WAEC Chemistry 2015 past questions

Checked by the Skolra question team · Last updated 15 October 2026

Ten questions from the 2015 WAEC Chemistry paper, with answers and explanations. We hold 48 questions from this paper, and the Skolra app has all of them.

WAEC Chemistry 2015 questions and answers

1. 1.Which of the following metals is the strongest reducing agent?
   1. A
      Copper
   2. B
      Potassium
      Correct
   3. C
      Silver
   4. D
      Iron
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   Answer: B

   A reducing agent loses electrons (is itself oxidized). The stronger the tendency to lose electrons, the stronger the reducing agent.

   In the electrochemical series, potassium has the most negative standard electrode potential (E° = −2.92 V), meaning it loses electrons most readily. Iron, copper, and silver are further down the activity series and are progressively weaker reducing agents.

2. 2.SO₄²⁻ + 2H⁺ + ye⁻ → SO₄²⁻ + H₂O. The value of y in the equation is
   1. A
      4
   2. B
      3
   3. C
      1
   4. D
      2
      Correct
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   Answer: D

   This half-equation represents the reduction of sulfate (SO₄²⁻) to sulfite (SO₃²⁻). Sulfur changes from oxidation state +6 in sulfate to +4 in sulfite — a gain of 2 electrons.

   Charge balance confirms this: left side charge = −2 + 2(+1) − y = −y; right side charge = −2. Therefore y = 2.

3. 3.Which of the following compounds is a secondary alkanol?
   1. A
      Methanol (CH₃OH)
   2. B
      Propan-2-ol (CH₃CH(OH)CH₃)
      Correct
   3. C
      2-Methylpropan-2-ol ((CH₃)₃COH)
   4. D
      Ethanol (C₂H₅OH)
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   Answer: B

   A secondary alcohol has the hydroxyl (–OH) group attached to a carbon that is bonded to exactly two other carbon atoms.

   In propan-2-ol, the central carbon bears the –OH group and is bonded to the two terminal methyl carbons — satisfying the definition of a secondary alkanol.

   Methanol and ethanol are primary alcohols (the –OH carbon carries only one carbon substituent or none). 2-Methylpropan-2-ol is a tertiary alcohol (the –OH carbon is bonded to three other carbons).

4. 4.A substance responsible for the sour taste of unripe orange is
   1. A
      citric acid
      Correct
   2. B
      tartaric acid
   3. C
      lactic acid
   4. D
      acetic acid
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   Answer: A

   Citric acid (2-hydroxypropane-1,2,3-tricarboxylic acid) is the principal organic acid in citrus fruits including oranges. It is present in higher concentrations in unripe fruit, giving it a pronounced sour taste.

   Tartaric acid is found mainly in grapes, lactic acid in sour milk, and acetic acid (ethanoic acid) in vinegar — none of these is the dominant acid in oranges.

5. 5.Consider equilibrium: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g). Addition of more O₂(g) shifts equilibrium to the
   1. A
      right, producing more SO₃
      Correct
   2. B
      left, with no change in SO₃
   3. C
      left, producing more SO₂
   4. D
      right, producing more O₂
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   Answer: A

   By Le Chatelier's principle, when a stress is applied to a system at equilibrium, the system responds to partially relieve that stress.

   Adding more O₂ increases the concentration of a reactant on the left side of the equation. The equilibrium position shifts to the right — towards the products — to consume the added oxygen, producing more SO₃ until a new equilibrium is established.

6. 6.Which of the following statements about intermolecular distances and cohesive forces between gas is correct?
   1. A
      Small intermolecular distances and weak cohesive forces
   2. B
      Large intermolecular distances and strong cohesive forces
   3. C
      Small intermolecular distances and strong cohesive forces
   4. D
      Large intermolecular distances and weak cohesive forces
      Correct
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   Answer: D

   Gas molecules are widely separated, so intermolecular distances are large. Because the molecules are so far apart, the attractive forces between them are negligible — cohesive forces are weak.

   This is why gases are highly compressible and expand to fill their containers. Liquids and solids, by contrast, have small intermolecular distances and stronger cohesive forces.

7. 7.Which of the following substances is a heavy chemical?
   1. A
      Aspirin
   2. B
      Synthetic dye
   3. C
      Perfume
   4. D
      Tetraoxosulphate(VI) acid (H₂SO₄)
      Correct
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   Answer: D

   Heavy chemicals (also called bulk chemicals) are produced in very large quantities by industry and are relatively inexpensive per tonne — examples include sulphuric acid, sodium hydroxide, ammonia, and sodium carbonate.

   Tetraoxosulphate(VI) acid (sulphuric acid, H₂SO₄) is the most widely produced industrial chemical in the world and is a classic heavy chemical.

   Aspirin, synthetic dyes, and perfumes are fine chemicals or specialty chemicals — produced in smaller quantities at higher cost per unit.

8. 8.The number of unpaired electrons in an atom of an element ₈Q is _______?
   1. A
      1
   2. B
      2
      Correct
   3. C
      0
   4. D
      4
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   Answer: B

   Element Q has atomic number 8 (oxygen) with the electronic configuration 1s² 2s² 2p⁴. By Hund's rule the four 2p electrons are distributed among the three 2p orbitals as follows: one orbital receives two electrons (paired) and each of the remaining two orbitals receives one electron (unpaired). This gives 2 unpaired electrons.

9. 9.Which of the following substances when boiled with aqueous solution of sodium hydroxide would be hydrolyzed?i. Protein ii. Fat iii. Polythene
   1. A
      ii only
   2. B
      i only
   3. C
      i, ii and iii
   4. D
      i and ii only
      Correct
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   Answer: D

   Proteins contain peptide (amide) bonds that undergo alkaline hydrolysis with NaOH, breaking them into amino acids. Fats are esters of glycerol and fatty acids; boiling with NaOH hydrolyzes the ester bonds in a process called saponification, yielding glycerol and soap (sodium salts of fatty acids). Polythene is an addition polymer of ethene with no ester, amide, or other hydrolyzable bonds; it is chemically inert towards NaOH and is unaffected.

10. 10.The complete hydrogenation of benzene gives
    1. A
       hexane
    2. B
       cyclohexadiene
    3. C
       cyclohexane
       Correct
    4. D
       cyclohexene
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    Answer: C

    Benzene (C₆H₆) undergoes catalytic hydrogenation in the presence of a nickel catalyst at high temperature and pressure. Each of the three double bonds in benzene adds one molecule of H₂:

    C₆H₆ + 3H₂ → C₆H₁₂ (cyclohexane).

    The product retains the six-membered ring structure but with all single C–C bonds and no remaining unsaturation, giving cyclohexane. Hexane would require ring opening, which does not occur under these conditions.

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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