Mark scheme

Use this to mark your own attempt. Accept any correct alternative that answers the question as set. Marks are for the ideas, not the exact words. Unless stated, ecf (error carried forward) applies in calculations. Chermistry practice paper – not an official examination paper.

Textbook page references are to Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023).

Question Number	Key
1	A
2	B
3	C
4	D
5	C

Question Number	Key
6	B
7	C
8	D
9	C
10	D

Question Number	Key
11	A
12	C
13	D
14	A
15	B

Question Number	Key
16	A
17	D
18	C
19	B
20	B

Comments on specific questions

Question 1Easy

A: a burette has a tap, so the aqueous sodium hydroxide can be run in a little at a time, and a scale from which the volume added is read. B: a gas syringe measures the volume of a gas, not a liquid. C: a measuring cylinder has no tap, so the liquid cannot be added drop by drop, and it is less accurate. D: a pipette delivers one fixed volume (here it would measure out the 25.0 cm³ of sports drink); it cannot add liquid gradually.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 3–6

Question 2Medium

B: water vapour (a gas) changing to liquid droplets is condensation. The cold air takes energy from the vapour, so its particles lose energy, move more slowly and come closer together until the attractive forces hold them as a liquid. A: the change is condensation, but the particles lose energy; they do not gain it. C, D: evaporation is the change from liquid to gas, which is the opposite of what happens here. C also has the particles gaining energy, which is what happens in evaporation, not in this change.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 24–34

Question 3Easy

C: the proton (atomic) number is the number of protons in the nucleus of an atom, and the nucleon (mass) number is the number of protons and neutrons (the nucleons) in the nucleus. A: the proton number is not the number of neutrons. B: the nucleon number includes the protons as well as the neutrons. D: the two definitions have been swapped.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), p. 40

Question 4Easy

D: a sodium atom (2.8.1) loses its one outer electron, leaving 10 electrons in the configuration 2.8, the same as the noble gas neon. The ion has 11 protons and 10 electrons, so it has a charge of 1+. A, B: a metal atom does not form a positive ion by gaining an electron; gaining one would give 12 electrons (2.8.2), which is not a noble gas configuration. C: losing one electron from 2.8.1 gives 2.8, which is neon; argon is 2.8.8.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 54–56

Question 5Medium

C: X and Y are the metals. A metal has a high melting point, conducts electricity when solid (and when molten) and is malleable, so hitting it with a hammer changes its shape instead of breaking it. W is an ionic compound: it conducts only when molten, not when solid, and it breaks into pieces when hit. Z is a simple molecular substance: it has a low melting point and does not conduct in either state. A, B, D each include W or Z.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 82–83

Question 6Easy

B: an alloy is a mixture of a metal with another element, so its structure has atoms of two different sizes in the layers; the pattern is no longer perfectly regular. A: this shows a pure metal, with only one kind of atom in a regular pattern. C: this shows an ionic lattice, with positive and negative ions (+ and −) alternating. D: this shows a simple molecular substance, with separate molecules, each made of two atoms joined together.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), p. 82

Question 7Easy

C: the relative atomic mass is the average mass of the atoms of an element (compared with one-twelfth of the mass of a carbon-12 atom). Chlorine atoms do not all have the same mass (the element has isotopes, with 18 or 20 neutrons), so the average is not a whole number. A: neutrons are whole particles; no atom contains a fraction of a neutron. B: the value is for one atom, and the fact that chlorine molecules contain two atoms does not change the average mass of the atoms. D: the mass of an electron is very small, and it does not make the value a fraction.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), p. 106

Question 8Medium

D: the formula has 3 Ca, and 2 groups of PO₄, which is 2 P and 8 O. M_r = (3 × 40) + (2 × 31) + (8 × 16) = 120 + 62 + 128 = 310. A: 135 = 40 + 31 + (4 × 16) ignores both the 3 and the 2 in the formula. B: 215 = (3 × 40) + 31 + (4 × 16) ignores the 2 that multiplies the whole bracket. C: 246 = (3 × 40) + (2 × 31) + (4 × 16) applies the 2 to the phosphorus only, not to the oxygen.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), p. 107

Question 9Easy

C: an acid reacts with a carbonate to form a salt, water and carbon dioxide. Hydrochloric acid forms a chloride, so the products are calcium chloride, water and carbon dioxide (CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂); the carbon dioxide is seen as bubbles. A: hydrogen forms when an acid reacts with a reactive metal, not with a carbonate. B: a salt and water alone form when an acid reacts with a base such as a metal oxide; a carbonate also gives carbon dioxide. D: calcium oxide and carbon dioxide are made by heating calcium carbonate, not by adding acid.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 125–126

Question 10Medium

D: nitrate ions are reduced by aluminium in aqueous sodium hydroxide to ammonia gas, which turns damp red litmus paper blue; the mixture is warmed to drive off the gas. A: this is the test for carbonate ions. B: acidifying with nitric acid and adding aqueous silver nitrate is the test for chloride ions. C: acidifying with nitric acid and adding aqueous barium nitrate is the test for sulfate ions.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 145–146

Question 11Easy

A: oxidation is the gain of oxygen, and iron gains oxygen to form iron(III) oxide, so iron is oxidised. B, D: iron does not lose oxygen; there is no oxygen in the iron at the start. C, D: reduction is the loss of oxygen, not the gain of oxygen.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 155–156

Question 12Easy

C: the period number is the number of occupied shells, so Period 3 means three shells; Group 17 means 7 outer electrons. The configuration is 2.8.7. A: 2.7 has only two shells (Period 2); it is fluorine. B: 2.8.1 has three shells but 1 outer electron (Group 1, sodium). D: 2.8.8 has three shells but a full outer shell (Group 18, argon).

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 172–173

Question 13Easy

D: silver is below hydrogen in the reactivity series, so it is not reactive enough to react with dilute hydrochloric acid. A, B, C: calcium, iron and magnesium are all above hydrogen in the reactivity series, so each reacts with dilute hydrochloric acid to give a salt and hydrogen gas.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 184–187

Question 14Medium

A: the more reactive a metal is, the harder it is to obtain from its compounds. Gold is found uncombined, so it is the least reactive; iron is difficult to obtain; sodium is the hardest to obtain, so it is the most reactive. B: this puts sodium, which is the hardest to obtain, as less reactive than iron. C: this puts gold, which is found uncombined, as more reactive than iron. D: this is the order of decreasing reactivity.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 190–191

Question 15Hard

B: statements 1, 2 and 4 are correct. Both formulae fit C_nH_2n+2 (n = 12 and n = 9), so V and W are alkanes in the same homologous series (statement 1). Members of a homologous series have similar chemical properties (statement 4) and a gradation in physical properties: V has larger molecules, so it has the higher boiling point (statement 2). Statement 3 is not correct: larger molecules make the liquid more viscous, so V, not W, is the more viscous. A, C, D each include statement 3 or leave out a correct statement.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 240–241

Question 16Hard

A: an alkane with n carbon atoms has the formula C_nH_2n+2, so the total number of atoms is n + (2n + 2) = 3n + 2. Then 3n + 2 = 14, so n = 4; the molecule is C₄H₁₀ (4 + 10 = 14 atoms). B: 5 comes from dividing 14 by 3 and rounding, which forgets the extra 2 atoms. C: 6 comes from treating the 14 atoms as all hydrogen (2n + 2 = 14). D: 7 comes from taking half of the 14 atoms, as if there were equal numbers of C and H atoms.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), p. 242

Question 17Easy

D: the molecule has three carbon atoms in a chain (prop-) and a C=C double bond (-ene), so it is propene, C₃H₆. A: ethane has two carbon atoms and only single bonds. B: ethene has two carbon atoms joined by a double bond. C: propane has three carbon atoms but only single bonds (it is saturated).

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 246–247

Question 18Easy

C: propanol is an alcohol, so its molecule has an –OH group, and it has three carbon atoms in a chain (prop-). A: ethanol has an –OH group but only two carbon atoms. B: propane has three carbon atoms but no –OH group. D: propene has three carbon atoms but a C=C double bond and no –OH group.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 260–261

Question 19Medium

B: poly(ethene) is used to make plastic bags and clingfilm because it is a flexible, waterproof plastic that can be made into thin sheets. A: poly(ethene) is used for clingfilm, but not because it conducts heat; plastics are poor conductors of heat. C: poly(ethene) is not biodegradable; it does not rot, which is why discarded plastic bags are a pollution problem. D: clingfilm has to be thin and flexible so that it clings to a container, not rigid.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), p. 279

Question 20Easy

B: carbon monoxide forms by the incomplete combustion of a carbon-containing fuel, when there is not enough oxygen for all the carbon to form carbon dioxide. A: complete combustion in plenty of oxygen forms carbon dioxide and water. C: the reaction of nitrogen with oxygen at high temperatures forms oxides of nitrogen, not carbon monoxide. D: burning sulfur compounds forms sulfur dioxide.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), p. 293

SCIENCE (CHEMISTRY) – Paper 1 Multiple Choice (Chemistry section) – mark scheme