WAEC Chemistry 2023 past questions

Checked by the Skolra question team · Last updated 23 October 2026

Ten questions from the 2023 WAEC Chemistry paper, with answers and explanations. We hold 41 questions from this paper, and the Skolra app has all of them.

WAEC Chemistry 2023 questions and answers

1. 1.

   Positive ions in a sea of electrons are found in

   1. A
      ionic bonding
   2. B
      covalent bonding
   3. C
      metallic bonding
      Correct
   4. D
      hydrogen bonding
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   Answer: C

   The metallic bonding model describes atoms as positive ions (cations) embedded in a 'sea' of delocalized electrons. This explains metals' electrical conductivity, malleability, and other unique properties.

2. 2.

   The primary component of natural gas

   1. A
      is nitrogen
   2. B
      is ethane
   3. C
      is propane
   4. D
      is methane
      Correct
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   Answer: D

   Methane (CH₄) comprises 70-90% of natural gas. It is the simplest hydrocarbon and is formed by anaerobic decomposition of organic matter in geological deposits.

3. 3.

   Why are $H_2SO_4$ and $CaCl_2$, not suitable for drying ammonia gas? They

   1. A
      react chemically with the gas being dried
      Correct
   2. B
      cannot withstand the pressure of the gas
   3. C
      are too acidic to absorb moisture effectively
   4. D
      produce coloured compounds with the gas
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   Answer: A

   Correct reasoning: they react chemically with the gas being dried.

   Ammonia gas, NH3, is basic (alkaline). A good drying agent must only remove water vapour from a gas — it must not react with the gas itself.

   Concentrated tetraoxosulphate(VI) acid, H2SO4, is a strong acid. When ammonia passes through it, an acid-base reaction occurs and ammonium tetraoxosulphate(VI) is formed: 2NH3 + H2SO4 → (NH4)2SO4. The acid therefore absorbs the ammonia gas itself, not just the moisture in it.

4. 4.

   Which of the following properties does not give evidence of the kinetic theory of matter?

   1. A
      Diffusion
   2. B
      Evaporation
   3. C
      Melting
   4. D
      Polymerization
      Correct
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   Answer: D

   The kinetic theory of matter says that all particles (atoms, ions or molecules) are in constant, random motion, and that this motion increases as the particles gain energy. Any property that can be traced directly to particles moving, spreading out, or gaining enough energy to change state counts as evidence for the theory.

   Diffusion is particles spreading from a region of higher concentration to one of lower concentration purely because they are in continuous random motion — direct evidence of moving particles.

   Evaporation happens because surface particles of a liquid gain enough kinetic energy from their random motion to break free into the gas phase — again, particle motion in action.

5. 5.

   A consequence of global warming is

   1. A
      decreased UV radiation
   2. B
      rising sea levels
      Correct
   3. C
      decreased CO₂ levels
   4. D
      increased ozone layer
   Show answerHide answer

   Answer: B

   Global warming causes thermal expansion of oceans and melting of polar ice, leading to rising sea levels. This threatens coastal communities and ecosystems. Increased UV radiation and CO₂ levels are causes, not consequences.

6. 6.

   Consider the following reaction equation:
   $2SO_3(g) → 2SO_2(g) + O_2$(g)
   ∆H = +198 kJ/mol
   Which of the following statements about the reaction is correct?

   1. A
      The number of gaseous particles decreases as the reaction proceeds
   2. B
      The reaction absorbs heat from the surroundings since ∆H is positive
      Correct
   3. C
      The reaction releases heat to the surroundings since ∆H is positive
   4. D
      An increase in pressure will favour the forward reaction
   Show answerHide answer

   Answer: B

   The sign of ∆H tells you the direction of heat flow. Here, ∆H = +198 kJ/mol for the decomposition 2SO₃(g) → 2SO₂(g) + O₂(g). A positive ∆H means the system takes in energy as the reaction goes forward, so the reaction absorbs heat from the surroundings — this makes it endothermic.

   Saying the reaction releases heat would be true only if ∆H were negative; a positive value always signals heat absorption, not release, so that statement does not fit the data given.

7. 7.

   An element X has two isotopes, $^{65}X_{30}$ and $^{66}X_{30}$ with relative abundance of 60 % and 40% respectively. The relative atomic mass of X is

   1. A
      65.0
   2. B
      64.6
   3. C
      65.4
      Correct
   4. D
      66.0
   Show answerHide answer

   Answer: C

   Relative atomic mass = (60 × 65 + 40 × 66) / 100 = (3900 + 2640) / 100 = 6540 / 100 = 65.4. The relative atomic mass is the weighted average based on the abundance of each isotope.

8. 8.

   The best indicator to use for the titration of ethanoic acid with sodium hydroxide is

   1. A
      Phenolphthalein
      Correct
   2. B
      Methyl red
   3. C
      Bromothymol blue
   4. D
      Methyl orange
   Show answerHide answer

   Answer: A

   Phenolphthalein (pH range 8.2-10.0) is ideal for weak acid-strong base titrations. The equivalence point occurs above pH 7, and phenolphthalein changes colour in this range. Methyl orange would change colour before the equivalence point.

9. 9.

   Alkenes can be manufactured by

   1. A
      fractional distillation of crude oil
   2. B
      polymerization of unsaturated hydrocarbons
   3. C
      fermentation of carbohydrates
   4. D
      cracking of petroleum fractions
      Correct
   Show answerHide answer

   Answer: D

   Alkenes are manufactured industrially by cracking petroleum fractions. Petroleum fractions from fractional distillation contain mostly large, saturated alkane molecules. When these are heated strongly (thermal cracking) or passed over a hot catalyst (catalytic cracking), the long carbon chains break apart at the C–C bonds, producing shorter-chain alkanes together with alkenes such as ethene and propene. Cracking is the step that actually creates the carbon-to-carbon double bond that defines an alkene.

10. 10.

    Which of the following gases has the lowest rate of diffusion?
    [H=1.0, C=12.0, N = 14.0, O= 16.0]

    1. A
       Nitrogen
    2. B
       Ammonia
    3. C
       Carbon dioxide
       Correct
    4. D
       Hydrogen
    Show answerHide answer

    Answer: C

    Rate of diffusion is inversely proportional to molar mass. CO₂ has the highest molar mass (44), so it diffuses slowest. Heavier gas molecules move more slowly and collide more frequently, reducing diffusion rate.

The questions come from past JAMB, WAEC and NECO papers. We use software to help write the answer options and explanations, and every answer is checked twice before it goes on the site. How we check

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Practise all 41 questions we hold from the 2023 paper, on a timed CBT screen

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