Alcohols. Ethanol Production. 182 minutes. 181 marks. Page 1 of 26

Transcription

1 ..0 Alcohols Ethanol Production 8 minutes 8 marks Page of 6

2 M. Condition = two from yeast (anywhere in question) Air excluded or sterile / clean () Ignore references to pressure / temperature / aqueous / dark / high alcohol conc Temperature too low inactivates / deactivates enzymes or reaction too slow () Temperature too high destroys or denatures yeast / enzymes () Not kills enzymes; not deactivates here Advantage = sugar / glucose / carbohydrate is renewable resource / source () Advantage = production uses low level technology / cheap equipment () Ignore references to energy Do not allow contra-arguments about ethene C 6 6 C C + C balanced () C + C + balanced () Allow C 6 but penalise C once [8] M. (a) % =.6 % () If % not calculated only M available C () =. =. =. Ratio: : 0: ( C 0 ) () If arithmetic error in any result lose M If percentage composition calculation done zero (b) (i) Type of alcohol: Tertiary () Reason: No hydrogen atom on central carbon () Penalise missing bonds / incorrect bonds once per paper Page of 6

3 (c) (i) Aldehyde () Ignore named aldehydes or their structures, penalise wrong named compound C C C C + [] C C C C + () Balanced () C 0 is K as a reactant [] can be over arrow C 7 C not accepted for product, but C C C is K If use C or C compounds no marks in C.E of wrong alcohol (iii) Name Butanoic acid () Structure: C C C C () mark conseq. or as stated (d) Advantage: Fast reaction R pure product R continuous process R cheap on manpower R high yield, 00% alcohol () Disadvantage: igh technology R ethene from non renewable source R expensive equipment not just costly () Not answers based on fermentation (e) [8] M. (a) (i) addition of water / steam () Ignore to the reaction Page of 6

4 Advantage: low technology renewable feedstock / resource allowed for use in drinks, perfumes considered to be green () any one NT infinite or non-finite resource Disadvantage: slow low yield significant land use has to be distilled labour intensive any one Ignore yeast NT (unqualified) batch production NT impure product (b) (i) Structure of aldehyde Structure of carboxylic acid () () NT C C NT C C Penalise incorrect R group once Reagent: sodium (/ potassium) dichromate (VI) (VI not essential) () M Conditions: acidified or sulphuric acid () Can be with reagent M (heat under reflux) () M r correct formula for M and M M depends on M (but M correct from Cr 7, K Cr 7 etc M mark independent Credit KMn for M Ignore T and P for M (c) (i) () () (d) (i) Al or S or P () Name or formula Page of 6

5 For M the + can be on or if - used For M the arrow must go to the + or to oxygen Synchronous loss without carbocation loses carbocation structure mark; can still score ¾ i.e. penalise M [] M. (a) ethan(e)-,-diol R,-ethan(e)diol () antifreeze () R production of Terylene / polyester feedstock for polyester / PET NT surfactant NT plasticizer NT solvent NT de-icer (b) Reaction or steam () Reaction () NT air Ignore reaction Reaction () Reaction N () For Reaction ; credit dil S R S (aq) R Cl (aq) but NT steam and NT Na(aq) Page of 6

6 (c) Penalise M incorrect δ+ / δ Penalise δ on alkene (M) Penalise dots on bonds once Penalise M (structure) for use of wrong alkene Penalise M for use of Br (d) Water R aqueous solution R (aq) in equation () Yeast R enzyme/zymase R T C but T not below 0 C and allow warm N.B. yeast and T=60 con Ignore p Ignore anaerobic / oxygen Ignore time Ignore pressure M M C 6 6 C (or C C ) + C Allow C if balanced equation M R M needs the use of good English and correct chemistry to gain credit M M: The rate of fermentation is slower () R The rate of hydration is faster QoL R (The rate of) fermentation is slow and (the rate of) hydration is fast reference correctly to time rather than rate gains credit M: The product of fermentation is less pure or lower purity R The product of hydration is more pure or higher purity R The product of fermentation is impure and that of hydration is pure R Specific reference to 0 % versus 90 00% R correct reference to higher or lower yield [] Page 6 of 6

7 (r C 6 or C C ) (In equation, allow additional on both sides of the equation) M. (a) (i) C 6 6 C + C (r C C ) (Ignore state symbols in the equation) Fermentation (b) (i) C + C + C or carbon monoxide or C or carbon NLY (iii) C + N C + N R N N + R N + C N + C R C N 8C + ½N + 9 (c) Elimination (Penalise additional words such as electrophilic ) M structure of protonated alcohol (allow C C ) M arrow to show breakage of C bond on protonated alcohol M structure of carbocation (allow ) M arrow from correct C bond on carbocation (penalise sticks once only for structures M and M) (synchronous mechanism using correct structure required for M, loses M) Page 7 of 6

8 (d) C 6 C + (d) Silver R silver-based (NT silver oxide) M correct structure for epoxyethane (Allow C =C or C in the equation) (Credit the structure of epoxyethane independently) (Credit M provided has been used and the atoms balance, but the structure is poor e.g. C or C C but NT C C) [] M6. (a) M fermentation M dehydration or elimination (b) (i) yeast R zymase R an enzyme concentrated sulphuric or phosphoric acid (penalise aqueous or dilute as a contradiction) (c) (i) primary or sugar or glucose or ethanol is renewable R ethanol does not contain sulphur-containing impurities R ethanol produces less pollution or is less smoky or less C/C (the objective is a positive statement about ethanol) (penalise the idea that ethanol is an infinite source or vague statements that ethanol has less impurities) (penalise the idea that ethanol produces no pollution) (e) Addition (ignore self or chain as a preface to addition ) (penalise additional) [8] Page 8 of 6

9 (penalise C 6 once only in this question) M7. (a) (i) C 6 6 C + C ; Concentrated S R concentrated P R Al ; (penalise aqueous or dilute as a contradiction) C C + R C C = C + ; (b) (penalise C. C and C -C and C : C for ethene) Nickel R Ni R platinum R Pt R palladium R Pd; ydrogen R ; (c) (i) C 8 nly; C 9 7 nly; (empirical formula is not consequential on molecular formula) (An unsaturated compound) contains (at least) one double bond R Contains C=C; (must be a positive statement) Page 9 of 6

10 (iii) M: Bromine water R Br (aq) R Bromine R Br ; (penalise bromide water, but mark on) M: decolourised or goes colourless R from brown/red/orange/yellow to colourless; (Must be colourless not clear for M) (chemical error if no reagent or wrong reagent, loses both marks) (credit KMn for M, (purple) to colourless for M (if acidified) R (purple) to brown/brown precipitate (if alkaline or unspecified) (No credit for hydrogen or iodine as reagents) [0] Page 0 of 6

11 M8. (a) M: aqueous or solution in water or (aq) in the equation M: yeast or zymase (do not credit an enzyme unless qualified) M: anaerobic/absence of oxygen/absence of air or neutral p/p value 6 8 M: T in the range 0 0 C only M: fermentation (ignore references to pressure) (ignore uv light) M6: C 6 6 C C + C (ignore state symbols but penalise M if the state symbol in the equation contradicts) M7: C C + C + (credit use of C ) (penalise use of C 6 once only in M6 or M7) (b) M: dehydration is the elimination of water or removal of combined water or qualified loss of/removal of water e.g. from a compound/molecule/alcohol or removal of and in the ratio : from a compound/ molecule/alcohol (do not credit from a substance ) (do not credit removal of water molecules unless qualified from a compound/molecule etc.) M: Catalyst = concentrated S or concentrated/oily/syrupy phosphoric acid or aluminium oxide/ pumice/porous pot M: C C C=C + (credit use of C ) (penalise use of C 6 here unless already penalised in part(a). Possible credit as repeat error) (credit C and C =C for ethene, but penalise C C, C. C, C :C ) (ignore S if it appears on both sides of equation) Page of 6

12 (c) M: large(r) to small(er) molecules/hydrocarbons/compounds or high(er) M r alkanes to low(er) M r alkanes (+ alkenes) (+ ) M: breakage/homolysis/splitting of C C/carbon chain/carbon skeleton (do not credit breaking C bonds alone, but ignore if accompanied by C C) M: reactive intermediate is (free/alkyl) radical or radical mechanism (do not credit free radical substitution and penalise M as a contradiction if mentioned with free radical intermediates) M: any T (or range) in the range 00 to 900 C or high temperature (ignore pressure ) M: C C C C (R C 0 ) C=C + C C (R C 6 ) or C C C C (R C 0 ) C=C + (credit C and C =C for ethene, but penalise C C, C.C, C :C and note possible RE from part(b)) [] M9. (a) Ag or silver or silver-based or silver on an alumina base epoxyethane (penalise specific silver compounds) Page of 6

13 (b) electrophilic addition M: curly arrow from C=C bond towards/alongside the side of atom on -S (penalise M if arrow to S R to formal charge on of - bond) (ignore partial charges on and of S, but penalise if these are incorrect on the atom being attacked) (credit M and M if correct curly arrow to + provided the anion is present) M: curly arrow from bond towards/alongside the side of the atom on S (credit the arrow even if there are partial or formal charges on and but the structure of S is correct) M: correct structure of the carbocation (penalise use of sticks in this structure) M: curly arrow from lone pair on an individual oxygen atom of (correct formula for) hydrogensulphate ion towards/alongside C atom bearing the positive charge (insist that the an ion has the correct formula with a lone pair of electrons and a negative charge) (c) (i) ethanal correct structure for ethanal (aldehyde functional group must be drawn out) oxidation or redox [0] Page of 6

14 M0. (a) Three conditions in any order for M to M M yeast or zymase M 0 C T C M anaerobic/no oxygen/no air R neutral p M C 6 6 C + C R C 6 6 C + C (b) M Carbon-neutral Mark independently Penalise bacteria and phosphoric acid using the list principle Ignore reference to aqueous or water (i.e. not part of the list principle) r other multiples Ignore biofuel M M 6 (mol/molecules) C /carbon dioxide taken in/used/used up (to form glucose or in photosynthesis) 6 (mol/molecules) C /carbon dioxide given out due to (mol/molecules) C /carbon dioxide from fermentation/ Process and (mol/molecules) C /carbon dioxide from combustion/process It is NT sufficient in M and M for equations alone without commentary or annotation or calculation (c) M (could be scored by a correct mathematical expression) (Sum of) bonds broken (Sum of) bonds made/formed = Δ R (Σ) B reactants (Σ) B products = Δ (where B = bond enthalpy/bond energy) For M there must be a correct mathematical expression using Δ or enthalpy change M Reactants = (+) 79 R Products = ( ) 70 Page of 6

15 M verall = 0 (kj mol ) (This is worth marks) Award full marks for correct answer. Ignore units. M is for either value underlined M is NT consequential on M Award mark NLY for +0 Candidates may use a cycle and gain full marks. M Mean bond enthalpies are not specific for this reaction R they are average values from many different compounds/molecules Do not forget to award this mark (d) M q = m c ΔT (this mark for correct mathematical formula) M M M = 6688 (J) R (kj) R 6.69 (kj) R 6.7 (kj) 0.6g is 0.0 mol therefore Δ = 669 kj mol R 670 kjmol R kj mol Award M, M and M for correct answer to the calculation Penalise M NLY if correct answer but sign is incorrect In M, do not penalise incorrect cases in the formula If m = 0.6 or m = 00.6 R if ΔT = 8, CE and penalise M and M If c =.8 (leads to 7696) penalise M NLY and mark on for M = R 770 Ignore incorrect units in M Incomplete combustion Do not forget to award this mark. Mark independently [] M. (a) to neutralise stomach acidity R as an antacid R eases indigestion/heartburn Ignore milk of magnesia Credit suitable reference to indigestion/laxative/relief of constipation Page of 6

16 (b) (i) an electron acceptor R (readily) gains/accepts/receives electron(s) NT an electron pair acceptor Ignore removes/takes away/attracts electrons Br NLY Ignore bromine Apply the list principle (iii) S e S + R S e S + Ignore state symbols Ignore absence of negative charge on electron r multiples of equations (c) (i) (acid) catalyst R catalyses (the reaction) R to speed up the reaction/increase the rate (of reaction) Ignore provides + ions Accept phonetic spelling M must show an arrow from the double bond towards the atom of the bond R on a compound with molecular formula for S (or accept S here) M could be to an + ion and M an independent bond break on a compound with molecular formula for S or S Page 6 of 6

17 M M M must show the breaking of the bond. must show an arrow from the lone pair of electrons on the correct oxygen of the negatively charged ion towards the positively charged carbon atom. is for the structure of the carbocation. NB The arrows here are double-headed M Ignore partial charges unless wrong M NT S (iii) For M, credit as shown or : S NLY with the negative charge anywhere on this ion R correctly drawn out with the negative charge placed correctly on oxygen Max marks for wrong reactant Do not penalise the use of sticks Primary R (alcohol) (iv) Displayed formula for ethanoic acid, C C All the bonds must be drawn out and this includes the bond Ignore bond angles. [] Page 7 of 6

18 M. (a) M C 6 6 C C + C (C ) Mark independently For M and M ignore state symbols and credit multiples For M and M penalise C 6 once only M fermentation M C C + C + (C ) M A specified process e.g. planting / harvesting / transport / extracting sugar / distilling ethanol solution / fertiliser production etc. M The specified process uses / burns (fossil) fuel that releases C For M, releases / increases carbon emissions is insufficient as an alternative to releases C Page 8 of 6

19 (b) M sodium or potassium hydroxide / Na / K Mark on to M from hydroxide ion M depends on correct M Ignore if K/ warm / heat / reflux and aqueous or (aq) or water For M ignore dilute For M penalise T > 00 C M nucleophilic substitution Acidified K/Na or S with K/Na loses M and M For M, both words required NB The arrows here are double-headed M must show an arrow from the lone pair of electrons on the oxygen atom of the negatively charged hydroxide ion to the C atom. Penalise M if covalent Na / K is used Penalise one mark from M or M if half-headed arrows are used M must show the movement of a pair of electrons from the C Br bond to the Br atom. Mark M independently provided it is from their original molecule. Penalise M for formal charge on C of the C Br or incorrect partial charges on C Br Penalise once only for a line and two dots to show a bond. For M and M, award full marks for an S N mechanism For M and M, maximum of marks if wrong reactant is used. Penalise M if an extra arrow is drawn from the Br of the C Br bond to, for example, K + span> Do not penalise the use of sticks M6 ne statement from The yield is (very) low / not a high yield R elimination occurs / ethene formed The rate of reaction slow Bromoethane has to be manufactured / made first Bromoethane is expensive For M6 ignore references to other costs and expenses 6 Page 9 of 6

20 (c) M concentrated phosphoric acid / conc. P R concentrated sulfuric acid / conc. S Answers in any order Ignore reference to support medium in M M hydration or (electrophilic) addition For M and M any two from Do not apply the list principle to these three chosen criteria in M and M Excess ethene R Excess steam / water / R remove the ethanol as it forms R recycle the ethene Specified Pressure 0 atm P 00 atm R 000 kpa P 0000 kpa R MPa P 0 MPa ightemperature unless they give a value that is not in the ranges given here; R 00 C T 600 C R 70 K T 870 K Accept a reference to low temperature if they specify a correct temperature range or a correct temperature in the range [] Page 0 of 6

21 M. (a) M Safety (in Process ) Sodium hydroxide / alkali is corrosive / harmful / caustic or sodium hydroxide is alkali(ne) Ignore references to chromium compounds R Bromine compounds are toxic / poisonous Carbon-neutral alone is insufficient for M M Environmental Ignore references to greenhouse gases Process could be used as a carbon sink / for carbon capture R uses waste / recycled C / C from the factory / C from the bioethanol (or biofuel) production R reduces or limits the amount of C released / given out (into the atmosphere) R Process uses renewable glucose / renewable resource(s) Page of 6

22 (b) (i) M nucleophilic substitution For M, both words required M must show an arrow from the lone pair of electrons on the oxygen atom of the negatively charged hydroxide ion to the C atom. Penalise M if covalent Na / K is used Penalise one mark from M or M if half-headed arrows are used M must show the movement of a pair of electrons from the C Br bond to the Br atom. Mark M independently provided it is from the original molecule Penalise M for formal charge on C of the C Br or incorrect partial charges on C Br Penalise once only for a line and two dots to show a bond. For M and M award full marks for an S N mechanism For M and M, maximum of marks for the mechanism if wrong reactant is used. Penalise M if an extra arrow is drawn from the Br of the C Br bond to, for example, K + Accept the correct use of sticks NB The arrows here are double-headed M B M C M A (c) M fermentation Mark M to M independently Three conditions in any order for M to M Penalise bacteria and phosphoric acid using the list principle M (enzymes from) yeast or zymase M C T C R 98 K T K Ignore reference to aqueous or water, closed container, pressure, lack of oxygen, concentration of ethanol and batch process (i.e. not part of the list principle) M anaerobic / no oxygen / no air R neutral p Page of 6

23 (d) M primary R (alcohol) Mark independently M acidified potassium or sodium dichromate For M, it must be a whole reagent and/or correct formulae R S / K Cr 7 R + / K Cr 7 Do not penalise incorrect attempt at formula if name is correct or vice versa Accept phonetic spelling If oxidation state given in name, it must be correct. For M accept acidified potassium manganate(vii) R correct combination of formula and name M C C C C + [] CC C C + For M structures must be correct and not molecular formula [] M. (a) (i) C Atoms in any order Accept a clear indication that C 6 6 yields C as the answer No peak / no absorption / no C= in the range 680 to 70 (cm ) (suggesting no evidence of C=) Allow the words dip, spike, low transmittance and trough as alternatives for absorption Ignore references to other wavenumbers (b) M C 6 6 C C + C Penalise (C ) 6 Allow multiples of the equation in M Either order M (enzymes from) yeast or zymase M C T C R 98 K T K For M and M Ignore aqueous Ignore anaerobic / absence of oxygen Ignore controlled p Ignore warm Page of 6

24 (c) (i) Displayed formula for C C All bonds must be drawn out, but ignore bond angles e Ignore state symbols Negative charge on electron not essential Accept multiples Accept electrons subtracted from RS (iii) C C + C C e (C 6 or C ) Ignore state symbols Negative charge on electron not essential Accept multiples Accept electrons subtracted from LS (iv) M Acidified potassium or sodium dichromate For M, it must be a whole reagent and / or correct formulae R S / K Cr 7 R + / K Cr 7 etc. Do not penalise incorrect attempt at formula if name is correct or vice versa R correct combination of formula and name If oxidation state given in name, it must be correct, but mark on from an incorrect attempt at a correct reagent. M (requires an attempt at M) orange to green Credit acidified potassium chromate(vi) / S + K Cr Possible alternative M (acidified) potassium manganate(vii) R KMn / S M purple to colourless ther alternatives will be accepted but M is dependent on M in every case M requires an attempt at a correct reagent for M Ignore reference to states Page of 6

25 (d) (i) An activity which has no net / overall (annual) carbon emissions to the atmosphere / air The idea that the carbon / C given out equals the carbon / C that was taken in from the atmosphere / air R An activity which has no net / overall (annual) greenhouse gas emissions to the atmosphere / air. Answer must refer to the atmosphere or air R (iii) There is no change in the total amount of carbon dioxide / carbon /greenhouse gas present in the atmosphere / air Renewable / sustainable NLY Ignore references to global warming or greenhouse gases Any one statement about this process from Subject to weather / climate Ignore batch R Depletes food supply R the land use for (specified) food R Requires use of / uses more fossil fuels R Not carbon-neutral R C produced during a named process (eg harvest, transport etc.) R Slow process / slow rate of reaction / takes a long time (to grow crops) R This route leads to the production of a mixture of water and ethanol / impure ethanol that requires separation / further processing [] Page of 6

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