RP 04- Identification of cations and anions

Chemistry

Test for group 2 metal cations

Place 10 drops of a group 2 compound in a test tube. Add 10 drops of sodium hydroxide to the tube and record results. Continue to add sodium hydroxide so it is in excess and record results

Magnesium chloride results with sodium hydroxide

10 drops: Slight white precipitate

Excess: White precipitate

Calcium bromide results with sodium hydroxide

10 drops: Slight white precipitate

Excess: Slight white precipitate

Strontium chloride results with sodium hydroxide

10 drops: Slight white precipitate

Excess: Slight white precipitate

Barium chloride results with sodium hydroxide

10 drops: Colourless solution

Excess: Colourless solution

How do you distinguish between calcium and strontium bromide?

Place 10 drops of the compound in a test tube. Add 10 drops of sulphuric acid and record results. Continue to add sulphuric acid so it is in excess and record results

Magnesium chloride results with sulphuric acid

10 drops: Slight white precipitate

Excess: Colourless solution

Calcium bromide results with sulphuric acid

10 drops: Slight white precipitate

Excess: Slight white precipitate

Strontium chloride results with sulphuric acid

10 drops: White precipitate

Excess: White precipitate

Barium chloride results with sulphuric acid

10 drops: White precipitate

Excess: White precipitate

How do you test for ammonium ions?

Add 10 drops of the compound and 10 drops of sodium hydroxide to a test tube. Shake and warm it. Test the gas released with damp red litmus paper. If it goes blue, ammonium ions are present

How do you test for halide ions?

Add the compound, nitric acid and silver nitrate to a test tube and record observations. Then add dilute and concentrated ammonia

Chloride ions results

Silver nitrate: White precipitate

Dilute ammonia: White precipitate disappears

Concentrated ammonia: Remains colourless

Bromide ions results

Silver nitrate: Cream precipitate

Dilute ammonia: Cream precipitate remains

Concentrated ammonia: Cream precipitate disappears

Iodide ions results

Silver nitrate: Yellow precipitate

Dilute ammonia: Yellow precipitate remains

Concentrated ammonia: Yellow precipitate remains

How do you test for hydroxide ions?

Turns damp red litmus paper blue

How do you test for carbonate ions?

Add limewater to a test tube.

To a separate test tube, add your compound and an equal volume of hydrochloric acid.

Add a delivery tube and bung to the test tube, with the open end into the limewater test tube.

Carbonate ions are present if it turns cloudy

How do you test for sulphate ions?

Add hydrochloric acid and barium chloride to the compound. If sulphate ions are present, a white precipitate of barium sulphate will form

What is the order of testing ions?

Carbonate, sulphate, halide

Prevents false positives