Last reviewed: 1 November 2026
Updated November 2026. Here are KCSE 2025 Chemistry Paper 2 questions and answers written as original practice in the 233/2 style, with full working for every calculation. Chemistry Paper 2 is a 2-hour theory paper worth 80 marks, made of longer structured questions, all compulsory, that usually combine a diagram or flow chart with calculations. The 2026 sitting is on Wednesday 4 November, 8.00 to 10.00 am, so these questions are timed for the last few days of revision.
Original CBC Guides questions written in the KCSE format. Not the KNEC 2025 paper and not a KNEC marking scheme.
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What the 2025 Chemistry Paper 2 (233/2) Looked Like
On the KNEC 2025 KCSE timetable, 233/2 Chemistry ran on Wednesday 5 November 2025 from 8.00 to 10.00 am. The KNEC 2026 KCSE timetable, instructions and guidelines gives the same 2 hours. Paper 2 typically has about seven structured questions, averaging about 11 marks each, and every question is compulsory. Paper 1 (233/1) has short questions and Paper 3 (233/3) is the practical.
That means roughly 15 minutes per question. The long questions reward candidates who write balanced equations with state symbols and show every step of a calculation.
KCSE 2025 Chemistry Paper 2 Answers: Structured Practice
Question 1: Organic chemistry (11 marks)
(a) Draw the structure and give the IUPAC name of the second member of the alkene series. Answer: propene, CH₂=CH–CH₃ (show all C–H bonds in an exam).
(b) Ethanol is converted to ethene. Name the reagent and condition. Answer: concentrated sulphuric acid at about 170°C (dehydration). Missing the temperature usually costs the condition mark.
(c) Write an equation for the reaction between ethanoic acid and ethanol and name the organic product. Answer: CH₃COOH(l) + CH₃CH₂OH(l) ⇌ CH₃COOCH₂CH₃(l) + H₂O(l); ethyl ethanoate (an ester), with a few drops of concentrated sulphuric acid as catalyst.
(d) A polymer has a relative molecular mass of 42,000. Its monomer is propene (C₃H₆). Find the number of monomers (C = 12, H = 1). Working: Mr of C₃H₆ = 36 + 6 = 42. n = 42,000 ÷ 42 = 1,000.
Question 2: Electrolysis (12 marks)
(a) Concentrated sodium chloride solution is electrolysed using carbon electrodes. Name the products at each electrode. Answer: chlorine gas at the anode (high Cl⁻ concentration means Cl⁻ is discharged in preference to OH⁻); hydrogen gas at the cathode (H⁺ is discharged rather than Na⁺, which is higher in the electrochemical series).
(b) A current of 2 A flows for 32 minutes 10 seconds through copper(II) sulphate solution. Calculate the mass of copper deposited (Cu = 63.5, 1 Faraday = 96,500 C). Working: t = 1,930 s; Q = 2 × 1,930 = 3,860 C. Cu²⁺ + 2e⁻ → Cu, so 2 × 96,500 = 193,000 C deposit 63.5 g. Mass = 3,860 ÷ 193,000 × 63.5 = 1.27 g.
(c) State one industrial use of electrolysis. Answer: electroplating; extraction of sodium or aluminium; purification of copper.
Question 3: Energy changes (10 marks)
50 cm³ of 2 M HCl was mixed with 50 cm³ of 2 M NaOH. The temperature rose from 22.0°C to 35.5°C. Calculate the molar heat of neutralisation (specific heat capacity 4.2 J g⁻¹ K⁻¹, density 1 g cm⁻³).
Working: ΔT = 13.5 K; mass of solution = 100 g. Heat = 100 × 4.2 × 13.5 = 5,670 J. Moles of water formed = 2 × 50/1,000 = 0.1 mol. ΔH = −5,670 ÷ 0.1 = −56,700 J/mol = −56.7 kJ/mol. The negative sign shows the reaction is exothermic; leaving it out loses a mark.
Question 4: Rates and equilibrium (8 marks)
In the Contact process, 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), ΔH is negative. (a) Name the catalyst. Answer: vanadium(V) oxide. (b) Explain the effect of raising the temperature on the yield of SO₃. Answer: the yield falls, because the forward reaction is exothermic and a higher temperature shifts the equilibrium to the left. (c) Why is SO₃ dissolved in concentrated sulphuric acid and not water? Answer: SO₃ reacts with water very exothermically, forming a mist of acid that is hard to condense; dissolving it in concentrated acid forms oleum safely.
Common Mistakes in Chemistry Paper 2
- Carbon atoms with three or five bonds in organic structures
- Forgetting that Cu²⁺ needs 2 Faradays per mole
- Dropping the sign or the unit in ΔH answers
- Learning flow charts without the conditions (temperature, pressure, catalyst)
Work through the full topic list in the KCSE Chemistry Paper 2 revision guide. Then sit the timed KCSE Chemistry Paper 2 challenge, drill short items in the KCSE Chemistry quiz, and browse the KCSE quiz index and KCSE challenges page for your other subjects. More papers are on the KCSE Chemistry practice papers page, and the KCSE 2026 hub has the full timetable.
Frequently Asked Questions
How long is KCSE Chemistry Paper 2?
2 hours for 80 marks. In 2026 it runs on Wednesday 4 November, 8.00 to 10.00 am.
Where is the KCSE 2025 Chemistry Paper 2 marking scheme PDF?
KNEC does not publish its marking schemes for sale. Use worked answers like these and check that your equations balance and your units are right.
Which topics carry the most marks in Chemistry Paper 2?
Organic chemistry, electrochemistry, energy changes, rates and equilibrium, and industrial processes appear most often, usually with a calculation.
Is there a KCSE Chemistry Paper 2 prediction for 2025?
No genuine prediction exists. Revise the whole syllabus and use any “prediction” paper as ordinary timed practice.
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