Negative Ion Tests

Negative Ion Tests

Topic 8 - Chemical Analysis

29 Jul

Written By Atheridge Tuition

A student is given an unknown sodium salt.

The student thinks it could be:

sodium carbonate
sodium sulphate
sodium chloride
sodium bromide
sodium iodide.

Describe the three chemical tests to prove if the salt contains carbonate ions, sulphate ions and halide ions.

[6 marks]

Test for Carbonate Ions

Add dilute acid. (1 mark)
Observe whether limewater turns milky. (1 mark)
If yes, Carbon Dioxide is present. So it is a Carbonate.

Two test tubes connected with each other, one with dilute acid and the salt being tested and gas is flowing to the other test tube which has limewater. Text reads limewater turns milky = carbonate ions.

Test for Sulphate Ions

Add dilute Hydrochloric Acid. (1 mark) This removes any present Carbonate ions.
Add Dilute Barium Chloride. (1 mark)
Observe whether a white precipitate is seen. (1 mark)
If yes, sulphate ions are present.

Visual guide to the GCSE chemistry sulphate ion test: first add dilute hydrochloric acid to remove carbonate ions, then add barium chloride. A white precipitate confirms sulphate ions (SO₄²⁻)

Test for Halide Ions

Add dilute Nitric Acid. (1 mark) This removes any present Carbonate ions. Do NOT use Hydrochloric Acid as it will react with Silver Nitrate.
Add dilute Silver Nitrate Solution. (1 mark)
Observe the colour of the precipitate: (1 mark)
- If white, chloride ions are present
- If cream, bromide ions are present
- If yellow, iodide ions are present

Visual guide to the GCSE chemistry halide ion test: first add dilute nitric acid to remove carbonate ions, then add silver nitrate. White precipitate indicates chloride (Cl⁻), cream indicates bromide (Br⁻), and yellow indicates iodide (I⁻).

Continue Revising Topic 8

GCSE Chemistry Visuals

Negative Ion Tests

Gas Tests

Chemical Tests