Chemistry Paper 2 June 2024

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1. Aaluminium and oxygen atoms share their outer electrons so tightly that the shared pairs cannot vibrate freely at room temperature.
2. Bthe small size of the ions lets them pack so closely that no space remains for the lattice to melt at ordinary temperatures.
3. Cthe weak forces between separate Al2O3 molecules only break apart well below room temperature, at a very low melting point.
4. Da great deal of energy is needed to overcome the many strong electrostatic forces holding the oppositely charged ions together.

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1. Aiodine sublimes directly from solid to vapour on heating, while sodium chloride does not and is left behind.
2. Bsodium chloride sublimes directly from solid to vapour on heating, while iodine melts and stays as a liquid.
3. Cthe two solids react together on heating to form a single new compound that is then filtered off.
4. Diodine dissolves completely in molten sodium chloride, leaving a single liquid that is then distilled.

1. Adissolved carbon dioxide makes rain water naturally slightly acidic, and this acid slowly reacts with and dissolves calcium carbonate.
2. Brain water is pure H2O with a pH of exactly 7, and pure water alone is able to dissolve calcium carbonate directly.
3. Crain water carries fine dust particles that physically scrape and wear away the surface of the stone over many years.
4. Drain water freezes inside the stone every night, and the repeated expansion of the ice alone cracks the surface apart.

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1. Aunable to tell from a chromatogram
2. Bbrown
3. Cgreen
4. Dpurple

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1. Athe paper adsorbs every dye by exactly the same amount, so the distance a dye travels shows only how soluble it is and nothing about adsorption.
2. Bthe solvent carries every dye at exactly the same speed, so any difference in how far dyes travel comes only from evaporation of the solvent.
3. Chow far a dye travels up the paper depends only on its colour, and darker colours are always adsorbed more strongly by the paper.
4. Dhow far a dye travels up the paper is set by the balance between adsorption to the paper and solubility in the solvent, and the dye rising least is the one the paper holds most strongly relative to how well the solvent dissolves it.

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1. Amelt a mixture of solids so that the one with the lowest melting point can be poured away first.
2. Btest an athlete's blood or urine sample for banned drugs, or identify the amino acids in a protein.
3. Cburn a fuel sample completely so that its total energy content can be measured directly.
4. Delectrolyse a molten salt so that the metal and non-metal it contains can be collected separately.

1. Azinc is the negative electrode, since it is more reactive than copper and loses electrons more readily, releasing them into the circuit.
2. Bzinc is the positive electrode, since it is more reactive than copper and so is the electrode where reduction occurs.
3. Ccopper is the negative electrode, since it is the less reactive metal and so loses electrons more readily than zinc.
4. Dneither electrode can be called positive or negative until the cell is connected to an external appliance that draws current.

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1. Ahydrogen at the anode and oxygen at the cathode.
2. Bhydrogen at the cathode and oxygen at the anode.
3. Coxygen at both the anode and the cathode.
4. Dsulphur at the cathode and oxygen at the anode.

1. A2H+(aq) + 2e- -> H2(g)
2. B4OH-(aq) -> O2(g) + 2H2O(l) + 4e-
3. CCu2+(aq) + 2e- -> Cu(s)
4. DSO4 2-(aq) -> SO4(g) + 2e-

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1. Athe lattice energy given out as gaseous nitrogen and hydrogen ions come together to form a solid ionic lattice.
2. Bthe reaction reaching dynamic equilibrium, where the forward and reverse reactions proceed at exactly equal rates.
3. Cthe activation energy being absorbed, as reacting particles must gain enough energy to break bonds, including the strong N to N triple bond, before reacting.
4. Dthe enthalpy change of the reaction, the overall difference in energy between the reactants and the final products of the reaction.

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1. Aenergy being absorbed as new N-H bonds form, making the overall reaction endothermic.
2. Benergy being released as new N-H bonds form in ammonia, with more energy given out than was absorbed breaking the original bonds, making the reaction exothermic.
3. Cthe activation energy of the reverse reaction only, with no bearing on whether the forward reaction is exothermic or endothermic.
4. Dunreacted nitrogen and hydrogen molecules cooling back down to the original reactant temperature without any new bonds forming.

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1. Aall of the reactants have been completely converted into products, so the reverse reaction can no longer occur at all.
2. Bthe concentrations of reactants and products are always exactly equal to one another at every point in the reaction.
3. Cthe forward and reverse reactions are still occurring, but at exactly equal rates, so the concentrations of reactants and products stay constant.
4. Dthe reaction has stopped completely, with neither the forward nor the reverse reaction taking place any longer.

1. Ashifts the position of equilibrium to the right, favouring the forward reaction, so the solution becomes more yellow.
2. Bsplits the equilibrium into two separate, unrelated equilibria that no longer interconvert with each other.
3. Chas no effect on the position of equilibrium, since H+ appears only on the product side of the equation.
4. Dshifts the position of equilibrium to the left, favouring the reverse reaction that uses up the added H+ ions, so the solution becomes more orange.

1. Ashifts the position of equilibrium to the right, favouring the forward reaction to replace some of the removed CrO4 2-, so the solution becomes more yellow.
2. Bstops the equilibrium reaction completely, since one of the two directions is no longer chemically possible.
3. Chas no effect on the position of equilibrium, since removing a product cannot influence a reaction already at equilibrium.
4. Dshifts the position of equilibrium to the left, so more of the yellow chromate is converted back into orange dichromate.

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1. AM has stopped losing heat completely for that period, so no further cooling occurs at all until heat loss resumes.
2. BM is changing state from gas to liquid at its boiling point, and the latent heat of vaporisation is being given out rather than the temperature falling.
3. CM is undergoing a chemical reaction with the air at that temperature, which releases heat and exactly balances the heat being lost.
4. Dthe thermometer used to record the curve cannot register any temperature change below 86 degrees C.

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1. Aimpurities always lower the boiling point and sharpen the flat section into a single, more exact temperature.
2. Bimpurities have no measurable effect on the boiling point of a substance under any circumstances.
3. Cimpurities lower the boiling point and widen the temperature range over which the substance changes state.
4. Dimpurities raise the boiling point and widen the temperature range over which the substance changes state, rather than boiling at one sharp temperature.

1. Aeach solid is chemically inert and cannot react with any other substance under any conditions.
2. Bthe particles in a solid are held in fixed positions in a rigid lattice and can only vibrate, not move from place to place.
3. Cthe particles of the two solids repel each other electrically, keeping them permanently apart.
4. Dthe two solids are always far too dense for their particles to move at all, even as a gas or liquid would.

1. Asmoke particles are in constant random motion and diffuse through the air, spreading from high to low concentration until they reach the by-stander.
2. Bsmoke particles carry an electric charge that is attracted directly towards any nearby person in the room.
3. Csmoke particles sink straight down to the floor and then spread out sideways only along the floor of the room.
4. Dthe air conditioning in the room actively pumps the smoke towards every person present, whatever the layout.

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1. Aare gradually converted to lead(II) sulphate, as lead in the negative electrode is oxidised and lead in the positive electrode is reduced, both combining with sulphate ions from the acid.
2. Bdissolve completely and irreversibly into the sulphuric acid electrolyte, which cannot be reversed by recharging.
3. Cstay chemically unchanged throughout discharge, since only the electrolyte concentration changes as the battery is used.
4. Dare both reduced to metallic lead, since discharging always favours reduction at every electrode of the cell.

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1. Athey release no pollutant gases at all, but are simply expensive compared with renewable sources of energy.
2. Bthey renew themselves within a few years of being extracted, so their supply can never actually run low.
3. Cburning them releases carbon dioxide, a greenhouse gas that contributes to global warming, and incomplete combustion can release toxic carbon monoxide.
4. Dthey burn at far too low a temperature to be useful for heating homes or generating electricity on any scale.

1. Aadd chlorine to the water to kill any microorganisms present in it before storage.
2. Bclump fine suspended particles together into larger flocs that settle out of the water.
3. Cphysically trap and remove suspended solid particles as the water passes through the small gaps between sand grains.
4. Draise the pH of the water so that it no longer reacts with the pipes carrying it to homes.

1. Aa chemical flocculant is added, making fine suspended particles clump into larger flocs, which then settle out under gravity and are removed.
2. Bchlorine gas is bubbled through the water to kill any remaining bacteria and other microorganisms before it is supplied to homes.
3. Cthe water is boiled to evaporate off any remaining dissolved impurities before the vapour is condensed and collected.
4. Dthe water is simply left to stand so that all of the dissolved salts in it crystallise out and can be filtered off.

1. Aboil the water thoroughly, or add a few drops of household bleach or chlorine tablets, to kill microorganisms in it.
2. Belectrolyse the water using a car battery and two metal electrodes placed directly in the drinking water.
3. Cleave the water uncovered outdoors overnight so that any microorganisms in it die from the cold alone.
4. Dadd a small amount of concentrated sulphuric acid to the water and stir it thoroughly before drinking.

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1. Adestroys the natural landscape and habitats of the area, and produces large amounts of dust and noise from blasting and heavy machinery.
2. Bpermanently removes carbon dioxide from the atmosphere, which upsets the natural balance of gases needed by plants.
3. Cproduces large volumes of toxic gas that immediately and permanently poison the groundwater for many kilometres around.
4. Duses so much electricity that it is the single largest cause of a country's greenhouse gas emissions.

1. Astop using calcium carbonate altogether, since there is no other source of it anywhere in the country.
2. Babandon the worked out quarry exactly as it is, since nothing further can practically be done to it.
3. Cincrease the rate of blasting so that the quarry is worked through and abandoned as quickly as possible.
4. Drehabilitate the worked out quarry by landscaping it and replanting vegetation once quarrying has finished.

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1. Aa colourless gas is given off that turns limewater milky.
2. Ba sweet, fruity smell develops in the reaction mixture.
3. Cthe mixture changes colour from orange to green.
4. Dthe mixture turns from colourless to a deep blue.

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1. Athe metal producing the least gas must simply be the densest of the three, since density and reactivity always vary together.
2. Ba more reactive metal has a higher melting point, which allows it to react faster with a cold, dilute acid solution.
3. Ca more reactive metal's atoms lose electrons more readily, reacting faster with the acid's hydrogen ions to displace more hydrogen gas in the same time; N produced no gas at all, showing it is the least reactive of the three.
4. Dgas volume collected in this experiment depends only on the size of the metal sample used, not on how reactive the metal itself is.

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1. Abiodegrades within a few days of being discarded, releasing large amounts of methane gas as it does so.
2. Bdissolves completely and harmlessly in rain water within a short time of being discarded outdoors.
3. Cis non-biodegradable, so discarded plastic persists in landfill, soil and waterways for a very long time and can harm wildlife.
4. Dreacts spontaneously with the oxygen in air at room temperature, releasing toxic gases without needing to be burned.

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1. Aboiling the sodium hydroxide solution alone until it evaporates completely, leaving solid sodium sulphate crystals directly in the container.
2. Bfiltering the sodium hydroxide solution to remove sodium sulphate crystals that are already dissolved and simply too big to stay in solution.
3. Cmixing the two solutions and immediately filtering off the crystals that form, without any heating, evaporation or cooling step at all.
4. Dadding acid to alkali until exactly neutralised, evaporating the solution to the point of crystallisation, then cooling it undisturbed so crystals form, before filtering, washing and drying them.

1. Abarium atoms are smaller than magnesium atoms, so their outer electrons are held more tightly by the nucleus.
2. Bbarium has more electron shells than magnesium, so its outer electrons are further from the nucleus and more shielded, and so are lost more easily.
3. Cbarium has the same number of outer electrons as magnesium, and reactivity in Group II does not depend on atomic size at all.
4. Dmagnesium has more electron shells than barium, so magnesium's outer electrons are lost more easily than barium's.

1. Amagnesium reacts vigorously with the cold water, while barium does not react with water at all, even as steam.
2. Bneither metal reacts with cold water at all, since both need steam before any reaction is observed.
3. Cboth metals react at exactly the same, moderate rate with cold water, since they are in the same group.
4. Dbarium reacts vigorously, even violently, with the cold water, while magnesium reacts only very slowly, needing steam to react quickly.

1. Amagnesium metal is displaced directly from solution by calcium and appears as a white solid coating on the calcium's surface.
2. Bcalcium is too unreactive to do anything in the solution, so the white solid is simply unreacted calcium metal settling out.
3. Ccalcium reacts with the water present to form calcium hydroxide, which then reacts with the magnesium sulphate to precipitate insoluble magnesium hydroxide.
4. Dmagnesium sulphate itself is white and simply becomes visible once the calcium is added, without any new reaction occurring.