Chemistry Paper 3 November 2023

1. A65.9
2. B66.5
3. C67.1
4. D67.5

1. Athe ionic charges are large and the ionic radii are small
2. Bthe ions are of equal size
3. Cthe compound has a low melting point
4. Dthe ionic charges are small and the ionic radii are large

1. Aa lower relative atomic mass than sodium
2. Ba higher charge and a smaller radius, giving it a much higher charge density
3. Ca larger radius, so more water molecules surround it
4. Da complete outer shell of electrons

1. AThe number of neutrons in one atom of an isotope, with no reference to carbon-12 at all
2. BThe mass of one atom of an isotope relative to 1/12 the mass of an atom of carbon-12
3. CThe average mass of all the isotopes of an element relative to 1/12 the mass of carbon-12
4. DThe mass of one mole of an isotope measured directly in grams

1. AThe enthalpy change when one mole of an ionic solid dissolves completely in excess water
2. BThe enthalpy change when one mole of an ionic solid is formed from its constituent gaseous ions
3. CThe enthalpy change when one mole of a gaseous atom loses one electron to form a gaseous ion of the same element
4. DThe enthalpy change when one mole of a covalent bond is broken in the gaseous state

1. AIonic radius -- larger ions give a shorter inter-ionic distance, resulting in a greater lattice enthalpy
2. BAtomic mass -- heavier ions are sometimes wrongly assumed to give a greater lattice enthalpy regardless of their size or charge
3. CIonic radius -- smaller ions give a shorter inter-ionic distance, resulting in a greater lattice enthalpy
4. DMelting point -- ions from a substance with a higher melting point are sometimes wrongly assumed to give a greater lattice enthalpy

1. AA hydrogen atom bonded to N, O or F, and a second N, O or F atom bearing a lone pair to accept it
2. BA hydrogen atom bonded to any carbon atom in the molecule, and a second carbon atom elsewhere bearing a lone pair
3. CAny two atoms of similar electronegativity joined by a single covalent bond
4. DA hydrogen atom bonded to any halogen atom, and a metal ion nearby in the same molecule

1. ANH3, since it has the strongest intermolecular forces (hydrogen bonding) among the three gases
2. BHe, since it has the strongest intermolecular forces (hydrogen bonding) among the three gases
3. CCO2, since it is thought to be the only one of the three gases with any intermolecular forces present at all
4. DAll three gases deviate from ideal behaviour by exactly the same amount at every pressure

1. AAt high pressure the gas molecules stop moving entirely, which increases the measured pressure
2. BAt high pressure intermolecular attractions suddenly disappear completely for every gas
3. CAt high pressure the molecules' own volume becomes significant compared with the container's volume
4. DAt high pressure the gases are sometimes wrongly thought to all condense into liquids, which is assumed to increase the PV product sharply

1. AHelium is chemically identical to NH3 in terms of its intermolecular attractions
2. BHelium atoms are large and have very strong interatomic forces between them, similar to NH3
3. CHelium atoms are thought to be large and to have very strong interatomic forces between them, similar to NH3 molecules
4. DHelium atoms are small and have only very weak interatomic (van der Waals) forces between them

1. Athe first step in the mechanism
2. Bthe fastest step in the mechanism
3. Cthe step with the largest enthalpy change
4. Dthe slowest step in the mechanism

1. A11 169 s
2. B22 338 s
3. C44 676 s
4. D5 585 s

1. Atrigonal pyramidal, 107°
2. Bbent, 104.5°
3. Ctetrahedral, 109.5°
4. Dtrigonal planar, 120°

1. AA straight line through the origin, since rate is directly proportional to [NO]
2. BA straight line with a negative gradient as [NO] increases
3. CAn upward-curving line (parabola), since rate is proportional to the square of [NO]
4. DA horizontal line, since the rate is thought not to depend on [NO] under these particular experimental conditions

1. ANo conclusion about temperature can be drawn from a change in the rate constant alone
2. BY is higher, since the rate constant increases with temperature as more molecules exceed the activation energy
3. CY is lower, since the rate constant increases with temperature as more molecules exceed the activation energy
4. DY is higher, since the rate constant is sometimes mistakenly thought to decrease as temperature rises for most reactions

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1. AH3O+ (acid) and H3PO4 (its supposed conjugate base), though this pairing does not actually match the definition
2. BH3PO4 (acid) and H3O+ (its supposed conjugate base), though this pairing does not actually match the definition
3. CH3PO4 (acid) and H2PO4- (its conjugate base)
4. DH2O (acid) and H2PO4- (its supposed conjugate base), though this pairing does not actually match the definition

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1. ABoth electrodes are converted to PbSO4 and the sulphuric acid is used up, so the e.m.f. falls
2. BThe cell's electrodes swap chemical identity, reversing the direction of current flow
3. CThe lead electrodes are thought to dissolve away completely during discharge, leaving no electrode surface behind at all
4. DThe sulphuric acid electrolyte evaporates completely during discharge

1. Athe equilibrium shifts to the right and more ions are formed
2. Bthe equilibrium shifts to the left
3. Cthe value of $K_w$ decreases
4. Dthe water becomes alkaline

1. Aacids do not affect the hydroxide ion concentration
2. B$K_w$ has no units
3. Can equilibrium constant depends only on temperature
4. Dwater is a pure liquid and cannot ionise further

1. A0.4400 moldm⁻³
2. B0.0968 moldm⁻³
3. C0.1210 moldm⁻³
4. D0.1730 moldm⁻³

1. AWhen a system at equilibrium is subjected to a change, the equilibrium position is sometimes wrongly thought to shift so as to reinforce that change
2. BA system at equilibrium is sometimes wrongly thought to be unable to respond to any change made to its temperature, pressure or concentration
3. CWhen a system at equilibrium is subjected to a change, the reaction is sometimes wrongly thought to simply stop proceeding altogether
4. DWhen a system at equilibrium is subjected to a change, the equilibrium position shifts to oppose that change

1. AThe equilibrium is completely unaffected, since HCl is a strong acid and does not interact with water's own equilibrium
2. BThe equilibrium shifts to the left, but only because HCl lowers the temperature of the water
3. CThe equilibrium shifts to the left (ionisation is suppressed), since the added H+ is a common ion that opposes further ionisation
4. DThe equilibrium shifts to the right (ionisation increases), since added H+ is sometimes wrongly assumed to push any equilibrium towards more ions

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1. Aa good conductor of electricity
2. Breadily soluble in water
3. Ceasily decomposed by heat below 100 °C
4. Dcheap, white and stable at the processing temperature of PVC

1. Avery cheap
2. Bunstable to heat
3. Csoluble in PVC
4. Dtoxic

1. A$Ca_3N_2 + 2H_2O \rightarrow 3Ca + 2NH_4OH$
2. B$Ca_3N_2 + 6H_2O \rightarrow 3Ca(OH)_2 + N_2 + 3H_2$
3. C$Ca_3N_2 + 3H_2O \rightarrow 3CaO + 2NH_3$
4. D$Ca_3N_2 + 6H_2O \rightarrow 3Ca(OH)_2 + 2NH_3$

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1. AN2 has a very strong triple bond, so a large activation energy (supplied by heating) is needed to break it
2. BCalcium metal is too unreactive at any temperature to react with nitrogen gas at all
3. CThe reaction is endothermic overall, so it is sometimes wrongly assumed that it could not proceed at any temperature at all
4. DNitrogen gas is completely unreactive under any conditions, including at high temperature

1. AAmmonia is thought to decompose completely at any pressure or temperature, so conditions make no real difference to the outcome reached
2. BThe forward reaction is exothermic and reduces gas moles: high pressure raises yield but is costly, and low temperature raises yield but is too slow, so a compromise is used
3. CThe reaction reaches its maximum possible yield instantly under any conditions, so optimisation is unnecessary
4. DThe forward reaction is endothermic, so high pressure and high temperature are sometimes wrongly assumed to maximise both the yield and the reaction rate together at the same time

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1. ANaHCO3 is the only component that does not react with heat at all under any conditions
2. BOnly NaHCO3 decomposes on gentle heating (releasing H2O and CO2); Na2CO3 and Na2SO4 are thermally stable at this temperature
3. CNitrogen gas is thought to be completely unreactive under any conditions whatsoever, including at very high temperature and pressure
4. DNa2CO3 and Na2SO4 both evaporate completely on gentle heating, leaving only NaHCO3 behind

1. Abrown fumes of bromine appear
2. Ba purple vapour of iodine is formed
3. Cno change is seen
4. Da white solid is formed

1. Ahas accessible d orbitals to which water can bond
2. Bis a metal
3. Cis more electronegative than carbon
4. Dforms ionic chlorides

1. A+0.11 V
2. B+1.36 V
3. C+2.83 V
4. D−2.83 V

1. ANo change is observed at all, since HBr is sometimes wrongly assumed not to decompose under any laboratory conditions
2. BThe gas immediately turns colourless and condenses into a liquid on the glass rod
3. COnly slight decomposition occurs, giving a faint brown colour of Br2, since the H-Br bond is fairly strong
4. DRapid, complete decomposition occurs, giving a dense purple vapour of iodine

1. AThe solution turns orange/yellow as bromine is displaced from solution
2. BA white precipitate forms immediately and no colour change is seen
3. CThe solution turns deep blue as a starch-halogen complex forms
4. DThe solution turns colourless as all the bromide ions are permanently destroyed

1. AThe solution remains completely colourless throughout, with no visible change
2. BA colourless gas is released with vigorous effervescence and no colour change
3. CThe solution turns brown/dark as iodine is displaced from solution
4. DThe solution turns bright green as a chlorine-iodine complex forms

1. AIt is a soft, water-soluble solid that dissolves completely to form a paste-like cement mixture
2. BIt is a highly reactive metal oxide that corrodes steel reinforcement bars over time
3. CIt is a giant covalent (macromolecular) solid that is very hard, has a high melting point and is chemically resistant, binding the mixture into a strong material
4. DIt is thought to be a simple molecular solid that melts very easily under gentle heat, which is assumed to let it flow and set quickly into shape for use in cement mixtures

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1. Athe molecules become more polar
2. Bthe van der Waals forces between the molecules become stronger
3. Chydrogen bonding develops between the molecules
4. Dthe carbon to carbon bonds become stronger

1. Ano catalyst is required
2. Ba small molecule such as water is eliminated as the monomers join
3. Cthe monomers must contain a carbon to carbon double bond
4. Dthe polymer is the only product formed

1. Aelectrophilic substitution
2. Belectrophilic addition
3. Cnucleophilic substitution
4. Dfree radical substitution

1. ARapid, complete decomposition occurs, giving a dense purple vapour of iodine forming throughout the whole container immediately
2. BA reaction in which a small molecule is removed from within a single larger molecule
3. CA reaction in which a molecule splits into two or more smaller fragments
4. DA reaction in which an atom or group in a molecule is replaced by a different atom or group

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1. AThey are thought to be geometric (cis-trans) isomers about a supposedly restricted carbon-carbon double bond within the ring
2. BThey are positional isomers -- cyclohexenes with the new double bond on either side of the carbon that carried the -OH group
3. CThey are the same single compound, simply named differently by two different conventions
4. DThey are unrelated compounds with completely different molecular formulae

1. ANeither ethene nor benzene reacts with chlorine under any laboratory conditions
2. BEthene is thought to need a halogen-carrier catalyst and to undergo substitution instead of addition, while benzene is assumed to react rapidly by simple addition at room temperature with no catalyst needed at all
3. CBoth ethene and benzene react with Cl2 in exactly the same way, needing the same catalyst and giving the same type of product
4. DEthene undergoes rapid electrophilic addition at room temperature with no catalyst, decolourising Cl2; benzene needs a halogen-carrier catalyst and undergoes substitution, keeping its ring intact

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1. A$C_{16}H_{34} \rightarrow 2C_8H_{18}$
2. B$C_{16}H_{34} \rightarrow C_8H_{18} + C_8H_{16}$
3. C$C_{16}H_{34} + 24.5O_2 \rightarrow 16CO_2 + 17H_2O$
4. D$C_{16}H_{34} \rightarrow C_{16}H_{32} + H_2$

1. A$LiAlH_4$ in dry ether
2. Bhydrogen with a nickel catalyst at room temperature
3. Ctin and concentrated hydrochloric acid under reflux, followed by NaOH
4. Dacidified potassium dichromate(VI) under reflux

1. Aesterification
2. Bnucleophilic substitution
3. Chydrolysis
4. Dcoupling

1. AThe replacement of hydrogen atoms in an alkane with halogen atoms
2. BThe breaking down of long-chain alkanes into smaller, more useful alkanes and alkenes
3. CThe joining together of small alkene molecules into a single, very long-chain polymer through repeated addition steps
4. DThe complete combustion of alkanes to give carbon dioxide and water only

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1. AIt permanently removes the need for crude oil refining of any kind
2. BIt converts alkanes directly into pure hydrogen gas with no other products
3. CIt is sometimes claimed to eliminate the need for transporting crude oil to a refinery at all, though this is not actually true
4. DIt converts surplus heavy fractions into high-demand petrol and alkenes for the chemical industry

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1. AThe amine group is oxidised to a nitro group, regenerating 4-nitrobenzoic acid
2. BThe ring is completely saturated by addition of hydrogen across it
3. CThe ester is thought by some to be unaffected, since esters are sometimes wrongly assumed not to hydrolyse in dilute acid at all
4. DThe ester hydrolyses back to give 4-aminobenzoic acid (as its salt) and ethanol

1. AThe ring is thought to be completely saturated by direct addition of hydrogen atoms across its delocalised pi system
2. BNo reaction occurs at all, since benzocaine's ring is strongly deactivated by its substituents
3. CBromine substitutes onto the ring at positions ortho to the activating -NH2 group, giving a dibromo derivative
4. DThe -NH2 group is completely replaced by bromine, giving a nitrobenzene derivative

1. ANeither compound dissolves in water at all, under any conditions or temperature
2. B4-nitrobenzoic acid, with a free -COOH group, is more water-soluble than benzocaine, whose polar -COOH is replaced by a less polar ester
3. CBenzocaine is sometimes wrongly thought to be more water-soluble than 4-nitrobenzoic acid, since esters are commonly assumed to be more soluble than acids
4. DBoth compounds are equally soluble in water, since both contain an aromatic ring of the same size

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1. Aoptical isomerism
2. Bcis-trans isomerism
3. Cstructural isomerism only
4. Dno isomerism

1. A$NaBH_4$ in ethanol
2. BHCN with a trace of KCN at 10–20 °C
3. C$LiAlH_4$ in dry ether
4. D$PCl_5$ at room temperature

1. Aeffervescence with aqueous sodium carbonate
2. Ba white precipitate with aqueous silver nitrate
3. Ca silver mirror with Tollens' reagent
4. Dan orange precipitate with 2,4-dinitrophenylhydrazine

1. AThey are thought to be geometric (cis-trans) isomers about a supposedly restricted carbon-carbon double bond within the molecule
2. BThey are positional isomers, with the -OH group attached to different ring carbons
3. CThey are not isomers of each other at all, but two entirely unrelated compounds
4. DThey are enantiomers -- non-superimposable mirror images of each other about the chiral carbon

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1. AIt has no real synthetic significance beyond simply changing the compound's colour
2. BIt is thought to remove a carbon atom from the existing chain, shortening the molecule for easier purification afterwards
3. CIt forms a new carbon-carbon bond, extending the carbon chain -- important for building larger molecules
4. DIt converts the molecule into an inorganic compound with no further synthetic value

1. AAdding dilute hydrochloric acid is thought to make benzaldehyde effervesce, while mandelic acid shows no reaction at all
2. BAdding Fehling's solution: only mandelic acid gives a positive brick-red precipitate
3. CAdding Na2CO3 or NaHCO3 solution: mandelic acid effervesces (releasing CO2), benzaldehyde does not
4. DAdding bromine water: benzaldehyde immediately decolourises it, mandelic acid does not

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