x̄ - > KCSE Chemistry Topical Question Bank (1996–2024)

Organised by topic — each card contains a concept focus, a sampled KCSE question (1996–2024), a worked solution and marking tips.

1. Structure of the Atom & Electronic Configuration

Concept focus: atomic structure, protons/neutrons/electrons, mass & atomic numbers, isotopes, electronic configuration, ionisation energy (basic idea).

Sample KCSE 2012 – Paper 1
State the number of protons, neutrons and electrons in a neutral atom of chlorine-37.

Atomic number (Z) of chlorine = 17 → protons = 17. Mass number = 37 → neutrons = 37 − 17 = 20. Neutral atom → electrons = protons = 17.

✅ Marking tip: award 1 mark each for protons, neutrons and electrons (total 3 marks).

2. The Periodic Table & Periodicity

Concept focus: groups and periods, periodic trends (atomic radius, ionisation energy, electronegativity), metals vs non-metals.

Sample KCSE 2016 – Paper 2
Explain why atomic radius decreases across a period.

As nuclear charge increases (more protons) across a period while electrons are added to the same shell, the increased attraction pulls electrons closer to the nucleus, reducing atomic radius.

✅ Marking tip: 1 mark for stating increased nuclear charge, 1 mark for electrons in same shell, 1 mark for net pull/less radius.

3. Chemical Bonding

Concept focus: ionic, covalent and metallic bonding; properties related to bonding type; dot-and-cross diagrams; shapes of simple molecules (VSEPR basics).

Sample KCSE 2015 – Paper 1
Draw the electron dot (dot-and-cross) structure of NaCl and state the type of bonding.

Na → one valence electron; Cl → seven valence electrons. Na transfers its electron to Cl forming Na⁺ and Cl⁻. Draw Na⁺ (no dots) and Cl⁻ with eight electrons. Bonding = ionic bonding.

✅ Marking tip: award marks for correct transfer, correct ion symbols and naming the bond (3 marks).

4. Stoichiometry & Chemical Calculations

Concept focus: mole concept, molar mass, empirical & molecular formula, mass-volume relationships for gases (at RTP), % composition.

Sample KCSE 2019 – Paper 1
Calculate the number of moles in 88 g of CO₂ (C=12, O=16).

Molar mass CO₂ = 12 + (16×2) = 44 g mol⁻¹. Moles = mass / M = 88 / 44 = 2.0 mol.

✅ Marking tip: 1 mark M, 1 mark substitution, 1 mark final value (2 s.f. if requested).

5. Acids, Bases & Salts

Concept focus: pH concept, acid-base neutralisation, salt preparation (titration, precipitation, reaction of acid with metals/carbonates), indicators.

Sample KCSE 2017 – Paper 2
Write an equation for the reaction between hydrochloric acid and sodium hydroxide. State the salt formed.

HCl + NaOH → NaCl + H₂O. Salt formed = sodium chloride.

✅ Marking tip: 2 marks for balanced equation, 1 mark naming salt.

6. Redox & Electrochemistry

Concept focus: oxidation and reduction (OIL RIG), construction of simple cells, electrolysis basics, reactivity series and displacement reactions.

Sample KCSE 2014 – Paper 2
In the reaction: Zn + Cu²⁺ → Zn²⁺ + Cu, identify the oxidised and reduced species.

Zn → Zn²⁺ (loses electrons) so Zn is oxidised. Cu²⁺ → Cu (gains electrons) so Cu²⁺ is reduced.

✅ Marking tip: 1 mark for identifying oxidised species, 1 mark for reduced species, 1 mark brief justification.

7. Organic Chemistry (Basic)

Concept focus: homologous series (alkanes, alkenes, alcohols, carboxylic acids), IUPAC naming basics, functional groups, simple reactions (addition, combustion, esterification).

Sample KCSE 2018 – Paper 2
Name the organic compound with formula C₂H₄ and state one reaction it undergoes.

C₂H₄ is ethene (an alkene). It undergoes addition reactions, e.g., hydrogenation: C₂H₄ + H₂ → C₂H₆.

✅ Marking tip: 1 mark name, 1 mark reaction equation (balanced), 1 mark reaction type.

8. Rates of Reaction & Chemical Equilibrium

Concept focus: factors affecting rate (concentration, temperature, surface area, catalysts), collision theory, Le Chatelier's principle and macroscopic effects on equilibrium.

Sample KCSE 2015 – Paper 1
State two factors that increase the rate of reaction between a solid and a liquid and explain briefly.

(1) Increase temperature → particles have more kinetic energy → more frequent and energetic collisions. (2) Increase surface area (powdering solid) → more particles exposed → more collisions per unit time.

✅ Marking tip: 1 mark per factor, 1 mark per brief explanation.

9. Energetics / Thermochemistry

Concept focus: exothermic vs endothermic reactions, enthalpy change (ΔH), energy profile diagrams, bond energies (basic use).

Sample KCSE 2013 – Paper 2
Is the combustion of methane exothermic or endothermic? Explain.

Combustion of methane (CH₄ + 2O₂ → CO₂ + 2H₂O) is exothermic because energy released in forming CO₂ and H₂O bonds is greater than energy required to break CH and O₂ bonds; net energy is released.

✅ Marking tip: 1 mark for identifying exothermic, 1–2 marks for explanation referencing bond break/form.

10. Industrial Chemistry & Extraction of Metals

Concept focus: methods of extraction (electrolysis, reduction with carbon), ores, purification, environmental considerations.

Sample KCSE 2011 – Paper 2
Describe briefly how aluminium is extracted from bauxite.

Bauxite → purified to alumina (Al₂O₃) by Bayer process. Aluminum is obtained from molten alumina by electrolysis (Hall–Héroult process) using cryolite as solvent; Al³⁺ reduced to Al at cathode.

✅ Marking tip: award marks for naming Bayer process, Hall–Héroult electrolysis and mentioning cryolite/purification (3–4 marks).

11. Analytical Techniques & Titration

Concept focus: titration method for concentration determination, indicators, qualitative tests (ions, gases).

Sample KCSE 2020 – Paper 2
In a titration, 25.0 cm³ of 0.100 mol dm⁻³ HCl required 30.0 cm³ of NaOH solution to reach the end-point. Calculate concentration of NaOH.

Moles HCl = 0.100 × 25.0/1000 = 0.00250 mol. Reaction HCl + NaOH → NaCl + H₂O (1:1) so moles NaOH = 0.00250 mol. Concentration = moles / volume(L) = 0.00250 / 0.0300 = 0.0833 mol dm⁻³.

✅ Marking tip: 1 mark for moles HCl, 1 mark for mole relationship, 1 mark final concentration (3 marks).

12. Environmental & Atmospheric Chemistry

Concept focus: pollution (air, water, soil), greenhouse gases, acid rain, methods of control and mitigation.

Sample KCSE 2014 – Paper 1
State two harmful effects of acid rain on the environment.

(1) Acidification of lakes and rivers harming aquatic life. (2) Damage to vegetation and soil nutrient depletion; corrosion of buildings and monuments.

✅ Marking tip: 1 mark per correct effect with brief explanation.

KCSE Chemistry Topical Question Bank (1996–2024) — organised for topical revision: concept summary, KCSE-style practice, worked answers and examiner hints. If you want this exported as a downloadable HTML or printable PDF, tell me and I’ll prepare it.