KCSE Chemistry Paper 3 (233/3) Practical Questions and Answers

Updated November 2026. If you are searching for KCSE chemistry paper 3 practical questions and answers, this page gives you original practical-style questions with full worked answers, written the way an examiner reads your results table. KCSE Chemistry Paper 3 (233/3) is the practical paper: it carries 40 marks and, on the KNEC 2026 KCSE Examination Timetable, Instructions and Guidelines, it runs on Friday 6 November 2026 from 8.00 to 10.15 am, a total of 2 hours 15 minutes.

These are original CBC Guide practice questions in the KCSE format. They are not an official KNEC paper, and they are not a leaked paper or confidential.

How the Chemistry Practical Paper Is Set Out

Most 233/3 papers have three questions. One is quantitative: a titration or a rate-of-reaction experiment where you fill a table, plot or read data and calculate. The others are qualitative: you test a solid or solution, record observations, and draw inferences about the ions or the functional group present. The marks are split between your table (complete, consistent, correct decimal places), your accuracy against the school’s own results, and your working. Observations and inferences are marked as a pair, so a correct inference after a wrong observation usually earns nothing.

What “Chemistry Paper 3 Confidential” Actually Means

Many students search for the “confidential”. It is simply the list of apparatus and reagents a school must prepare before the practical, for example “0.1 M sodium hydroxide, 2 M hydrochloric acid, solid Q”. It does not contain the questions or the answers. Getting or sharing an exam paper before it is sat is an irregularity under the KNEC rules for the KCSE examination, and results can be cancelled. Practising the skills below is the only preparation that reliably earns marks.

KCSE Chemistry Paper 3 Practical Questions and Answers

Question 1: Titration (quantitative)

You are given solution A, 0.10 M hydrochloric acid, and solution B, sodium hydroxide of unknown concentration. 25.0 cm³ of B is titrated with A using phenolphthalein. Three titres are 24.60, 24.50 and 24.55 cm³. (a) Find the average titre. (b) Find the moles of HCl used. (c) Find the concentration of B in mol dm^-3.

Worked answer: (a) All three titres are within 0.10 cm³ of each other, so all three are averaged: (24.60 + 24.50 + 24.55) ÷ 3 = 24.55 cm³. (b) Moles of HCl = 0.10 × 24.55 ÷ 1000 = 0.002455 mol. (c) NaOH + HCl → NaCl + H₂O is 1:1, so moles of NaOH in 25.0 cm³ = 0.002455. Concentration = 0.002455 × 1000 ÷ 25.0 = 0.0982 M.

Where marks go: burette readings to 2 decimal places, initial and final readings in the table, and only consistent titres averaged. Writing 24.6 instead of 24.60 can cost the decimal mark.

Question 2: Rate of reaction

Different volumes of sodium thiosulphate solution are diluted to 50 cm³ and reacted with 10 cm³ of 2 M HCl. The time for a cross under the beaker to disappear is recorded. (a) Why does the cross disappear? (b) How should 1/t change as the thiosulphate volume rises? (c) What would a graph of volume against 1/t look like?

Worked answer: (a) The acid reacts with thiosulphate to form a yellow precipitate of sulphur, which makes the mixture opaque. (b) More thiosulphate in the same total volume means a higher concentration, more frequent effective collisions, a shorter time t, and therefore a larger 1/t. (c) A straight line through or near the origin, showing that rate is directly proportional to concentration. Label both axes with units and use at least half the grid.

Question 3: Qualitative analysis of a solution

Solution C is tested. (i) Adding aqueous sodium hydroxide dropwise then in excess gives a white precipitate that dissolves in excess. (ii) Adding aqueous ammonia dropwise then in excess gives a white precipitate that is insoluble in excess. (iii) Adding acidified barium nitrate gives a white precipitate.

Worked answer: From (i) the cation is Zn²⁺, Pb²⁺ or Al³⁺. From (ii), Zn²⁺ is ruled out because its precipitate dissolves in excess ammonia, leaving Pb²⁺ or Al³⁺. From (iii), SO₄^2- is present. Lead(II) sulphate is insoluble, so a lead salt would not stay in solution with sulphate ions. The inference is therefore Al³⁺ and SO₄^2-. Write the ions you infer, not the name of a compound.

Question 4: Organic test

Solid D dissolves in water. The solution turns acidified potassium manganate(VII) from purple to colourless and effervesces with sodium hydrogen carbonate. What can you infer?

Worked answer: Decolourising acidified KMnO₄ suggests a C=C bond (or another reducing group). Effervescence with NaHCO₃ shows an H⁺ ion, that is, a carboxylic acid group (–COOH). Both inferences score separately, so state each one against its own observation.

Five Habits That Lift a Chemistry Practical Score

• Read the whole question for two minutes before touching any apparatus.
• Draw your results table in ink, with units in the headings, before you start.
• Record what you see (“white precipitate, soluble in excess”), never what you expect.
• Use “effervescence” or “bubbles”, and say which gas only if you tested it.
• Leave 15 minutes for calculations; they are often the easiest marks on the paper.

Want a full practical paper to time yourself on? The first questions on every CBC Guide paper are free. A Day Pass (KSh 20) or Weekly Pass unlocks complete practice papers with worked answers for all three Chemistry papers, paid once with no auto-renewal. Compare passes.

Frequently Asked Questions

When is KCSE Chemistry Paper 3 (233/3) in 2026?

According to the KNEC 2026 timetable, it is on Friday 6 November 2026 from 8.00 to 10.15 am, which is 2 hours 15 minutes.

How many marks is KCSE Chemistry Paper 3?

The practical paper is out of 40 marks and usually has three questions: one quantitative (titration or rates) and two qualitative analysis questions.

Is the KCSE Chemistry Paper 3 confidential the same as the answers?

No. The confidential is the list of reagents and apparatus a school prepares. It does not contain questions or answers, and anyone selling “leaked” practicals is running a scam.

Are these the official KNEC marking scheme answers?

No. These are original practice questions with worked answers written by CBC Guide to match the KCSE practical format.