Test of Anion & Cation

Colors of Salts:

Salt	Formula	Solid	In Solution
Hydrated copper sulfate	CuSO4.5H2O	Blue crystals	Blue
Anhydrous copper sulfate	CuSO4	White powder	Blue
Copper nitrate	Cu(NO3)2	Blue crystals	Blue
Copper chloride	CuCl2	Green	Green
Copper carbonate	CuCO3	Green	Insoluble
Copper oxide	CuO	Black	Insoluble
Iron(II) salts	E.g.: FeSO4, Fe(NO3)2	Pale green crystals	Pale green
Iron(III) salts	E.g.: Fe(NO3)3	Reddish brown	Reddish brown

Tests for Gases:

Gas	Formula	Tests
Ammonia	NH3	Turns damp red litmus paper blue
Carbon dioxide	CO2	Turns limewater milky
Oxygen	O2	Relights a glowing splint
Hydrogen	H2	‘Pops’ with a lighted splint
Chlorine	Cl2	Bleaches damp litmus paper
Nitrogen dioxide	NO2	Turns damp blue litmus paper red
Sulfur dioxide	SO2	Turns acidified aqueous potassium dichromate(VI) from orange to green

Tests for Anions:

Anion	Test	Result
Carbonate (CO32-)	Add dilute acid	Effervescence, carbon dioxide produced
Chloride (Cl-) (in solution)	Acidify with dilute nitric acid, then add aqueous silver nitrate	White ppt.
Iodide (I-) (in solution)	Acidify with dilute nitric acid, then add aqueous silver nitrate	Yellow ppt.
Nitrate (NO3-) (in solution)	Add aqueous sodium hydroxide, then aluminium foil; warm carefully	Ammonia produced
Sulfate (SO42-)	Acidify, then add aqueous barium nitrate	White ppt.

Tests for aqueous cations:

Cation	Effect of aqueous sodium hydroxide	Effect of aqueous ammonia
Aluminium (Al3+)	White ppt., soluble in excess giving a colourless solution	White ppt., insoluble in excess
Ammonium (NH4+)	Ammonia produced on warming	–
Calcium (Ca2+)	White ppt., insoluble in excess	No ppt. or very slight white ppt.
Copper (Cu2+)	Light blue ppt., insoluble in excess	Light blue ppt., soluble in excess, giving a dark blue solution
Iron(II) (Fe2+)	Green ppt., insoluble in excess	Green ppt., insoluble in excess
Iron(III) (Fe3+)	Red-brown ppt., insoluble in excess	Red-brown ppt., insoluble in excess
Zinc (Zn2+)	White ppt., soluble in excess, giving a colourless solution	White ppt., soluble in excess, giving a colourless solution