Tests for Anions

The test for Carbon Dioxide:

1. You can test to see if a gas is carbon dioxide by bubbling it through limewater. If it is carbon dioxide, the limewater turns milky/cloudy.

2. You can use this to test for carbonates, since carbonates react with dilute acids to form carbon dioxide.

Remember:

Acid + Carbonate -> Salt + Water + Carbon dioxide

Some Carbonates Change Colour when they Decompose:

A colour change during a reaction gives you a clue to what substance you are dealing with. 

1. Method: put one spatula of carbonate into a test tube and heat strongly, then allow to cool.

2. Copper carbonate turns from green to black and it stays black when cool.

3. Zinc carbonate turns from white to yellow, but when it cools down it turns back to white. 

Test for sulfate ions:

1. To test for a sulfate ion, add dilute HCL followed by barium chloride solution.

2. A white precipitate of barium sulfate is formed which means that the original compound was a sulfate. (most sulfates are soluable but barium sulfate is not)

Chloride, Bromide or Iodide Ions (Halide ions):

To test for halide ions, add silver nitrate solution

A chloride gives a white precipitate of silver chloride.

A bromide gives a cream precipitate of silver bromide.

An iodide gives a yellow precipitate of silver iodide.

The test for nitrate ions:

1. Add aluminium powder to your mystery compound.

2. Add a few drops of sodium hydroxide solution and heat. If your compound was a nitrate it will be reduced to ammonia.

3. You will be able to smell the ammonia or you could use damp red litmus paper (which will turn blue).

To detect ammonium ions add sodium hydroxide.

With a positive result ammonia gas is produced. It has a distinctive smell and turns red litmus paper blue.