Chemistry WAEC 2023 Past Questions (Objective & Theory)
Attempt this paper, then reveal the answers to mark yourself.
Section A — Objective
Question 1
Which of the following is a physical change?
A. Melting of ice
B. Rusting of iron
C. Burning of wood
D. Fermentation of sugar
Answer: A. Melting is a physical change (no new substance). Rusting, burning and fermentation are chemical changes.
Question 2
An element with 17 protons and 18 neutrons has a mass number of
A. 35
B. 17
C. 18
D. 1
Answer: A. Mass number = protons + neutrons = 17 + 18 = 35 (chlorine-35).
Question 3
The substance that speeds up a reaction without being used up is a
A. Catalyst
B. Solvent
C. Reactant
D. Precipitate
Answer: A. A catalyst speeds up a reaction without being consumed.
Question 4
The pH of a neutral solution is
A. 0
B. 1
C. 7
D. 14
Answer: C. A neutral solution has pH = 7 (e.g. pure water).
Question 5
The separation of a mixture by passing it through a porous material is called
A. Filtration
B. Distillation
C. Evaporation
D. Chromatography
Answer: A. Filtration separates a solid from a liquid using a porous material (filter paper).
Question 6
The gain of oxygen or loss of electrons in a reaction is called
A. Oxidation
B. Reduction
C. Neutralisation
D. Hydrolysis
Answer: A. Oxidation is the gain of oxygen or loss of electrons. Reduction is the loss of oxygen or gain of electrons.
Section B — Theory
Question 1 — Theory
State the products at the anode and cathode during the electrolysis of dilute sodium chloride solution.
Answer: At the cathode, hydrogen gas is produced; at the anode, oxygen gas is produced (in dilute solution, OH⁻ is discharged in preference to Cl⁻).
Question 2 — Theory
Define isotopes and give one example.
Answer: Isotopes are atoms of the same element with the same atomic number but different mass numbers (different neutron numbers). Example: carbon-12 and carbon-14.
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