If you’re preparing for WAEC Chemistry, this set of Most Repeated WAEC Chemistry Questions and Answers is here to help you revise smarter. It brings together the topics that often appear in exams, such as mole concept, atomic structure, acids and bases, electrolysis, organic chemistry, and basic calculations. The goal is to make your revision easier by giving you clear questions and answers you can study and practice with.
Most Repeated Chemistry WAEC Questions and Answers
Hydrogen chloride gas is best collected by
A. Upward delivery
B. Downward delivery
C. Over water
D. Fractional distillation
Answer: B
When dilute hydrochloric acid reacts with zinc, the gas evolved is
A. Oxygen
B. Carbon dioxide
C. Chlorine
D. Hydrogen
Answer: D
Which of the following is a product of complete combustion of hydrocarbons?
A. Carbon monoxide
B. Carbon dioxide and water
C. Carbon only
D. Hydrogen
Answer: B
The gas that turns limewater milky is
A. Carbon dioxide
B. Oxygen
C. Hydrogen
D. Nitrogen
Answer: A
In electrolysis of acidified water, the gas collected at the cathode is
A. Oxygen
B. Hydrogen
C. Chlorine
D. Nitrogen
Answer: B
The pH of a strong acid is usually
A. Above 7
B. Exactly 7
C. Below 7
D. 14
Answer: C
Which of the following metals reacts most vigorously with cold water?
A. Iron
B. Sodium
C. Copper
D. Silver
Answer: B
The ore of aluminium is
A. Bauxite
B. Haematite
C. Galena
D. Zinc blende
Answer: A
Fractional distillation of crude oil is based on differences in
A. Density
B. Boiling point
C. Solubility
D. Colour
Answer: B
Which of the following is a saturated hydrocarbon?
A. Ethene
B. Ethyne
C. Ethane
D. Benzene
Answer: C
The process of removing hardness of water by boiling is called
A. Filtration
B. Temporary hardness removal
C. Distillation
D. Sedimentation
Answer: B
A substance that speeds up a reaction without being used up is
A. Product
B. Catalyst
C. Reactant
D. Inhibitor
Answer: A
Most Repeated Chemistry WAEC Questions and Answers
Which gas is produced when ammonium compound reacts with sodium hydroxide?
A. Oxygen
B. Hydrogen
C. Ammonia
D. Chlorine
Answer: C
The method used to separate crude oil is
A. Filtration
B. Fractional distillation
C. Evaporation
D. Chromatography
Answer: B
Which of the following is an acidic oxide?
A. Na₂O
B. SO₂
C. CaO
D. MgO
Answer: B
The gas used in welding is
A. Nitrogen
B. Helium only
C. Carbon dioxide
D. Oxygen and acetylene
Answer: D
Which of the following is a base?
A. HCl
B. HNO₃
C. H₂SO₄
D. NaOH
Answer: D
The gas that extinguishes fire is
A. Oxygen
B. Carbon dioxide
C. Hydrogen
D. Nitrogen
Answer: B
Electrolysis of molten sodium chloride produces
A. Sodium and chlorine
B. Sodium and oxygen
C. Hydrogen and chlorine
D. Sodium and hydrogen
Answer: A
Which of the following is used to dry gases?
A. Water
B. Concentrated H₂SO₄
C. Limewater
D. Sodium chloride
Answer: B
Rusting of iron requires
A. Oxygen only
B. Water only
C. Oxygen and water
D. Carbon dioxide only
Answer: C
The functional group of alcohol is
A. –COOH
B. –OH
C. –CHO
D. –CO–
Answer: B
Which of the following is an alkali?
A. HCl
B. H₂SO₄
C. CH₃COOH
D. NaOH
Answer: D
The gas that burns with a pop sound is
A. Oxygen
B. Hydrogen
C. Chlorine
D. Carbon dioxide
Answer: B
The process of removing electrons is
A. Reduction
B. Neutralization
C. Oxidation
D. Hydrolysis
Answer: C
Which of the following is used to test for water?
A. Blue litmus paper
B. Anhydrous CuSO₄
C. Limewater
D. Starch solution
Answer: B.
Most Repeated Chemistry WAEC Questions and Answers
The formula of sulphuric acid is
A. HCl
B. HNO₃
C. H₂SO₄
D. CH₃COOH
Answer: C
Which of the following is a noble gas?
A. Oxygen
B. Argon
C. Nitrogen
D. Hydrogen
Answer: B
The gas that supports combustion is
A. Nitrogen
B. Ammonia
C. Carbon dioxide
D. Oxygen
Answer: D
Which of the following is used in soft drinks?
A. Oxygen
B. Carbon dioxide
C. Hydrogen
D. Nitrogen
Answer: B
The empirical formula of water is
A. H₂O
B. HO
C. H₂O₂
D. H₃O
Answer: A
Which of the following is a physical change?
A. Burning
B. Rusting
C. Melting of ice
D. Digestion
Answer: C
The number of moles in 24g of carbon (C = 12) is
A. 1
B. 2
C. 3
D. 4
Answer: B
The instrument used in electrolysis is
A. Voltmeter
B. Electrolytic cell
C. Ammeter
D. Thermometer
Answer: B
Which of the following is an oxidation reaction?
A. Gain of hydrogen
B. Loss of oxygen
C. Gain of oxygen
D. Loss of electrons only
Answer: C
The main component of natural gas is
A. Ethane
B. Methane
C. Propane
D. Butane
Answer: B
Which of the following is a polymer?
A. Ethene
B. Polyethene
C. Methane
D. Ethanol
Answer: B
The pH of pure water is
A. 0
B. 1
C. 14
D. 7
Answer: D
Most Repeated Chemistry WAEC Questions and Answers
Which of the following is used as fertilizer?
A. NaCl
B. NH₄NO₃
C. CaCO₃
D. CO₂
Answer: B
The gas that turns acidified potassium dichromate green is
A. Sulphur dioxide
B. Oxygen
C. Hydrogen
D. Nitrogen
Answer: A
Which of the following is a strong acid?
A. CH₃COOH
B. HCl
C. H₂CO₃
D. NH₄OH
Answer: B
The separation method for ink components is
A. Filtration
B. Decantation
C. Evaporation
D. Chromatography
Answer: D
Which of the following is an element?
A. Water
B. Air
C. Iron
D. Salt
Answer: C
The valency of chlorine is
A. 1
B. 2
C. 3
D. 4
Answer: A
Which gas is produced when acids react with carbonates?
A. Hydrogen
B. Oxygen
C. Carbon dioxide
D. Nitrogen
Answer: C
The process of adding hydrogen is
A. Oxidation
B. Reduction
C. Neutralization
D. Hydrolysis
Answer: B
Which of the following is used in fire extinguishers?
A. Oxygen
B. Carbon dioxide
C. Hydrogen
D. Nitrogen
Answer: B
The formula for methane is
A. CH₄
B. C₂H₆
C. C₃H₈
D. C₄H₁₀
Answer: A
Which of the following is a product of photosynthesis?
A. Oxygen
B. Carbon dioxide
C. Nitrogen
D. Hydrogen
Answer: A
The gas that relights a glowing splint is
A. Oxygen
B. Hydrogen
C. Carbon dioxide
D. Nitrogen
Answer: A
The process of heating a substance in absence of air is
A. Distillation
B. Calcination
C. Filtration
D. Crystallization
Answer: B
The bond in NaCl is
A. Covalent
B. Hydrogen
C. Metallic
D. Ionic
Answer: D
Most Repeated Chemistry WAEC Questions and Answers
The acid present in vinegar is
A. Citric acid
B. Acetic acid
C. Sulphuric acid
D. Nitric acid
Answer: B
Which of the following is a hydrocarbon?
A. CO₂
B. NaCl
C. CH₄
D. H₂O
Answer: C
The gas used in balloons is
A. Oxygen
B. Helium
C. Carbon dioxide
D. Nitrogen
Answer: B
The process of separating solid from liquid is
A. Filtration
B. Chromatography
C. Electrolysis
D. Cracking
Answer: A
The law of conservation of mass was proposed by
A. Dalton
B. Lavoisier
C. Rutherford
D. Bohr
Answer: B
Which of the following is a reducing agent?
A. Oxygen
B. Chlorine
C. Hydrogen
D. Nitrogen
Answer: C
The gas used for ripening fruits is
A. Oxygen
B. Ethene
C. Methane
D. Carbon dioxide
Answer: B
The process of breaking large hydrocarbons is
A. Cracking
B. Fractionation
C. Distillation
D. Condensation
Answer: A
The number of electrons in the outermost shell is called
A. Atomic number
B. Valency
C. Mass number
D. Isotope number
Answer: B
The gas that turns limewater milky is
A. Oxygen
B. Nitrogen
C. Hydrogen
D. Carbon dioxide
Answer: D
The symbol of potassium is
A. P
B. Pt
C. K
D. Po
Answer: C
The gas that supports respiration is
A. Nitrogen
B. Oxygen
C. Carbon dioxide
D. Helium
Answer: B
The process of separating a solid dissolved in liquid is
A. Evaporation
B. Filtration
C. Distillation
D. Chromatography
Answer: A
Mostly Repeated Chemistry WAEC Questions On theories
1. Explain the difference between physical change and chemical change.
A physical change does not form a new substance and is usually reversible (e.g., melting ice), while a chemical change produces a new substance and is often irreversible (e.g., burning wood).
2. Define atomic number and mass number.
Atomic number is the number of protons in an atom, while mass number is the sum of protons and neutrons in the nucleus.
3. State three differences between elements and compounds.
Elements consist of one type of atom, cannot be broken down chemically, and have unique symbols; compounds consist of two or more elements chemically combined, can be decomposed chemically, and have chemical formulas.
4. What is electrolysis?
Electrolysis is the chemical decomposition of a compound in molten or aqueous form by the passage of electric current.
5. Explain the term molar mass.
Molar mass is the mass of one mole of a substance expressed in grams per mole (g/mol).
6. State Boyle’s law.
Boyle’s law states that the volume of a fixed mass of gas is inversely proportional to its pressure at constant temperature.
7. What is an acid according to Arrhenius?
An acid is a substance that produces hydrogen ions (H⁺) when dissolved in water.
8. Calculate the percentage composition of oxygen in water (H₂O). [H = 1, O = 16]
Molar mass of H₂O = (1 × 2) + 16 = 18 g/mol
Mass of oxygen = 16 g
Percentage of oxygen = (16 ÷ 18) × 100
= 88.9% (approximately)
Answer = 88.9% oxygen
9. State two properties of ionic compounds.
They have high melting and boiling points and conduct electricity when molten or dissolved in water.
10. What is a catalyst?
A catalyst is a substance that increases the rate of a chemical reaction without being consumed.
11. Explain the concept of pH.
pH is a measure of the acidity or alkalinity of a solution, ranging from 0 to 14.
12. State the law of conservation of mass.
Matter cannot be created or destroyed in a chemical reaction; the total mass of reactants equals the total mass of products.
13. What is a homologous series?
A homologous series is a family of organic compounds with similar chemical properties, same general formula, and successive members differing by CH₂.
14. A solution contains 5 g of NaOH dissolved in 250 cm³ of solution. Calculate its concentration in g/dm³.
Answer: Convert 250 cm³ to dm³: 250 ÷ 1000 = 0.25 dm³
Concentration = mass ÷ volume
= 5 ÷ 0.25 = 20 g/dm³
15. Explain the difference between exothermic and endothermic reactions.
Exothermic reactions release heat, while endothermic reactions absorb heat.
16. What is meant by chemical equilibrium?
Chemical equilibrium is a state where the forward and backward reactions occur at the same rate, resulting in no net change.
17. State two uses of chlorine.
Chlorine is used in water purification and in the manufacture of bleach and disinfectants.
18. Define isomerism.
Isomerism is the existence of compounds with the same molecular formula but different structural arrangements.
19. Calculate the number of moles in 11 g of carbon dioxide (CO₂). [C = 12, O = 16]
Molar mass of CO₂ = 12 + (16 × 2) = 44 g/mol
Number of moles = mass ÷ molar mass
= 11 ÷ 44 = 0.25 mol
20. Explain the term valency.
Valency is the combining capacity of an atom, determined by the number of electrons it can lose, gain, or share.
These most repeated WAEC Chemistry questions and answers are meant to guide your revision and help you focus on what really matters in the exam. Go through them regularly, test yourself, and make sure you understand the concepts behind the answers, not just memorizing them. Consistent practice is what will give you confidence on exam day.
RELATED ARTICLES