Qualitative Analysis

What is the use of qualitative analysis?

To identify unknown cations and anions through the formation of ppt and gases.

What physical tests can identify unknown substances?

• Observe colour of substance • Test its solubility in water

What is the chemical test for carbonate (CO₃²⁻)?

• Add nitric acid • Effervescence observed. Gas forms white ppt with limewater.

What is the equation for CO₂ reacting with limewater?

Ca(OH)2​(aq)+CO2​(g)→CaCO3​(s)+H2​O(l)

What is the solubility rule for chlorides?

All chlorides are soluble except silver chloride and lead chloride.

How do you test for chloride (Cl⁻)?

• Add nitric acid • Add aqueous silver nitrate • White ppt (AgCl) formed.

What is the solubility rule for iodides?

All iodides are soluble except silver iodide and lead iodide.

How do you test for iodide (I⁻)?

• Add nitric acid • Add aqueous silver nitrate • Pale yellow ppt (AgI) formed.

What is the solubility rule for sulfates?

All sulfates are soluble except barium sulfate, calcium sulfate, lead sulfate.

How do you test for sulfate (SO₄²⁻)?

• Add nitric acid • Add aqueous barium nitrate • White ppt (BaSO₄) formed.

What is the test for nitrate (NO₃⁻)?

• Add aqueous sodium hydroxide and aluminium foil • Warm mixture • Ammonia gas turns red litmus blue.

What reagents identify cations?

Aqueous sodium hydroxide and aqueous ammonia.

How is NH₄⁺ identified?

• Add aqueous sodium hydroxide • Warm mixture • Ammonia gas turns red litmus blue.

What is observed when NaOH is added to Cu²⁺?

(a) Pale blue ppt (b) Insoluble in excess.

What happens when NH₃ is added to Cu²⁺?

(a) Pale blue ppt (b) ppt dissolves to form dark blue solution

What is observed with Fe²⁺ and NaOH?

(a) Green ppt (b) Insoluble in excess.

What is observed with Fe³⁺ and NaOH?

(a) Red-brown ppt (b) Insoluble in excess.

What happens when NaOH is added to Al³⁺?

(a) White ppt (b) Dissolves in excess NaOH to form colourless solution.

What happens when NH₃ is added to Al³⁺?

(a) White ppt (b) Insoluble in excess.

What is observed with Zn²⁺ and NaOH?

(a) White ppt (b) Dissolves in excess NaOH to form colourless solution

What is observed with Fe²⁺ and NH3?

(a) green ppt (b) insoluble in excess

What is observed with Fe³⁺ and NH3?

a) red-brown ppt (b) insoluble in excess

What is observed when NaOH is added to Ca²⁺?

(a) white ppt (b) insoluble in excess

What is observed when NH3 is added to Ca²⁺?

No ppt/ No observable chnage

What is observed when NH3 is added to Zn²⁺?

(a) white ppt (b) dissolves in excess NH3 to form a colourless solution

test for NH3

turns damp red litmus paper bluet

test for co2

forms white ppt in limewater Ca(OH)2

test for chlorine

bleaches damp litmus paper

test for H2

extinguish lighted splint with a pop

test for O2

relights glowing splint

test for sulfur dioxide SO2

turns aqueous acidified potassium manganate(IV) from purple to colourless