Chemistry Paper 2 November 2021

1. Ahalf of the products to decompose
2. Bthe concentration of a reactant to fall to half its original value
3. Cthe rate constant to fall to half its value
4. Dthe reaction to reach equilibrium

1. A$2.31 \times 10^{-4}$
2. B$2.31 \times 10^{-5}$
3. C$3.33 \times 10^{-5}$
4. D$6.93 \times 10^{-5}$

1. A45 %
2. B50 %
3. C55 %
4. D60 %

1. Aphysically filters out the metal ions as solid particles that become mechanically trapped within the tiny pores of the resin beads, much like a sieve traps grains of sand.
2. Bneutralises the acidic waste by reacting the metal ions directly with hydroxide ions released from the resin, forming an insoluble metal hydroxide precipitate that settles.
3. Coxidises the metal ions to a higher, less soluble oxidation state that precipitates out of solution and settles to the bottom of the treatment tank.
4. Dexchanges the toxic metal ions in the waste for harmless ions (e.g. $Na^+$ or $H^+$) held on the resin, removing them from solution.

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1. A$79(1-x) + 81x = 2 \times 79.9$
2. B$79x + 81(1-x) = 79.9$
3. C$79x + 81x = 79.9$
4. D$(79+81)x = 79.9$

1. A$ClCH_2CO_2H > Cl_2CHCO_2H > CH_3CO_2H$
2. B$Cl_2CHCO_2H > CH_3CO_2H > ClCH_2CO_2H$
3. C$Cl_2CHCO_2H > ClCH_2CO_2H > CH_3CO_2H$
4. D$CH_3CO_2H > ClCH_2CO_2H > Cl_2CHCO_2H$

1. A$[CoCl_4]^{2-}$, tetrahedral
2. B$[CoCl_6]^{4-}$, octahedral
3. C$[Co(H_2O)_6]^{2+}$, octahedral
4. D$[CoCl_2(H_2O)_4]$, octahedral

1. Aexothermic
2. Bendothermic
3. Cneither, since colour is not related to energy
4. Dcatalysed by heat

1. Asimply increase the molecular mass of the acid, making the O-H bond mechanically easier to break by sheer mass alone, with no electronic effect.
2. Bhydrogen bond directly to the acidic proton in solution, weakening the O-H bond well before any ionisation of the acid can occur.
3. Cwithdraw electron density inductively from the carboxylate group, stabilising the anion and increasing acid strength.
4. Ddonate electron density inductively into the carboxylate group instead, which would destabilise the anion and so weaken rather than strengthen the acid.

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1. Acovalent, simple molecular, square planar
2. Bionic, giant lattice, octahedral
3. Ccovalent, giant lattice, tetrahedral
4. Dcovalent, simple molecular, tetrahedral

1. Ais the most electronegative element in the group
2. Bis a non-metal while the others are metals
3. Chas no available d orbitals to accept a lone pair from water
4. Dforms unusually strong bonds to chlorine

1. Aincreases, because the atoms get larger
2. Bdecreases, because the $X-Cl$ bond becomes weaker
3. Cis unchanged, because all are covalent
4. Dincreases, because the $+4$ state becomes more stable

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1. Athe ns2 electron pair becomes increasingly reluctant to take part in bonding as atomic size increases (the inert pair effect).
2. Bthe larger atoms further down the group can no longer form four strong covalent bonds at all, due to steric hindrance from the bulky chlorine atoms around them.
3. Cthe +4 ions become increasingly unstable simply due to greater electron-electron repulsion between the four surrounding ligand atoms as atomic size grows.
4. Dthe +2 ion is always more thermodynamically stable than the +4 ion for absolutely any p-block element, regardless of its position in the periodic table.

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1. Aan aromatic nitro compound with tin and hydrochloric acid
2. Ban amide with bromine and alkali
3. Ca diazonium salt with a phenol to give an azo dye
4. Da primary aromatic amine with nitrous acid below 10 °C

1. ASn and concentrated HCl, then alkali; reduction
2. Baqueous bromine; electrophilic substitution
3. C$NaNO_2$ and HCl below 10 °C; diazotisation
4. Dconcentrated $HNO_3$ and $H_2SO_4$; nitration

1. Athe mixture solidifies
2. Bbubbles of nitrogen are seen as the diazonium salt decomposes
3. Ca violet colour appears as the dye forms early
4. Da white precipitate of the amine is formed

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1. Acontain an extended conjugated system that absorbs visible light, giving them colour.
2. Bare strongly acidic, which lets them form a permanent ionic bond directly with the amine and hydroxyl groups on any fabric fibre.
3. Care completely insoluble in water, meaning they cannot ever be washed out of a dyed fabric once it has been treated and dried.
4. Dreact explosively with atmospheric oxygen, and this exothermic reaction is what fixes them permanently onto the fabric surface.

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1. Areduces each C=O group in the polypeptide backbone all the way to a $-CH_2-$ group, breaking the chain apart into separate fragments.
2. Bprotonates only the single terminal amino group at one end of the chain, causing the whole molecule to unfold without ever breaking any covalent bonds.
3. Chydrolyses each amide (peptide) linkage, adding water across the C-N bond to regenerate a $-COOH$ and an $-NH_2$ (or $-NH_3^+$) group.
4. Doxidises every peptide bond along the backbone, releasing carbon dioxide gas at each site and progressively shortening the chain.

1. Aaldehyde and ester
2. Bcarboxylic acid and amide
3. Ccarboxylic acid and ester
4. Dphenol and amide

1. Aacidified potassium dichromate(VI)
2. Bphosphorus pentachloride
3. Cethanol and concentrated $H_2SO_4$
4. Dethanoic anhydride

1. Aparacetamol, because it contains a free phenol group
2. Bboth, because both contain a benzene ring
3. Caspirin, because it contains a carboxylic acid group
4. Daspirin, because it contains an ester group

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1. Aring must first be reduced by bromine before any substitution can take place.
2. Bamide group strongly withdraws electron density from the ring, directing bromine to the least deactivated position.
3. Cbromine substitutes only at the position furthest from any existing substituent, regardless of ring activation.
4. Dphenolic $-OH$ group activates the ring towards electrophilic substitution by donating electron density into it.

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1. Aoptical isomerism
2. Bcis-trans isomerism
3. Clinkage isomerism
4. Dhydration isomerism

1. Aopposite each other, so the bond dipoles cancel
2. Boutside the coordination sphere
3. Cnext to each other at 90°
4. Dbonded to each other

1. Aadding water to the ether layer
2. Bshaking once with one large volume of ether
3. Cshaking several times with small portions of fresh ether
4. Dwarming the mixture before shaking

1. Athe chloride ions lying outside the coordination sphere (ionic, uncoordinated) react with $Ag^+$; coordinated chloride does not.
2. Bthe chloride ions bonded directly to chromium react fastest of all with $Ag^+$ ions in solution, while any free ionic chloride never reacts at all.
3. Csilver nitrate instead reacts with the water of crystallisation present, releasing an amount of chloride exactly proportional to the water content.
4. Deach of the three complexes carries a different overall ionic charge, and this charge alone determines how many silver ions can approach and react.

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1. Afully automatic identification of every separated spot without ever needing any locating or staining reagent to be applied.
2. Bfaster separation with sharper, better-resolved spots, since the thinner, more uniform stationary phase speeds up and sharpens solvent movement.
3. Ccheaper plates are used since every TLC plate can be reused indefinitely, unlike paper which must always be thrown away completely after just one single run.
4. Dthe ability to separate mixtures completely without ever needing any solvent system or mobile phase at all during the run.