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

D: a gas syringe is a graduated barrel with a plunger that the gas pushes out as it is made, so the volume of gas can be read straight from the scale. A: a burette measures volumes of liquid run out through its tap. B: a pipette measures out one fixed volume of liquid. C: a measuring cylinder measures volumes of liquid; standing upright, as drawn, it cannot collect or measure a gas.

A: this is distillation: the water boils off as steam, the steam is cooled in a condenser and the pure liquid that forms (the distillate) is collected, while the dissolved salts stay behind in the flask. B: the liquid left in the flask is the water that still contains the dissolved salts, in a more concentrated solution. C: dissolved salts pass through filter paper, so the filtrate is still tap water; filtration only removes undissolved solids. D: this collects the dissolved salts as a solid and loses the water.

C: a colouring in the icing is one of the known colourings only if its spot is level with a spot of that known colouring. Spot 3 is not level with any spot in the lanes of W, X, Y or Z (the single spots of Y and Z are lower and higher), so it must be caused by a different colouring. A: spot 1 is level with the spot of W. B, D: spots 2 and 4 are level with the two spots of X (X is itself a mixture of two colourings).

A: the proton number is the number of protons in the nucleus (11); the nucleon number is the number of protons plus neutrons (11 + 12 = 23). B: adds the 11 electrons as well; electrons are not nucleons. C: uses the number of neutrons (12) as the proton number. D: the two numbers are the wrong way round.

B: each overlap holds two pairs of electrons shared between the carbon atom and one oxygen atom (a double bond). Counting the shared electrons, the carbon atom has 4 + 4 = 8 outer electrons and each oxygen atom has 4 + 4 = 8: all three atoms have the electronic configuration of neon. A: the atoms share electrons; none are gained or lost, so there are no ions. C: the diagram shows four electrons (two pairs) in each overlap, not two. D: the carbon atom also reaches eight electrons, because it shares two pairs with each oxygen atom.

B: A_r compares the average mass of an atom of the element (an average because of isotopes) with one-twelfth of the mass of an atom of carbon-12, and has no unit. A: this is the actual mass of an atom, not a relative mass. C: leaves out the one-twelfth (carbon-12 itself would then have A_r = 1 instead of 12). D: this is the nucleon number of an atom, not its relative atomic mass.

B: an alkali reacting with an acid is neutralisation: the hydrogen ions from the acid and the hydroxide ions from the alkali combine to form water, and the potassium and nitrate ions are unchanged. A: the hydroxide ions react with ammonium ions to give ammonia gas and water. C: the hydrogen ions react with carbonate ions, so carbon dioxide is formed as well as water. D: the hydrogen ions react with zinc atoms to give hydrogen gas.

C: aluminium oxide is a metal oxide that reacts with both acids and alkalis (amphoteric); carbon dioxide is a non-metal oxide that dissolves in water to form an acid and reacts with alkalis (acidic); carbon monoxide is a non-metal oxide that reacts with neither acids nor alkalis (neutral). A: aluminium oxide also reacts with acids, so it is not simply acidic. B: carbon monoxide does not react with alkalis, so it is not acidic. D: aluminium oxide also reacts with alkalis, so it is not simply basic.

D: in the rusting of iron, each iron atom loses electrons and its oxidation state increases from 0 to +3, while each oxygen atom gains electrons and its oxidation state decreases from 0 to −2: electrons are transferred, so this is a redox reaction. A, B and C: no element changes its oxidation state, so there is no electron transfer (in A, calcium stays +2, carbon +4, oxygen −2, hydrogen +1 and chlorine −1; in B, calcium stays +2, carbon +4, oxygen −2 and hydrogen +1; in C, sodium stays +1, oxygen −2, hydrogen +1 and chlorine −1). A gas is given off in A, but forming a gas does not make a reaction redox.

B: atoms with only a few outer shell electrons (1 to 3) are atoms of metals, and metal atoms tend to lose their outer electrons to form positive ions. A: an atom with 2 outer electrons is a metal, but it loses them; metals do not gain electrons. C: an atom with 6 outer electrons is a non-metal, not a metal. D: an atom with 7 outer electrons is a non-metal, but non-metal atoms gain electrons (or share them); they do not lose them.

C: the faster a metal gives hydrogen with the acid, the more reactive it is. Y gives no gas, so it is the least reactive; X is slowest (150 s), then Z (75 s), and W is the fastest (30 s) and so the most reactive. A: this runs from the most reactive to the least reactive, the wrong direction for increasing reactivity, and X and Z are also the wrong way round. B: the order is right but runs from the most reactive to the least reactive, the wrong direction (a long time means a less reactive metal). D: the direction is right but X and Z are the wrong way round.

A: bioethanol is made from sugarcane, which can be grown again each year, so it is a renewable fuel that can replace natural gas and crude oil, which will run out. B: every fuel is used up when it burns; a fuel is renewable when its source can be replaced quickly. C: natural gas and crude oil are the fossil fuels; bioethanol is made from plants that grow now. D: bioethanol is ethanol, an alcohol, and is made from sugarcane, not from crude oil.

B: the alkanes form a homologous series, so their physical properties show a gradation: the boiling point rises as the molecules get larger, by a smaller and smaller amount each time (73, 47, 41 °C), so pentane is expected to boil about 35 to 40 °C above butane, at about 36 °C. A: this is the boiling point of butane; the boiling point does not stay the same as the molecules get larger. C: adds the first, much larger, increase (73 °C) instead of following the trend. D: far too large an increase for one more CH₂ unit.

D: propene, C₃H₆, has a carbon–carbon double bond. It is unsaturated and the double bond reacts with (adds) bromine, which decolourises aqueous bromine. A: propane, C₃H₈, has more hydrogen atoms than propene, not fewer; it is saturated, with no double bond for the bromine to react with. B: propane has only single bonds, so it is saturated, not unsaturated. C: propene has a double bond, so it is unsaturated, not saturated.

C: margarine is made by adding hydrogen to the unsaturated vegetable oil: hydrogen adds across the carbon–carbon double bonds, so each molecule has fewer C=C bonds (it is more saturated), and the product is a solid at room temperature. A: fewer C=C bonds is right, but margarine is a solid, not a liquid. B, D: adding hydrogen removes double bonds; it cannot give more of them (B is also wrong about the state).

D: in complete combustion an alcohol burns in excess oxygen to form carbon dioxide and water, and this equation is balanced (2 C, 6 H and 7 O on each side). A: this shows the oxidation of ethanol to a carboxylic acid, ethanoic acid, not combustion. B: the products are right but the equation is not balanced. C: this forms carbon monoxide, which is the product of incomplete combustion.

A: statements 1 and 2 are correct. A polymer is a very large molecule built up from many small molecules (monomers) joined together; the monomer of poly(propene) is propene. Statement 3 is not correct: the double bond of each propene molecule opens when the monomers join, so the polymer has only single bonds between its carbon atoms. Statement 4 is not correct: different polymers have different monomers; poly(ethene) is made from ethene. B, C, D each include statement 3 or 4 and so are wrong.

D: non-biodegradable plastics cannot be broken down by bacteria, so they stay in landfills, rivers and the sea for a very long time and can harm animals that eat them or become trapped in them. A: bacteria cannot break them down, so they are not quickly broken down. B: plastics are insoluble in water and do not form acids. C: plastics do not rot (rotting is the breakdown of plant and animal material).

B: carbon monoxide and methane are both common atmospheric pollutants. A: argon is a harmless noble gas that makes up part of clean air (nitrogen dioxide is a pollutant). C: oxygen is a gas in clean air (methane is a pollutant). D: nitrogen is the main gas in clean air (sulfur dioxide is a pollutant).

C: statements 2 and 4 are correct. Carbon monoxide is toxic: it lowers the ability of the blood to carry oxygen. Sulfur dioxide irritates the lungs and can make breathing difficult. Statement 1 is not correct: methane is hardly soluble in water and does not form an acid; acid rain is caused by sulfur dioxide and nitrogen dioxide. Statement 3 is not correct: acid rain makes the water in lakes and ponds more acidic, which can kill fish and other water life. A, B, D each include statement 1 or 3 and so are wrong.