tests for cations and anions

How to test for GROUP 2 IONS

• From Mg to Ba

• Add NaOH (increase in solubility as you go down)

• Add H2SO4 (decrease in solubility as you go down)

How to test for ammonium ions

• add NaOH

• NH4+ + OH- → NH3 (g) + H2O

• Turns red litmus paper blue

How to test for GROUP 7 IONS (1)

Option 1: Acidified silver nitrate

Chloride ions- white precipitate

Bromide ions- cream precipitate

Iodide ions- yellow precipitate

Then to further identify, add dilute NH3:

Chlorine will dissolve

Bromine will stay the same

Then add concentrated NH3:

Bromine will dissolve

iodine will remain same for both

How to test for group 7 ions (2)

All acid base reactions first. Then bromide and iodide react redox after

How to test for carbonate ions

• add acid

• Effervescence (bubbled through limewater which can make it cloudy)

How to test for sulphate ions

• add acidified barium chloride

• Ba 2+ + SO4 2- → BaSO4 (s) which is a white precipitate

How to test for hydroxide ions

Turns damp red litmus paper blue