Elements, Compounds and Mixtures Exam Questions
Practice IGCSE Chemistry exam questions on elements, compounds and mixtures. Covers definitions, distinguishing between types of substance, and interpreting particle diagrams with mark schemes and examiner notes.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
These questions test every angle examiners use on elements, compounds and mixtures. Write full answers before checking mark schemes.
Question 1 (3 marks, Core)
Define the following terms:
(a) Element (1)
(b) Compound (1)
(c) Mixture (1)
Mark scheme
(a) A substance that contains only one type of atom / cannot be broken down into simpler substances by chemical methods [1]
(b) A substance formed when two or more elements are chemically combined in a fixed ratio [1]
(c) Two or more substances (elements or compounds) that are not chemically combined / can be separated by physical methods [1]
Examiner note: For compound, both “chemically combined” and “fixed ratio” are expected for full marks at the 1-mark level. Simply saying “two elements joined” is too vague.
Question 2 (3 marks, Core)
The diagrams below show particle representations of four substances, W, X, Y and Z.
- W: contains only one type of atom, atoms are single (e.g. Ar)
- X: contains only one type of atom, atoms are in pairs (e.g. O2)
- Y: contains molecules each made of two different types of atom
- Z: contains a mix of single atoms and paired atoms of different types
Classify each substance as an element, compound, or mixture.
Mark scheme
- W = element [1]
- X = element [1]
- Y = compound [1]
- Z = mixture [1]
Award [1] for any three correct and [1] bonus for all four. (Total 3 marks.)
Examiner note: W and X are both elements — W is monatomic (like a noble gas), X is diatomic (like O2 or H2). Both contain only one type of atom. Many candidates wrongly classify X as a compound because the atoms are paired.
Question 3 (3 marks, Core)
Iron and sulfur are mixed together in a dish. The mixture is then heated strongly until it glows. A new substance, iron sulfide, is formed.
(a) State one difference between the mixture of iron and sulfur, and the compound iron sulfide. (1)
(b) Describe one test that shows iron sulfide is different from the original mixture. (2)
Mark scheme
(a) Any one of: the mixture can be separated by physical methods (e.g. magnet) but the compound cannot [1] / the mixture has variable composition but the compound has a fixed ratio [1] / the mixture shows properties of both iron and sulfur but the compound has different properties [1]
(b) A magnet attracts iron from the mixture [1] but does not attract iron sulfide because the iron is chemically combined with sulfur [1]
OR: Adding dilute acid to the mixture releases hydrogen gas (from iron reacting) [1] but adding dilute acid to iron sulfide produces hydrogen sulfide gas (toxic, rotten egg smell) [1]
Examiner note: The question asks you to describe a test, not just name one. State what you do and what you observe for both the mixture and the compound.
Question 4 (2 marks, Core)
Air is a mixture. State two pieces of evidence that show air is a mixture and not a compound.
Mark scheme
Any two from:
- Air has a variable composition / the proportions of gases vary in different locations [1]
- The components of air can be separated by physical methods such as fractional distillation [1]
- Air shows the properties of its individual gases [1]
- No energy change occurs when the gases in air are mixed [1]
Examiner note: “Air contains different gases” is not evidence that it is a mixture — a compound also contains different elements. Focus on variable composition and physical separation.
Question 5 (4 marks, Supplement)
Water (H2O) is a compound. Hydrogen and oxygen are elements.
(a) Explain why water is classified as a compound, not a mixture. (2)
(b) Explain why the properties of water are different from the properties of hydrogen and oxygen. (2)
Mark scheme
(a) The hydrogen and oxygen are chemically combined / bonded together [1] in a fixed ratio of 2:1 (by atoms) [1]
(b) When elements chemically combine to form a compound, a new substance is formed [1] with different physical and chemical properties because the bonding/structure is different [1]
Examiner note: Writing “water is wet but hydrogen and oxygen are gases” describes the difference but does not explain why the properties differ. You need to state that chemical combination produces a new substance with its own properties.
Question 6 (2 marks, Core)
Classify each of the following as an element, compound, or mixture:
(a) Carbon dioxide (1)
(b) Bronze (1)
Mark scheme
(a) Compound [1]
(b) Mixture (it is an alloy — a mixture of metals) [1]
Examiner note: Bronze is an alloy of copper and tin. Although it is often treated as a single material, alloys are mixtures because the metals are not chemically combined — they are mixed at the atomic level but with variable composition.
Question 7 (3 marks, Core)
A student draws particle diagrams for three substances. In diagram 1, all particles are identical single atoms. In diagram 2, all particles are identical molecules made of three atoms (two of one kind and one of another). In diagram 3, there is a mix of single atoms and the same type of molecule shown in diagram 2.
(a) Which diagram represents a compound? (1)
(b) Which diagram represents a mixture? (1)
(c) Draw a particle diagram to represent a mixture of two different elements, one monatomic and one diatomic. (1)
Mark scheme
(a) Diagram 2 [1]
(b) Diagram 3 [1]
(c) A diagram showing single atoms of one type and pairs of atoms of a different type, clearly mixed together [1]
Examiner note: In part (c), the two types of atom must be visually different (different size or shading). The diatomic molecules must consist of two identical atoms bonded together, not two different atoms.
Question 8 (3 marks, Supplement)
Sodium chloride is a compound with the formula NaCl.
(a) State the elements present in sodium chloride. (1)
(b) Explain why sodium chloride cannot be separated into sodium and chlorine by physical methods. (1)
(c) State the type of process needed to decompose sodium chloride into its elements. (1)
Mark scheme
(a) Sodium and chlorine [1]
(b) The sodium and chlorine are chemically bonded/combined, so physical methods cannot break these bonds [1]
(c) A chemical process / electrolysis [1]
Examiner note: Filtration, distillation, and chromatography are all physical separation methods — they cannot break chemical bonds. Electrolysis is the standard method for decomposing sodium chloride.
What to revise if you scored below 6
If definitions caused problems (Question 1), memorise the three-word triggers: element = “one type of atom,” compound = “chemically combined, fixed ratio,” mixture = “not chemically combined.” If particle diagrams were tricky (Questions 2, 7), practise drawing and classifying at least five examples. Revisit the elements, compounds and mixtures notes.
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