KCSE Chemistry Paper 1 (233/1): Revision Guide and Questions

Last reviewed: 31 October 2026

Updated October 2026. KCSE Chemistry Paper 1 (233/1, Chemistry Paper 1 (Theory)) is a 2 hours paper. Around 25 to 30 short structured questions, all compulsory, 80 marks. On the KNEC 2026 timetable it is on Monday 2 November 2026, 2.00 to 4.00 pm. Below: what the paper covers, how to answer for marks, original practice questions with answers, and a timed KCSE Chemistry Paper 1 challenge you can try free.

What is in KCSE Chemistry Paper 1?

Around 25 to 30 short structured questions, all compulsory, 80 marks. Always follow the instructions printed on your own paper; layouts can change.

Topics that come up most in Chemistry Paper 1

• Structure of the atom and the periodic table
• Chemical bonding and families
• Acids, bases and salts
• The mole and stoichiometry
• Carbon and its compounds, gas laws, air and combustion, separation methods

How to answer Chemistry Paper 1 for marks

1. Write equations with state symbols.
2. Show working in mole calculations and give units.
3. Answer in the space given; long answers waste time.
4. Read every question twice and underline the command word (state, explain, describe, calculate).
5. Budget time by marks: roughly one minute per mark, plus checking time.

Topic weighting: where the marks are in Chemistry Paper 1

All questions are compulsory and short, so marks are spread widely across Form 1 to 4 topics. Calculations (mole, gas laws) and periodic table questions appear every year.

Common mistakes in KCSE Chemistry Paper 1

• Unbalanced equations or missing state symbols
• Confusing atomic number and mass number
• Writing ‘gas’ instead of naming it
• Not showing working in mole calculations

Examiner-style tips for Chemistry Paper 1

• Give the observation and the explanation when a question says ‘explain’.
• Use electron arrangement (2.8.1) to justify group and period.
• Learn common gas tests: hydrogen pops, oxygen relights a glowing splint, carbon(IV) oxide turns lime water milky.

KCSE Chemistry Paper 1 questions and answers (practice)

These are original practice questions written for revision, not KNEC papers.

Question 1

Calculate the number of moles in 4.4 g of carbon(IV) oxide (C = 12, O = 16).

Answer: Molar mass = 44 g/mol, so moles = 4.4 ÷ 44 = 0.1 mol.

Question 2

Why is sodium stored in paraffin?

Answer: It reacts vigorously with oxygen and water vapour in air, so paraffin keeps air away.

Question 3

State the electron arrangement of chlorine (atomic number 17) and its group.

Answer: 2.8.7, group VII.

Question 4

Write a balanced equation for magnesium burning in oxygen.

Answer: 2Mg(s) + O₂(g) → 2MgO(s).

Question 5

Give one difference between a mixture and a compound.

Answer: A mixture can be separated by physical means; a compound needs chemical means.

Chemistry Paper 1 revision checklist

Tick each line only when you can do it from memory, under time:

• I can answer an exam-style question on structure of the atom and the periodic table without notes.
• I can answer an exam-style question on chemical bonding and families without notes.
• I can answer an exam-style question on acids, bases and salts without notes.
• I can answer an exam-style question on the mole and stoichiometry without notes.
• I can answer an exam-style question on carbon and its compounds, gas laws, air and combustion, separation methods without notes.
• I have done at least one full 2 hours practice paper and marked it.
• I have listed my last five mistakes and redone them correctly.

On the day of Chemistry Paper 1

Monday 2 November 2026, 2.00 to 4.00 pm. Be seated 15 minutes early. Carry blue or black pens, a pencil, a ruler and a rubber, a mathematical set and an approved non-programmable calculator. Read the whole paper in the first five minutes and mark the questions you will answer first. Leave the last ten minutes to check your answers and that your index number is on every page you hand in.

Three-day plan for Chemistry Paper 1

Practise Chemistry Paper 1 online

The KCSE Chemistry Paper 1 challenge gives timed questions with a score, a leaderboard rank and a share card. For full papers with worked answers see KCSE practice papers, the KCSE Chemistry revision quiz and this related guide. Check dates in the KCSE 2026 timetable and use the last-minute revision plan.

How this guide differs from past-paper sites

The top Google results for KCSE Chemistry Paper 1 are mostly PDF downloads of old papers and marking schemes. Those are useful, but they rarely explain where the marks sit, what candidates get wrong or how to practise under time. This guide adds that, with original questions and a timed online challenge with instant marking.

Frequently asked questions

How many questions are in KCSE Chemistry Paper 1?

Usually about 25 to 30 short questions, all compulsory, for 80 marks.

Where can I get the KCSE Chemistry Paper 1 marking scheme?

Official marking schemes are not published by KNEC for sale. Use practice papers with worked answers and the answers on this page, and be wary of anyone selling ‘marking schemes’ for the coming exam.

Are KCSE Chemistry Paper 1 leaked papers real?

No. Papers sold online before the exam are scams, and holding them is an exam irregularity that can lead to cancelled results (see KCSE exam rules).

How long is KCSE Chemistry Paper 1?

2 hours on the 2026 timetable.

Can I download the KCSE Chemistry Paper 1 2025 PDF here?

We do not host KNEC papers. Practise with original papers in the same format, with worked answers, in KCSE practice papers; schools keep past KNEC papers for their candidates.

Is there a KCSE Chemistry Paper 1 prediction for 2026?

Prediction papers are teachers’ practice papers, not the real exam. Use them like any past paper and focus on the topics listed above.

Want marked practice? Try the first questions free. A Day Pass (KSh 20) or Weekly Pass unlocks full papers with worked answers, paid once by M-Pesa, no auto-renewal. See all passes.

Keep revising with these: KCSE 2026 Paper-by-Paper Revision Challenges.