Chemistry Paper 2 November 2020

1. A$NH_3 + H_2O \rightleftharpoons NH_4^+ + OH^-$
2. B$NH_3 + H_2O \rightarrow NH_2^- + H_3O^+$
3. C$NH_3 \rightarrow \frac{1}{2}N_2 + \frac{3}{2}H_2$
4. D$2NH_3 + H_2O \rightarrow N_2H_4 + H_2O_2$

1. Areleases electrons towards the nitrogen atom
2. Bwithdraws electrons from the nitrogen atom
3. Cforms hydrogen bonds with water
4. Dincreases the relative molecular mass

1. Atrigonal planar, because there are three bonding pairs
2. Bbent, because sulphur also carries a lone pair
3. Ctetrahedral, because sulphur has four electron pairs
4. Dlinear, because there are two bonding regions

1. Aphenylamine has a much larger molecular mass, which spreads out and weakens its lone pair.
2. Bthe nitrogen lone pair is delocalised into the benzene ring, reducing its availability to accept a proton.
3. Cphenylamine is far less soluble in water than ammonia, limiting how well it can donate protons in aqueous solution.
4. Dthe benzene ring withdraws electron density only through the sigma-bond framework, not the lone pair.

1. Aclose to 90°, because the molecule adopts a tetrahedral arrangement of its electron pairs around sulfur.
2. Bgreater than 120°, because the lone pair on sulfur pushes the two S-O bonding pairs further apart than another bonding pair would.
3. Cexactly 120°, because a lone pair and a bonding pair repel each other exactly as strongly as two bonding pairs.
4. Dslightly less than 120° (about 119°), because lone pair-bond pair repulsion is greater than bond pair-bond pair repulsion.

1. Apure aluminium
2. Bsteel
3. Cplatinum
4. Dgraphite

1. Aincreases in mass as impurities collect on it
2. Bdecreases in mass as nickel dissolves
3. Cincreases in mass as nickel is deposited
4. Dremains unchanged in mass

1. A$+0.26\ V$
2. B$+1.07\ V$
3. C$+1.33\ V$
4. D$+2.40\ V$

1. Agenerates harmful ionising radiation from the graphite electrodes as they slowly wear away during operation.
2. Bcauses the molten aluminium oxide itself to ignite spontaneously in air.
3. Creleases toxic, corrosive fumes containing fluorine compounds from the molten cryolite-alumina mixture.
4. Dproduces large volumes of explosive hydrogen gas that collect dangerously at the cathode during electrolysis.

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1. A$Ag^+/Ag$ has a more positive electrode potential than $H^+/H_2$, so $H^+$ ions cannot oxidise silver metal.
2. Bsilver has a full outer electron shell, making it completely unreactive towards any acid.
3. Csilver forms a thin, protective oxide layer on its surface that prevents any acid from ever reaching the metal underneath.
4. Dthe reaction between silver and dilute acids is far too slow to be observed under normal conditions.

1. A$2NH_4Cl + Ca(OH)_2 \rightarrow CaCl_2 + 2NH_3 + 2H_2O$
2. B$NH_4Cl + CaO \rightarrow CaCl_2 + NH_3 + H_2$
3. C$2NH_4Cl + CaCO_3 \rightarrow CaCl_2 + 2NH_3 + CO_2 + H_2O$
4. D$NH_4Cl + Ca(OH)_2 \rightarrow CaCl_2 + NH_3 + H_2O$

1. Aoxidises ammonia to nitrogen
2. Bis acidic and reacts with the ammonia
3. Cis not a drying agent
4. Ddissolves in the ammonia

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1. A$-715$
2. B$-694$
3. C$-347$
4. D$-22.6$

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1. Athe direct chemical poisoning of fish and other aquatic animals, caused when nitrate ions are absorbed through their gills and skin over a long period of exposure.
2. Bthe gradual thinning of the Earth's protective ozone layer, a separate environmental problem caused mainly by certain industrial and refrigerant gases, not nitrates.
3. Cthe physical warming of a water body's temperature, caused by dissolved nitrate fertilisers absorbing sunlight more strongly than the surrounding pure water does.
4. Denrichment of water bodies with nutrients like nitrates, triggering algal blooms whose decay depletes dissolved oxygen and kills aquatic life.

1. Aapplying as much fertiliser as possible in a single large dose, to reduce the total number of separate applications needed each season.
2. Bspreading fertiliser deliberately during periods of heavy rainfall, so that it washes evenly into the soil across the whole field.
3. Capplying fertiliser in recommended amounts, avoiding it just before heavy rain, and leaving buffer strips near water.
4. Dswitching entirely to fertilisers containing phosphates instead of nitrates, since phosphate compounds never dissolve in water at all.

1. Athe specific heat capacity value used for water in this calculation was significantly too high for the experiment's conditions.
2. Bfar too much oxygen reached the flame during combustion, making the temperature rise unusually and unrealistically large.
3. Cheat was lost to the surroundings, and some methanol evaporated or burned incompletely before releasing its energy.
4. Dthe theoretical Data Booklet value itself was calculated using an incorrect molecular formula for methanol in the first place.

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1. Aphenylamine is insoluble in water
2. Bonly ammonia can form hydrogen bonds
3. Cthe relative molecular masses increase in the same order
4. Dalkyl groups release electrons to nitrogen while the benzene ring delocalises the lone pair

1. Aare held together by strong ionic bonds
2. Bare extensively cross-linked
3. Care held only by weak van der Waals forces and can slide over one another
4. Dcontain many carbon-carbon double bonds

1. Aprotonates the carbonyl oxygen
2. Bhydrolyses the carbonyl group
3. Coxidises the hydrogen cyanide
4. Dremoves the $CN^-$ nucleophile by forming HCN

1. Athe propyl chain forms strong, direct hydrogen bonds with any hydrogen ions that happen to be nearby in solution.
2. Bnitrogen in propylamine carries a permanent partial positive charge that strongly attracts nearby hydrogen ions.
3. Cnitrogen's lone pair can accept a proton, and the electron-donating propyl group increases its availability.
4. Dit readily loses a proton from one of its own N-H bonds, releasing hydroxide ions directly into the surrounding solution.

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1. Aethanol with a trace of acid
2. Bethanoic anhydride
3. Cacidified potassium dichromate(VI)
4. Daqueous sodium hydroxide

1. A2-methylphenol
2. B2-hydroxybenzoic acid
3. Cbenzene-1,2-diol
4. D2-(hydroxymethyl)phenol

1. Areleases electrons into the ring
2. Bmakes the molecule polar
3. Cincreases the size of the molecule
4. Dwithdraws electrons, reducing the electron density of the ring

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1. A2-hydroxybenzaldehyde + ethanoic anhydride -> the ethanoate ester of 2-hydroxybenzaldehyde + ethanoic acid.
2. B2-hydroxybenzaldehyde + ethanoic anhydride -> the ethanoate ester of 2-hydroxybenzaldehyde + carbon dioxide.
3. C2-hydroxybenzaldehyde + ethanoic anhydride -> the ethanoate ester of 2-hydroxybenzaldehyde + water.
4. D2-hydroxybenzaldehyde + ethanoic anhydride -> the ethanoate ester of 2-hydroxybenzaldehyde + hydrogen gas.

1. Avigorous effervescence, with gas bubbling out of the mixture.
2. Ba distinct white precipitate forming and slowly settling at the bottom of the reaction flask.
3. Cthe smell of ethanoic acid developing, with no other dramatic visible change.
4. Da deep purple colour developing immediately in the reaction mixture.

1. Amethylbenzene undergoes an actual chemical reaction with carbon tetrachloride, but simply does not react with water molecules at all.
2. Bwater molecules are simply far too large in size to fit between methylbenzene's own molecules, unlike the smaller carbon tetrachloride molecules.
3. Cmethylbenzene and carbon tetrachloride are both non-polar (like dissolves like), but methylbenzene cannot hydrogen-bond with polar water.
4. Dcarbon tetrachloride is considerably denser than water, so methylbenzene naturally sinks into it rather than mixing with the water layer above.

1. Athe indicator does not dissolve in acid
2. Bthe high $[H^+]$ shifts the equilibrium to the left
3. Cthe indicator is destroyed by the acid
4. D$In^-$ is colourless in acid

1. A0.070
2. B0.70
3. C1.43
4. D7.00

1. Ait is colourless in both solutions
2. Bammonia destroys the indicator
3. Cthe end point occurs in the acidic region, outside its pH range
4. Dthe reaction is too slow to reach an end point

1. Aacting as a contrast-free alternative that skips medical imaging in diagnosis.
2. Btargeted drug delivery, where nanoparticles carry medication directly to diseased cells.
3. Cproviding a stand-alone cure for common viral infections through nanoparticle injection.
4. Dusing nanoscale robots as a general replacement for surgical instruments in routine operations.

1. Amay be toxic or cause damage to cells if they accumulate within the body over time.
2. Bare too large in size to ever enter human cells, causing blockages in small blood vessels.
3. Ccannot currently be manufactured on any scale large enough for practical medical use.
4. Ddissolve completely and harmlessly in body fluids, leaving no biological trace behind.

1. Amedical imaging and diagnostics, using nanoparticles as contrast agents or biosensors.
2. Bediting a patient's own DNA directly at the nanoscale in order to cure inherited genetic diseases.
3. Creplacing vaccination programmes with nanoparticle-based immune boosters.
4. Dusing nanoparticles as a permanent substitute for donated blood in transfusions.

1. Amanufacturing cost makes them entirely impractical for any medical application.
2. Blong-term health and environmental effects are not yet fully understood.
3. Cphysical size makes them too large to be inhaled or absorbed by the body.
4. Dchemical structure makes them completely immune to any form of degradation.