Qualitative analysis — KCSE Chemistry

KCSE Chemistry · 58 practice questions · 4 syllabus objectives

11 easy29 medium18 hard

What You'll Learn

Key learning outcomes for this topic, aligned to the KNEC KCSE syllabus.

Describe tests for common anions: carbonate (CO₃²⁻), sulphate (SO₄²⁻), chloride (Cl⁻) and nitrate (NO₃⁻)

Describe tests for common cations using aqueous sodium hydroxide and aqueous ammonia

Identify an unknown salt by systematic qualitative analysis and write equations for the reactions observed

Qualitative analysis

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easySHORT ANSWER4 marks

List the steps and observations to confirm if a solution contains lead(II) ions using aqueous sodium hydroxide and aqueous ammonia. (4 marks)

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Part (a) — 4 marks

Add a few drops of aqueous sodium hydroxide to the solution — a white precipitate of lead(II) hydroxide, Pb(OH)₂, forms (1 mk)

Add excess sodium hydroxide — the precipitate does not dissolve (1 mk)

Add a few drops of aqueous ammonia to the same solution — a white precipitate of lead(II) hydroxide, Pb(OH)₂, is also formed (1 mk)

Add excess ammonia — the precipitate does not dissolve (1 mk)

easySHORT ANSWER2 marks

State the expected observation when aqueous ammonia is added to a solution containing iron(III) ions. (2 marks)

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Part (a) — 2 marks

A reddish-brown precipitate of iron(III) hydroxide, Fe(OH)₃, is formed (1 mk)

The precipitate does not dissolve in excess ammonia (1 mk)

easySHORT ANSWER2 marks

List the observations made when a few drops of aqueous sodium hydroxide are added to a solution containing zinc ions. (2 marks)

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Part (a) — 2 marks

A white precipitate of zinc hydroxide, Zn(OH)₂, is formed (1 mk)

The precipitate is soluble in excess sodium hydroxide, forming a clear solution (1 mk)

Define the procedure to test for the presence of iron(II) ions (Fe²⁺) in a solution. (4 marks)