CHEMISTRY – Paper 1 Multiple Choice – mark scheme

C: the starting line is drawn in pencil because pencil does not dissolve in the solvent, so it stays on the line; the level of the solvent at the start must be below the starting line, so that the dyes are carried up the paper by the solvent and are not dissolved into the solvent in the container. A: the solvent is below the line, which is right, but ink is a mixture of dyes that would dissolve in the solvent, run up the paper and give extra coloured spots. B: ink is the wrong choice for the line, and with the solvent above the line the dyes would dissolve into the solvent in the container. D: pencil is right, but if the solvent is above the starting line the dyes wash off the paper into the solvent and nothing is separated on the paper.

D: to change from solid to gas, the particles must take in energy from the surroundings (statement 2) so that they can overcome the forces of attraction holding them together (statement 3). Statement 1 is wrong: in a gas the particles are far apart, so they move further apart, not closer together. A, B and C all include statement 1, which is wrong; B also leaves out statement 3 and C also leaves out statement 2.

B: at the same temperature, the gas with the lowest relative molecular mass has the lightest particles, which move fastest, so it diffuses fastest; this is methane (M_r = 16). The gas with the highest relative molecular mass, carbon dioxide (M_r = 44), has the heaviest particles, which move slowest, so it diffuses slowest. A: carbon monoxide (M_r = 28) is heavier than methane, so it is not the fastest. C: carbon monoxide is lighter than carbon dioxide, so it is not the slowest. D: this has the order reversed; a gas with a higher relative molecular mass diffuses more slowly, not faster.

A: the nucleus contains 5 protons (grey) and 6 neutrons (white), and the 5 electrons are arranged in shells as 2,3, so there are 3 electrons in the outer shell. B: 5 is the total number of electrons (2 + 3), not the number in the outer shell. C: 11 is the total number of particles in the nucleus (protons plus neutrons), not the number of neutrons. D: the protons and neutrons are the wrong way round; the key shows that the grey particles are protons and the white particles are neutrons.

C: the compound is neutral, so the charges must balance: three X ions and two Y ions balance when the ions are X²⁺ and Y³⁻ (3 × 2+ = 6+ and 2 × 3− = 6−). An X²⁺ ion has lost two electrons, so it has 10 electrons and the atom has 10 + 2 = 12 protons. A Y³⁻ ion has gained three electrons, so it has 10 electrons and the atom has 10 − 3 = 7 protons. A: this gives the right charges to the wrong elements (X as 3− and Y as 2+), so the proton numbers are the wrong way round. B: this takes the signs the wrong way round (X as 2− and Y as 3+): a metal atom loses electrons and a non-metal atom gains them. D: this reads the subscripts as the charges (X³⁺ and Y²⁻), but the subscripts show the numbers of ions, not their charges.

D: each sodium atom (2,8,1) loses its one outer electron to form Na⁺, which has a full outer shell of 8 electrons; the oxygen atom (2,6) gains these two electrons, one from each sodium atom, to form O²⁻ with 8 outer electrons. Two Na⁺ ions balance one O²⁻ ion, giving Na₂O. A: the oxide ion is drawn with only its own six electrons, so the two electrons that it gained from sodium are missing and it could not have a 2− charge. B: each sodium ion is drawn still holding its outer electron, although the + charge shows that it has been lost. C: only one sodium ion is drawn, which is the formula NaO; one sodium atom can give oxygen only one electron, so the oxygen ion drawn has 7 outer electrons and is not complete, and oxygen needs two electrons to fill its outer shell.

A: a molecule of methane, CH₄, has one carbon atom and four hydrogen atoms. Carbon has 4 outer electrons and each hydrogen atom has 1, so each hydrogen atom shares a pair of electrons with carbon. There are four shared pairs, so each hydrogen atom has 2 electrons, like helium, and the carbon atom has 8 electrons in its outer shell, and no electrons are left over. B: this shows only three hydrogen atoms, so it is CH₃; the carbon atom has 7 electrons round it, one of them unshared. C: all four shared pairs are shown, but the carbon atom is also drawn with an extra pair of electrons that it does not have; it would have 10 electrons round it, and its 4 outer electrons are all used in the shared pairs. D: this shows only two hydrogen atoms, so it is CH₂; the carbon atom has only 6 electrons round it.

B: a metal such as aluminium is a lattice of positive ions surrounded by a ‘sea’ of outer electrons that are free to move through the lattice; this is why it conducts electricity. A: shared pairs of electrons join the atoms of non-metals in covalent bonds; the atoms of a metal are not joined in this way. C: a lattice of positive and negative ions is an ionic compound, such as sodium chloride; a metal contains only positive ions, with electrons between them. D: small molecules held together by weak forces are found in simple molecular substances, such as iodine; a metal is a giant lattice with strong bonds.

D: an alloy is a mixture of a metal with another element; its diagram shows a giant lattice of metal atoms in which atoms of a different size are mixed in among the others. A: all the atoms are the same size and in regular layers, so this is a pure metal. B: the atoms are joined in pairs of the same element and are far apart, so this is a molecular element (a gas), not a metal or an alloy. C: the atoms are joined in pairs of two different elements and are far apart, so this is a compound made of small molecules, not a lattice of metal atoms.

C: iron(III) oxide is an insoluble solid, hydrochloric acid is aqueous, iron(III) chloride is a soluble chloride so it is (aq), and water is a liquid, (l); there are 2 Fe, 3 O, 6 H and 6 Cl on each side, so the equation is balanced. A: iron(III) chloride is soluble in water (all chlorides are soluble except those of silver and lead), so it should be (aq), not (s). B: water formed in a reaction is a pure liquid, (l); (aq) is used for a substance dissolved in water. D: this is not balanced: there are only 2 Cl on the left but 6 Cl on the right, and 3 O on the left but only 1 O on the right.

C: relative atomic mass is the average mass of one atom of the element (an average because atoms of an element can be isotopes with different masses) compared with one-twelfth of the mass of one atom of carbon-12. A: the standard for the scale is carbon-12, not hydrogen. B: the standard is one-twelfth of the mass of a carbon-12 atom, not the whole atom; with the whole atom as the standard, every value would be twelve times too small. D: this is the nucleon number of one atom, a whole number; relative atomic mass is a ratio of masses and need not be a whole number (for example chlorine, 35.5).

B: one mole of a substance contains 6.02 × 10²³ particles (the Avogadro constant), and the particles of oxygen are molecules, so the number of moles is 1.20 × 10²⁴ ÷ 6.02 × 10²³ = 2.0 mol. A: this divides the Avogadro constant by the number of molecules, which is upside down (6.02 × 10²³ ÷ 1.20 × 10²⁴). C: 4.0 mol is the number of moles of oxygen atoms (each molecule has two atoms), but the question asks for molecules. D: this has the power of ten wrong (1.20 × 10²⁴ ÷ 6.02 × 10²²).

B: the equation shows that 2 mol of Mg react with 1 mol of O₂, so 3.0 mol of magnesium reacts with 3.0 × 1/2 = 1.5 mol of oxygen. One mole of any gas occupies 24 dm³ at r.t.p., so the volume is 1.5 × 24 = 36 dm³. A: this is the volume of 1.0 mol of oxygen, the number in the equation, and it does not use the 3.0 mol of magnesium. C: this is the volume of 3.0 mol of oxygen, which ignores the ratio in the equation. D: this uses the ratio upside down (3.0 mol of magnesium × 2 = 6.0 mol of oxygen, 6.0 × 24).

A: Universal Indicator is red in an acid, green in a neutral liquid and purple in a strong alkali. An acid has more H⁺ ions than OH⁻ ions; in a neutral liquid, such as pure water, the numbers of H⁺ and OH⁻ ions are equal; an alkali has more OH⁻ ions than H⁺ ions. B: a neutral liquid does contain H⁺ and OH⁻ ions (in equal numbers); it is not true that it has none. C and D: the acid and the alkali are the wrong way round; red shows an acid, which has more H⁺ ions, and purple shows an alkali, which has more OH⁻ ions (D also says that pure water has no ions).

A: calcium oxide is a base (the oxide of a metal); a base reacts with an acid to form a salt and water, so it neutralises the acid: CaO + H₂SO₄ → CaSO₄ + H₂O. B and D: carbon dioxide and sulfur dioxide are acidic oxides (oxides of non-metals); they dissolve in water to give acids, so they would not neutralise an acid. C: sodium chloride is a neutral salt; it does not react with an acid.

B: in 1, magnesium carbonate forms, because carbonates are insoluble except those of Group 1 and ammonium (potassium sulfate stays dissolved); in 4, copper(II) hydroxide forms, because hydroxides are insoluble except those of Group 1 and ammonium (sodium sulfate stays dissolved). In 2, the possible products zinc sulfate and sodium nitrate are both soluble (all nitrates are soluble, and zinc sulfate is not one of the insoluble sulfates of barium, calcium and lead), so there is no precipitate. In 3, the products barium nitrate and ammonium chloride are both soluble (all nitrates, all ammonium salts), so there is no precipitate, even though barium forms an insoluble sulfate. A includes 3, C includes 2 and 3, and D includes 2; none of these three mixtures gives an insoluble product.

C: with aqueous ammonia, aluminium ions give a white precipitate that does not dissolve in excess, and copper(II) ions give a light blue precipitate that dissolves in excess to give a dark blue solution. At the end, the white aluminium hydroxide precipitate is left in the dark blue copper solution. A: this is what copper(II) ions alone would give; it ignores the aluminium ions, whose white precipitate does not dissolve in excess aqueous ammonia. B: this is what the mixture would show with excess aqueous sodium hydroxide (the aluminium precipitate dissolves in excess and the light blue copper(II) precipitate does not), not with aqueous ammonia. D: the light blue precipitate of copper(II) hydroxide dissolves in excess aqueous ammonia to give a dark blue solution, so it is not left as a precipitate.

A: oxidation is gain of oxygen: carbon gains oxygen to form carbon dioxide, so carbon is oxidised. B: carbon does gain oxygen, but gaining oxygen is oxidation, not reduction. C: lead(II) oxide does lose oxygen, but losing oxygen is reduction, not oxidation. D: lead(II) oxide does not gain oxygen; it loses oxygen as it is changed to lead. Losing oxygen is reduction, so lead(II) oxide is reduced, but this statement gives the wrong reason.

D: reduction is gain of electrons. In this half-equation copper(II) ions gain two electrons to form copper atoms, and the oxidation state of copper falls from +2 to 0. A, B, C: in each of these an ion or atom loses electrons (the electrons are on the right-hand side), which is oxidation: iron(II) is oxidised to iron(III), bromide ions to bromine, and zinc atoms to zinc ions.

B: the same current passes through both electrodes, so for every two electrons used to change a copper(II) ion into a copper atom at the negative electrode, a copper atom at the positive electrode gives up two electrons and forms a copper(II) ion. Copper(II) ions are therefore formed and used up at the same rate, the concentration of copper(II) ions in the electrolyte does not change, and the blue colour stays the same; the copper simply moves from the impure positive electrode to the pure negative electrode. A: copper(II) ions are used up at the negative electrode, but they are replaced at the positive electrode. C: copper(II) ions are added at the positive electrode, but they are also removed at the negative electrode. D: the copper(II) ions are not all used up; the positive electrode keeps replacing them, and the solution stays blue.

B: in a simple cell the voltage is greater the further apart the two metals are in the reactivity series, because one metal then has a much greater tendency than the other to lose electrons and form positive ions. In order of decreasing reactivity the metals are magnesium, zinc, iron, copper, so magnesium and copper are the furthest apart (three places) and give the highest voltage. A: copper and iron are next to each other in this list, so they give a low voltage. C: iron and magnesium are only two places apart, so the voltage is lower than for magnesium and copper. D: iron and zinc are next to each other, so they give a low voltage.

C: the elements in the Periodic Table are arranged in order of increasing proton number. An atom has as many electrons as protons, so W has 20 protons and Z has 17. An ion has gained or lost electrons: X has 2 more electrons than protons (charge 2−), so it has 18 − 2 = 16 protons, and Y has 1 fewer electron than protons (charge 1+), so it has 18 + 1 = 19 protons. The order of increasing proton number is X (16), Z (17), Y (19), W (20). B: this is the order of increasing nucleon number (32, 37, 40, 41); the elements are not arranged by nucleon number: W has a smaller nucleon number than Y but more protons, so it comes after Y in the Periodic Table. D: this is the order of increasing number of electrons, which is not the same as the number of protons for ions. A: this is the exact reverse of the Periodic Table order.

B: a magnesium atom has 12 electrons arranged 2,8,2. It has three occupied shells, so it is in Period 3, and two outer electrons, so it is in Group 2. A: Group 2 is right but only two shells would put the element in Period 2. C, D: the group number equals the number of outer electrons (2), not the number of shells (3). Row C also swaps the group and the period.

D: the Group 1 metals become more reactive with water down the group, so potassium reacts much more vigorously than lithium. Lithium floats and fizzes steadily; potassium floats, melts into a ball, moves quickly over the surface and burns with a lilac flame. A: potassium does not sink; like lithium it is less dense than water. B: the two metals are the wrong way round; it is potassium, the more reactive metal, that burns. C: lithium does not sink (lithium, sodium and potassium all float).

B: copper is a transition element, and the compounds of transition elements are usually coloured; aqueous copper(II) nitrate is blue. A, C, D: aluminium, magnesium and sodium are not transition elements. Their compounds are colourless in aqueous solution.

A: heating a metal carbonate gives the metal oxide and carbon dioxide, which turns limewater milky. The carbonates of the less reactive metals are less stable to heat and decompose more easily, so the carbonate of the least reactive metal here, copper, breaks down first: CuCO₃ → CuO + CO₂. B, C, D: zinc, magnesium and calcium are all more reactive than copper, so their carbonates are more stable to heat. They need more heating before they decompose, and the more reactive the metal the longer this takes, so calcium carbonate is the last of the four.

D: galvanising is coating iron or steel with a layer of zinc. The zinc is a barrier that keeps oxygen and water away from the steel, which stops it rusting. A, B, C: grease, paint and plastic coating are also barrier methods of preventing rusting, but none of them is called galvanising.

C: a negative ΔH means that the reaction is exothermic: energy is given out to the surroundings, so the products have less energy than the reactants. A: an endothermic reaction has a positive ΔH. B: an exothermic reaction gives out heat, so the surroundings become warmer, not colder. D: an exothermic reaction gives out heat; once the hydrogen has been lit, the heat given out keeps it burning.

B: statement 1 makes the acid more concentrated, so there are more acid particles in each dm³ and they collide with the zinc more often. Statement 3 makes the surface area of the zinc larger, so more zinc particles are exposed to the acid and the collisions are more frequent. Statement 2 does not change the rate at the start: the acid is as concentrated as before (1.0 mol / dm³), so there are the same number of acid particles in each dm³; it only means that there is more acid in the beaker. Statement 4 makes the acid more dilute, so the reaction is slower. A, C and D each include statement 2 or statement 4.

C: crude oil is separated by fractional distillation because its hydrocarbons have different boiling points. The larger the hydrocarbon molecule (the more carbon atoms it has), the higher its boiling point, so the fraction that boils above 360 °C contains the largest molecules. A, D: the fractions that boil from 40 to 180 °C and from 180 to 360 °C contain molecules that are smaller than those in fraction R. B: the fraction that boils below 40 °C contains the smallest molecules of the four.

D: propane is an alkane with three carbon atoms (prop-) in a chain, joined to each other and to eight hydrogen atoms by single bonds, C₃H₈. A: this is butane, which has four carbon atoms. B: this is ethane, which has two carbon atoms. C: this has three carbon atoms, but it contains a C=C double bond, so it is the alkene propene, C₃H₆.

A: isomers are compounds with the same molecular formula but different structural formulae, that is, the same atoms joined together in a different arrangement. B: this is the reverse of the definition; isomers have different structures but the same molecular formula. C: the molecules contain the same atoms, so isomers have the same relative molecular mass. D: all the isomers of C₈H₁₈ are alkanes (C_nH_2n+2), so they belong to the same homologous series.

B: the molecule has four carbon atoms in a chain (but-) and a C=C double bond, so it is an alkene, butene (C₄H₈). A: butane also has four carbon atoms, but it is an alkane and has only single bonds. C, D: ethene has two carbon atoms and propene has three; this molecule has four.

C: butanol, CH₃CH₂CH₂CH₂OH, has a chain of four carbon atoms with an –OH group on the end. There are 3 + 2 + 2 + 2 = 9 hydrogen atoms bonded to carbon atoms and 1 hydrogen atom in the –OH group, so 10 in all. B: 9 forgets the hydrogen atom of the –OH group. A: 8 is the number of hydrogen atoms in an alkene with four carbon atoms, C₄H₈; butanol has no double bond. D: 12 treats every carbon atom as a CH₃ group, but only the carbon atom at the end of the chain has three hydrogen atoms.

D: in fermentation, yeast changes glucose into ethanol and carbon dioxide: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂. Ethanol is also made by the addition of steam to ethene, with a catalyst: C₂H₄ + H₂O → C₂H₅OH. A, B: ethane and ethene cannot be fermented; fermentation needs a sugar such as glucose. A, C: ethane is saturated, so steam cannot add to it; the addition of steam needs the C=C double bond of ethene. B: the two substances are the wrong way round.

A: ethene has a C=C double bond, so it reacts with aqueous bromine by addition and the orange colour disappears. In addition polymerisation the C=C bonds of the ethene molecules open up to join the molecules end to end, so poly(ethene) has only single bonds between its carbon atoms. It is saturated and does not react with aqueous bromine, which stays orange. B, C, D: each of these rows gives a wrong result for ethene (orange would mean that it does not react) or for poly(ethene) (colourless would mean that it still contains C=C bonds).

C: poly(ethene) is made by joining ethene molecules, and plastic bags (like clingfilm) are made from this typical plastic. A: clingfilm is a use of poly(ethene), but ethane is saturated and cannot be a monomer. B: the monomer is right, but fishing line is made from a man-made fibre, nylon, not from poly(ethene). D: clingfilm is a use of poly(ethene), but propene is the monomer of a different polymer.

D: statement 2 is an economic disadvantage, because the plastic must be collected, cleaned and sorted into its different types before it can be recycled, and this costs money. Statement 3 is an environmental disadvantage, because the lorries use fuel, which releases carbon dioxide. Statement 1 is an advantage, not a disadvantage: recycling saves crude oil, a non-renewable resource, and the energy used to extract and process it. A, B and C each include statement 1.

A: nitrogen oxides form when nitrogen and oxygen from the air react at very high temperatures, in lightning and in internal combustion engines such as those of cars. B: volcanoes are a source of sulfur dioxide, not of nitrogen oxides. C: lightning is a source of nitrogen oxides, not of sulfur dioxide; sulfur dioxide is formed when fossil fuels that contain sulfur are burnt. D: volcanoes are a natural source of sulfur dioxide, but sulfur dioxide from human activity comes from burning sulfur-containing fossil fuels; incomplete combustion is the source of carbon monoxide.

A: acid rain contains acids such as nitric acid, formed when nitrogen dioxide from vehicle engines dissolves in rain. An acid reacts with a carbonate to give a salt, water and carbon dioxide, so the statue slowly dissolves: CaCO₃ + 2HNO₃ → Ca(NO₃)₂ + H₂O + CO₂. B: hydrogen is given off when an acid reacts with a reactive metal, not with a carbonate. C: no oxygen gas is formed; the oxygen atoms of the carbonate end up in the carbon dioxide and the water. D: sulfur dioxide is one of the gases that dissolve in rain to form the acid, but it is not made when the acid reacts with the limestone.