WAEC 2026 CHEMISTRY ANSWERS (OBJ & ESSAY)

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CHEMISTRY OBJ

PLEASE USE THIS ANSWERS TO TRACE OUT YOUR EXACT ANSWERS;

1. B – 50 cm³

2. D – Period 2 and Group V

3. C – XCl₃

4. A – bipolar

5. C – electrons in the d-orbitals

6. A – allotropes

7. B – 12

8. D – Iron rod

9. A – Sucrose

10. D – 3d

11. B – fermentation

12. A – NaCl would crystallize first

13. C – of the presence of mobile electrons

14. A – 37

15. C – 5

16. A – Atomic radius

17. D – Na

18. A – number of molecules

19. A – planting of trees

20. A – 8

21. B – The pressure in the balloon would be a sum of the partial pressures of H₂, He and N₂

22. A – X₂Y

23. D – Zinc

24. A – FeCl₂

25. A – Funnel

26. A – LiAlH₄

27. C – Brine

28. D – reduction

29. D – 44

30. B – an element

31. A – HCl

32. A – 2

33. B – empirical formula

34. B – is essential for healthy plant growth

35. D – 20 g

36. C – sugar cane

37. D – losing two electrons

38. D – the oxidation number of X increases

39. A – a cation

40. D – a basic oxide

41. A – the same subshell having equal energy

42. A – CₙH₂ₙ₊₁

43. D – HCl

44. C – poisonous

45. A – Zn

46. D – Combustion and neutralization

47. D – hydrolysis

48. C – an acid-base indicator

49. A – Carbon(IV) oxide

50. A – calcium oxide

COMPLETED
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SECTION A: ANSWER ALL QUESTIONS IN THIS SECTION

(1a)
(i) Suspension: Sand in water
(ii) Colloid: Fog

(1b)
An isoelectronic series is a group of atoms, ions, or molecules that have the same number of electrons but different nuclear charges.

(1ci)
Heat of formation is the enthalpy change when one mole of a compound is formed from its constituent elements in their standard states under standard conditions.

(1cii) Heat of combustion is the enthalpy change when one mole of a substance is completely burned in oxygen under standard conditions.

(1d)
Helium is preferred because it is non-flammable and chemically inert, whereas hydrogen is highly flammable and explosive, making helium safer for use.

(1e)
(i) CO₂: Linear
(ii) CH₄: Tetrahedral
(iii) NH₃: Trigonal pyramidal

(1f)
(i) Sulfur
(ii) Phosphorus

(1g)
(i) They form colored compounds
(ii) They have variable oxidation states
(iii) They act as good catalysts.

(1h)
(i) Aluminium (Al)
(ii) Sodium (Na)

(1i)
The atomic number is the number of protons in the nucleus of an atom of an element.

(1j)
(i) Covalent bond
(ii) Coordinate (dative covalent) bond
(iii) Ionic bond
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SECTION B: ANSWER THREE(3) QUESTIONS ONLY

(2a)
(i) M
(ii) O
(iii) R
(iv) O
(v) V
(vi) T

(2bi)
A saturated solution is a solution containing the maximum amount of solute that can dissolve in a given amount of solvent at a particular temperature.

(2bii)
Given:
-Volume of saturated solution = 60cm³
-Mass of KNO₃ = 15.6g

Molar mass of KNO₃ = 39 + 14 + (16 × 3)
= 39 + 14 + 48 = 101gmol⁻¹

Number of moles of KNO₃ = Mass / Molar mass
= 15.6 / 101 = 0.154mol

60cm³ = 60/1000dm³
= 0.060 dm³

Concentration (solubility) = Moles / Volume
= 0.154 / 0.060
= 2.57mol dm⁻³

(2ci)
(i) Prepare an aqueous solution of lead(II) nitrate, Pb(NO₃)₂(aq).
(ii) Add dilute hydrochloric acid, HCl(aq), to the solution.
(iii) A white precipitate of lead(II) chloride forms.
(iv) Filter the mixture to collect the precipitate.
(v) Wash the precipitate with distilled water and dry it.

(2cii)
Pb(NO₃)₂(aq) + 2HCl(aq) –> PbCl₂(s) + 2HNO₃(aq)

(2di)
This is because a completely filled 3d subshell (3d¹⁰) is more stable than a partially filled 3d⁹ subshell. Therefore, one electron from the 4s orbital is transferred to the 3d orbital.

(2dii)
(i) +2 (as in FeCl₂)
(ii) +3 (as in FeCl₃)

(2diii)
The Haber Process for the manufacture of ammonia.
N₂(g) + 3H₂(g) ⇌ 2NH₃(g)
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(3ai)
Enthalpy of neutralization is the heat change when one mole of water is formed by the reaction between an acid and a base in dilute solution.

(3aii)
H⁺(aq) + OH⁻(aq) –> H₂O(l)

(3bi)
W – Sodium propanoate (C₂H₅COONa)
X – Ethyl propanoate (C₂H₅COOC₂H₅)
Y – Propan-1-ol (C₃H₇OH)
Z – Propene (C₃H₆)

(3bii)
CH₃CH₂COOH + CH₃CH₂OH ⇌ CH₃CH₂COOCH₂CH₃ + H₂O

(3ci)
An acid anhydride is an oxide that reacts with water to produce the corresponding acid.

(3cii)
(i) SO₃
(ii) N₂O₅
(iii) CO₂

(3di)
(i) Aluminium oxide is dissolved in molten cryolite.
(ii) The mixture is electrolysed in a steel tank lined with carbon.
(iii) Graphite rods serve as the anodes.
(iv) Al³⁺ ions gain electrons at the cathode to form molten aluminium.
(v) The molten aluminium collects at the bottom and is tapped off periodically.

(3dii)
Graphite

(3diii)
The oxygen produced at the anode reacts with the carbon (graphite) anode, forming carbon dioxide, so the anode is gradually burnt away and must be replaced.

(3ei)
Using Graham’s law:
Rate of diffusion of X / Rate of diffusion of O₂ = √(Mr of O₂ / Mr of X)
2 = √(32 / Mr of X)
4 = 32 / Mr of X
Mr of X = 8

(3eii)
Volume of X = 5 dm³
Molar volume at s.t.p = 22.4 dm³ mol⁻¹
Number of moles = 5 / 22.4
= 0.223 mol
Mass = moles × molar mass
= 0.223 × 8
= 1.79g
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(4ai)
Hydrogen gas is tested by bringing a lighted splint to the gas. It produces a squeaky pop sound, confirming the presence of hydrogen.

(4aii)
(i) It is used as a fuel in rockets
(ii) It is used in the manufacture of ammonia (Haber process)
(iii) It is used in the hydrogenation of vegetable oils to make margarine

(4aiii)
(I) Hydrogen + sodium metal:
2Na + H₂ –> 2NaH

(II) Hydrogen + copper(II) chloride solution:
H₂ + CuCl₂ –> Cu + 2HCl

(III) Hydrogen + chlorine gas:
H₂ + Cl₂ –> 2HCl

(4bi)
(I) Tin in food cans:
Tin is used because it is non-toxic and resistant to corrosion, so it prevents food contamination.
(II) Copper in wires:
Copper is used because it has high electrical conductivity and is ductile.

(4bii)
(I) Iron ore: Haematite (Fe₂O₃)
(II) Tin ore: Cassiterite (SnO₂)

(4biii)
(I) Iron alloy: Steel
(II) Copper alloy: Brass

(4ci)
Coke

(4cii)
C + H₂O (steam) –> CO + H₂

(4ciii)
Water gas

(4di)
(I) Tin: Reduction of its oxide using carbon (smelting)
(II) Iron: Blast furnace reduction using carbon (coke)
(III) Aluminium: Electrolysis of molten aluminium oxide (Hall-Héroult process)

(4dii)
Used in the manufacture of aircraft bodies
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(5ai)
(I) Filtration
(II) Coagulation (flocculation)
(III) Aeration

(5aii)
(I) Chlorine
(II) Lime
(III) Iodine
(IV) Aluminium sulphate

(5bi)
(I) Concentrated HCl
(II) MnO₂

(5bii)
(I) Sodium chloride and sodium hypochlorite
(II) Bleaching powder (calcium oxychloride)

(5biii)
The products are used as bleaching agents for whitening clothes and removing stains.

(5ci)
Heating is required

(5cii)
NaCl(s) + H₂SO₄(l) –> NaHSO₄(s) + HCl(g)

(5ciii)
Aqueous silver nitrate solution (AgNO₃)

(5civ)
A white precipitate is formed.

(5cv)
Lead(II) chloride (PbCl₂)

(5di)
-Heat the solution to evaporate some water until it becomes saturated.
-Allow the hot saturated solution to cool slowly.
-Blue crystals of copper(II) sulphate separate out.
-Filter off the crystals and dry them between filter papers.

(5di)
(i) Copper
(ii) Tin.
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