Qualitative Analysis (O Level Pure Chem)

Al³⁺

Add NaOH(aq)

White ppt., dissolves in excess NaOH(aq) to give a colourless solution

Add NH₃(aq).

White ppt., insoluble in excess NH₃(aq)

Pb²⁺

Add NaOH(aq)

White ppt., dissolves in excess NaOH(aq) to give a colourless solution

Add NH₃(aq)

White ppt., insoluble in excess NH₃(aq)

Zn²⁺

Add NaOH(aq)

White ppt., dissolves in excess NaOH(aq) to give a colourless solution

Add NH₃(aq)

White ppt., dissolves in excess NH₃(aq) to form a colourless solution

Ca²⁺

Add NaOH(aq)

White ppt., insoluble in excess NaOH(aq).

Add NH₃(aq)

No ppt.

Cu²⁺

Add NaOH(aq)

Blue ppt., insoluble in excess NaOH(aq)

Add NH₃(aq)

Blue ppt., dissolves in excess NH₃(aq) to form a dark blue solution

Fe²⁺

Add NaOH(aq)

Green ppt., insoluble in excess NaOH(aq) Precipitate turns brown on standing

Add NH₃(aq)

Green ppt., insoluble in excess NH₃(aq)

Precipitate turns brown on standing

Fe³⁺

Add NaOH(aq)

Reddish-brown ppt., insoluble in excess NaOH(aq)

Add NH₃(aq)

Reddish-brown ppt., insoluble in excess NH₃(aq)

NH₄⁺

Add NaOH(aq) and warm

Pungent gas evolved turns moist red litmus paper blue

NO₃⁻

Add NaOH(aq), Al and warm

Effervescence observed. Pungent gas evolved turns moist red litmus paper blue

CO₃²⁻

Add dilute nitric acid. Bubble gas evolved into limewater

Effervescence observed. White ppt. formed in limewater

Cl⁻

Add dilute nitric acid followed by aqueous silver nitrate.

White ppt. formed

SO₄²⁻

Add dilute nitric acid followed by aqueous barium nitrate.

White ppt. formed

I⁻

Add dilute nitric acid followed by aqueous silver nitrate.

Yellow ppt. formed

CO₂

Bubble the gas through limewater

White ppt. formed in limewater

H₂

Put a lighted wooden splint into the mouth of the test tube

If hydrogen gas is present, lighted splint extinguishes with a 'pop' sound

NH₃

Hold a damp red litmus paper at the mouth of the test tube

If ammonia gas is present, damp red litmus paper turns blue

O₂

Put a glowing wooden splint into the mouth of the test tube

If oxygen gas is present, glowing splint rekindles

Cl₂

Hold a damp blue litmus paper at the mouth of the test tube

If chlorine gas is present, damp blue litmus paper turns red and is then bleached

SO₂

Pass the gas through aqueous acidified potassium manganate(VII) solution

If sulfur dioxide gas is present, potassium manganate(VII) solution turns from purple to colourless