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	C
2	B
3	C
4	D
5	A

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

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

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

Comments on specific questions

Question 1Easy

C: the 10.0 g of solid is measured with a balance (1), the 50 cm³ of water with a measuring cylinder (3) and the temperature with a thermometer (4). A, B, D: all three include the gas syringe (2), which measures the volume of a gas; no gas is formed when ammonium nitrate dissolves. A also leaves out the thermometer, B the measuring cylinder and D the balance, so the temperature, the volume of water or the mass could not be measured.

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

Question 2Easy

B: in distillation the water boils off, its vapour is cooled in the condenser and condenses as pure water; the dissolved salts stay behind in the flask. A: the dissolved salts do not boil off with the water. C: dissolved salts pass through filter paper with the water, so filtering cannot remove them. D: heating until all of the water has gone is evaporation; it gives the salts, not the pure water.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 9–17

Question 3Medium

C: the cloth gives four spots, so it contains four dyes. Its lowest, third and top spots are level with the spots of J, L and M, so these three known dyes are present; its second spot is not level with the spot of any known dye, so it is a fourth dye that is not J, K, L or M. B: this ignores the second spot, which is a dye that is not one of the known dyes. A, D: these include K, but the spot of K is slightly above the lowest spot of the cloth, which is level with the spot of J (A also leaves out M).

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 13–15

Question 4Easy

D: each chlorine atom has 7 outer shell electrons and the two atoms share one pair of electrons, one from each atom; each atom then has the 3 lone pairs and the shared pair, making 8 outer electrons, the electronic configuration of argon. A: shows an electron transferred from one atom to the other to form ions; two atoms of the same element share electrons and do not form ions. B: each atom has only two lone pairs, so only 6 electrons around it; it has not reached a noble gas configuration. C: no electrons are shared, so the atoms are not bonded; the diagram shows two separate chlorine atoms.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 62–63

Question 5Easy

A: the symbol of lead is Pb, the symbol of potassium is K and calcium hydroxide, which has one Ca²⁺ ion for every two OH⁻ ions, is Ca(OH)₂. B: CaOH₂ means one calcium, one oxygen and two hydrogen atoms; the bracket is needed so that the 2 applies to the whole OH group. C: P is the symbol of phosphorus, not potassium. D: Pl is not the symbol of any element; lead is Pb.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 91–93

Question 6Easy

A: neutralisation is the reaction of hydrogen ions from the acid with hydroxide ions from the alkali, H⁺ + OH⁻ → H₂O. B: H⁺ and SO₄²⁻ both come from the acid and do not react with each other. C: Na⁺ and OH⁻ both come from the alkali. D: Na⁺ and SO₄²⁻ are spectator ions: they do not react but stay in solution as sodium sulfate.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), p. 128

Question 7Medium

B: oxide X reacts with an acid only, so it is a basic oxide, and basic oxides are formed by metals; oxide Y reacts with an alkali only, so it is an acidic oxide, and acidic oxides are formed by non-metals. A: oxide Y is acidic, so it is formed by a non-metal. C: the types are the wrong way round. D: oxide X is basic, so it is formed by a metal.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 134–136

Question 8Medium

C: each zinc atom loses 2 electrons to form Zn²⁺, so its oxidation state increases from 0 to +2; a loss of electrons and an increase in oxidation state both mean oxidation. A: zinc is oxidised, but its atoms lose electrons; they do not gain them. B: losing electrons is oxidation, not reduction. D: an increase in oxidation state is oxidation, not reduction.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 156–161

Question 9Easy

A: the elements are arranged in order of increasing proton (atomic) number. B: an order of nucleon number would put potassium (39) before argon (40), but argon (18 protons) comes before potassium (19 protons). C: elements in the same group have the same number of outer shell electrons; the number of electron shells is the number of the period. D: elements in the same period have the same number of electron shells; their numbers of outer shell electrons increase from left to right.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 170–171

Question 10Easy

D: the configuration 2.8.6 has 6 electrons in the outer shell. Atoms with only a few outer shell electrons (1, 2 or 3) are metals and atoms with more (5, 6 or 7) are non-metals, so Z is a non-metal. A, B: 3 is the number of electron shells, not the number of outer shell electrons. C: the number of outer shell electrons is right, but atoms with 6 outer shell electrons are non-metals.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 172–174

Question 11Medium

B: the more reactive the metal, the more hydrogen it gives in the same time: X gives none (it does not react, so it is the least reactive), then Z (9 cm³), W (28 cm³) and Y (74 cm³), so the order of increasing reactivity is X, Z, W, Y. A: W and Z are swapped. C: this is the order of decreasing reactivity, with Y the most reactive. D: this is also the wrong direction, and W and Z are swapped.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 186–187

Question 12Easy

D: growing plants take in carbon dioxide from the air by photosynthesis, which offsets the carbon dioxide released when the bioethanol burns, so bioethanol adds less to the carbon dioxide in the air than a fossil fuel does. A: combustion releases carbon dioxide. B: decay of dead plants releases carbon dioxide. C: fermentation of the sugar to make the bioethanol also releases carbon dioxide.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), p. 233

Question 13Medium

B: the formulae follow the pattern C₃H₆, C₄H₈, C₅H₁₀ (general formula C_nH_2n), so hexene is C₆H₁₂; the boiling points rise as the molecules get larger, so hexene boils above 30 °C; and the members of a homologous series have similar chemical properties, so hexene reacts like propene. A: the chemical properties of the members of a homologous series are similar, not different. C: the boiling point rises, it does not fall, as the molecules get larger. D: C₆H₁₄ does not fit the pattern C_nH_2n; it is the formula of an alkane.

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

Question 14Easy

A: X has a C=C double bond, so it is unsaturated: it reacts with aqueous bromine, which turns from orange to colourless. B: X has a C=C double bond; it does not have only single bonds. C, D: Y has only single bonds, so it is a saturated hydrocarbon and does not react with aqueous bromine, which stays orange.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 253–254

Question 15Easy

C: C₄H₉OH has the –OH group of an alcohol and one more CH₂ than propanol, so it is the next member of the same series. A: C₃H₆ is propene, an alkene with a C=C double bond. B: C₃H₈ is propane, an alkane with the same number of carbon atoms but no –OH group. D: CH₃CO₂H is ethanoic acid, a carboxylic acid; its O–H is part of the –CO₂H group, not the –OH group of an alcohol.

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

Question 16Medium

C: oxidation changes the CH₂OH end of the alcohol into the –CO₂H group of a carboxylic acid, so the acid has the same number of carbon atoms: CH₃CH₂CH₂OH gives CH₃CH₂CO₂H. A: this has only two carbon atoms, so a carbon atom has been lost. B: this is propene, an alkene; it has no –CO₂H group and is not a carboxylic acid. D: this has four carbon atoms, so a carbon atom has been added.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), p. 262

Question 17Medium

B: each molecule of chloroethene has two carbon atoms and becomes one CH₂–CHCl unit of the chain. The part shown has six carbon atoms, so it was made from 6 ÷ 2 = 3 molecules (it also has 3 chlorine atoms, one from each molecule). A: 2 is the number of carbon atoms in one monomer molecule. C: 6 is the number of carbon atoms in the part shown. D: 9 is the number of hydrogen atoms in the part shown.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 272–273

Question 18Easy

A: statements 1 and 2 are environmental benefits: recycling saves crude oil, a non-renewable resource, and means less plastic waste is dumped in landfill sites, where non-biodegradable plastics last for a very long time. Statement 3 is an economic issue (the cost) and statement 4 is a social issue (people have to take part). B: statement 4 is a social issue. C: statement 3 is an economic issue. D: neither statement is an environmental benefit.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 283–285

Question 19Medium

B: carbon monoxide and ozone are common atmospheric pollutants (two gases). Argon, nitrogen and oxygen are gases of clean air and are not pollutants. A: leaves out ozone, which protects us high in the atmosphere but is a pollutant at ground level. C, D: count argon, nitrogen or oxygen, which are in clean air.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 292–293

Question 20Easy

D: burning coal that contains sulfur forms sulfur dioxide, which irritates the lungs and causes breathing problems and dissolves in rain water to form acid rain, which reacts with the stone of buildings and wears it away. A: carbon dioxide does not cause acid rain. B: carbon monoxide is toxic, but it does not dissolve in rain water to form acid rain. C: methane causes neither problem.

Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 293–294

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