O level GCE Notes of subjects

Testing for CATIONS:

With this table, you don’t need to memorise the colours of different salts!

Just draw out this table during your O‐Levels

CATION NaOH NH3

Colour Soluble or

Insoluble

Colour Soluble or

Insoluble

Cu2+ B I B S

Fe2+ G I G I

Fe3+ R I R I

Ca2+ W I - -

NH4+ N - - -

Zn2+ W S W S

Al3+ W S W I

Pb2+ W S W I

The CATIONS table shows the colour changes observed when the salt is added to

Sodium Hydroxide, NaOH, or Aqueous Ammonia, NH3.

Testing for ANIONS:

ANION Tested

with

Observations

Chlorine AgNO3 AgCl White

Colour of Observation

Soluble or

Insoluble in excess

Alkali

Carbonate Acid CO2 Carbon Dioxide

(Turn Limewater chalky)

Sulphate Ba(NO3) BaSO4 White

Nitrate Al, NaOH NH3 Ammonia

(Turn red litmus blue)

Iodide Pb(NO3)2 PbI2 Yellow

Test for GASES:

• Ammonia → Use damp litmus Paper → Turns from red to blue

• Carbon Dioxide → Use Limewater → White ppt formed (Turns Chalky)

• Chlorine → Use Damp blue litmus paper → Bleaches Litmus paper (Litmus Turns colourless)

• Hydrogen → Use Burning Splint → 'Pop' Sound Heard

• Oxygen → Use Glowing Splint → Glows Brighter or Burst into flames

• Sulphur Dioxide → Place a drop of Potassium Dichromate(VI) on Filter paper

‐ Orange Dichromate turns green.