O Level / IGCSE Chemistry MCQs with answers
Practise O Level / IGCSE Chemistry (5070 / 0620) with 1065 exam-style MCQs, each with the answer and a short explanation. Every test is marked the moment you finish and shows your score chapter by chapter, so you know what to revise next. It is free and needs no sign-up.
1065 questions · 12 chapters · 14 Cambridge past papers · 5 mock exams
What each chapter covers 12 chapters
The questions follow the syllabus chapter by chapter. You can test the whole subject or one chapter at a time.
- States of matter 44 questionsSolids, liquids and gases, Diffusion
- Atoms, elements and compounds 156 questionsElements, compounds and mixtures, Atomic structure and the Periodic Table, Isotopes, Ion and ionic bonds, Simple molecules and covalent bonds, Giant covalent structures, Metallic bonding
- Stoichiometry 70 questionsFormulae, Relative masses of atoms and molecules, The mole and the Avogadro constant
- Electrochemistry 24 questionsElectrolysis
- Chemical energetics 24 questionsExothermic and endothermic reactions
- Chemical reactions 92 questionsPhysical and chemical changes, Rate of reaction, Reversible reactions and equilibrium, Redox
- Acids, bases and salts 70 questionsThe characteristic properties of acids and bases, Oxides, Preparation of salts
- The Periodic Table 111 questionsArrangement of elements, Group I properties, Group VII properties, Transition elements, Noble gases
- Metals 132 questionsProperties of metals, Uses of metals, Alloys and their properties, Reactivity series, Corrosion of metals, Extraction of metals
- Chemistry of the environment 70 questionsWater, Fertilisers, Air quality and climate
- Organic chemistry 184 questionsFormulae, functional groups and terminology, Naming organic compounds, Fuels, Alkanes, Alkenes, Alcohols, Carboxylic acids, Polymers
- Experimental techniques and chemical analysis 88 questionsExperimental design, Chromatography, Separation and purification, Identification of ions and gases
Sample O Level / IGCSE Chemistry MCQs with answers 12 questions
12 questions from the test, one or two from each chapter. Try each one, then open the answer.
1. Oxygen, O2, and carbon dioxide, CO2, are at the same temperature. Which statement is correct?
- A
CO2 molecules move faster on average, because each contains more atoms
- B
both move at the same average speed, because they are at the same temperature
- C
the molecules have the same average kinetic energy, but O2 molecules move faster because they are lighter
- D
O2 molecules have more kinetic energy, which is why they diffuse faster
Show answer
Answer: C. Temperature fixes the average kinetic energy, not the speed. With equal energy, the lighter O2 (Mr 32) moves faster than CO2 (Mr 44) and diffuses faster.
2. Why is the relative atomic mass of chlorine 35.5 and not a whole number?
- A
chlorine atoms contain half a neutron
- B
it is the average mass of the isotopes of chlorine, weighted by how common each one is
- C
it is the simple average of chlorine-35 and chlorine-37
- D
the electrons add 0.5 to the mass
Show answer
Answer: B. Ar is a weighted average: there is much more chlorine-35 than chlorine-37. A simple average would give 36.
3. Why is the relative atomic mass of chlorine, 35.5, not a whole number?
- A
chlorine atoms contain half a neutron on average
- B
the mass of the electrons is included
- C
chlorine atoms lose mass when they form molecules
- D
it is an average of the masses of its isotopes, weighted by how common each one is
Show answer
Answer: D. Relative atomic mass is the weighted average mass of the isotopes compared with 1/12 of the mass of a carbon-12 atom. No single chlorine atom has a mass of 35.5.
4. Which substance could not be formed at the anode during electrolysis?
- A
chlorine
- B
oxygen
- C
bromine
- D
hydrogen
Show answer
Answer: D. Metals and hydrogen form at the cathode, because they come from positive ions gaining electrons. Non-metals other than hydrogen, such as chlorine, oxygen and bromine, form at the anode.
5. Which change is endothermic?
- A
adding water to anhydrous copper(II) sulfate
- B
burning magnesium in air
- C
heating calcium carbonate to form calcium oxide and carbon dioxide
- D
neutralising sodium hydroxide with hydrochloric acid
Show answer
Answer: C. Thermal decomposition takes in energy, so calcium carbonate must be heated strongly to keep it decomposing. Hydrating copper(II) sulfate, burning and neutralisation all give out thermal energy.
6. A catalyst is added to a reversible reaction in a closed system. What is the effect?
- A
equilibrium is reached faster, but its position does not change
- B
the position of equilibrium moves to the right, giving more product
- C
only the rate of the forward reaction increases
- D
the reaction stops being reversible
Show answer
Answer: A. A catalyst speeds up the forward and reverse reactions equally, so equilibrium is reached sooner with the same yield.
7. A few drops of methyl orange are added to aqueous sodium hydroxide. Dilute hydrochloric acid is then added until it is in excess. What colour change is seen?
- A
red to yellow
- B
blue to colourless
- C
colourless to blue
- D
yellow to red
Show answer
Answer: D. Methyl orange is yellow in alkali and red in acid, so the colour goes from yellow to red once the acid is in excess. Blue to colourless would be thymolphthalein.
8. Which statement describes the change going down Group VII from chlorine to iodine?
- A
density decreases and reactivity increases
- B
density and reactivity both increase
- C
density increases and reactivity decreases
- D
the elements change from diatomic to monatomic
Show answer
Answer: C. The halogens become denser and less reactive down the group. All exist as diatomic molecules: Cl2, Br2, I2.
9. Which statement about the uses of aluminium is correct?
- A
it is used for cables because it is a better conductor than copper
- B
it is used for food containers because it reacts with acids in food
- C
it is used for aircraft because it is denser than steel
- D
it is used for aircraft because of its low density
Show answer
Answer: D. Aluminium’s low density suits aircraft. It conducts less well than copper, but its low density makes it better for long cables; it is used for food containers because it does not corrode.
10. What is needed for photosynthesis to take place in a green leaf?
- A
carbon dioxide and oxygen, with heat energy
- B
glucose and oxygen, with chlorophyll
- C
carbon dioxide and water, with chlorophyll and light energy
- D
water and nitrogen, with light energy
Show answer
Answer: C. Carbon dioxide and water react using light energy absorbed by chlorophyll to make glucose and oxygen.
11. Ethanol burns completely: C2H5OH + 3O2 → 2CO2 + 3H2O. What volume of oxygen, at room temperature and pressure, is needed to burn 0.10 mol of ethanol? (molar gas volume 24 dm3)
- A
2.4 dm3
- B
4.8 dm3
- C
7.2 dm3
- D
9.6 dm3
Show answer
Answer: C. 0.10 mol ethanol needs 3 × 0.10 = 0.30 mol O2; 0.30 × 24 = 7.2 dm3. 4.8 dm3 is the volume of carbon dioxide produced, not of oxygen used.
12. Salt is to be obtained from a mixture of salt and sand. Which sequence of steps is correct?
- A
distil the dry mixture and collect the salt in the condenser
- B
filter the dry mixture and collect the salt from the filtrate
- C
add water, stir, filter, then evaporate the filtrate to crystallise
- D
add water, evaporate, then filter off the salt
Show answer
Answer: C. Salt dissolves but sand does not. Filtering removes the sand; the salt is then recovered from the filtrate.
Try 1053 more questions
Ways to practise 7 ways
- Quick check. 10 questions drawn fresh each time, about 10 minutes.
- By chapter. 10 questions from one chapter, for the topic you are revising now.
- Full paper. A full-length timed paper across the whole syllabus.
- Past papers. 14 Cambridge multiple-choice papers, answered on screen and marked for you.
- Mock exams. 5 full papers of our own questions in the style of the real paper.
- Practice mode. See the right answer and an explanation after every question, with no clock.
- Exam mode. Timed like the real paper, with no going back.
When you get a question wrong, a short note called "The idea behind this" explains the topic it belongs to, with the rules to remember and a worked example.
Topics explained 47 topics
Each topic has a short explanation, the rules to remember, a worked example and practice questions.
Solids, liquids and gasesDiffusionElements, compounds and mixturesAtomic structure and the Periodic TableIsotopesIons and ionic bondsSimple molecules and covalent bondsGiant covalent structuresMetallic bondingFormulaeRelative masses of atoms and moleculesThe mole and the Avogadro constantElectrolysisExothermic and endothermic reactionsPhysical and chemical changesRate of reactionReversible reactions and equilibriumRedoxThe characteristic properties of acids and basesOxidesPreparation of saltsArrangement of elementsGroup I propertiesGroup VII propertiesTransition elementsNoble gasesProperties of metalsUses of metalsAlloys and their propertiesReactivity seriesCorrosion of metalsExtraction of metalsWaterFertilisersAir quality and climateFormulae, functional groups and terminologyNaming organic compoundsFuelsAlkanesAlkenesAlcoholsCarboxylic acidsPolymersExperimental designChromatographySeparation and purificationIdentification of ions and gases
All O Level / IGCSE Chemistry rules on one pageO Level / IGCSE Chemistry past papers: solve online
O Level / IGCSE Chemistry: frequently asked questions
Is this O Level / IGCSE Chemistry test free?
Yes. Every test, answer and explanation is free, and you do not need an account. Sign in only if you want your results kept across devices.
How many O Level / IGCSE Chemistry questions are there?
1065 MCQs with answers, covering 12 chapters of the syllabus. Each test draws new questions, so you can practise many times.
Are these O Level / IGCSE Chemistry past paper questions?
No. The 1065 MCQs are our own, written to the syllabus in the style of the exam. The 14 Cambridge past papers are listed separately inside the test.
How is the test marked?
Instantly. You see your score, the right answer and an explanation for every question, and the topics to work on next. Questions you got wrong are saved so you can retry them.
Can I practise one chapter or only my weak topics?
Yes. Pick a chapter, build your own test from chosen topics, or practise your weakest topics and your past mistakes.
Does it work on a phone?
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