WAEC Chemistry Past Questions (2025): Complete Guide with Answers
The West African Examinations Council (WAEC) Chemistry exam is one of the most important subjects for science students across West Africa. It plays an important role in determining eligibility for higher education, especially for courses like Medicine, Engineering, Pharmacy, and other science related fields.
One of the most effective ways to prepare for this exam is by studying WAEC Chemistry past questions as much as you can. These questions not only help you understand the exam pattern but also reveal frequently tested topics, marking schemes, and examiner expectations.
In this comprehensive guide, we will explore the importance of WAEC Chemistry past questions, how to use those questions effectively, and provide fully answered 2025 WAEC Chemistry theory questions (excluding practicals) to help you prepare better.
Why WAEC Chemistry Past Questions Are Important
Studying past questions offers several advantages:
1. Familiarity with Exam Format
WAEC Chemistry exams typically consist of multiple-choice (Objective) and theory sections. Practicing past questions helps you understand how questions are structured.
2. Identification of Repeated Topics
Topics such as atomic structure, chemical bonding, organic chemistry, and electrolysis frequently appear in WAEC exams, make sure you chew those topics very well my friend.
3. Time Management Skills
Working with past questions helps you learn how to allocate time effectively during the exam. I seriously practiced this in the year 2020 when I was preparing for my WAEC exam and it really helped me during the exam.
4. Improved Confidence
The more questions you solve, the more confident you become. Imagine you coming across some specific questions which you had solved two or three times before, it’s going to be a quick chop and leave for you.
WAEC Chemistry 2025 Past Questions and Answers (Theory)
Below are sample WAEC 2025 Chemistry theory questions with complete answers, designed based on WAEC standards and syllabus. This might not be the exact question but I promise you these are the format in which WAEC chemistry past questions are:
Question 1
(a) Define the following terms:
(i) Atom
(ii) Molecule
(iii) Ion
(b) State three differences between compounds and mixtures.
Answer:
(a)
(i) Atom: The smallest particle of an element that retains the chemical properties of that element.
(ii) Molecule: The smallest unit of a substance that can exist independently and retains the chemical properties of that substance.
(iii) Ion: A charged particle formed when an atom or group of atoms loses or gains electrons.
(b) Differences between compounds and mixtures:
Compounds are chemically combined, while mixtures are physically combined.
Compounds have fixed compositions, whereas mixtures have variable compositions.
Compounds have definite melting and boiling points; mixtures do not.
Question 2
(a) Explain the term electrolysis.
(b) State Faraday’s first law of electrolysis.
(c) Calculate the mass of copper deposited when a current of 2A flows for 30 minutes through a copper(II) sulfate solution.
(Electrochemical equivalent of copper = 0.00033 g/C)
Answer:
(a)
Electrolysis is the chemical decomposition of an electrolyte by passing an electric current through it.
(b)
Faraday’s first law states that the mass of a substance deposited during electrolysis is directly proportional to the quantity of electricity passed through the electrolyte.
(c)
Given:
Current (I) = 2A
Time (t) = 30 minutes = 1800 seconds
Charge (Q) = I × t
Q = 2 × 1800 = 3600 C
Mass deposited = Z × Q
= 0.00033 × 3600
= 1.188 g
Question 3
(a) What is a homologous series?
(b) List three characteristics of members of a homologous series.
(c) Write the general formula for alkanes and give the first three members.
Answer:
(a)
A homologous series is a group of organic compounds with the same functional group and similar chemical properties.
(b) Characteristics:
Same functional group
Similar chemical properties
Gradual change in physical properties
(c)
General formula: CnH₂n+2
First three members:
Methane (CH₄)
Ethane (C₂H₆)
Propane (C₃H₈)
Question 4
(a) Define pH.
(b) State the pH range for:
(i) Acidic solutions
(ii) Neutral solutions
(iii) Alkaline solutions
(c) Explain why strong acids have low pH values.
Answer:
(a)
pH is a measure of the acidity or alkalinity of a solution.
(b)
(i) Acidic: pH 0–6
(ii) Neutral: pH 7
(iii) Alkaline: pH 8–14
(c)
Strong acids completely ionize in water, producing a high concentration of hydrogen ions (H⁺), which results in a low pH.
Question 5
(a) State the law of conservation of mass.
(b) Balance the equation:
Fe + H₂O → Fe₃O₄ + H₂
(c) Calculate the molar mass of H₂SO₄.
Answer:
(a)
The law states that matter can neither be created nor destroyed in a chemical reaction.
(b)
Balanced equation:
3Fe + 4H₂O → Fe₃O₄ + 4H₂
(c)
H₂SO₄ = (2×1) + (32) + (4×16)
= 2 + 32 + 64
= 98 g/mol
Question 6
(a) Define oxidation and reduction.
(b) Identify the oxidizing and reducing agents in the reaction:
Zn + Cu²⁺ → Zn²⁺ + Cu
Answer:
(a)
Oxidation: Loss of electrons
Reduction: Gain of electrons
(b)
Zinc loses electrons → oxidized → reducing agent
Copper ion gains electrons → reduced → oxidizing agent
Question 7
(a) Explain the term chemical equilibrium.
(b) State Le Chatelier’s principle.
(c) Predict the effect of increasing pressure on this reaction:
N₂ + 3H₂ ⇌ 2NH₃
Answer:
(a)
Chemical equilibrium is a state where the forward and reverse reactions occur at equal rates.
(b)
Le Chatelier’s principle states that a system at equilibrium will adjust to oppose any change imposed on it.
(c)
Increasing pressure favors the side with fewer gas molecules → ammonia (NH₃) production increases.
Question 8
(a) Define isomerism.
(b) Give two types of isomerism.
(c) Draw structures of two isomers of C₄H₁₀.
Answer:
(a)
Isomerism is the existence of compounds with the same molecular formula but different structures.
(b)
Structural isomerism
Geometrical isomerism
(c)
Butane: CH₃–CH₂–CH₂–CH₃
Isobutane:
CH₃
|
CH₃–CH–CH₃
Question 9
(a) What is hardness of water?
(b) State two types of hardness.
(c) Mention one method of removing each type.
Answer:
(a)
Hardness of water is the inability of water to lather easily with soap.
(b)
Temporary hardness
Permanent hardness
(c)
Temporary hardness: Boiling
Permanent hardness: Ion exchange method
Question 10
(a) Define catalyst.
(b) State two characteristics of catalysts.
(c) Give one example of a catalyst used in industry.
Answer:
(a)
A catalyst is a substance that speeds up a chemical reaction without being consumed.
(b)
Not used up in the reaction
Increases reaction rate
(c)
Iron is used as a catalyst in the Haber process.
How to Use WAEC Chemistry Past Questions Effectively
I wouldn’t have wanted to say this here but I just need to say it to boost your confidence too, during our time myself and some of my friends were masters in answering past questions and I believe you can do it too.
To get the best results ensure to:
- Study topic by topic
- Practice under exam conditions
- Check marking schemes
- Revise weak areas consistently
Common Topics in WAEC Chemistry Past Questions
Focus on these high frequency topics like:
Atomic structure
Chemical bonding
Organic chemistry
Electrolysis
Acids, bases, and salts
Gas laws
Frequently Asked Questions (FAQ’s)
Let me also quickly drop some Objective questions which are likely to surface again for you to learn them: I’m going to answer many and hint others.
How many moles of copper would be deposited by passing 1 Faraday through CuCl₂ solution?
Very common electrolysis question
How many grams of NaOH are needed to produce 100 cm³ of 0.20 mol/dm³ solution?
This is a Standard concentration question
What is the empirical formula of a compound with 40% C, 6.7% H, 53.3% O?
Empirical formula calcs show up yearly
Which gas is evolved when a carbonate reacts with an acid?
Answer: CO₂
What is the relative molar mass of a gaseous hydrocarbon if vapour density = 15?
Vapour density = RMM/2 → RMM = 30
Which of these gases is NOT acidic: SO₃, NO₂, CO₂, CO?
Answer: CO is neutral
When magnesium reacts with oxygen, is heat absorbed or evolved?
Answer: Evolved, exothermic
What is the valency of phosphorus in PCl₃?
Answer: 3
State Le Chatelier’s Principle
Big theory question for Paper 2
What is electrolysis?
When you define this also include the application
How many atoms are present in 2.5 moles of a triatomic gas?
Uses Avogadro’s number
Which substance is a non-electrolyte: H₂SO₄, CH₃COOH, C₆H₁₂O₆, NH₄Cl?
Answer: C₆H₁₂O₆ glucose
What is the oxidation number of sulfur in H₂SO₃?
Answer: +4
What products are formed at anode/cathode during electrolysis of dilute NaCl?
Answer: O₂ at anode, H₂ at cathode
What is the molecular formula if empirical formula is CH₂ and molar mass = 42?
Answer: C₃H₆
You can also check out some carefully written articles on WAEC just for you:
- WAEC 2026 Chemistry Syllabus
- WAEC Syllabus for Civic Education 2026
- WAEC Mathematics Syllabus 2026/2027 Fully Explained
- WAEC 2026 English Language Syllabus
- When Will WAEC 2026 Result Be Out? See Latest Update Here
- How to Pass WAEC 2026 in One Sitting (Proven Guide)
- WAEC 2026 Biology Syllabus [Science]
- WAEC 2026 Syllabus for Agriculture
- 2026 WAEC Geography Syllabus (Complete Guide for Students)
Conclusion
WAEC Chemistry past questions remain one of the most reliable tools for exam preparation. By studying them consistently and understanding the answers, students can significantly improve their performance.
The 2025 theory questions and answers provided above reflect the standard expected by WAEC examiners. With proper practice, dedication, and smart study techniques, success in WAEC Chemistry is achievable.