Cracking. 191 minutes. 186 marks. Page 1 of 21

Transcription

1 ..6. Cracking 9 minutes 86 marks Page of

2 M. (a) Missing fraction = naphtha (allow naphtha from list if not quoted separately) () rder = mineral oil (lubricating oil), gas oil (diesel), kerosene (paraffin), naphtha, petrol (gasoline) () Mark order consequential on M (if no missing fraction given, M = 0) Accept correct reversed order Negative temperature gradient on the column or temperature of column decreases upwards () Larger molecules or heavier fractions condense at higher temperatures or lower down the column or reference to different boiling points (ignore mp) () (b) Type of mechanism = (free) radical / homolytic fission - used in complete sentence/phrase () C C + C 6 + C 9 0 correct alkenes () Accept C C & C CC all correct () (c) (i) Sulphur (containing impurities) burn to form or forms S or oxides of sulphur (if oxide identified, must be correct) () R equation: e.g. S + S or S + ½ S + Leading to acid rain (must have specified oxides of S or burning) or toxic product or respiratory problems () N formed by reaction between N and from the air () R N + N igh combustion temperature or spark in engine () provides E A or sufficient heat / energy to break N N () Need to remove N as forms acid rain or toxic product or causes respiratory problems () N + N () N + + N () Need to remove C as it is poisonous () Catalytic converter () uses Pt / Rh / Pd / Ir (wrong answer cancels a correct one) () Provides active sites / reduces E A () Forms N + C () N + C N + C (correct equation worth last marks) () Max 0 [7] Page of

3 M. (a) Crude oil is heated to vaporise it / oil vaporised () (Vapour passed into fractionating) tower / column () Top of tower cooler than bottom or negative temperature gradient () fractions separated by b.p R condensed at different temperatures R levels R low boiling fractions at the top R at the top small molecules or light components () max (b) (i) Identify shortfall in supply - e.g. petrol / small molecules () igher value products R more useful products () R cracking produces more of material (problem solving) Motor fuels Aromatic hydrocarbons Branched alkanes / hydrocarbons Cycloalkanes Any two () Ignore specific fractions, alkanes, shorter alkanes, penalise alkenes, and hydrogen (c) Catalyst: Zeolite / aluminosilicate () Type of mechanism: Carbocation / heterolytic fission () Conditions: igh temp R around 50 C [00 600] C NT heat / warm () Slight pressure [> atm 0 atm R megapa, 000 kpa] () NT high pressure [] M. (a) (i) A molecule/compound/it consists/it is composed/it is made up of hydrogen/ and carbon/c only () QoL release (heat) energy (when burned) () R provides a (useable form of) energy R is a source of energy Accept heat energy NT is energy / is heat NT burns exothermically C 0 + 6½ C + 5 () R C 0 + 8C + 0 ignore state symbols (iv) C 0 + ½ C + 5 () R C C + 0 ignore state symbols and (iv) if not C 0 = CE Page of

4 (v) Limited or reduced supply of air / oxygen () R low temperature R poor mixing R insufficient oxygen / air R shortage of NT no oxygen / lack of oxygen / not in excess 5 (b) Structure Structure Structure allow credit for positive charge around C atom no alternative carbocations allowed (c) (i) C 6 / C C C =C / C=C / C + / C C. NT C C Al R Zeoli(y)te R aluminosilicate () NT bauxite ignore Si NT Aluminium Silicate NT porous pot NT Si alone More useful / needed fuels / products R implied R more valuable products R qualified demand exeeds supply R to produce motor fuels R petrol R cycloalkanes R aromatic hydrocarbons R balanced alkanes R smaller molecules R alkenes [0] M. (a) (i) A molecule / compound / Consists / composed of hydrogen and carbon only () or clearly implied only single bonds (or clearly implied) () R has no double bond NT has maximum number of hydrogen atoms Page of

5 (b) (i) Fractional distillation R fraction () Name of fraction Number of carbon atoms LPG (liquefied petroleum gas) Petrol (gasoline) Naphtha 7 Kerosine or Kerosene or Paraffin () (Ignore uses) 5 Gas oil (diesel) 5 9 Mineral oil (lubricating oil) 0 0 Fuel oil 0 0 (c) (i) C 0 only () NT C C C C C C C C C C C 0 C + C 6 + C 7 6 R C 0 C + C 6 + () alkene formula () balanced (free) radical R homolysis R homolytic fission () NT radical substitution NT thermal decomposition [8] M5. (a) (i) fractional distillation or fractionation (iv) C 9 0 only C + 7 C + C + 6 C + Page 5 of

6 (b) (i) C 0 C 6 + C 7 6 correctly drawn structure of methylpropene (insist on clearly drawn C-C and C=C bonds) (c) Any two from o o o chemically similar or chemically the same or react in the same way same functional group same general formula o differ by C (penalise same molecular formula or same empirical formula) [8] M6. (a) (i) compounds/mixtures/alkanes/hydrocarbons/molecules with a boiling point range/similar boiling point/similar number of carbon atoms/similar chain length; (insist on similar rather than same ) (ignore references to size or M r ) (penalise references to bond breaking/cracking as contradictions) molecules have different boiling points/intermolecular forces/sizes/chain lengths/m r ; (ignore references to melting points) (credit the idea that molecules condense at different temperatures) the column has a higher temperature at the base (Q of L mark) R the column has a lower temperature at the top; (the statement needs to be expressed in good English and show a clear understanding of the correct temperature difference) (penalise negative R positive temperature gradient without qualification to what the candidate means, otherwise ignore) (ignore references to the boiling points of the molecules) (credit correct statements which use specific temperatures with a maximum temperature of 500 C at the base) Page 6 of

7 (b) (i) C ½ 8C + 9 ; (or double this equation) correctly drawn structure of,,-trimethylpentane (penalise the use of sticks once on the paper, including the structures in the (a) and (c)(iii )mechanisms) (credit correctly condensed structures) (c) cracking produces/makes ethene/propene/alkenes/motor fuels/petrol R cracking makes more useful products/high(er) value products R cracking satisfies the high demand for small(er) products; (ignore the idea that cracking makes or leads to plastics or polyethene) (high demand needs to be qualified) (d) (i) carbocation R carbonium ion; (do not credit examples or formulae, but otherwise ignore) (credit carbon cation ) zeolite R aluminosilicate R Al ; (e) (i) M: (free) radical; (credit alkyl radical) (do not credit examples or formulae, but otherwise ignore) (penalise radical substitution R hydrocarbon radical as contradictions) M: homolysis R homolytic fission/splitting/cleavage R C-C / C- bonds break; Page 7 of

8 alkene(s); (credit small or short chain alkenes ) (penalise cycloalkenes ) (penalise additional types of compounds (e.g. branched alkanes) as a contradiction) (do not credit examples or formulae, but ignore if these are correct and in addition to the word alkene ) [] M7. (a) (i) Prevents release of toxic C More energy efficient (releases more energy on combustion) C C + 7 Suitable product eg C or C Balanced equation Detect C gas or C (soot or particles) in exhaust gases (b) C C C C(C ) -methylpentane C C C(C )C C etc (c) (i) C C C C=C Alumino silicate etc Can be made into polymers (or alcohols etc) (d) (i) % atom economy = mass C Cl /total mass reactants = 85 00/58 = 5.8% Page 8 of

9 Because expensive chlorine is not incorperated into desired product Raise money by selling Cl [] M8. (a) Single bonds only /no double or multiple bonds; Contains carbon and hydrogen only; C and only not C and molecules Alkanes; (b) (c) () Fractions or hydrocarbons or compounds have different boiling points/ separation depends on bp; Ignore mp and vdw () bp depends on size/ M r / chain length; If refer to bond breaking/cracking/ blast furnace/oxygen/air max () Temp gradient in tower or column / cooler at top of column or vice versa; QWC () igher bp / larger or heavier molecules at bottom (of column) or vice versa; Not increasing size of fraction Not gases at top Large molecules or compounds or long chain hydrocarbons (broken) into smaller molecules or compounds or smaller chain hydrocarbons; QWC Zeolite or aluminosilicate (catalyst); C 0 C C 6 ; nly Smaller chain molecules are in more demand or have higher value or vice versa; Insufficient to say more useful/have more uses Page 9 of

10 (d) C ½ 8C + 9 ; (e) (f) Allow multiples Rh/ Pd/Pt/lr or in words; Penalise contradiction of name and symbol C + N C + N / C + C ; Allow multiples Greenhouse gas/ absorbs infrared radiation; car less powerful/ car stops/ reduced performance/ won t run smoothly/ can t accelerate; Not incomplete combustion or bad effect on engine Not doesn t go as far. Test it (before sale) /Quality control etc; (compounds with) same molecular formula / same no and type of atoms; Not atoms/elements with same molecular formula. If same chemical formula, can allow M And different structure/ structural formula; M consequential on M Allow displayed formula for M,,-trimethylpentane; nly (but allow numbers in any order) [0] M9. (a) (i) single (C-C) bonds only/no double (C=C) bonds Allow all carbon atoms bonded to four other atoms Single C- bonds only = 0 C= CE C and (atoms) only/purely/solely/entirely Not consists or comprises Not completely filled with hydrogen C molecules = CE Element containing C and = CE Page 0 of

11 C n n+ Formula only C x x+ (b) (i) C C + 6 Accept multiples Ignore state symbols gases produced are greenhouse gases/contribute to Global warming/effect of global warming/climate change Allow C or water is greenhouse gas/causes global warming Acid rain/ozone CE = 0 (c) carbon Allow C Allow soot (d) (i) C 9 0 C 5 + C 8 R C 9 0 C 5 + C Accept multiples Plastics, polymers Accept any polyalkene/haloalkanes/alcohols so the bonds break R because the bonds are strong IMF mentioned = 0 (e) (i),-dibromo--chloropentane/-chloro-,-dibromopentane Ignore punctuation Chain/position/positional Not structural or branched alone [] M0. (a) (Different) boiling points Ignore mp s, references to imf, different volatilities Page of

12 (b) (i) Compound which have the same molecular formula Accept same no and type of atom for M But If same (chemical) formula M = 0 but allow M If empirical formula CE = 0/ but different structures/different structural formulae/different displayed formulae M dependent on M -methylbut--ene only ignore commas and hyphens Allow any correct structure with a cyclic alkane Do not allow i.e with an missing on one C Page of

13 (c) C 8 only Making plastics/used to make polymers or polythene/used to make antifreeze/make ethanol/ripening fruit/any named additional polymer not used as a plastic/polymer/antifreeze not just polymers we need to see that they are being made [6] M. (a) C n n+ Allow x in place of n (b) Chain Must show every bond Allow branched chain (c) C 9 0 nly To break the (C-C and/or C-) bonds M=0 if break C=C To make products which are in greater demand / higher value / make alkenes Not more useful products Allow specific answers relating to question Page of

14 (d) C 5 + 5C + 6 Allow other balanced equations which give C and C/C Causes global dimming / exacerbates asthma / causes breathing problems / makes visibility poor / smog Apply list principle Ignore causes cancer / toxic (e) (x 00) 7.8% Allow 7.5% nly (f),-dichloro--methylpentane Ignore punctuation C 6 Cl nly [] M. (a) (i) Crude oil / oil / petroleum Do not allow petrol Fractional distillation / fractionation / fractionating Not distillation alone (b) (i) 5 Allow five / V Chain (isomerism) Allow branched chain / chain branched / side chain (isomerism) Ignore position (isomerism) Do not allow straight chain / geometric / branched / function Page of

15 (c) (i) C 6 / 6 C nly Thermal cracking If not thermal cracking, CE = 0/ If blank mark on igh temperature Allow high heat for high temperature (00 C < T < 900 C) or (650 K < T < 00 K) Not heat alone If no T, units must be and igh pressure (> 0 atm, > MPa, >000 kpa) To produce substances which are (more) in demand / produce products with a high value / products worth more Ignore to make more useful substances (d) (i) Corrosive or diagram to show this hazard symbol Ignore irritant, acidic, toxic, harmful ( ) ( ) =76.75(%) or 76.8(%) Allow answers > sig figs (e),-dichloro- methylpentane Ignore punctuation Any order C 6 Cl [] M. (a) (i) C n n / C x x Fractional distillation / GLC / gas liquid chromatography / fractionation Do not allow cracking / distillation Page 5 of

16 (b) (i) But--ene / butene Ignore hyphens and commas Do not allow butene- / but--ene / butane / butane /alkene / C 8 / propene / straight-chain alkene A structure of cyclobutane or methyl-cyclopropane Allow skeletal formula. (c) (i) C 5 C 8 + C 7 6 Do not accept multiples. Thermal cracking Not catalytic cracking or cracking. To produce products that are in greater demand / more valuable / more expensive / more profitable The (unsaturated) alkene or the (unsaturated) molecule or X produced can be polymerised or can be made into plastics. Ignore more useful products. Break (C C or C ) bonds Allow to overcome the activation energy. Allow to break the carbon chain. Penalise breaking wrong bonds. (d) (i) nly. Fuel / LPG Allow camping gas, lighter fuel, propellant, refrigerant, cordless appliances. Do not allow petrol or motor fuel. Ignore natural gas. C C + 5 Accept multiples. (iv) S / sulfur dioxide If other sulfur oxides, mark on. Page 6 of

17 Calcium oxide / Ca / lime / quicklime Allow CaC / allow Ca() or names. (v) Allow any solid base. M dependent on M. Do not allow limewater. Neutralisation Allow acid-base reaction. Allow flue gas desulfurisation / FGD (e) (Molecules) are similar sizes / have similar M r / have similar number of electrons Chemical error CE = 0/ if breaking bonds. Allow similar number of carbon and hydrogen atoms / similar surface area / similar chain length. Can accept same number of carbon atoms. Do not accept same number of atoms / same number of bonds. Ignore similar amount of bonds. Similar van der Waals forces between molecules / similar intermolecular forces (IMF) Not similar incorrect IMF eg dipole-dipole [6] M. (a) Fractional distillation / fractionation / GLC / gas liquid chromatography (b) C 0 Need C 0 and the reason for the mark Because it has a higher bp / has stronger IMF / larger molecule / longer chain / larger surface (area) (c) C 0 + 6½ C + 5 (d) Accept multiples Ignore state symbols C or evolved is a greenhouse gas / C or evolved contribute to global warming / the products are greenhouse gases Ignore climate change Page 7 of

18 (e) C C C C +.5 C (C) + Accept multiples Allow with or without a number before the organic molecules (f) (i) C 5 S +.5 C + + S Accept multiples Calcium oxide / calcium carbonate Allow any base or alkali Allow correct formulae Neutralises the S / acid base reaction / it is a base Can only score M if base or alkali used in M Allow M if blank in M Ethanol contains hydrogen bonding Breaking covalent bonds CE = 0 / Which is stronger than IMF (VDW / dipole-dipole forces) in ethanethiol / ( bonding) is the strongest IMF nly award M if M given, but allow IMF in ethanol are stronger than in ethanethiol for maximum mark (g) (i) (,-)dimethylpropane Ignore punctuation Because molecule is smaller / less polarisable / has less surface (area) / is more spherical / molecules can t get as close to one another (to feel the vdw forces) Allow converse answers referring to straight chain isomers CE = 0 / if breaking bonds vdw intermolecular forces or vdw force between molecules are weaker or fewer Need vdw rather than just IMF or one (h) (i) C C 9 Thermal (cracking) If not thermal cracking CE = 0 / Page 8 of

19 igh pressure AND high temperature If blank mark on Allow high P and T R Pressure of 0 atm, MPa 000 kpa AND temp of 00 C T 000 C or 650 K T 00 K Do not allow high heat If no units for T, then range must be [7] M5. (a) (i) (Compounds with the) same molecular formula Allow same number and type of atom for M Ignore same general formula. But different structural formula / different displayed formula / different structures / different skeletal formula M dependent on M Not different positions of atoms / bonds in space. But--ene Allow but--ene. Allow but ene. Ignore punctuation. ()-methylprop-()-ene Do not allow -methyleprop--ene. (iv) Do not allow skeletal formulae. Penalise missing and missing C Page 9 of

20 (b) (i) C 8 + C + Accept multiples. Exacerbates asthma / breathing problems / damages lungs / smog / smoke / global dimming Ignore toxic / pollutant / soot / carcinogen. Do not allow greenhouse effect / global warming / acid rain / ozone. (c) (i) C 6 Allow C6 C and must be upper case. Jet fuel / diesel / (motor) fuel / lubricant / petrochemicals / kerosene / paraffin / central heating fuel / fuel oil Ignore oil alone. Not petrol / bitumen / wax / LPG / camping fuel. (d) (i) C N 8C +.5 N + 9 Accept multiples. Ir / iridium R Pt / platinum R Pd / palladium R Rh / rhodium [] Page 0 of

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