Chemistry Higher Level Paper 3 (markscheme)
EINTERNATIONALINTERNACIONALMARKSCHEMENovember 2001CHEMISTRYHigher LevelPaper 317 pagesN01/420/H(3)M
–6–M01/420/H(3)MOPTION C – HUMAN BIOCHEMISTRYC1. (a)(b)CH 2 OH–CHOH–CH 2 OH[1]–COOH[1]HHHHHHHHCCCCCCCHHHHHHHOCOH(Accept CH 3 (CH 2 )6 COOH or any correct alternative, including branchedstructures or alkenoic acids.)(c)Molecules of saturated fats contain only single C—C bonds in the carbon chains /contain no double bonds.Molecules of unsaturated fats contain at least one C C double bond.The degree of unsaturation can be found by determining the number of moles ofiodine that react with one mole (or a stated mass) of fat.Iodine adds across the C C double bond in a 1:1 stoichiometric ratio.[1][1][1][1][1]Total [7 marks]C2. (a)(b)(c)(d)(e)–NH 2 / amino group / amine.[1]Peptide bond (accept amide bond)[1]OHCN(must show C O bond for mark.)[1]First hydrolyse the peptide bonds to release individual amino acidsthen use chromatography (comparison of R f values) (accept electrophoresis / massspectrometry).(Award both marks if X-ray crystallography is given.)The secondary structure describes the type of coil or sheet / folding of polypeptide /α-helix and β-pleated sheet.Tertiary structure describes the interactions between the R groups of the amino acidresidues.Hydrogen bond.[1][1][1][1][1]Total [8 marks]
–7–C3. (a)(b)M01/420/H(3)MEnzymes provide an alternative pathway with a lower activation energy.Enzymes posses an active site where the substrate binds to the enzyme.Mention of ‘lock and key’ and/or induced fit hypothesis.[1][1][1]Competitive inhibitors (resemble the substrate in shape) compete with thesubstrate for the active site (and therefore slow the rate of reaction).Non-competitive inhibitors bind to the enzyme away from the active site.[1]([1])K m for uninhibited enzyme 12 Vmax 7 1 µ mol dm 3[1]With a competitive inhibitor K m is higher, Vmax is the same.At high [S] effect of inhibitor is negligible so no change to Vmax but more substrateneeded to reach 12 Vmax so K m is higher.[1]With a non-competitive inhibitor K m is the same but Vmax is lower.Adding a non-competitive inhibitor has the same effect as lowering [enzyme](hence Vmax is lower), but does not affect the way the substrate interacts with thoseenzyme molecules that are uninhibited (hence K m is unchanged).[1][1][1]Total [10 marks]
–8–M01/420/H(3)MOPTION D – ENVIRONMENTAL CHEMISTRYD1. (a)(i)2CO 2NO 2CO 2 N 2(Award [1] for correct products and [1] for balanced equation.)(ii)[2]CaO SO 2 CaSO3 (or 2CaO 2SO 2 O 2 2CaSO 4 )(Award [1] for reactants and [1] for product.)(b)(c)[2]2NO O 2 2NO 2 [1]4NO 2 2H 2 O O 2 4HNO3 [1]OR2SO 2 O 2 ! 2SO3 [1]SO3 H 2O H 2SO 4 (accept SO2 H 2 O H 2SO3 ) [1][2]Irritation of the mucous membranes / fatigue / weakness / confusion (e.g. fromexposure to C6 H 5CH 3 ) / cancer forming / respiratory problems.[1][2]Total [7 marks]D2. (a)(b)(i)(ii)(c)[1]Polychlorinated biphenyls(i)(ii)LD50 – lethal dose in 50 % of the population (the amount of poison that killshalf the organisms in a randomly chosen batch of a named species).Maximum daily tolerance – the highest amount or concentration that has ‘noeffect’ on any of the organisms in a specified batch.LD50 :Advantage: clearly measurable value.Disadvantage: not done on human population so effect on humans ‘unknown’.ORMaximum daily tolerance value:Advantage: gives idea of ‘safe amount’.Disadvantage: same as for LD50 so has to be divided by ‘safety factor’.[1][1][1][1][1][1]Batteries / seed dressings to prevent mould / chlor-alkali process(do not accept “mercury fillings in teeth”).[1](Award [1] for any of the following:)inflammation of the mouth / muscle spasms / nausea / diarrhoea / kidneydamage / blindness / deafness / damage to CNS / personality change.[1](iii) The Hg ions interfere with the normal functioning of enzymes (e.g. by2 replacing the Ca 2 or Mg ions).[1]Total [10 marks]
–9–M01/420/H(3)MD3. Water is a highly polar substance (due to shape and high electronegativity of oxygen).Capable of hydrogen bonding (that allows it to dissolve many chemicals).Fresh water not available uniformly around the world / ‘locked up’ in glaciers andicebergs.Where the consumption is necessarily high it is easily contaminated with water bornediseases / by micro-organisms from human waste / from flooding / due to inadequatechemical treatment of water supplies.Reverse osmosis:Uses high pressureto force water from salt-water through partially- (semi)-permeable membrane;the partially-permeable membrane does not allow the passage of dissolved ions.OR Osmosis is the net movement of water molecules from a region of highconcentration, i.e. pure water to one of lower concentration, i.e. less pure waterthrough a partially-permeable membrane / osmosis is the tendency to equaliseconcentrations.Due to osmosis, pure water will move through a partially-permeable membrane intosalt water, thus diluting it.If pressure greater than osmotic pressure is applied, the flow of solvent takes placein the opposite direction, called reverse osmosis.Ion exchange:Requires the use of both a positive ion exchange (which can replace metal ions in sea water with H ions) and a negative ion exchange (which can replace anions with OH ions). The H and OH ions combine to form fresh/pure water.[1][1][1][1][1][1][1][1][1][1][1][1][1]Total [10 marks]
– 10 –M01/420/H(3)MOPTION E – CHEMICAL INDUSTRIESE1. (a)[1](i)N 2 obtained from the fractional distillation of liquid air.(Not enough to just state ‘from air’.)(ii)H 2 obtained from cracking of petroleum products / from water usingreduction with methane / from water using reduction with naptha / catalyticreforming / electrolysis of sodium chloride solution.[1](b)There are four volumes (moles) of gas on LHS and only two on RHSso increasing the pressure will move the position of equilibrium to the rightIncreasing the pressure increases the concentration of the gasesSo reaction rate increases.[1][1][1][1](c)The yield of ammonia is lowso most of the N 2 and H 2 needs to go round again (to save waste/cost).[1][1]Total [8 marks]E2. (a)The free radical electron ( HO–CH 2 –CH 2i ) attacks one of the C atoms inH 2 C CH 2 .An electron from one of the bonds in the double bond joins this electron to form asingle C–C bond.The double bond is now a single bond with the electron on the end carbon.[1][1][1](b)HO–CH 2 –CH 2 –CH 2 –CH 2i H 2 C CH 2 HO–CH 2 –CH 2 –CH 2 –CH 2 –CH 2 –CH 2i[1](c)High density is ionic.[1](d)(Award [1] each for two conditions from the following:)" Temperature about 60 # C ;" Pressure 2–6 atmospheres;" Ziegler (Natta) catalyst/triethylaluminium with titanium(IV) chloride.[2]OO(e)OCOOR–O–H and HH /OCCl and H 2 N –OOC[2]ONH/ ClCNHTotal [9 marks]
– 11 –M01/420/H(3)ME3. Tabulated form of answer.(For each, give [1] for the process, [1] for the reactants, [1] for the products, and [1] forexplaining the conditions.)Choose from the following:TemperatureThermal cracking / cokingThermal decomposition of very heavy fractions to givemainly lower alkanes and alkenes and a high coke yield.Steam crackingThermal cracking of C2 hydrocarbons ( C4 – C12 ) toalkenes (ethene, 1,3-butadiene, etc.) in the presence ofsteam. Temperature around 800 # C .CatalystCatalytic crackingAccelerated decomposition, with some aromatisation, ofmiddle/higher fractions over solid acidiccatalysts/zeolites. Gives lower alkanes, alkenes,aromatics.HydrocrackingAccelerated hydrogenolysis / decomposition of heavyfractions to naptha over metal/acid catalysts e.g.palladium on zeolite.Catalytic reforming(platforming etc.)Metal/acid-catalysed e.g. platinum on acidic aluminarearrangement / cyclisation and dehydrogenisation ofalkanes and aromatisation of napthas.Thermal / autothermalMore general term, including methane to ethene – crackingautothermal, with partial combustion.[8]By choosing a suitable catalyst, the temperature required is lower which makes it moreefficient (and less costly) / helps to give the desired products by dictating the mechanism.Total [8 marks]
– 12 –M01/420/H(3)MOPTION F – FUELS AND ENERGYF1. (a)(b)Anode:zincCathode:graphite (carbon)Electrolyte: ammonium chloride OR zinc chloride and ammonium chloride andwater.Anode:Cathode:2 Zn Zn 2e 2NH 4 2e 2NH 3 H 2[1][1][1][1][1]OR 2MnO2 2NH 4 2e Mn 2 O3 2NH 3 H 2O(State symbols are not required.)(c)(d)(Award [1] each for any two from the following:)No decline in performance under high loads / no gases formed at cathode / longershelf life / able to produce more current for a longer time / good for emergencylighting.[2]Voltage does not changevoltage depends primarily on materials used.[1][1]Total [9 marks]F2. (a)(b)(i)10901441n 23592 U 37 Rb 55 Cs 2 0 n(Give [1] for correct isotopes and [1] for two neutrons.)[2](ii)E mc2 1 0.001 (3.0 108 ) 2 9.0 1013 J (9.0 1010 kJ)[1][1]Four half-lives57.2so t 1 2 14.3 days4[1][1]Total [6 marks]
– 13 –F3. (a)The crude oil is heated;Fed into the base of a fractionating column;Temperature gradient across column / lower boiling fractions distil first;Fractions emerging in boiling range not pure compounds.[1][1][1][1](Award [1] each for any three correct fractions from: (any two from number of Catoms, boiling range, and uses must be correct for each mark).)[3]Fraction(b)M01/420/H(3)MNumber of C atoms Boiling range / # CUsesGases1–40–200cooking, heatingNaptha5–720–100solventsGasoline (petrol)5–1240–175motor car fuelKerosene12–18175–300jets / dieselGas oil18–24300–400diesel fuelLubricating oil20–30non volatilelubricantsParaffin wax25–40solidcandlesBitumen / tar 30solidroad surfacesC12 H 26 C8 H18 2C 2 H 4 (or C4 H8 )(must show an alkene for mark).Octane for car engines and alkenes for polymers.[1][2]Total [10 marks]
– 14 –M01/420/H(3)MOPTION G – MODERN ANALYTICAL CHEMISTRYG1. (a) (i)The positive molecular ion or M / parent ion.The molecular formula of compound A is C9 H10 O(Accept “the relative molecular mass of compound A is 134”.)[1][1](ii)Due to the presence of 13 C isotopes in the compound.[1] (iii) 105 due to (M–C2 H 5 ) / (C7 H5O ) [1] 9(also accept (M – CHO) / (C8 H ) ) 77 due to (M–C3H 5O) / C6 H 5(must have sign to gain mark, but only penalize once if omitted)(b)(c)[1](i)It contains a carbonyl / either alkanal or alkanone / C O group.(Do not accept acid or ester.)[1](ii)C–H bond vibration (in alkanes, alkenes, arenes)[1](iii) It does not contain an alkanol or phenol group / no –OH group present.[1](i)Molecular formula: SiC 4 H12 (accept Si(CH 3 ) 4 )[1](Award [1] each for any two from the following:)" Gives a sharp single peak;" Strong peak as 12 protons in identical environment;" Volatile so can be easily removed from the sample afterwards;" Occurs well away from other peaks (which are shifted downfield from it).[2]They are in the ratio 3 : 2 : 5 (since there are only 10 protons this is the actualnumber).[1](ii)(iii) It contains (–C2 H 5 ) group / a –CH 3 group next to a CH 2 groupThe C 2 H5 group is attached to a C atom containing no other H atomsbonded to it.[1](iv) It contains an aromatic (benzene) ring.[1][1]continued
– 15 –M01/420/H(3)MQuestion G1 continued(d)OHCHCCHHHO(Give [1] for correctly showing aromatic ring and [1] forCC2H5 group.)[2]Total [17 marks]G2. (a)(b)The five d orbitals are split into different levels.When an electron is excited from a lower to a higher level it absorbs light/energy.The wavelength of the transmitted light / complementary colour lies in the visibleregion of the spectrum.A spectrum is run with the copper(II) sulfate solution to determine the wavelengthof maximum absorption / λmax .The standard solution is diluted to give several solutions of different knownconcentrations.The absorbance for each of these solutions at a fixed wavelength / λmax is recorded.A calibration curve of absorption versus concentration is plotted.The absorption of the unknown solution is recorded at the same wavelength and theconcentration obtained from the graph.[1][1][1][1][1][1][1][1]Total [8 marks]
– 16 –M01/420/H(3)MOPTION H – FURTHER ORGANIC CHEMISTRYH1. (a)C6 H 6 Br2 C6 H5 Br HBr Br2OR(b)(c)[1]Br HBrAddition of a halogen carrier / AlBr3 / Fe / FeBr3Heat / reflux[1]Electrophile: Br [1]Br—Br [1] [1]AlBr3 Br AlBr4(d)Br BrH AlBr4Br AlBr3 HBr[1](e)[1][2]Phenol is more reactive than benzene.No halogen carrier necessary for the reaction to proceed.A pair of electrons on the oxygen atom delocalises with the π electrons in the ringwhich increases the electron density on the ring (thus attracting electrophiles morereadily).Br[1][1]Main product: Br[1]OH[1]BrTotal [11 marks]
– 17 –H2. (a)(b)M01/420/H(3)MThe π bond prevents the double bond from rotating in both cases.In but-2-ene the atoms in the two isomers are arranged differently in space / containtwo different groups attached to each carbon HThey rotate the plane of polarised light in opposite directions.Due to the presence of an asymmetric carbon atom / enantiomers / chirality.[1][1]Total [6 marks]H3. (a)HH CH(b)[1]HH C HCBrH C HH(accept C(CH 3 )3 Br )[1]Electrophilic additionCδ H[1]HCC [1][1]C Br HBrδ (must have δ and δ to gain mark, but curly arrow is not essential)HCH3C C[3]CH3CH3HOR primary carbocationCH3C CH3[1]tertiary carbocationTertiary more stabledue to electron donating / positive inductive effect of the alkyl group. R C– HOR R C R HR[1][1]Total [8 marks]
Gives lower alkanes, alkenes, aromatics. Catalytic cracking Catalyst Thermal cracking of C2 hydrocarbons (Π)C4 C 12 to alkenes (ethene, 1,3-butadiene, etc.) in the presence of steam. Temperature around 800 .#C Steam cracking Thermal decomposition of very heavy fractions to give mainly lower alkane
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