WAEC Chemistry 2019 past questions

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

Ten questions from the 2019 WAEC Chemistry paper, with answers and explanations. We hold 63 questions from this paper, and the Skolra app has all of them.

WAEC Chemistry 2019 questions and answers

1. 1.

   When excess chlorine is mixed with ethane at room temperature, the product formed is?

   1. A
      chloroethane
   2. B
      1,2-dichloroethane
   3. C
      hexachloroethane
      Correct
   4. D
      1,1,2,2-tetrachloroethane
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   Answer: C

   The reaction of ethane with chlorine in the presence of UV light or at room temperature proceeds by free-radical substitution. When chlorine is present in excess, successive substitution reactions replace every hydrogen atom in the ethane molecule.

   Ethane has six hydrogen atoms (C₂H₆). With excess chlorine, all six are replaced by chlorine atoms, giving hexachloroethane (C₂Cl₆) as the final product.

2. 2.

   A sample of air was bubbled into water. The PH of the water slowly changed from 7 to 6. Which of the following gases in the samples caused the change?

   1. A
      oxygen
   2. B
      nitrogen
   3. C
      hydrogen
   4. D
      carbon dioxide
      Correct
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   Answer: D

   A decrease in pH from 7 to 6 means the water became more acidic. Of the major components of air, only carbon dioxide (CO₂) reacts with water to form an acid:

   CO₂(g) + H₂O(l) ⇌ H₂CO₃(aq) ⇌ H⁺(aq) + HCO₃⁻(aq)

   The carbonic acid formed dissociates partially, releasing hydrogen ions and lowering the pH. Nitrogen and oxygen do not react with pure water under normal conditions, so they cannot cause the observed acidification.

3. 3.

   Which of the following apparatus isNOTused in volumetric analysis?

   1. A
      Crucible
      Correct
   2. B
      Volumetric flask
   3. C
      Burette
   4. D
      Pipette
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   Answer: A

   Volumetric analysis involves measuring precise volumes of solutions to determine concentration. The apparatus used includes the burette (for delivering measured variable volumes of titrant), the pipette (for measuring a fixed, accurate volume of the analyte solution), and the volumetric flask (for preparing solutions of accurately known concentration). A crucible is a heat-resistant vessel used in gravimetric analysis or for heating and igniting solids — it measures mass, not volume, and plays no part in volumetric analysis.

4. 4.

   A solid with higher melting and boiling points is likely to be?

   1. A
      a simple covalent compound
   2. B
      a noble gas solid
   3. C
      an ionic compound
      Correct
   4. D
      a molecular solid
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   Answer: C

   The melting and boiling points of a solid depend on the strength of the forces holding its particles together.

   Ionic compounds are held together by strong electrostatic attractions between oppositely charged ions, which extend throughout the entire crystal lattice. A large amount of energy is needed to overcome these attractions, resulting in high melting and boiling points (often above 500 °C).

   Simple covalent (molecular) solids, noble gas solids, and other molecular solids are held together only by weak van der Waals or dipole–dipole forces, giving much lower melting and boiling points.

5. 5.

   What is the solubility of a salt X at 25ºC if the saturated solution of the salt contains 0.28g in 100cm$^3$ of the solution in mol\dm$^3$?

   [ X = 56.0g ]

   1. A
      0.05 mol dm⁻³
      Correct
   2. B
      0.10 mol dm⁻³
   3. C
      0.28 mol dm⁻³
   4. D
      0.50 mol dm⁻³
   Show answerHide answer

   Answer: A

   First, calculate the number of moles of the salt:

   moles = mass ÷ molar mass = 0.28 ÷ 56.0 = 0.005 mol

   Then convert the volume to dm³:

   100 cm³ = 0.1 dm³

   Finally, calculate the concentration:

   concentration = 0.005 mol ÷ 0.1 dm³ = 0.05 mol dm⁻³

6. 6.

   If the value of $\Delta H$ is positive for a reaction, it means that the reaction is?

   1. A
      spontaneous
   2. B
      exothermic
   3. C
      irreversible
   4. D
      endothermic
      Correct
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   Answer: D

   The enthalpy change ΔH represents the heat exchanged between a system and its surroundings at constant pressure.

   • A positive ΔH means the products have more enthalpy than the reactants, so the system must absorb heat from the surroundings — the reaction is endothermic.
   • A negative ΔH means heat is released to the surroundings — the reaction is exothermic.

   An endothermic reaction causes the surroundings to cool down during the process.

7. 7.

   The most suitable indicator for the reaction between NaOH and HCOOH is?

   1. A
      phenolphthalein
      Correct
   2. B
      methyl red
   3. C
      litmus
   4. D
      methyl orange
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   Answer: A

   NaOH is a strong base and methanoic acid (HCOOH) is a weak acid. At the equivalence point of a strong base–weak acid titration, the solution is alkaline (pH typically between 8 and 10) because the salt formed (sodium methanoate) hydrolyses to give a basic solution.

   Phenolphthalein changes colour in the pH range 8.2–10.0, which coincides with the equivalence-point pH of this titration. Methyl orange (range 3.1–4.4) and methyl red (range 4.4–6.2) change colour in the acidic region and would give an inaccurate endpoint. Litmus has too broad and imprecise a range for accurate titration work.

8. 8.

   Stoichiometryis basedon the law?

   1. A
      conservation of mass
      Correct
   2. B
      partial pressures
   3. C
      multiple proportions
   4. D
      conservation of energy
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   Answer: A

   Stoichiometry is the quantitative study of the relationships between reactants and products in chemical reactions. It is grounded in the law of conservation of mass, which states that the total mass of reactants equals the total mass of products in a chemical reaction.

   This law, established by Lavoisier, means that atoms are neither created nor destroyed during a reaction, only rearranged. Balanced chemical equations express this conservation and form the basis of all stoichiometric calculations.

9. 9.

   All your burette readings (initials and final) as well as the size of your pipette must be recorded but no account of experimental procedure is required. All calculations must be done in your answer booklet.

   C is a mixture of two inorganic compounds. Carry out the following exercises on C. Record your observations and identify any gas(es) evolved. State the conclusions you draw from the result of each test.

   (a) Put all of C in a boiling tube and add about 10 cm$^3$ of distilled water. Shake thoroughly and filter. Keep both the residue and the filtrate.

   (b)(i) To about 2 cm$^3$ of the filtrate add a few drops of Silver trioxoitrate (V) followed by dilute HNO$_{3}$

   (ii) Add excess NH$_3$ solution to the resulting mixture in (b)(i).

   (C)(i) Put the residue in a test tube, add about 2 cm$^3$ of dilute HCl and shake.

   (ii) Add NH$_3$ Solution in drops to the mixture from (c)(i) and then in excess.

   1. A
      No precipitate forms and the solution remains colourless
   2. B
      A white precipitate forms that dissolves completely when excess ammonia solution is added
      Correct
   3. C
      A yellow precipitate forms that is insoluble in excess ammonia solution
   4. D
      A white precipitate forms that dissolves in dilute nitric acid
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   Answer: B

   When silver trioxonitrate(V) (AgNO₃) is added to a filtrate containing chloride ions, silver chloride (AgCl) precipitates as a white solid that is insoluble in dilute HNO₃. This confirms the presence of chloride ions. When excess ammonia solution is then added, the AgCl dissolves to form the soluble diamminesilver(I) complex, [Ag(NH₃)₂]⁺, so the white precipitate disappears. A yellow precipitate insoluble in excess NH₃ would indicate silver iodide (AgI); a cream precipitate partly soluble in concentrated ammonia would indicate silver bromide (AgBr).

10. 10.

    (a) In the Solvay process, explain briefly with equations the functions of the following substances:

    • limestone;
    • ammonia.

    (b) (i) Write a chemical equation for the fermentation of glucose.

    (ii) Explain briefly why a tightly-corked glass bottle filled to the brim with fresh palm-wine shatters on standing for some time.

    (c) Consider the following metals: Na, Fe, K and Cu.

    (i) Arrange the metals in order of increasing reactivity.

    (ii) Which of the metals will react with cold water?

    (ii) Which of the metals could form coloured salts?

    (d)(i) What is a redox reaction?

    (ii) Identify which of the following reaction equations are redox.

    (I) 2Na + Cl$_2$ 2NaCl

    (II) AgCl + 2NH$_3$ [Ag(NH$_3$)$_2$]Cl

    (III) C$_2$H$_2$ + H$_2$ C$_2$H$_4$

    (IV) HCl + KOH KCl + H$_2$O

    (V) 2FeCl$_3$ + 2KI 2FeCl$_2$ + 2KCl + I$_2$

    (iii) Give a reason for each of the answers in (d)(ii).

    (iv) Write balanced equations of the half reactions for any two of the redox reactions in (d)(ii).

    1. A
       Fe < Cu < K < Na
    2. B
       Cu < Fe < Na < K
       Correct
    3. C
       K < Na < Fe < Cu
    4. D
       Cu < Na < Fe < K
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    Answer: B

    Arranged in increasing order of reactivity (least reactive first): copper is the least reactive transition metal, not reacting with water or dilute acids; iron reacts slowly with steam and dilute acids; sodium reacts vigorously with cold water; potassium is the most reactive of the four, reacting violently with cold water. This order matches the standard electrochemical series: Cu (+0.34 V) < Fe (−0.44 V) < Na (−2.71 V) < K (−2.93 V), where a more negative standard electrode potential indicates a more reactive (more easily oxidised) metal.

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