Edexcel IGCSE Chemistry - Chemical Tests

Flame test for sodium

Yellow

Test for hydrogen gas

A lit splint is extinguished with a squeaky pop

Test for carbon dioxide

Bubbles the gas through lime water (calcium hydroxide). As a result, the lime water turns cloudy

Flame test for lithium

Red

Flame test for copper

Blue-green

Test for ammonium ions

Add sodium hydroxide and warm, ammonia gas is produced and tested for (damp red litmus goes blue)

What colour precipitate is formed when NaOH is added to a solution containing Cu2+ ions?

Blue

What colour precipitate is formed when NaOH is added to a solution containing Fe2+ ions?

Green

What colour precipitate is formed when NaOH is added to a solution containing Fe3+ ions?

Brown

Test for chloride ions

Add nitric acid and silver nitrate solution (AgNO3). A white precipitate (AgCl) is formed.

Test for bromide ions

Add nitric acid and silver nitrate solution (AgNO3). A cream precipitate (AgBr) is formed.

Test for iodide ions

Add nitric acid and silver nitrate solution (AgNO3). A yellow precipitate (AgI) is formed.

Test for sulfate ions SO₄²⁻

Add dilute hydrochloric acid, add drops of barium chloride solution.
White precipitate (of barium sulphate) formed

Test for oxygen gas

Relights a glowing splint

Test for ammonia gas

Damp red litmus paper turns blue

Test for chlorine gas

Damp blue litmus paper turns red then is bleached white

What are flame tests used for?

Flame tests are used to identify metal ions

Flame test for potassium

Lilac

Flame test for calcium

Orange-red

Test for carbonate ions

Add dilute HCl. Fizzing is observed as carbon dioxide gas is released. Bubble through limewater which turns cloudy.

Chemical test for water

Anhydrous copper sulfate is added to liquid, if it goes from white to blue, it will be water

Physical test for water

Boil the liquid and measure it's boiling point. If it boils at 100C it is water

Why is nichrome wire used in a flame test?

Inert (unreactive) so will not affect the colour of the flame and has a high melting point.

Why does acid need to be added before some tests?

Removes carbonate ions from the solution which may give a false positive test

Why must you use a roaring bunsen flame in flame tests?

It has no colour so will not affect the result.