EDEXCEL iGCSE Chemistry: Testing for anions and cations

Flame colour of lithium (Li+)

Crimson (red)

Flame colour of Copper (Cu2+)

Green

Describe the test for a halide (X-) ion

Firstly add nitric acid to dissolve impurities, followed by silver nitrate solution

Precipitate colour for the chloride (Cl-) ion

White (AgCl)

Precipitate colour for the bromide (Br-) ions

Cream (AgBr)

Precipitate colour for the iodide (I-) ion

Yellow (AgI)

Flame Colour of Sodium (Na+)

yellow

Flame colour of calcium (Ca2+)

Orange

Flame colour of Potassium (K+)

Lilac

State a material that can be used as the wire for flame testing

Platinum or nichrome

Why is the wire in flame testing first dipped in acid before the metal?

To remove impurities

The chemical test for the sulfate ion (SO42-)

Barium chloride gives a white precipitate of barium sulfate (BaSO4)

The chemical test for carbon dioxide gas

Turns lime water cloudy

What is the test for hydrogen gas?

A lit flame gives a squeaky pop

What is the test for oxygen gas?

A glowing splint relights

Describe the chemical test for chlorine gas

Bleaches damp litmus paper

Precipitate colour for Fe(II) ions with sodium hydroxide

Green precipitate of Fe(OH)2

Precipitate colour for Cu2+ ions with sodium hydroxide

Blue precipitate of Cu(OH)2

Precipitate colour for Fe(III) ions with sodium hydroxide

Brown precipitate of Fe(OH)3

Explain why hydrochloric acid is not an appropriate acid for halide testing

It dissociates (breaks apart) into H+ and Cl- so the chloride ion contaminates the solution

How to test for both ions in LiCl?

Flame test crimson red (Li+) and halide test with nitric acid and silver nitrate gives a white precipitate (AgCl)

The chemical test for the carbonate ion (CO32-)

Add an acid. Bubbles of carbon dioxide are made. The gas turns lime water cloudy