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

A: liquid petrol changing to vapour is evaporation (boiling). The particles take in energy from the hot engine, so their energy increases; they move faster and break away from each other, so the distance between them increases. B: the particles of a vapour are much further apart than in the liquid, not closer together. C, D: a liquid changing to a vapour needs energy to be supplied; the energy of the particles does not decrease. D: this describes the opposite change, condensation, in which the particles lose energy and come closer together.

C: a neutron has no charge (0) and a relative mass of 1, the same as a proton. A: a charge of −1 belongs to an electron. B: a relative mass of 1/1840 belongs to an electron; a neutron is about as heavy as a proton. D: a charge of +1 belongs to a proton.

D: an aluminium atom has the electronic configuration 2,8,3. A metal atom forms a positive ion by losing its outer electrons, so it loses 3 electrons and forms Al³⁺ with the configuration 2,8, the same as neon. A: gaining 5 electrons would give 2,8,8 (argon), but metal atoms lose electrons to form positive ions. B: gaining electrons would not give the configuration of neon (2,8). C: after losing 3 electrons the ion has 10 electrons (2,8), not the 18 electrons (2,8,8) of argon.

B: the diagram shows one X²⁺ ion and two Y⁻ ions. The two outer electrons of an atom of X are transferred, one to each of two atoms of Y (each Y⁻ ion has 7 dots of its own and 1 cross from X), so every ion has a full outer shell. A: sharing electrons makes a covalent bond; here the electrons are transferred and ions form. C: if both electrons went to one atom of Y, that ion would be Y²⁻; the diagram shows each Y ion with only one cross. D: the diagram has only one X ion for two Y ions, and it shows X with a 2+ charge, so one atom of X loses two electrons.

A: an alloy is a mixture of a metal with one or more other elements; brass, for example, is a mixture of the metals copper and zinc. B: the elements in an alloy are mixed, not chemically combined, so an alloy is a mixture, not a compound. C: an alloy is not a pure metal. D: an alloy always contains a metal.

D: sulfuric acid is H₂SO₄ (two hydrogen atoms, one sulfur atom, four oxygen atoms). A: the formula of ammonia is NH₃; NH₄ is the start of the ammonium ion. B: carbon monoxide is CO; CO₂ is carbon dioxide. C: nitrogen dioxide is NO₂; N₂O has only one oxygen atom.

C: the relative formula mass is the sum of the relative atomic masses of all the atoms in the formula: 23 + (3 × 14) = 65. A: 37 = 23 + 14 counts only one nitrogen atom. B: 40 = 23 + 3 + 14 adds the number 3 instead of multiplying 14 by 3. D: 111 = (23 + 14) × 3 multiplies the sodium as well; the subscript 3 applies only to nitrogen.

B: one mole of any substance contains 6.02 × 10²³ particles (the Avogadro constant). The sample has half as many molecules as this, so it is 3.01 × 10²³ ÷ 6.02 × 10²³ = 0.50 mol. A: 0.050 mol is ten times too small. C: 1.0 mol would need 6.02 × 10²³ molecules. D: 2.0 mol comes from dividing the other way round, 6.02 × 10²³ ÷ 3.01 × 10²³.

D: magnesium is a metal, so it reacts with the acid to form a salt and hydrogen gas; zinc carbonate reacts to form a salt, water and carbon dioxide gas. Copper(II) oxide is a base, so it reacts to form copper(II) sulfate and water only, and no gas is produced. A, B, C: each of these includes statement 1, copper(II) oxide, which produces no gas.

A: tests 3 and 4 identify the anion. No precipitate with acidified barium nitrate means that sulfate ions are absent, and ammonia from aluminium foil and aqueous sodium hydroxide shows nitrate ions. Tests 1 and 2 identify the cation: a white precipitate that dissolves in excess aqueous sodium hydroxide is formed by Al³⁺ or Zn²⁺, but only aluminium hydroxide does not dissolve in excess aqueous ammonia, so the cation is aluminium. X is aluminium nitrate. B: sulfate ions would give a white precipitate in test 3. C, D: zinc hydroxide dissolves in excess aqueous ammonia, but the precipitate in test 2 did not dissolve; D also has sulfate.

C: the oxidation state of aluminium increases from 0 to +3 because each aluminium atom loses three electrons to form Al³⁺. Loss of electrons (an increase in oxidation state) is oxidation. A, B: a positive ion forms by losing electrons, not by gaining them. B, D: reduction is gain of electrons and a decrease in oxidation state; it is the iron in iron(III) oxide that is reduced.

B: a magnesium atom has 12 electrons arranged 2,8,2. The 2 outer electrons put it in Group 2, and the 3 occupied shells put it in Period 3. A: the period is the number of occupied shells (3), not the number of outer electrons. C: the group and period numbers have been swapped. D: the group number is not the proton number; magnesium has 2 outer electrons.

A: with dilute hydrochloric acid and with steam, magnesium reacts the most vigorously, zinc reacts less vigorously, and iron reacts only slowly; copper does not react with water, steam or dilute acid. So the order is magnesium, zinc, iron, copper. B: iron is placed above zinc, but zinc reacts faster than iron with steam and with dilute acid. C: copper is the least reactive metal; it does not react with dilute acid, but iron does. D: magnesium is more reactive than zinc; it reacts faster with steam and with dilute acid.

D: iron rusts when it is in contact with both oxygen and water. The open tube contains air, which supplies the oxygen, and the water below the cotton wool makes the air damp, so the nail is in contact with both and rusts, even though it is not under the water. A: boiling removes dissolved oxygen from the water, and the layer of oil stops air from dissolving again, so there is no oxygen. B: anhydrous calcium chloride absorbs water vapour, so the air in the sealed tube is dry and there is no water. C: the layer of grease is a barrier that keeps oxygen and water away from the iron, even though the nail is in water.

C: alkanes have the general formula C_nH_2n+2. With n = 8 the number of hydrogen atoms is (2 × 8) + 2 = 18, so the formula is C₈H₁₈. A, B: C₈H₁₄ and C₈H₁₆ have too few hydrogen atoms to be saturated; C₈H₁₆ (C_nH_2n) fits an alkene. D: C₈H₂₀ has two hydrogen atoms too many (2n + 4).

B: the molecule has three carbon atoms in a chain joined by single bonds only, so it is the alkane propane; counting the atoms gives 3 carbon atoms and 8 hydrogen atoms, C₃H₈. A: the name is right but C₃H₆ has two hydrogen atoms too few; the molecule has 8. C, D: propene has a C=C double bond and the formula C₃H₆; there is no double bond in this molecule, so it is not propene.

A: hydrogen adds across the C=C double bond of ethene (an addition reaction) to form the saturated alkane ethane: C₂H₄ + H₂ → C₂H₆. B: ethanol contains oxygen, which is not present in the reactants. C: poly(ethene) is made when many ethene molecules join to each other; no hydrogen is needed. D: propane has three carbon atoms, but the carbon chain is unchanged in this reaction.

B: statements 1 and 4 are correct. Yeast acts on the glucose solution (C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂), and the ethanol is then separated from the water in the mixture by fractional distillation. Statement 2 is not correct: carbon dioxide is formed as well as ethanol. Statement 3 is not correct: fermentation takes place in the absence of oxygen. A: includes statement 2 and leaves out statement 4. C: both statements are incorrect. D: includes statement 3 and leaves out statement 1.

D: burning plastics releases poisonous gases (and carbon dioxide) into the air, which pollutes the air. A: this problem is caused by plastic litter that is left on the ground and washed into drains. B: this problem is caused by burying waste plastic in landfill sites, because plastics are not biodegradable. C: this problem is caused by dumping waste plastic in rivers and the sea.

C: carbon monoxide is toxic: it stops the blood from carrying oxygen round the body. Nitrogen dioxide dissolves in rain water, together with sulfur dioxide, to form acid rain, which damages buildings and kills plants and fish. A, B: carbon monoxide does not form acid rain. B, D: nitrogen dioxide is not one of the greenhouse gases; carbon dioxide and methane are.