Mark schemePaper 1 Multiple Choice (Chemistry section)
SCIENCE (CHEMISTRY) – Paper 1 Multiple Choice (Chemistry section) – 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.
Total marks: 20
Level: Easy Easy 12, Medium 7, Hard 1
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 | D |
| 3 | A |
| 4 | D |
| 5 | C |
Question
Number | Key |
|---|
| 6 | C |
| 7 | B |
| 8 | A |
| 9 | A |
| 10 | A |
Question
Number | Key |
|---|
| 11 | B |
| 12 | B |
| 13 | C |
| 14 | B |
| 15 | D |
Question
Number | Key |
|---|
| 16 | B |
| 17 | B |
| 18 | D |
| 19 | D |
| 20 | C |
Comments on specific questions
Question 1Easy
C: the gas jar is filled with water and the gas pushes the water out, so the gas must be insoluble in water. Y is the only insoluble gas. How its density compares with air does not matter when a gas is collected over water, so Y can be collected even though it is denser than air. A: W is less dense than air, which suits an upside-down jar of air, but it is very soluble and would dissolve in the water. B, D: X and Z are soluble and would dissolve in the water.
Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 6–7
Question 2Easy
D: insoluble mud is separated from the liquid by filtration; the clear liquid is a solution of salts in water, and pure water is obtained from it by distillation, in which the water boils off and is condensed and collected. A, B: evaporation cannot remove mud from a liquid; it only turns the liquid into vapour. A, C: crystallisation gives the dissolved salts as crystals; it does not give pure water.
Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 8–18
Question 3Easy
A: the protons and neutrons (nucleons) are in the nucleus, and the 3 electrons are in shells around it: 2 in the first (innermost) shell, which holds a maximum of 2, and the third in the second shell. B: electrons are not in the nucleus; it contains only protons and neutrons. C: three electrons cannot all fit in the first shell. D: the first shell fills before the second, so the arrangement is 2 then 1, not 1 then 2.
Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 38, 44–45
Question 4Medium
D: in a simple molecular substance the forces between the molecules are weak, so little energy is needed to separate the molecules and the melting point is low. A: the covalent bonds within each molecule are strong and do not break when menthol melts. B: this is true, but it explains why menthol does not conduct electricity, not why it melts easily. C: a giant lattice of strongly bonded particles would give a high melting point; menthol is made of separate molecules.
Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 78–80
Question 5Easy
C: the charges must balance: one Fe3+ ion (3+) is balanced by three Cl− ions (3−), so the formula is FeCl3. A: FeCl has a charge of 3+ against 1−, so it ignores the charges. B: FeCl2 is the formula of the compound made from Fe2+ ions, which is not the ion given here. D: Fe3Cl has 9+ against 1−: the numbers in the charges have been used as subscripts on the wrong ions.
Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 94–97
Question 6Easy
C: calcium hydroxide is a base. It neutralises the excess acid in the soil, so the pH of the soil increases towards 7, the pH at which most crops grow best. A, B: calcium hydroxide is a base, not an acid; an acid added to acidic soil would make it more acidic, not less. B, D: a base neutralises acid, so the pH of the soil rises; it does not fall.
Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 132–133
Question 7Easy
B: magnesium hydroxide is a base, and a base reacts with an acid to form a salt and water. The salt comes from the acid used: hydrochloric acid gives a chloride, so the products are magnesium chloride and water (Mg(OH)2 + 2HCl → MgCl2 + 2H2O). A, C: hydrogen is formed when an acid reacts with a reactive metal, not with a base. C, D: sulfates are formed by sulfuric acid; hydrochloric acid forms chlorides.
Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 127–129
Question 8Hard
A: carbon dioxide is changed into glucose: it loses oxygen and gains hydrogen, so it is reduced. B: glucose is a product; it is formed by the reduction of carbon dioxide and is not itself reduced in this reaction. C: oxygen is a product; it is formed when water loses hydrogen. D: water loses hydrogen to form oxygen, so water is oxidised, not reduced.
Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 155–156
Question 9Easy
A: metallic character decreases from left to right across a period, from the metals on the left (sodium, magnesium, aluminium) to the non-metals on the right (phosphorus, sulfur, chlorine), so aluminium is more metallic than sulfur. B: chlorine is further to the right than sulfur, so it is less metallic. C: phosphorus is to the right of silicon, so it is less metallic. D: sulfur is to the right of magnesium, so it is less metallic.
Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), p. 173
Question 10Medium
A: going down Group 1 the melting point falls and the reaction with water becomes more vigorous. Sodium is above potassium, so it has the higher melting point (98 °C compared with 63 °C) and reacts less vigorously. B, C, D: each of these has the direction of one or both trends wrong; potassium, not sodium, has the lower melting point and the more vigorous reaction.
Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), p. 175
Question 11Medium
B: the rate of reaction is inversely proportional to the time taken: the time falls from 120 s to 60 s, so the rate doubles. A: the time gets shorter as the concentration rises, which means the rate increases, not decreases. C: the time falls from 120 s to 40 s, so the rate at 1.5 mol / dm3 is three times the rate at 0.5 mol / dm3, not four times. D: the time falls from 60 s to 30 s, so the rate at 2.0 mol / dm3 is twice (not half) the rate at 1.0 mol / dm3.
Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 209–212
Question 12Easy
B: a non-renewable source of energy is used faster than it can be replaced; natural gas and crude oil take millions of years to form, so once they are used up they are not replaced in a useful time. A: crude oil is a mixture of hydrocarbons and natural gas is mainly methane, but this describes what they are, not why they cannot be replaced. C: where they are found has nothing to do with whether they can be replaced. D: burning them forms carbon dioxide, which is a pollution problem, not the reason they are non-renewable (bioethanol, a renewable fuel, also forms carbon dioxide).
Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 227–228
Question 13Medium
C: statements 2 and 3 are correct. An alkane is generally unreactive, but it burns (completely, in plenty of air, to form carbon dioxide and water) and it reacts with chlorine in ultraviolet light in a substitution reaction. Statement 1 is not correct: alkanes are saturated and do not decolourise aqueous bromine; alkenes do. Statement 4 is not correct: addition polymerisation needs a C=C double bond, which alkanes do not have.
Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 244–245
Question 14Easy
B: ethene, C2H4, has two carbon atoms joined by a C=C double bond, and each carbon is bonded to two hydrogen atoms. A: this is ethane, which has two carbon atoms but only single bonds (it is saturated). C: this is propane, which has three carbon atoms and only single bonds. D: this is propene, which has a C=C double bond but three carbon atoms.
Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 246–247
Question 15Medium
D: statements 2 and 3 are correct. Polyunsaturated means that each molecule has two or more C=C double bonds, so the fat is unsaturated and decolourises aqueous bromine. Statement 1 is not correct: “poly” here refers to the number of double bonds in each molecule; the fats are not polymers made by joining monomers. A, B, C each include statement 1, 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), p. 254
Question 16Easy
B: the molecule has two carbon atoms in a chain (eth-) and an –OH group, so it is the alcohol ethanol. A: ethane also has two carbon atoms but no –OH group (it is an alkane, not an alcohol). C: methanol has one carbon atom. D: propanol has three carbon atoms.
Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 260–261
Question 17Easy
B: ethanol is oxidised to ethanoic acid by oxygen in the air (acidified potassium manganate(VII) does the same job in the laboratory). A, C: nitrogen is unreactive and is not the oxidising agent in air. C, D: forming ethanoic acid from ethanol is oxidation (ethanoic acid has more oxygen than ethanol), not reduction.
Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), p. 266
Question 18Medium
D: dry air is approximately 21% oxygen, so 126 dm3 of oxygen is 21% of the total volume: 126 ÷ 0.21 = 600 dm3. A: 26 dm3 comes from multiplying by 0.21 instead of dividing. B: 126 dm3 is only the volume of oxygen. C: 468 dm3 is the volume of nitrogen in the cylinder (78% of 600 dm3).
Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 290–291
Question 19Easy
D: sulfur dioxide is released into the air by volcanic eruptions (and by the burning of fossil fuels that contain sulfur). A: the decay of plants releases methane and carbon dioxide. B: photosynthesis takes in carbon dioxide and releases oxygen. C: rusting uses up oxygen to form iron oxide; no sulfur compounds are involved.
Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), p. 293
Question 20Medium
C: methane is released when vegetation rots (for example in wetlands and landfill sites), and it is a greenhouse gas, so higher levels may contribute to global warming, with effects such as more extreme weather and melting polar ice. A, B: burning coal releases carbon dioxide and sulfur dioxide, not methane. B, D: acid rain is caused mainly by sulfur dioxide and oxides of nitrogen, not by methane.
Textbook: Discover Chemistry GCE 'O' Level Science and Normal (A) Level Science Textbook, 3rd Edition (Marshall Cavendish Education, 2023), pp. 298–303