67. Tests for Anions (Carbonate, Sulfate, and Halide Ions)

1. Test for Carbonates (CO3 2-)

• Method:

  1. Add dilute hydrochloric acid to the test sample.

  2. If fizzing occurs, bubble any gas produced through limewater.

• Positive Result: The limewater turns cloudy.

• Explanation: Carbonates react with acid to produce carbon dioxide (CO2), which causes the cloudiness in limewater.

2. Test for Sulfates (SO4 2-)

• Method:

  1. Add dilute hydrochloric acid (to remove any carbonate impurities that might give a false positive).

  2. Add barium chloride solution.

• Positive Result: A white precipitate forms (barium sulfate).

3. Test for Halides (Cl-, Br-, I-)

• Method:

  1. Add dilute nitric acid (to remove impurities).

  2. Add silver nitrate solution.

• Positive Results: The color of the precipitate identifies the specific halide:

  • Chloride (Cl-): White precipitate (silver chloride)

  • Bromide (Br-): Cream precipitate (silver bromide)

  • Iodide (I-): Yellow precipitate (silver iodide)

Summary Table