CHEMISTRY – Paper 1 Multiple Choice – mark scheme

C: G is less dense than air, so it rises and pushes the air out of the open bottom of an upside-down gas jar; the delivery tube must reach the top of the jar. A: G is very soluble in water, so it would dissolve in the water of the trough. B: G would rise and escape through the open top of an upright jar; an upright jar is for gases that are denser than air. D: the flask is closed, so the air cannot escape; very little gas can enter and the bung may be blown out.

B: sand is an insoluble solid in a liquid, so it is removed by filtration; ethanol and water are miscible liquids with different boiling points, so they are separated by fractional distillation. A: crystallisation obtains a dissolved solid from its solution; it cannot separate two liquids. C, D: a separating funnel only separates liquids that do not mix (immiscible liquids), and ethanol and water mix completely. D also does not remove the sand.

D: sugars are colourless, so no spots can be seen on the dried paper; the locating agent reacts with them to form coloured substances and shows where each sugar is. A: the sugars dissolve in the solvent as it rises up the paper, before the locating agent is used. B: the sugars have already moved different distances (they differ in how well they dissolve in the solvent and how strongly the paper holds them); the spraying only makes the spots visible. C: the locating agent does not affect the spots, which stay where they are.

A: impurities in medicines (and in foods) can be harmful, which is why their purity is measured. B: in chemistry a pure substance contains only one substance; a food made from natural ingredients can still be a mixture. C: a pure medicine can still be harmful if too much is taken. D: a medicine can dissolve in water and still contain impurities; purity is checked by measurements such as the melting point.

A: steam condenses on the cold glass, so the molecules lose energy to the glass; the forces of attraction between them then hold them close together as a liquid. B: energy is given out when a gas condenses; energy is taken in when a liquid boils. C: the molecules stay the same size; a change of state changes the spacing and movement of the molecules, not their size. D: this describes boiling or evaporation, the opposite change.

B: the particles of the solid and of the water are always moving randomly; the purple particles spread out from where they are crowded together until they are evenly mixed (diffusion). A: particles move in random directions, not in straight lines towards the top of the beaker. C: diffusion does not depend on one kind of particle pushing another; both kinds move on their own. D: particles do not change size; the colour spreads because the particles move apart, not because they expand.

C: statement 1 is correct, because each bond is a shared pair of electrons, one from hydrogen and one from sulfur. Statement 3 is correct: a sulfur atom has 6 outer electrons and shares 2, so in the molecule it has 8 in its outer shell, the configuration 2,8,8 of argon. Statement 2 is not correct: each hydrogen atom has only 2 electrons in its outer shell, the configuration of helium. A, B and D each include statement 2 or leave out statement 1 or 3.

D: the zinc atoms are a different size from the copper atoms, so the atoms are not in a regular pattern; the layers cannot slide over each other easily when a force is applied, so brass is harder than pure copper. A: this describes a pure metal, where the layers of identical atoms slide easily. B: the atoms in the diagram are not in a regular pattern; a regular arrangement of identical atoms would let the layers slide easily. C: the arrangement is irregular, but if the layers slid easily brass would be as soft as pure copper.

B: statement 1 is correct, because the state symbol of copper is (s). Statement 3 is correct, because the coefficients of zinc and copper(II) sulfate are both 1, so they react in a 1 : 1 mole ratio. Statement 2 is not correct: zinc sulfate is (aq), so it stays dissolved and is not a precipitate. Statement 4 is not correct: zinc is (s), a solid, at the start. A, C and D each include statement 2 or 4.

C: Q gives hydrogen (it ‘pops’ with a lighted splint), so Q is a metal reacting with the acid to form a salt and hydrogen. R dissolves to form a blue solution with no gas, so R is a base (for example copper(II) oxide) reacting with the acid to form a salt and water. S gives carbon dioxide (it turns limewater milky), so S is a carbonate reacting to form a salt, water and carbon dioxide. A, B and D each give at least one solid the wrong type: only a metal gives a gas that ‘pops’, only a carbonate gives a gas that turns limewater milky, and a base gives no gas.

B: the soil in plot L (pH 4.5) is too acidic for the vegetables; calcium hydroxide is a base, so it neutralises the excess acid and raises the pH into the range 6.0 to 7.0. A, D: the soil in plots K (pH 6.5) and N (pH 7.0) is already in the pH range in which the vegetables grow best, so it needs no treatment. C: the soil in plot M (pH 8.5) is alkaline; adding more of a base would raise the pH still further, not lower it.

D: carbon monoxide is a neutral oxide (an oxide of a non-metal), so it reacts with neither an acid nor an alkali; this is oxide Z. A: W reacts with both, so it is an amphoteric oxide, such as the oxide of a metal like zinc or aluminium. B: X reacts only with the acid, so it is a basic oxide, such as the oxide of a metal like copper. C: Y reacts only with the alkali, so it is an acidic oxide, such as sulfur dioxide or carbon dioxide.

A: both reactants and ammonium sulfate are soluble, so there is no solid to filter; the exact volumes that just neutralise each other are found by titration with an indicator, then the reaction is repeated with those volumes and no indicator, and the pure solution is crystallised. B: aqueous ammonia is a solution, so excess ammonia cannot be filtered off. C: ammonium sulfate is soluble, so no precipitate forms. D: if the volumes are not matched, some acid or ammonia is left over and the crystals are impure.

C: the breakdown of ammonium chloride is a reversible reaction, so when the hot gases reach the cooler part of the tube, ammonia and hydrogen chloride combine again to re-form white solid ammonium chloride. A: ammonium chloride is not melting; it breaks down into two gases when heated. B: the question states that the compound breaks down into ammonia and hydrogen chloride, which are new substances, so a chemical reaction takes place and the change is not just a change of state. D: ammonia and hydrogen chloride are gases that react together; they do not condense into separate solids.

D: a yellow precipitate with acidified silver nitrate shows iodide (chloride gives a white precipitate); a white precipitate with acidified barium nitrate shows sulfate; bubbles of a gas that turns limewater milky (carbon dioxide) with a dilute acid show carbonate. A, B: X is not chloride, because the precipitate is yellow, not white. B, C: Y is not carbonate; the nitric acid added first would remove a carbonate as carbon dioxide, so no white precipitate would form with barium nitrate. B, C: Z is not sulfate; a sulfate does not give a gas with a dilute acid.

C: sulfur dioxide loses oxygen (it becomes sulfur), so it is reduced; hydrogen sulfide loses hydrogen (it becomes sulfur), so it is oxidised. Oxidation is gain of oxygen or loss of hydrogen; reduction is loss of oxygen or gain of hydrogen. A, B: sulfur dioxide is not oxidised, because it loses oxygen and does not gain any. B, D: hydrogen sulfide is not reduced, because it loses hydrogen and does not gain any. In D both reactants lose something, but loss of oxygen is reduction and loss of hydrogen is oxidation, so the two cannot both be reduced.

B: lead(II) bromide is an ionic compound; when it is molten its ions are free to move, so it conducts, and the current decomposes it into lead at the negative electrode and bromine at the positive electrode. A: glucose is a covalent compound; its solution contains no ions, so it does not conduct. C: in solid sodium chloride the ions are held in fixed positions in the lattice, so it does not conduct. D: zinc conducts because of its delocalised electrons, but it is an element, not an ionic compound, so no chemical change takes place at the electrodes.

A: statement 1 is correct, because the ions of sodium chloride are free to move when it is molten, so the current can pass; statement 2 is correct, because the negative chloride ions move to the positive electrode and lose electrons to form chlorine gas. Statement 3 is not correct: the positive sodium ions move to the negative electrode and gain electrons to form sodium. Statement 4 is not correct: there is no water, so no hydrogen forms; sodium forms at the negative electrode. B, C and D each include statement 3 or 4.

A: the object to be plated is made the negative electrode; the positive chromium ions are attracted to it and form a thin layer of chromium that protects the steel from rusting. B: positive ions move towards the negative electrode, not away from it. C: positive ions cannot move towards a positive electrode, because like charges repel. D: the ions do move away from a positive electrode, but then the chromium would not form on the handlebar; the handlebar would have to be the negative electrode.

D: statement 3 is correct: an atom with 7 outer electrons gains 1 electron to complete its outer shell of 8, so it forms a 1− ion (as fluorine and chlorine do). Statement 1 is not correct: the atoms with 2 outer electrons that form ions (beryllium, magnesium and calcium) are metals that lose them to form 2+ ions. Statement 2 is not correct: an atom with 5 outer electrons gains 3 electrons, so it forms a 3− ion (as nitrogen and phosphorus do). A, B and C each include statement 1 or 2.

C: from lithium to fluorine the atoms have 1, 2, 3, ... 7 outer shell electrons, so the number increases; the elements change from metals (lithium, beryllium) on the left to non-metals (carbon, nitrogen, oxygen, fluorine) on the right, so metallic character decreases. A: metallic character does decrease, but the number of outer shell electrons goes up by one at each element; it does not fall. B: both changes are the wrong way round. D: the number of outer shell electrons does increase, but metallic character does not: oxygen and fluorine on the right are non-metals, lithium and beryllium on the left are metals.

B: statement 1 is correct (Cl₂, Br₂ and I₂ are diatomic molecules); statement 2 is correct (chlorine is a pale yellow-green gas, bromine a red-brown liquid and iodine a grey-black solid); statement 3 is not correct: reactivity falls down Group 17, so iodine is less reactive than bromine and cannot displace it (bromine displaces iodide ions, not the other way round). A: includes the incorrect statement 3. C: includes 3 and leaves out the correct statement 1. D: leaves out the correct statement 1.

C: the outer shell of an argon atom (2,8,8) is full, which is a very stable arrangement, so its atoms have no tendency to lose, gain or share electrons and they form no bonds. A: the outer shell is not empty; it holds 8 electrons. B: an argon atom has 18 electrons in total; it is the full outer shell, not the total number of electrons, that makes it stable. D: atoms gain electrons to fill an outer shell that is not yet full (for example chlorine, 2,8,7); a full outer shell removes the tendency to gain electrons.

D: zinc does not react with cold water, but it reacts when heated strongly in steam to form zinc oxide and hydrogen. A, C: calcium and sodium are high in the reactivity series and react with cold water to form hydrogen and the metal hydroxide; they also react with steam. B: copper is below hydrogen in the reactivity series and does not react with water or steam.

A: the more reactive the metal, the faster it reacts with dilute hydrochloric acid, so the shorter the time taken to collect the hydrogen. P forms no gas, so it is the least reactive (it is below hydrogen in the reactivity series); then Q (150 s), S (35 s) and R (6 s), the most reactive: P → Q → S → R. B: Q and S are swapped; the longer time for Q shows that Q is less reactive than S. C: P and Q are swapped; P forms no gas, so it must be less reactive than Q. D: this is the order from most reactive to least reactive, the wrong way round (a longer time has been read as a more reactive metal).

C: magnesium is high in the reactivity series, so its compounds are very stable and magnesium is difficult to obtain from its ore (it needs electrolysis); copper is low in the series and is easily obtained, for example by heating its oxide with carbon. The more reactive a metal, the more difficult it is to obtain. A, B: copper is the metal that is easier to obtain, not more difficult. D: magnesium is more difficult to obtain, but the reason is that it is higher in the series, not lower.

D: zinc is more reactive than iron, so when the two metals are in contact the zinc corrodes in preference to the iron (sacrificial protection) and the iron does not rust while some zinc remains. A, B, C: copper, lead and silver are all less reactive than iron, so they do not protect it; the iron would corrode in preference to them, and it would rust at least as quickly as an iron nail on its own.

D: the rate is proportional to 1 ÷ time, so experiment 4 (20 s) is 160 ÷ 20 = 8 times as fast as experiment 1 (160 s). This agrees with the two changes: doubling the concentration doubles the rate (experiment 1 to 2: 160 ÷ 80 = 2) and raising the temperature from 20 °C to 40 °C makes it four times as fast (experiment 1 to 3: 160 ÷ 40 = 4); 2 × 4 = 8. A: 2 is the effect of doubling the concentration alone. B: 4 is the effect of the temperature rise alone. C: 6 comes from adding the two effects (2 + 4) instead of multiplying them.

B: sugarcane can be grown again within a short time, so more bioethanol can be made as it is used: it is a renewable fuel, and so an alternative to natural gas and crude oil, which are non-renewable. A: bioethanol is made from sugarcane grown recently; it is the fossil fuels (crude oil, natural gas) that were formed from organisms that died millions of years ago. C: bioethanol does form carbon dioxide when it burns; it is renewable because its source can be regrown. D: the sugar is replaced by growing more sugarcane, so it is not a limited supply.

A: isomers are compounds with the same molecular formula but different structural formulae. The hydrocarbon shown is C₄H₁₀ with a branched chain (methylpropane); butane is also C₄H₁₀ but its four carbon atoms are in an unbranched chain. B: this is the same molecule turned over (one carbon atom is still bonded to three other carbon atoms), so it is the same compound, not an isomer. C: propane is C₃H₈, a different molecular formula. D: but-1-ene is C₄H₈, a different molecular formula (it has a C=C bond).

B: statement 1 is correct (cracking makes alkenes), statement 2 is correct (hydrogen is also made) and statement 4 is correct (fractional distillation of crude oil gives too little of the small molecules that are in demand, so large molecules are cracked into smaller ones). Statement 3 is not correct: alkenes are unsaturated hydrocarbons. A, C, D: each includes statement 3, which is incorrect, and leaves out a correct statement (4, 2 or 1).

A: margarine is made by adding hydrogen to unsaturated vegetable oils, using a nickel catalyst. Hydrogen adds across the C=C bonds, so the number of C=C bonds decreases; the more saturated molecules pack together more closely and the product is a solid. B: hydrogen is correct, but adding hydrogen uses up C=C bonds; it cannot increase their number. C: steam adds to the C=C bond of ethene to make ethanol, but it is not used to make margarine. D: steam is not used, and addition would not increase the number of C=C bonds.

C: in a plentiful supply of air ethanol burns completely to form carbon dioxide and water, and the equation is balanced (2 C, 6 H and 7 O on each side). A: this equation shows ethanol being oxidised to ethanoic acid; that is the oxidation reaction of an alcohol, not combustion. B: carbon monoxide forms in a limited supply of air (incomplete combustion). D: the products are correct but the equation is not balanced (5 oxygen atoms on the left, 7 on the right).

D: propanoic acid has three carbon atoms in an unbranched chain, counting the carbon of the −CO₂H group: CH₃CH₂CO₂H. A: this structure has four carbon atoms in the chain, so it is butanoic acid. B: this structure has two carbon atoms, so it is ethanoic acid. C: this is propan-1-ol; it has three carbon atoms, but its functional group is −OH (an alcohol), not −CO₂H.

A: a carboxylic acid reacts with an alcohol to form an ester and water: CH₃CO₂H + C₂H₅OH → CH₃CO₂C₂H₅ + H₂O. Statements 1 and 2 are correct; the ester, ethyl ethanoate, has the sweet smell. Statement 3 is not correct: concentrated sulfuric acid is a catalyst, so it is not used up. B: leaves out statement 2, which is also correct. C: includes the incorrect statement 3 and leaves out statement 1. D: leaves out statement 1, which is also correct.

B: a polymer is a large molecule built up from many small units called monomers. A: different polymers are built up from different units; poly(ethene) is made from ethene, whereas nylon and Terylene are made from other monomers. C: this describes the reverse process, depolymerisation. D: different polymers can have different linkages: poly(ethene) has only carbon-carbon bonds in its chain, nylon has amide linkages and Terylene has ester linkages.

A: poly(ethene) is a typical plastic, and clingfilm (like plastic bags) is one of its uses. B: clingfilm is made from poly(ethene), but poly(ethene) is a plastic, not a man-made fibre; the man-made fibres are nylon and Terylene. C: poly(ethene) is a plastic, but fishing line is a typical use of the man-made fibre nylon, not of poly(ethene). D: fishing line is a use of nylon, which is a man-made fibre; neither part describes poly(ethene).

C: melting small pieces of waste poly(ethene) into pellets that can be moulded again is a physical method (no new substance forms); cracking the waste into smaller molecules for use as fuel is a chemical method. A: burying waste in landfill sites is a way of disposing of plastic, not a method of recycling it. B: the methods are the wrong way round: melting is physical and cracking is chemical. D: melting is physical, but burying waste in landfill sites is disposal, not a chemical method of recycling.

C: dry air is about 21% oxygen by volume, so 200 cm³ of air contains 200 × 21 ÷ 100 = 42 cm³ of oxygen, which reacts with the hot copper to form copper(II) oxide. A: 2 cm³ is 1% of 200 cm³, about the share of argon and the other gases in air, not of oxygen. B: 21 is the percentage of oxygen, used as if it were a volume in cm³. D: 156 cm³ is 78% of 200 cm³, the volume of nitrogen.

B: carbon monoxide gains oxygen to form carbon dioxide (the oxidation state of carbon rises from +2 to +4), so it is oxidised. A: carbon monoxide is oxidised, not reduced. C: nitrogen dioxide loses oxygen to form nitrogen (the oxidation state of nitrogen falls from +4 to 0), so it is reduced, not oxidised. D: unburnt hydrocarbons gain oxygen to form carbon dioxide and water, so they are oxidised, not reduced.