WAEC & NECO Chemistry Past Questions and Answers (2020–2024)

Using Chemistry past questions is one of the smartest ways to prepare for WAEC and NECO. This guide gives you more than 50 exam-style questions with full answers and simple explanations to help you understand important Chemistry ideas and to see how examiners set their questions.

Why Chemistry Past Questions Help You Score High

Many SS3 students in Nigeria fear Chemistry because of calculations, equations and strange names. But WAEC and NECO repeat the same ideas again and again. When you solve past questions, you:

• See the most tested topics and know where to focus.
• Understand how questions are asked and how marks are shared.
• Practise how to write answers the way examiners want.
• Reduce fear, because questions look familiar on exam day.

All questions below are written in simple English for Nigerian SS3 students and are arranged by key topics.

WAEC Chemistry Past Questions and Answers (2020–2024)

The following WAEC-style questions cover: atomic structure and bonding, acids, bases and salts, organic chemistry, electrochemistry, chemical equilibrium, rates of reaction, periodic table and periodicity, and metals and non-metals.

Section A: Atomic Structure, Periodic Table and Bonding (WAEC Questions 1–12)

WAEC Question 1 (Atomic number and mass number)
An element X has 17 protons and 18 neutrons.

1. Write the nuclear symbol of X.
2. State the number of electrons in a neutral atom of X.

Answer:
1. Nuclear symbol: ³⁵₁₇Cl
2. Number of electrons: 17

Explanation:
Atomic number = number of protons = 17. Mass number = protons + neutrons = 17 + 18 = 35. The element with atomic number 17 is chlorine (Cl). In a neutral atom, number of electrons = number of protons, so electrons = 17.

WAEC Question 2 (Electronic configuration and position in periodic table)
Write the full electronic configuration of magnesium and state the group and period it belongs to in the periodic table.

Answer:
Electronic configuration: 1s² 2s² 2p⁶ 3s² (or 2, 8, 2)
Group: Group 2
Period: Period 3

Explanation:
Magnesium has atomic number 12, so it has 12 electrons arranged as 2, 8, 2. Two electrons in the outer shell means Group 2. It has three main shells, so it is in Period 3.

WAEC Question 3 (Isotopes)
(a) What are isotopes?
(b) Give one use of isotopes in medicine.

Answer:
(a) Isotopes are atoms of the same element with the same atomic number but different mass numbers.
(b) Radioactive isotopes are used to treat cancer (radiotherapy) or as tracers in medical scans.

Explanation:
Isotopes have the same number of protons but different numbers of neutrons. Because some are radioactive, they can be used to kill cancer cells or trace blood flow in the body.

WAEC Question 4 (Ionic bonding)
Explain briefly how sodium and chlorine atoms combine to form sodium chloride.

Answer:
Sodium donates one electron to chlorine to form Na⁺ and Cl⁻ ions, which attract each other to form NaCl.

Explanation:
Sodium (2, 8, 1) loses one electron to form Na⁺. Chlorine (2, 8, 7) gains one electron to form Cl⁻. The strong electrostatic attraction between the oppositely charged ions gives an ionic bond.

WAEC Question 5 (Covalent bonding)
(a) Define a covalent bond.
(b) State one property of covalent compounds.

Answer:
(a) A covalent bond is a bond formed when two atoms share one or more pairs of electrons.
(b) Many covalent compounds have low melting and boiling points and are gases or liquids at room temperature.

Explanation:
Covalent compounds consist of separate molecules. Forces between the molecules are weak, so little energy is needed to separate them.

WAEC Question 6 (Periodic trends – atomic radius)
State what happens to the atomic radius of elements across a period from left to right, and explain why.

Answer:
Atomic radius decreases across a period from left to right.

Explanation:
Across a period, more protons are added to the nucleus and more electrons are added to the same shell. The increased nuclear charge pulls the electrons closer, so atomic size reduces.

WAEC Question 7 (Periodic trends – ionization energy)
How does first ionization energy generally change down a group in the periodic table? Give one reason for this trend.

Answer:
First ionization energy decreases down a group.

Explanation:
Down a group, atoms have more shells. Outer electrons are farther from the nucleus and are more shielded by inner shells, so they are removed more easily and less energy is needed.

WAEC Question 8 (Valency and bonding)
Phosphorus has atomic number 15. State its valency in:
(a) PCl₃
(b) PCl₅

Answer:
(a) Valency of P in PCl₃ = 3
(b) Valency of P in PCl₅ = 5

Explanation:
In PCl₃, phosphorus combines with three chlorine atoms, so valency is 3. In PCl₅, it combines with five chlorine atoms, so valency is 5.

WAEC Question 9 (Electronic configuration and group)
An element Y has electronic configuration 2, 8, 7.
(a) To which group does Y belong?
(b) Is Y a metal or a non-metal?

Answer:
(a) Group: Group 17 (Group VII)
(b) Y is a non-metal (a halogen)

Explanation:
Seven electrons in the outer shell means Group 17. Elements in this group are non-metals called halogens.

WAEC Question 10 (Relative atomic mass from isotopes)
Chlorine exists mainly as two isotopes: ³⁵Cl (75%) and ³⁷Cl (25%). Calculate the relative atomic mass of chlorine.

Answer:
Relative atomic mass, Ar(Cl) = 35.5

Explanation:
Ar = (35 × 75/100) + (37 × 25/100) = 26.25 + 9.25 = 35.5.

WAEC Question 11 (Types of bonding)
State the main type of bonding present in:
(a) Sodium metal
(b) Sodium chloride crystal
(c) Oxygen molecule (O₂)

Answer:
(a) Sodium metal – metallic bonding
(b) Sodium chloride – ionic (electrovalent) bonding
(c) Oxygen molecule – covalent bonding

Explanation:
Metals have a lattice of positive ions and a “sea” of delocalized electrons (metallic bond). Ionic compounds have attraction between positive and negative ions. Covalent molecules share electrons between atoms.

WAEC Question 12 (Noble gases)
Why are noble gases like neon and argon generally unreactive?

Answer:
They have completely filled outer electron shells, so they are stable and do not easily gain or lose electrons.

Explanation:
A full outer shell gives a stable electronic configuration, so noble gases seldom form compounds.

Section B: Acids, Bases and Salts (WAEC Questions 13–20)

WAEC Question 13 (Arrhenius definition)
(a) Define an Arrhenius acid.
(b) Define an Arrhenius base.

Answer:
(a) An Arrhenius acid is a substance that produces H⁺ ions in aqueous solution.
(b) An Arrhenius base is a substance that produces OH⁻ ions in aqueous solution.

Explanation:
For example, HCl(aq) → H⁺(aq) + Cl⁻(aq); NaOH(aq) → Na⁺(aq) + OH⁻(aq).

WAEC Question 14 (Neutralization)
Hydrochloric acid reacts with sodium hydroxide as shown:
HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)
(a) What type of reaction is this?
(b) State one everyday use of this reaction.

Answer:
(a) It is a neutralization reaction.
(b) Used to treat excess acid in the stomach using antacids (or to neutralize acidic soil using lime).

Explanation:
In neutralization, an acid reacts with a base to form salt and water. H⁺ from the acid combines with OH⁻ from the base to form water.

WAEC Question 15 (Strong and weak acids)
Explain the difference between a strong acid and a weak acid, giving one example of each.

Answer:
A strong acid ionizes completely in water (e.g. HCl), while a weak acid ionizes only partially (e.g. CH₃COOH).

Explanation:
In solution, strong acids produce many H⁺ ions; weak acids produce fewer H⁺ ions because not all molecules ionize.

WAEC Question 16 (pH and indicators)
A solution has pH = 2.5.
(a) Is the solution strongly acidic, weakly acidic, neutral, weakly basic or strongly basic?
(b) What colour will blue litmus paper show in the solution?

Answer:
(a) The solution is strongly acidic.
(b) Blue litmus paper turns red.

Explanation:
On the pH scale (0–14), values less than 7 are acidic; values close to 0 show strong acids. Acids turn blue litmus red.

WAEC Question 17 (Salt preparation – titration)
Describe briefly how you would prepare a pure dry sample of sodium chloride crystals from dilute hydrochloric acid and sodium hydroxide solution.

Answer (outline):
Titrate the acid with the base using an indicator to find the exact volumes, repeat without indicator, then evaporate the solution and crystallize the salt.

Explanation (steps):
1. Put a measured volume of NaOH into a conical flask and add a few drops of phenolphthalein or methyl orange.
2. Run in dilute HCl from a burette until the indicator just changes colour (end point). Note the volume of acid used.
3. Repeat using the same volumes of NaOH and HCl but without indicator.
4. Evaporate the solution gently to concentrate and allow to cool for crystals to form.
5. Filter and dry the crystals between filter papers.

WAEC Question 18 (Types of salts)
(a) What is a basic salt?
(b) Give one example of a basic salt.

Answer:
(a) A basic salt is a salt that still contains replaceable hydroxide (OH⁻) ions.
(b) Example: basic copper(II) carbonate, CuCO₃.Cu(OH)₂.

Explanation:
Basic salts are formed when a base is not completely neutralized by an acid and still contains OH⁻ in the crystal.

WAEC Question 19 (Hydrolysis of salts)
State whether the solution of each of the following salts is acidic, basic or neutral:
(a) NaCl
(b) NH₄Cl
(c) CH₃COONa

Answer:
(a) NaCl – neutral solution
(b) NH₄Cl – acidic solution
(c) CH₃COONa – basic (alkaline) solution

Explanation:
NaCl is from a strong acid and strong base → neutral. NH₄Cl is from strong acid (HCl) and weak base (NH₄OH) → acidic. CH₃COONa is from weak acid (CH₃COOH) and strong base (NaOH) → basic.

WAEC Question 20 (Buffer solutions)
What is a buffer solution and why is it important in the human blood?

Answer:
A buffer solution is a solution that resists change in pH when small amounts of acid or base are added.
It is important in blood because it keeps the pH of blood almost constant so that body enzymes can work properly.

Section C: Organic Chemistry (WAEC Questions 21–28)

WAEC Question 21 (Homologous series)
(a) Define a homologous series.
(b) State two characteristics of a homologous series.

Answer:
(a) A homologous series is a family of organic compounds with the same general formula, similar chemical properties and successive members differing by a CH₂ group.
(b) Characteristics:
(i) Members have similar chemical properties.
(ii) They show a gradual change in physical properties such as boiling point as the number of carbon atoms increases.

WAEC Question 22 (General formulae)
State the general formula for each of the following homologous series:
(a) Alkanes
(b) Alkenes
(c) Alkynes

Answer:
(a) Alkanes: CₙH₂ₙ₊₂
(b) Alkenes: CₙH₂ₙ
(c) Alkynes: CₙH₂ₙ₋₂

WAEC Question 23 (Naming simple compounds)
Give the IUPAC names of the following compounds:
(a) CH₃–CH₂–CH₃
(b) CH₂=CH–CH₃
(c) CH≡C–CH₃

Answer:
(a) Propane
(b) Propene
(c) Propyne

WAEC Question 24 (Functional groups)
(a) What is a functional group?
(b) State the functional group for:
  (i) alcohols
  (ii) carboxylic acids
  (iii) alkenes

Answer:
(a) A functional group is an atom or group of atoms in an organic molecule that is responsible for its characteristic chemical properties.
(b) (i) Alcohols – –OH (hydroxyl group)
(ii) Carboxylic acids – –COOH (carboxyl group)
(iii) Alkenes – C=C double bond

WAEC Question 25 (Isomerism)
Explain the term structural isomerism and give one example using C₄H₁₀.

Answer:
Structural isomerism is the existence of compounds with the same molecular formula but different structural formulae.
Example for C₄H₁₀: n-butane (CH₃–CH₂–CH₂–CH₃) and 2-methylpropane (CH₃–CH(CH₃)–CH₃).

WAEC Question 26 (Combustion of ethanol)
Write a balanced chemical equation for the complete combustion of ethanol (C₂H₅OH) in excess oxygen.

Answer:
C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l)

WAEC Question 27 (Laboratory test for unsaturation)
Describe one simple test that can be used to distinguish between an alkane and an alkene in the laboratory.

Answer:
Add bromine water to each sample. The alkene quickly decolourizes the brown bromine water, while the alkane does not.

Explanation:
Alkenes are unsaturated and add bromine across the double bond; alkanes are saturated and do not react under these conditions.

WAEC Question 28 (Polymerization)
(a) What is polymerization?
(b) Name the type of polymerization by which polyethene is formed from ethene.

Answer:
(a) Polymerization is a chemical process in which many small molecules (monomers) join together to form a large molecule (polymer).
(b) Polyethene is formed by addition polymerization.

Section D: Electrochemistry and Redox (WAEC Questions 29–32)

WAEC Question 29 (Electrolytes and non-electrolytes)
(a) What is an electrolyte?
(b) Give one example each of an electrolyte and a non-electrolyte.

Answer:
(a) An electrolyte is a substance that conducts electricity in molten or aqueous state and is decomposed in the process.
(b) Electrolyte: aqueous NaCl or dilute H₂SO₄.
Non-electrolyte: distilled water or sugar solution.

WAEC Question 30 (Electrolysis of acidified water)
During the electrolysis of acidified water using platinum electrodes:
(a) State the gas produced at the anode.
(b) State the gas produced at the cathode.
(c) State the ratio of their volumes.

Answer:
(a) Anode – oxygen gas
(b) Cathode – hydrogen gas
(c) Volume ratio H₂ : O₂ = 2 : 1

WAEC Question 31 (Simple electrochemical cell)
A simple cell is made using zinc and copper electrodes placed in solutions of their salts and connected by a salt bridge.
(a) Which metal acts as the anode?
(b) Which metal is more reactive?
(c) In which direction do electrons flow in the external circuit?

Answer:
(a) Anode – zinc (Zn)
(b) More reactive – zinc
(c) Electrons flow from zinc to copper in the external circuit.

WAEC Question 32 (Redox – oxidation numbers)
In the reaction: Zn + Cu²⁺ → Zn²⁺ + Cu,
(a) Which species is oxidized?
(b) Which species is reduced?

Answer:
(a) Oxidized: Zn
(b) Reduced: Cu²⁺

Explanation:
Zinc goes from 0 to +2 (loss of electrons) → oxidation. Copper goes from +2 to 0 (gain of electrons) → reduction.

Section E: Chemical Equilibrium and Rates of Reaction (WAEC Questions 33–38)

WAEC Question 33 (Dynamic equilibrium)
State what is meant by dynamic equilibrium in a reversible reaction.

Answer:
Dynamic equilibrium is a state in a reversible reaction where the forward and backward reactions occur at the same rate and the concentrations of reactants and products remain constant.

WAEC Question 34 (Le Chatelier’s principle – temperature)
For the reaction: N₂(g) + 3H₂(g) ⇌ 2NH₃(g) + heat,
what is the effect of increasing temperature on the yield of ammonia? Explain your answer.

Answer:
Increasing temperature decreases the yield of ammonia.

Explanation:
The forward reaction is exothermic. By Le Chatelier’s principle, increasing temperature favours the endothermic (reverse) reaction, so less NH₃ is formed at equilibrium.

WAEC Question 35 (Le Chatelier’s principle – pressure)
For the same equilibrium: N₂(g) + 3H₂(g) ⇌ 2NH₃(g), explain the effect of increasing pressure on the yield of ammonia.

Answer:
Increasing pressure increases the yield of ammonia.

Explanation:
On the left there are 4 moles of gas; on the right there are 2 moles. Increasing pressure favours the side with fewer moles of gas, so the reaction shifts to the right and more NH₃ is produced.

WAEC Question 36 (Definition of rate of reaction)
(a) Define rate of reaction.
(b) Explain briefly how temperature affects rate of reaction.

Answer:
(a) Rate of reaction is the change in concentration of reactants or products per unit time.
(b) Increasing temperature increases the rate of reaction.

Explanation:
At higher temperature, particles move faster and collide more often and with more energy. More collisions have energy equal to or greater than the activation energy, so the reaction is faster.

WAEC Question 37 (Factors affecting rate)
State three factors, apart from temperature, that affect the rate of a chemical reaction.

Answer:
(i) Concentration of reactants
(ii) Surface area (particle size) of solid reactants
(iii) Presence of a catalyst

WAEC Question 38 (Graph of volume vs time)
In an experiment, marble chips (CaCO₃) reacted with excess dilute HCl and the volume of CO₂ gas was measured with time. The graph of volume against time becomes flat after some time. Explain why the curve becomes flat.

Answer:
The curve becomes flat because the reaction has finished; all the CaCO₃ has reacted, so no more CO₂ is produced.

Section F: Metals and Non-metals (WAEC Questions 39–42)

WAEC Question 39 (Physical properties of metals)
State three physical properties of metals that make them useful for making electrical wires and cooking pots.

Answer:
(i) Good conductors of heat
(ii) Good conductors of electricity
(iii) Malleable and ductile (can be hammered into sheets and drawn into wires)

WAEC Question 40 (Extraction of metals)
(a) Name the main ore from which iron is extracted in the blast furnace.
(b) State one function of limestone (CaCO₃) in the blast furnace.

Answer:
(a) Main ore: haematite (Fe₂O₃)
(b) Limestone is used to remove acidic impurities such as silica by forming slag (calcium silicate).

WAEC Question 41 (Alloys)
(a) What is an alloy?
(b) Give one example of an alloy and state one use.

Answer:
(a) An alloy is a mixture of a metal with other metals or non-metals, usually to improve its properties.
(b) Example: bronze (copper and tin), used for making statues and medals (or steel used for building and tools).

WAEC Question 42 (Non-metals and their uses)
State two important uses of non-metallic element chlorine.

Answer:
(i) Used for disinfecting and treating water to kill germs
(ii) Used in making household bleaches and some plastics (e.g. PVC)

Section G: Extra WAEC Mixed Revision Questions (WAEC Questions 43–35+)

WAEC Question 43 (Gas laws – Charles’ law)
State Charles’ law.

Answer:
Charles’ law states that at constant pressure, the volume of a fixed mass of gas is directly proportional to its absolute temperature (in kelvin).

WAEC Question 44 (Mole concept – molar mass)
Calculate the molar mass of CaCO₃. [Ca = 40, C = 12, O = 16]

Answer:
Molar mass = 40 + 12 + (16 × 3) = 100 g mol⁻¹

WAEC Question 45 (Stoichiometry – moles of gas)
How many moles of oxygen molecules are present in 32 g of O₂? [O = 16]

Answer:
Moles of O₂ = mass / molar mass = 32 / (16 × 2) = 32 / 32 = 1 mole

WAEC Question 46 (Water hardness)
Explain the difference between temporary and permanent hardness of water.

Answer:
Temporary hardness is caused mainly by dissolved calcium hydrogen carbonate and can be removed by boiling. Permanent hardness is caused by calcium or magnesium sulphates/chlorides and cannot be removed by boiling.

WAEC Question 47 (Environmental chemistry)
State two harmful effects of acid rain on the environment.

Answer:
(i) It corrodes buildings and metal structures
(ii) It damages plant leaves and can make lakes and rivers too acidic for fish

WAEC Question 48 (Industrial chemistry – Haber process)
State the main raw materials and one use of ammonia produced by the Haber process.

Answer:
Raw materials: nitrogen gas (from air) and hydrogen gas (from natural gas, methane).
Use: for making nitrogenous fertilizers such as ammonium nitrate.

WAEC Question 49 (Industrial chemistry – Contact process)
Name the catalyst used in the contact process for making sulphuric acid and state one use of sulphuric acid.

Answer:
Catalyst: vanadium(V) oxide, V₂O₅.
Use: for making fertilizers, detergents or car batteries (lead-acid).

WAEC Question 50 (Laboratory preparation of CO₂)
Which pair of reagents can be used to prepare carbon dioxide in the laboratory, and how is the gas collected?

Answer:
Reagents: dilute HCl and marble chips (CaCO₃).
Collection: by downward delivery or over water because CO₂ is denser than air and only slightly soluble in water.

NECO Chemistry Past Questions and Answers (2020–2024)

The following NECO-style questions also cover key SSCE topics. Answers are in bold for quick revision.

NECO Question 1 (States of matter)
Which statement about particles in a gas is correct?

1. They are very close and vibrate in fixed positions.
2. They move randomly and are far apart.
3. They are arranged in layers and slide over each other.
4. They do not move at all.

Answer: (2) They move randomly and are far apart.

NECO Question 2 (Periodic trends)
Across a period in the periodic table, the atomic radius generally:

1. increases
2. decreases
3. remains the same
4. changes irregularly

Answer: (2) decreases

NECO Question 3 (Acid strength)
Which of the following is a strong acid?

1. CH₃COOH
2. H₂CO₃
3. HCl
4. NH₄OH

Answer: (3) HCl

NECO Question 4 (Acid, base and salt)
Which of the following is correctly matched?

1. NaOH – salt
2. H₂SO₄ – base
3. NaCl – salt
4. CaCO₃ – acid

Answer: (3) NaCl – salt

NECO Question 5 (Mole concept)
What is the molar mass of CaCO₃? [Ca = 40, C = 12, O = 16]

Answer: 100 g mol⁻¹

NECO Question 6 (Stoichiometry)
How many moles of oxygen molecules are present in 32 g of O₂? [O = 16]

Answer: 1 mole of O₂

NECO Question 7 (Organic chemistry – alkanes)
The general formula of the alkanes is:

1. CₙH₂ₙ₊₂
2. CₙH₂ₙ
3. CₙH₂ₙ₋₂
4. CₙHₙ

Answer: (1) CₙH₂ₙ₊₂

NECO Question 8 (Isomerism)
Compounds with the same molecular formula but different structural formulae are called:

1. homologs
2. isotopes
3. isomers
4. allotropes

Answer: (3) isomers

NECO Question 9 (Electrolysis products)
During the electrolysis of molten NaCl using inert electrodes, the product at the cathode is:

1. chlorine gas
2. sodium metal
3. hydrogen gas
4. oxygen gas

Answer: (2) sodium metal

NECO Question 10 (Redox)
In the reaction: Zn + Cu²⁺ → Zn²⁺ + Cu, which species is oxidized?

1. Zn
2. Cu²⁺
3. Zn²⁺
4. Cu

Answer: (1) Zn

NECO Question 11 (Equilibrium)
Which of the following changes will shift the equilibrium position to the right for an exothermic reaction A ⇌ B + heat?

1. Increase in temperature
2. Decrease in temperature
3. Addition of an inert gas
4. Decrease in pressure

Answer: (2) Decrease in temperature

NECO Question 12 (Rates of reaction)
Which change will increase the rate of a reaction involving a solid and a solution?

1. Using larger pieces of the solid
2. Lowering the temperature
3. Grinding the solid into powder
4. Adding water to dilute the solution

Answer: (3) Grinding the solid into powder

NECO Question 13 (Gas laws)
At constant pressure, the volume of a gas is directly proportional to its absolute temperature. This statement is known as:

1. Boyle’s law
2. Charles’ law
3. Graham’s law
4. Avogadro’s law

Answer: (2) Charles’ law

NECO Question 14 (Water hardness)
Temporary hardness of water can be removed by:

1. adding slaked lime
2. boiling
3. adding washing soda
4. using an ion-exchange resin

Answer: (2) boiling

NECO Question 15 (Laboratory preparation)
Which pair of reagents can be used to prepare carbon dioxide in the laboratory?

1. HCl and CaCO₃
2. NaOH and HCl
3. H₂SO₄ and NaCl
4. CuO and H₂

Answer: (1) HCl and CaCO₃

Most Tested Chemistry Topics in WAEC and NECO

From recent WAEC and NECO papers (2020–2024), the following topics appear very often. Make sure you are strong in them before the exam:

• Atomic structure and periodic table – electronic configuration, periodic trends, ionization energy.
• Chemical bonding – ionic, covalent and metallic bonding, properties of compounds.
• Gas laws and mole concept – Boyle’s and Charles’ laws, Avogadro’s law, molar volume, simple mole calculations.
• Acids, bases and salts – pH, indicators, neutralization, salt preparation, hydrolysis, titrations.
• Redox reactions and electrochemistry – oxidation numbers, simple cells, electrolysis and products at electrodes.
• Chemical equilibrium – Le Chatelier’s principle, effect of temperature, pressure and concentration.
• Rates of reaction – factors affecting rate, graphs, collision theory.
• Organic chemistry – naming compounds, homologous series, isomerism, simple reactions and polymerization.
• Water and environmental chemistry – hardness of water, purification, pollution, greenhouse effect.
• Industrial chemistry – Haber process, contact process, soap and detergents, fertilizers.

Exam Tips for WAEC & NECO Chemistry

1. How to Balance Chemical Equations

Many students lose marks because they cannot balance equations. Use these simple steps and practise with past questions:

• Step 1: Write correct formulas. Make sure all reactants and products are correct before you start.
• Step 2: Count atoms. Write how many atoms of each element are on both sides.
• Step 3: Balance one element at a time. Start with the element that appears in fewer compounds.
• Step 4: Use whole numbers as coefficients. Put numbers in front of formulas, not inside them.
• Step 5: Check again. Recount all atoms to be sure they are equal on both sides.

Example: Balance: Fe + O₂ → Fe₂O₃

Start: Fe + O₂ → Fe₂O₃
Balance Fe: put 2 in front of Fe₂O₃ → 4 Fe on right, so put 4 in front of Fe:
4Fe + O₂ → 2Fe₂O₃
Balance O: 2Fe₂O₃ has 6 O atoms, so put 3 in front of O₂:
4Fe + 3O₂ → 2Fe₂O₃ (balanced).

2. Memorization Tips for Organic Chemistry

Organic chemistry seems hard because of many names and formulas, but you can use simple tricks to remember them.

• Use short mnemonics. For the first five alkanes: “My Elephant Plays Big Trumpet” for Methane, Ethane, Propane, Butane, Pentane.
• Group by homologous series. Learn all alkanes first, then alkenes, then alkynes, then alcohols. Do not mix them.
• Write and say aloud. Write the names and formulas many times and say them as you write. This helps your brain see and hear the pattern.
• Connect name to structure. “Meth-” = 1 carbon, “Eth-” = 2, “Prop-” = 3, “But-” = 4, “Pent-” = 5. Use this to draw structures quickly.
• Use flashcards. Put the name on one side and the structure or formula on the other side. Test yourself and your friends.

3. Common Chemistry Mistakes to Avoid

• Not reading the question fully. Always check key words like “state”, “explain”, “calculate”, “give two reasons”. They show how long and detailed your answer should be.
• Wrong units and symbols. Always write correct units (mol dm⁻³, g mol⁻¹, K, atm) and correct chemical symbols (e.g. CO is not the same as Co).
• Guessing formulas. If you are not sure of a formula, leave it and come back later. A wrong formula can cancel many correct steps.
• Forgetting state symbols. When WAEC or NECO asks for complete equations, include (s), (l), (g), (aq).
• Ignoring working steps. In calculations, always show your working clearly. Examiners give method marks even if the final answer is wrong.
• Poor time management. Do not spend too long on one question. Answer easier questions first, then return to the difficult ones if you have time.

Conclusion: You Can Pass WAEC & NECO Chemistry

Chemistry is not only for “very brilliant” students. If you practise past questions, understand the main ideas and use good exam strategies, you can score very high in WAEC and NECO Chemistry.

Start small today: choose one topic (for example, acids and bases), read your notes for 30–45 minutes, then answer at least five past questions from that topic. Mark yourself honestly and correct your mistakes. If you repeat this every day, by the time you enter the exam hall, Chemistry questions will look simple and familiar.

Keep believing in yourself. With steady practice, prayer and smart use of past questions, you can pass WAEC and NECO Chemistry with confidence.