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ÿþM00/420/H(3)M INTERNATIONAL BACCALAUREATE BACCALAURÉAT INTERNATIONAL BACHILLERATO INTERNACIONAL MARKSCHEME May 2000 CHEMISTRY Higher Level Paper 3 18 pages  6  M00/420/H(3)M OPTION C  HUMAN BIOCHEMISTRY C1. (a) (i) CHO C OH HO C C OH C OH CH2OH (Award [1] for either circled C and [1] for the whole structure.) [2] (ii) In the ring structure of glucose, on the C1 atom/the  carbonyl C [1] [1] the H/OH are in different positions in ±/² OR illustration of this (diagrammatically). (b) (i) glucose and fructose [2] (ii) glucose (and glucose) [1] (c) (Award [1] for any of the below.) Food or energy reserves/resources/stores/glycogen/starch Structure/cell walls/cellulose/chitin. [1] Total [8 marks]  7  M00/420/H(3)M C2. (a) 6. [1] (b) (i) Chromatography and electrophoresis. [2] (ii) (Award up to [4] for the following points for EITHER paper chromatography OR electrophoresis.) Paper chromatography: hydrolyse/release amino acids/heat with acid; [1] place sample spot on paper; [1] place paper in solvent (or suitable named solvent); [1] compare distances travelled/R values with known values. [1] f OR Electrophoresis: hydrolysis; [1]  loading onto origin; [1] variable voltage/distance moved from origin; [1] compare isoelectric points (standards) etc. [1] (c) pH 4.5 pH 6 pH 7.5 + + H3 N H3 N COO- H2N COO- [1] [1] [1] [3] Looking for functional groups only. (In absence of other marks: three correct structures at wrong pH, award [1].) Total [10 marks]  8  M00/420/H(3)M C3. (a) Substrate concentration: activity/rate increases initially (first order); [1] becomes constant/flattens out. [1] A labelled correct diagram (i.e. axes labelled, correct shape) could score these two marks, for example: Initial rate of reaction Substrate concentration Satisfactory explanation of one region of graph: Many free active sites initially; [active sites being occupied/becoming more saturated]. [1] (b) Temperature: increased rate initially; [1] but then reduced markedly (Æ 0); [1] A labelled correct diagram (i.e. axes labelled, correct shape) could score these two marks, for example: Initial rate of reaction Temperature enzyme destroyed/denatured; [1] since stabilising H bonds disrupted (or words to that effect). [1] Total [7 marks]  9  M00/420/H(3)M OPTION D  ENVIRONMENTAL CHEMISTRY Source Reduction of emission D1. (a) (i) Incomplete combustion of Use catalytic converter* [1] C-containing fuel/named fuel [1] (ii) Burning sulfur-containing fuel/coal [1] Desulfurisation/scrubbing (flue gases) [1] (iii) Reaction of gases in air/nitrogen and Use catalytic converter* [1] oxygen (at high temperatrure) [1] * allow catalytic converter once only (Award final mark for correct product from one of the above:) (i) Carbon dioxide; (ii) Sulfur/sulfate/hydrogen sulfide; [1] (iii) Nitrogen. [6] (b) One of SO2 or NOx (however described) [1] EITHER SO2 + H2O l H2SO3 [1] 1 OR 2NO +1 O2 + H2O ’! 2HNO3 (for example) 2 Total [8 marks] D2. (a) Amount of oxygen needed to break down organic wastes; [1] Reduced availability of oxygen/fewer living organisms. [1] (b) Secondary treatment; [1] Activated sludge process; [1] Organic matter broken down/oxidised by bacteria. [1] (c) Plant growth encouraged; [1] Oxygen concentration reduced by plant decay. [1] (Allow eutrophication as alternative to either of the above.) Total [7 marks]  10  M00/420/H(3)M D3. (a) (i) Lethal dose [1] Amount needed to kill 50 % of animals given the dose. [1] (ii) Advantage: Gives good indication of relative toxicities (of different chemicals) [1] Disadvantage: does not indicate acceptable environmental level of chemical [1] /does not help to make accurate assumptions re effect on humans. (b) Lead: Source: paints/PbEt4 in petrol, therefore exhaust gas/lead pipes in [1] plumbing; [1] Effect: brain damage (especially in children); [1] Reducing: unleaded petrol/lead-free paints/use of copper or plastic pipes. Nitrates: Source: leaching of nitrate fertilisers into rivers& [1] Effect: stomach cancer/affects haemoglobin (in the young)/ blue baby [1] syndrome; Reducing: use less fertiliser/avoid use before rain is due. [1] Total [10 marks]  11  M00/420/H(3)M OPTION E  CHEMICAL INDUSTRIES [1] E1. (a) Accept a temperature range 400 500 C in each case. Pressure 150 500 atm (Haber) 1 2 atm (Contact) [1] Catalyst iron/iron oxide Vanadium (pent/V) oxide [1]+[1] (For each process, 3 correct conditions [2], 2 correct [1].) (b) N2 + 3H2 l2NH3 (state symbols NOT required). [1] (Don t penalise absence of reversible symbol.) High temperature increases rate/gives greater rate of reaction [1] But low yield of NH3 [1] Some comment on a compromise temperature [1] (c) Raw Materials  naphtha, methane, other hydrocarbon (saturated); [1]  high temperature/heat/catalyst ([1] for any one of the three.) [1] (Award [1] for any one of the following equations.) C7H16 ’! C6H5CH3 + 4H2O C6H14 ’! C6H6 + 4H2 C2H6 ’! C2H4 + H2 etc. (even) CH4 + H2O ’! CO + 3H2 [1] Total [11 marks]  12  M00/420/H(3)M E2. (a) (Award [2] for any two of the following:)  close to C2H4 source; close to industries needing polythene; workforce; away from residential areas etc. [2] (b) Polar C Cl bonds in PVC; [1] stronger intermolecular forces (than polythene). [1] 1 (c) C2H3Cl + 2 O2 Æ 2CO2 + H2O + HCl (or doubled). [1] 2 (Credit polymer equations if correct. Equations given are intentionally simplified.)  C2H4  +3O2 Æ 2CO2 + 2H2O [1] Comment on HCl being toxic or poisonous/no poisonous gases from polyethene. [1] (d) (Radical mechanism): Free radical mentioned e.g. or Ai or R O Oi [1] Ri [1] e.g. Ri + CH2 == CH2 ’! R  CH2  CH2i [1] e.g. R CH2  CH2i + CH2 == CH2 ’! R CH2  CH2  CH2  CH2i [1] equation for termination step, e.g. 2Ri ’! R2 (Detailed word descriptions of above may be awarded marks. If none of above marks are scored, [1] may be awarded for mention of initiation, propagation and termination.) (Ionic mechanism): (Ziegler) catalyst. [1] e.g. A B + CH2 == CH2 ’! A CH2  CH+ (+B-) [1] 2 + e.g. A CH2  CH+ + CH2 == CH2 ’! A CH2  CH2  CH2  CH2 [1] 2 (Detailed word descriptions of above may be awarded marks.) Total [14 marks]  13  M00/420/H(3)M OPTION F  FUELS AND ENERGY F1. (a) (i) 219; [1] 86. [1] (ii) Mass number No change; [1] [1] Atomic number +1. (b) (i) Time taken for activity to decrease by half (or words to that effect). [1] (ii) 11.7 days. [1] Some working essential, e.g. 3-half lives mentioned. [1] 7 (iii) or 0.875 or 87.5 %. [1] 8 1 (iv) 12.5 % or 8 . [1] Total [9 marks] F2. (a) Zinc [1] and graphite (accept carbon). [1] (b) Voltage  potential difference between electrodes; [1] Power  total quantity of electricity available. [1] Voltage affected by the materials used; [1] Power affected by the quantity of materials used. [1] Total [6 marks]  14  M00/420/H(3)M F3. (a) Energy released when nucleus is synthesised from protons and neutrons/energy needed to split a nucleus into protons and neutrons. [1] 223 Ra needs to become more stable. [1] [1] This is achieved by losing mass/an ±-particle. (b) Nature of Source Characteristic Storage Waste Hospitals / Activity is low / Stored until checking welds short half-life / activity is Low-level / monitoring high volume [1] reduced [1] waste thickness of e.g. paper [1] Nuclear Activity is high / Making High-level industry / long half-life / low into glass / waste military [1] volume [1] deep burial [1] [6] (Award final mark for one extra point from list above.) [1] Total [10 marks]  15  M00/420/H(3)M OPTION G  MODERN ANALYTICAL CHEMISTRY G1. (a) Accelerating + plates [1] Magnets [1] - Source of e- [1] Gas inlet (e- gun) (vapourised sample) [1] Detector [1] Light ions deflected more than heavy ions/> 1 signal obtained OR ions(+) of different mass/charge ratio give > 1 line [1]. (General shape needed for full marks.) [6] 75 25 (b) (i) 35× + 37 × [1] 100 100 = 35.50 [1] (ii) Relative intensity / abundance 70 72 74 m/z OR mass number Both axes correctly labelled; [1] Three lines at 70, 72 and 74; [1] Heights of lines in correct order (70 > 72 > 74) [1] Total [11 marks]  16  M00/420/H(3)M distance travelled by  solute G2. (a) R = [1] f distance travelled by solvent (b) (i) Measure distance travelled by blue spot (centre) and solvent [1] Divide one by the other [1] (ii) Each dye has different attractions/affinities for the paper [1] and the solvent (or words to that effect). [1] (Solvent reference may be to solubility rather than attraction/affinity.) (iii) Negligible attraction between the dye and paper [1] compared with that of dye and solvent (or solubility of dye in solvent). [1] (In absence of the above award [1] for the distance moved by the dye = distance moved by the solvent.) Total [7 marks] G3. (a) H O H O N H N H H H [1] [1] [2] (If both structures and bonding are correct but non-bonding electrons are not shown award a maximum of [1].) (b) ONH3 HONH2 1 [1] 2 [1] Number of Peaks 1:2 [1] Relative Areas Reasoning All protons chemically Protons in different equivalent (or words to that chemical environment [1] effect) [1] [5] Total [7 marks]  17  M00/420/H(3)M OPTION H  FURTHER ORGANIC CHEMISTRY H1. (a) Electrophilic addition. [1] [1] Arrow from double bond to H+ (or H of H Cl) + Structure of carbocation (CH3  CH CH3) [1] Arrow showing attack by Cl- on central carbon of carbocation [1] (b) CH3CH2CH2Cl [1] + Primary carbocation/CH3CH2CH2 is less stable or less likely to be formed (or secondary carbocation is more stable or more likely to be formed). [1] Explanation of different stabilities of carbocations (in terms of inductive effect or sharing of charge). [1] - (c) (Substitution by) an electron-rich species (e.g. NH3 ; X ) [1] (lone pair)/Lewis base/Brønsted base (d) Arrow from C Cl bond to Cl atom [1] + Structure of carbocation (CH3  CH CH3) [1] - Arrow showing attack by on central carbon of carbocation [1] OH OR Arrow from C Cl bond to Cl atom [1] - Arrow showing attack by on central carbon of halogenoalkane [1] OH Structure of intermediate (Cl and OH both bonded by --- to central C) [1] Total [11 marks]  18  M00/420/H(3)M H2. (a) dichlorodifluoromethane (accept difluorodichloromethane) [1] 1,1,2-trichloro,1,2,2-trifluoroethane (accept 1,1,2-trifluoro,1,2,2-trichloroethane) [1] (b) absorbs UV-radiation from the sun. [1] (c) (i) (Saturated) compounds with high bond energies. [1] (ii) C Cl bond weaker than C F [1] C Cl more easily broken (than C F). [1] (d) Cl "+O3 Æ OCl " + O2 [1] (more correctly ClO") Total [7 marks] H3. (a) Chiral carbon atom/C atom joined to 4 different groups [1] Two drawings showing enantiomers/chiral structures (object-mirror images). [2] (These may be incomplete showing only the  chiral centre .) (b) Light vibrating in one plane only. [1] Optically active compounds  rotate plane of polarisation of plane-polarised light. [1] When racemic mixture obtained [1] equimolar concentrations of stereoisomers affecting plane of polarisation equally and oppositely. [1] Total [7 marks]

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