contained carbonate ions.