Testing for Negative Ions

To test for Carbonate Ions;

Add DILUTE Hydrochloric Acid (HCl) to the substance and see if it fizzes.

If it fizzes and the gas produced turns limewater cloudy (or milky), the substance contains carbonate ions.

You may be told in the exam that you have a carbonate substance and you need to identify which carbonate it is. If so do the following;

Heat the carbonate over a bunsen burner.

• If the substance goes black it is Copper Carbonate (green before heating)
• If the substance turns yellow it is Zinc Carbonate (white before heating and after it cools down)

To test for Halide Ions we;

Add DILUTE Nitric Acid and then Silver Nitrate solution to the substance.

• If a White precipitate forms then Chloride ions are present
• If a Cream precipitate forms then Bromide ions are present
• If a Yellow precipitate forms then Iodide ions are present

*NOTE - The precipitate gets darker as the ions present are those of elements going down the group in the periodic table

To test for Sulfate ions ;

Add DILUTE Hydrochloric Acid (HCl) and them Barium Chloride solution to the substance.

If a White precipitate forms, sulfate ions are present

To test for Nitrate ions;

Add Aluminium Powder and then Sodium Hydroxide solution to the substance

Warm and test the gas given off with damp red litmus paper

If the litmus paper turns blue, the gas produced was ammonia and nitrate ions are present