WAEC GCE 2025 CHEMISTRY ANSWERS (OBJ & ESSAY)

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CHEMISTRY OBJ!

NOTE:Please trace it from your system. The options are being reshuffled, so you might see “1” as any number, trace quickly. You could also see option A as option C, B, or D. Use the answers in words and trace carefully to avoid errors. 🙏

1: (B) hygroscopic

2; (A) Fructose

3; (C) molecule

4; (C) 2, 2, 4-trimethylpentane.

5; (A) working capital.

6; (C) sublimation.

7; (A) CCI₄

8; (D) 0.040 moldm-³

9; (C) Fe(s) +Cl_²(g) FeCl-²

10; (B) is attacked by moist air.

11: (B) N₂(g) + O₂(g)—>2NO(g)

12: (A) 19 protons, 19 electrons and 20 neutrons

13: (D) HNO₃

14: (A) in which large hydrocarbon molecules are broken into smaller units

15: (A) AgF

16: (B) +6

17: (B) ΔH₁ < ΔH₂

18: (C) neutral

19: (D) CuO

20; (D) 1.00 mol

21: (B) are widely spaced.

22: (A) activation energy

23: (C) less dissociated in solution.

24: (B) almost the entire mass of the atom is in the nucleus.

25: (B) 0.05 mol/dm³

26: (B) occurs in gases.

27: (D) Displacement.

28: (D) paraffin oil.

29: (D) Hex-1-ene.

30: (B) Na, Mg, Al.

31: (B) Alkaline earth metals

32: (C) I-

33: (C) saturated solution

34: (A) Iron

35: (C) Cl,Cl-Cl+

36: (D) Atomic number

37: (C) cracking

38: (A) Na²CO³

39: (C) Si

40: (B) C + e – —-> C-

41: (A) electron

42: (C) solubility

43: (D) tertiary alkanol

44: (C) H²CO³

45: (B) neutral oxides

46: (B) Separation of sand from water

47: (D) rise in boiling point and fall in melting point.

48: (A) hardness

49: (D) melting

50: (A) esterification

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(1a)
(i) Law of Conservation of Mass
(ii) Law of Definite (Constant) Proportions
(iii) Law of Multiple Proportions

(1b)
A standard solution is a solution whose concentration is accurately known.

(1c)
(i) Iodine molecules have stronger intermolecular forces (van der Waals forces) than bromine molecules.
(ii) Iodine has a larger molecular size and mass than bromine.
(iii) More energy is required to separate iodine molecules, making it a solid, while bromine needs less energy and remains a liquid.

(1d)
Dalton’s Law states that the total pressure of a mixture of non reacting gases is equal to the sum of the partial pressures of the individual gases.

(1e)
(PICK ANY TWO)
(i) Intermolecular forces exist between gas molecules.
(ii) Gas particles have finite volume.
(iii) Collisions between gas particles are not perfectly elastic.

(1fi)
(PICK ANY ONE)
(i) It is largely covalent in nature.
(ii) It does not contain free or mobile ions.
(iii) It involves electron sharing instead of electron transfer.
(iv) The ions are strongly held and cannot move freely.

(1fii)
(PICK ANY TWO)
(i) High charge density of Al³⁺ ion.
(ii) Small ionic radius of aluminium.
(iii) Strong polarization of chloride ions.
(iv) Formation of covalent molecules instead of ionic ions.
(v) Electron sharing forms a molecular structure

(1gi)
Sodium (Na)

(1gii)
Phosphorus (P)

(1h)
(PICK ANY TWO)
(i) Manufacture of plastics (e.g. polyethene).
(ii) Production of synthetic rubber.
(iii) Used as raw materials in petrochemical industries.
(iv) Manufacture of alcohols (e.g. ethanol from ethene).
(v) Used in making detergents.

(1i)
=SIMILARITY=
(i) Both involve sharing of electrons between atoms.

=DIFFERENCE=
(i) In a covalent bond, each atom contributes electrons, while in a dative bond the shared pair is supplied by only one atom.

(1j)
(i) Oxidizing agent: Cl₂
(ii) Product of reduction: Cl⁻
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(2ai)
A transition element is a d-block element that has an atom or ion with an incomplete d-subshell.

(2aii)
(α) Coloured compound formation: Transition metals form coloured compounds due to d-d electron transitions within the partially filled d-orbitals when they absorb certain wavelengths of light.

(β) Complex ion formation: Transition metals can form complex ions by bonding with ligands due to their ability to use empty d orbitals for coordinate covalent bonding.

(γ) Catalytic abilities: Transition metals act as catalysts because they can change oxidation states easily and provide a surface for reactants to adsorb, lowering activation energy.

(2bi)
(α) Potassium and oxygen: K₂O
(β) Sulphur and aluminium: Al₂S₃
(γ) Nitrogen and magnesium: Mg₃N₂

(2bii)
K₂O: Potassium oxide
Al₂S₃: Aluminium sulphide
Mg₃N₂: Magnesium nitride

(2ci)
(α) Atom
An atom is the smallest particle of an element that can exist alone and retains the chemical properties of that element; it consists of a nucleus (protons and neutrons) surrounded by electrons.

(β) Molecule
A molecule is a neutral group of two or more atoms chemically bonded together, representing the smallest particle of a substance that can exist while retaining its chemical identity.

(γ) Ion
An ion is an atom or group of atoms that has acquired a net electrical charge by losing or gaining electrons.

(2cii)
Atom: Cl (chlorine atom)
Molecule: Cl₂ (chlorine molecule)
Ion: Cl⁻ (chloride ion)
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(3ai)
Hydrochloric acid with zinc metal
Zn + 2HCl -> ZnCl₂ + H₂

(ii) Hydrochloric acid with zinc oxide
ZnO + 2HCl -> ZnCl₂ + H₂O

(iii) Hydrochloric acid with zinc trioxocarbonate(IV) (“zinc trioxocarbonate(IV)” = zinc carbonate, ZnCO3)
ZnCO₃ + 2HCl -> ZnCl₂ + CO₂ + H₂O

(3b)
Moles of sodium (Na):
moles Na = (4.6g) /23g mol⁻¹ = 0.2 mol

Number of atoms in 4.6 g Na:
atoms = 0.2 mol × 6.02 × 10²³ atoms mol⁻¹ = 1.204 × 10²³ atoms

Moles of H₂ required = (1.204 × 10²³)/ (6.02 × 10²³) = 0.2 mol.

molar mass of H₂ = 2g mol⁻¹.
mass of  H₂ = 0.2mol × 2g mol⁻¹ = 0.4 g

(3c)
(i) Hydration (addition of water)
(ii) Concentrated H₂SO₄(sulphuric acid)
(iii) Presence of acid catalyst and suitable temperature
(iv) Propene: CH₃-CH=CH₂
Product C₃H₈O (major): CH₃-CH(OH)-CH₃

(v) Chemical equation (hydration, showing catalyst):
CH₃CH=CH₂ + H₂O —> CH₃CH(OH)CH₃ (H₂SO₄ to be written at the top of the arrow)

(vi) 2‑Propanol (propan‑2‑ol)
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(5a)
(i)2NaOH + Cl_2 NaCl + NaClO + H2O
(ii)Cl_2 + H2O HOCl + HCl

(5aii)
(I)Chlorine: Gas
(II) Fluorine: Gas
(III) Astatine: Solid

(5aiii)
The strength of Van der Waal’s forces increases down the group due to the increase in atomic size and polarizability.

(5bi)
(i)Low temperature
(ii)High pressure

(5bii)
The choice of conditions is governed by Le Chatelier’s principle, which states that a system at equilibrium will adjust to counteract any changes in concentration, temperature, or pressure.

(5biii)
(i) For fertilizer production.
(ii)For cleaning agent
(iii)For Industrial applications

(5ci)
(i)High electrical conductivity
(ii)Ductility
(iii)Resistance to corrosion

(5cii)
(i)Oxidizing properties.
(ii)Antimicrobial activity.

(5di)
(i)For Construction.
(ii)It is use as an food and nutrition for humans.
(iii)It is use for manufacturing  products, including paper, glass, and ceramics.

(5dii)
(i)Coke
(ii)Coal tar

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