Penalise reagent and condition if dilute H S 4 / H P 4 4 M.B [] M.B [] M. (a) Reaction : NaH KH () M alcohol (ic) ethanol (ic)() M ignore heat Condition mark linked to correct reagent but award M if H or base or alkali mentioned Reaction : concentrated H S 4 H P 4 M () heat () M 50 C - 00 C Condition mark linked to correct reagent but award M if H S 4 or H P 4, but not concentrated (b) Mechanism: Award M independently M and M must be to / from correct places E mechanism possible in which M Name: of mechanism = elimination () NT dehydrohalogenation Ignore base nucleophilic before elimination Reason: Reaction has (very) low yield () QoL chloroethane has to be made (from ethane) chloroethane is expensive chloroethane is not redily available 5 Page of
(c) Mechanism: Name of mechanism = elimination () NT dehydration alone Reason: Ethanol could come from (fermentation of) renewable QoL sugars / glucose / carbohydrates / sources () 6 [5] M4.A [] M5. (a) Three conditions in any order for M to M M yeast or zymase M 0 C T 4 C M anaerobic/no oxygen/no air neutral ph M4 C 6 H 6 C H 5 H + C C 6 H 6 4C H 5 H + 4C 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 4 Page of
(b) M Carbon-neutral 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 4 (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 = ΔH (Σ) B reactants (Σ) B products = ΔH (where B = bond enthalpy/bond energy) For M there must be a correct mathematical expression using ΔH or enthalpy change M Reactants = (+) 479 Products = ( ) 5750 M verall + 479 5750 = 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. M4 Mean bond enthalpies are not specific for this reaction they are average values from many different compounds/molecules Do not forget to award this mark Page of
(d) M q = m c ΔT (this mark for correct mathematical formula) M M M4 = 6688 (J) 6.688 (kj) 6.69 (kj) 6.7 (kj) 0.46g is 0.0 mol therefore ΔH = 669 kj mol 670 kjmol 668.8 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 = 0.46 or m = 00.46 if ΔT = 8, CE and penalise M and M If c = 4.8 (leads to 7696) penalise M NLY and mark on for M = 769.6 770 Ignore incorrect units in M Incomplete combustion Do not forget to award this mark. Mark independently 4 [5] M6.D [] M7. Figure Further oxidation will occur / ethanoic acid formed Do not accept poor yield without qualification Can gain this mark if logic correct but has chosen wrong Figure [] M8. (a) Compounds with the same molecular formula but different structures due to different positions of the same functional group on the same carbon skeleton/chain (b) Compound A is butan--ol only Compound C is butanone or butan--one (penalise but--ol, but allow repeat error for but--one) (credit butane--ol) Page 4 of
(c) (i) oxidation or redox (ii) (iii) (iv) (v) K Cr 7 or potassium dichromate(vi) (penalise the dichromate ion or incorrect oxidation state, but mark on) acidified or H S 4 (or other identified strong acid) (penalise H + ) (do not credit the acid unless M has been correctly attempted) (heat under) reflux use excess oxidising agent correctly drawn structure of -methylpropan--ol (insist on clearly drawn C-C and C-0 bonds) correctly drawn structure of methanoic acid (insist on C-0 and C= displayed in the formula) (d) (i) Tollens reagent or this whole reagent specified (ammoniacal silver nitrate) Fehling s solution acidified potassium dichromate(vi) (ii) correctly drawn structure of methylpropanal (insist on C-H and C= of aldehyde displayed in the formula) [] M9. (a) M: CH CH CH CH H; M: CH CH(H)CH CH ; (b) (penalise incorrect alcohols in part (a), but mark consequentially in part (b) and in part (c), if relevant) (if three alcohols drawn, award MAX. mark) M, M and M: Correct structures for butanal, butanone and butanoic acid; (award these structure marks wherever the structures appear, but insist that the C= is shown in each structure and additionally, the C- in the carboxylic acid Page 5 of
M4: balanced equation for the reaction of butan--ol with [] to produce butanal and water; M5: balanced equation for the reaction of butan--ol with [] to produce butanoic acid and water balanced equation for the reaction of butanal with [] to produce butanoic acid; M6: balanced equation for the reaction of butan--ol with [] to produce butanone and water; (Credit condensed structures or molecular formulas in each equation, provided it is obvious to which reaction the equation refers) (Insist that whatever formula is used in each equation that it is a conventional representation of the compound; for example penalise CH CH CH CH for butanal) (c) M: Correct structure for -methylpropan--ol; M: -methylpropan--ol methylpropan--ol; (penalise on every occasion in parts (a) and (c), structures for the alcohols that are presented with the alcohol functional group as C- H-) [0] Page 6 of
M0. (a) M Displayed formula for butan--ol M Alcohol X is M displayed formula must have all bonds drawn out, including the H but ignore angles Penalise sticks M structure must be clearly identifiable as -methylpropan--ol and may be drawn in a variety of ways. M Alcohol Y is named ()-methylpropan--ol NLY M must be correct name, but ignore structures (b) M The infrared spectrum shows an absorption/peak in the range 0 to 550 (cm )(which supports the idea that an alcohol is present) In M, allow the words dip, spike, low transmittance and trough as alternatives for absorption. M Reference to the fingerprint region or below 500 (cm ) M Match with or same as known sample/database spectra Check the spectrum to see if alcohol H is labelled and credit. M Run infrared spectra (of the alcohols) M Find which one matches or is the same as this spectrum. Page 7 of
(c) M balanced equation C 6 H 6 CH CH CH CH H + C + H or C 4 H 9 H r multiples for M and M In M and M penalise use of C 4 H 0 or butan--ol once only M Any one from excess/adequate/sufficient/correct amount of/enough/plenty/ a good supply of oxygen or air good mixing of the fuel and air/oxygen For M, do not accept simply oxygen or air alone Ignore reference to temperature M CH CH CH CH H + 6 4C + 5H or C 4 H 9 H M4 A biofuel is a fuel produced from (renewable) biological (re)source(s) (renewable) (re)source(s) from (a specified) plant(s)/fruit(s)/tree(s) In M4 Ignore references to carbon neutral Ignore sugar and glucose 4 (d) M butan--ol is a primary or (alcohol) M Displayed formula (NLY) for butanal CH CH CH CH M Displayed formula (NLY) for butanoic acid CH CH CH CH M and M displayed formula must have all bonds drawn out including the H but ignore angles. If butanal and butanoic acid formulae are both correctly given but not displayed, credit one mark out of two. M4 xidation (oxidised) Redox M5 orange to green Both colours required for M5 Ignore states 5 [5] Page 8 of
(penalise C H 6 once only in this question) M. (a) (i) C 6 H 6 C H 5 H + C ; (ii) Concentrated H S 4 concentrated H P 4 Al ; (penalise aqueous or dilute as a contradiction) C H 5 H C H 4 + H C H 5 H H C = CH + H ; (b) (penalise CH. CH and CH -CH and CH : CH for ethene) Nickel Ni platinum Pt palladium Pd; Hydrogen H ; (c) (i) C 8 H 4 nly; C 9 H 7 nly; (empirical formula is not consequential on molecular formula) (ii) (An unsaturated compound) contains (at least) one double bond Contains C=C; (must be a positive statement) Page 9 of
(iii) M: Bromine water Br (aq) Bromine Br ; (penalise bromide water, but mark on) M: decolourised or goes colourless 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 4 for M, (purple) to colourless for M (if acidified) (purple) to brown/brown precipitate (if alkaline or unspecified) (No credit for hydrogen or iodine as reagents) [0] M. (a) Eliminate / reduce fire risk; Allow ethanol flammable / burns / combusts. (b) range to green; Need full colour change to score mark. [] M. Add Tollens / Fehling s / Benedict s reagent / ir spectra Accept any other chemically correct reagent and observation Silver mirror / blue to red red precipitate (with ethanal) / peak at 700 cm (in ethanal) Must have correct test to access second mark Accept silver. Do not accept silver solution Give one mark for silver mirror test and silver mirror Accept correct answer based on n.m.r. spectra [] Page 0 of
Therefore, molecular formula is same as the empirical formula - C H 4 (b) C 6 H 6 C H 5 H + C M4. (a) Percentage of oxygen by mass = 00 40.9 4.5 = 54.6 C H % Divide by A r =.4 = 4.5 =.4 Divide by smallest = Nearest whole number ratio =. = :.96 : Nearest integer ratio = : 4 : Empirical formula C H 4 Empirical formula mass = 88 = molecular formula mass (c) Advantage ethanol is produced at a faster rate (d) (e) Disadvantage more energy is used / required in the reaction Air gets in / oxidation occurs Alcohol H absorption in different place (0 550 cm ) from acid H absorption (500 000 cm ) The C= in acids has an absorption at 680 750 cm [0] Page of
M5. (a) to neutralise stomach acidity as an antacid eases indigestion/heartburn Ignore milk of magnesia Credit suitable reference to indigestion/laxative/relief of constipation (b) (i) an electron acceptor (ii) (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) H S 4 + H + + e S + H S 4 + 4H + + e S + H Ignore state symbols Ignore absence of negative charge on electron r multiples of equations (c) (i) (acid) catalyst catalyses (the reaction) to speed up the reaction/increase the rate (of reaction) Ignore provides H + ions Accept phonetic spelling Page of
(ii) M must show an arrow from the double bond towards the H atom of the H bond H on a compound with molecular formula for H S 4 (or accept H S here) M could be to an H + ion and M an independent H bond break on a compound with molecular formula for H S 4 or H S M M M4 must show the breaking of the H 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 HS 4 (iii) For M, credit as shown or : S H NLY with the negative charge anywhere on this ion correctly drawn out with the negative charge placed correctly on oxygen Max marks for wrong reactant Do not penalise the use of sticks Primary (alcohol) 4 (iv) Displayed formula for ethanoic acid, CH CH All the bonds must be drawn out and this includes the H bond Ignore bond angles. [] Page of
M6. (a) (i) Hexan--ol NLY (ii) Homologous (series) NLY (iii) Displayed formula for butan--ol All bonds must be drawn out including the H bond Ignore bond angles (iv) CH CH CH CH H + [] CH CH CH CH + H Require this whole equation as written or formulae drawn out Penalise sticks (v) Displayed formula for butanone (credit possible enols, ethers and cyclic structures for C 4 H 8 ) All bonds must be drawn out Ignore bond angles Page 4 of
(b) M q = m c ΔT calculation 75 4.8 8 M = 585 (J) 5.85 (kj) 5.9 (kj) (This also scores M) M 0.005 mol, therefore ΔH = 70 (kj mol ) ΔH = 70.4 (kj mol ) ΔH = 00 (kj mol ) Award full marks for correct answer In M, do not penalise incorrect cases in the formula Ignore incorrect units in M Penalise M NLY if correct answer but sign is incorrect value is in J mol If m = 5 0 if ΔT = 8, CE and only allow one mark for correct mathematical formula for M If c = 4.8 (leads to 674) penalise M NLY and mark on for M = 50 ( 47) (c) (i) M The enthalpy change (or heat change at constant pressure) when mol of a compound/substance/alcohol M is burned completely in oxygen burned in excess oxygen M with all reactants and products/all substances in standard states all reactants and products/all substances in normal states under standard conditions 00 kpa/ bar and a specified T/98 K For M Ignore reference to atmosphere Page 5 of
(ii) M (could be scored by a correct mathematical expression) M ΔH = ΣΔH f (products).σδh f (reactants) a correct cycle of balanced equations M = 4( 94) + 5( 86) ( 7) (This also scores M) M = 679 (kj mol ) 680 (kj mol ) Award mark NLY for (+) 679 (+) 680 Correct answer to calculation gains full credit Credit mark if + 679 (kj mol ) For other incorrect or incomplete answers, proceed as follows check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication; this would score marks (M and M) If no AE, check for correct method; this requires either a correct cycle with 4C and 5H a clear statement of M which could be in words and scores only M (d) (i) M This is about the change in formula up the series Each alcohol in the series (compared with the previous one) increases by/has an extra CH has one more C-C and two more C-H M This is about the reaction and bond breaking/making Combustion of each alcohol in the series breaks one more C-C and two more C-H compared with the previous one AND forms one more mol C and one more mol H A statement in which there is the idea that the extra additional difference in number of bonds broken and formed (as the series increases) is the same has the same difference in energy N.B. If the first statement here for M is given, both marks score Page 6 of
(ii) For the two marks M and M heat loss or heat absorbed by the apparatus incomplete combustion/not completely burned The idea that the water may end up in the gaseous state (rather than liquid) reactants and/or products may not be in standard states. [8] M7. (a) (i) Green Ignore shades of green. (ii) Excess acidified potassium dichromate(vi) Reflux (for some time) In the diagram credit should be given for a vertical condenser Lose M and M4 for a distillation apparatus. an apparatus which would clearly work Do not allow this mark for a flask drawn on its own. Penalise diagrams where the apparatus is sealed. (iii) Distillation Immediately (the reagents are mixed) (b) Keep away from naked flames Allow heat with water-bath or heating mantle. If a list is given ignore eye protection, otherwise lose this mark. (c) (i) Tollens or Fehling s reagents Incorrect reagent(s) loses both marks. Accept mis-spellings if meaning is clear. Page 7 of
Silver mirror / red ppt. formed Accept blue to red but not red alone. (ii) Sodium carbonate (solution) / Group II metal Allow indicator solutions with appropriate colours. Accept any named carbonate or hydrogen carbonate. Effervescence / evolves a gas Accept fizzes. (d) Propanoic acid If this mark is lost allow one mark if there is reference to stronger intermolecular forces in the named compound. Lose M and M. Contains hydrogen bonding Some comparison with other compounds explaining that the intermolecular forces are stronger in propanoic acid [5] M8. (a) To prevent vigorous boiling / uneven boiling / bubbling vigorously Reference to an effect on reaction here loses this mark. (b) Condenser Accept condensation chamber or condensation tube. Should show effective water jacket and central tube If a flask is also drawn then the condenser must be at an appropriate angle. Apparatus must clearly work. Ignore direction of water flow. Diagram must have a clear flow of vapour and water eg unblocked central tube or flow indicated by arrows. [] M9. (Mix the alcohol with warm) K Cr 7 / H + allows identification by lack of reaction Scheme must allow the alcohol to be distinguished to get all marks. Page 8 of
Distillation of initial product needed for / If distillation stage not clear then max. (M and M). Awareness of correct reactions / lack of reaction relating to each class of alcohol is worth mark. Effect of Tollens / Fehling s on oxidation product to identify or (by default) Reacting Tollens / Fehling s with alcohols directly is incorrect and gains no M or M. Detailed observations relating to the reactions are not needed but should be penalised where incorrect. [] M0. (a) (i) CH Atoms in any order Accept a clear indication that C 6 H 6 yields CH as the answer (ii) No peak / no absorption / no C= in the range 680 to 750 (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 H 6 CH CH H + C Penalise (C H ) 6 Allow multiples of the equation in M Either order M (enzymes from) yeast or zymase M 5 C T 4 C 98 K T 5 K For M and M Ignore aqueous Ignore anaerobic / absence of oxygen Ignore controlled ph Ignore warm (c) (i) Displayed formula for CH CH All bonds must be drawn out, but ignore bond angles Page 9 of
(ii) + 4H + + 4e H Ignore state symbols Negative charge on electron not essential Accept multiples Accept electrons subtracted from RHS (iii) CH CH H + H CH CH + 4H + + 4e (C H 6 or C H 5 H) Ignore state symbols Negative charge on electron not essential Accept multiples Accept electrons subtracted from LHS (iv) M Acidified potassium or sodium dichromate For M, it must be a whole reagent and / or correct formulae H S 4 / K Cr 7 H + / K Cr 7 etc. Do not penalise incorrect attempt at formula if name is correct or vice versa 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) / H S 4 + K Cr 4 Possible alternative M (acidified) potassium manganate(vii) KMn 4 / H S 4 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 0 of
(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 An activity which has no net / overall (annual) greenhouse gas emissions to the atmosphere / air. Answer must refer to the atmosphere or air (ii) (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 Depletes food supply the land use for (specified) food Requires use of / uses more fossil fuels Not carbon-neutral C produced during a named process (eg harvest, transport etc.) Slow process / slow rate of reaction / takes a long time (to grow crops) This route leads to the production of a mixture of water and ethanol / impure ethanol that requires separation / further processing [] Page of
M. (a) M Safety (in Process ) Sodium hydroxide / alkali is corrosive / harmful / caustic or sodium hydroxide is alkali(ne) Ignore references to chromium compounds 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 uses waste / recycled C / C from the factory / C from the bioethanol (or biofuel) production reduces or limits the amount of C released / given out (into the atmosphere) Process uses renewable glucose / renewable resource(s) Page of
(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 NaH / KH 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 (ii) M B M C M A (c) M fermentation Mark M to M4 independently Three conditions in any order for M to M4 Penalise bacteria and phosphoric acid using the list principle M (enzymes from) yeast or zymase M 5 C T 4 C 98 K T 5 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) M4 anaerobic / no oxygen / no air neutral ph 4 Page of
(d) M primary (alcohol) Mark independently M acidified potassium or sodium dichromate For M, it must be a whole reagent and/or correct formulae H S 4 / K Cr 7 H + / 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) correct combination of formula and name M HCH CH CH CH H + 4[] HCCH CH CH + H For M structures must be correct and not molecular formula [5] M. Acidified potassium dichromate Either bs with -methylpropan--ol Accept words or formulae. Accept acidified potassium permanganate. Accept Lucas reagent (conc HCl, ZnCl ) (cloudy in 5 mins for, instantly for ). Mark on for incomplete reagent. Incorrect reagent CE = 0 / Inclusion of Tollen s etc with acidified potassium dichromate is incorrect reagent. Not no reaction. No visible change bs with butan--ol range to green (both colours needed) or bs with -methylpropan--ol bs with butan--ol orange green [] Page 4 of
M. (a) H S 4 Allow H P4 or HCl (b) Dichromate / Cr(VI) reduced or Cr(III) formed. Allow Cr 6+ and Cr + (c) The alcohol is flammable Allow enables temperature to be controlled (d) Tollens Silver mirror Fehling s Red precipitate Benedict s Red precipitate [5] M4. (a) (i) C 6 H 6 CH CCH + C + H r multiples (ii) to speed up the reaction (provide a) catalyst or catalyses the reaction or biological catalyst release / contain / provides an enzyme Ignore fermentation Ignore to break down the glucose Not simply enzyme on its own (b) (i) CH CH(H)CH + [] CH CCH + H Any correct representation for the two organic structures. Brackets not essential. Not sticks for the structures in this case (ii) Secondary (alcohol) (alcohol) Page 5 of
(c) M q = m c ΔT q =50 4.8 8.0 Award full marks for correct answer In M, do not penalise incorrect cases in the formula M M = (±) 506 (J) 5.06 (kj) 5.0 (kj) (also scores M) This mark is for dividing correctly the number of kj by the number of moles and arriving at a final answer in the range shown. Using 0.00450 mol therefore ΔH = 5 (kj mol ) 4.6 to 0 (kj mol ) Range (+)4.6 to (+)0 gains marks BUT 0 gains marks and +0 gains marks AND 00 gains marks and +00 gains marks Award full marks for correct answer In M, do not penalise incorrect cases in the formula Penalise M NLY if correct numerical answer but sign is incorrect; (+)4.6 to (+)0 gains marks Penalise M for arithmetic error and mark on If ΔT = 8; score q = m c ΔT only If c = 4.8 (leads to 577) penalise M NLY and mark on for M = 8 Ignore incorrect units in M If units are given in M they must be either kj or kj mol in this case (d) M The enthalpy change / heat change at constant pressure when mol of a compound / substance / element M is burned / combusts / reacts completely in oxygen burned / combusted / reacted in excess oxygen M with (all) reactants and products / (all) substances in standard / specified states (all) reactants and products / (all) substances in normal states under standard conditions / 00 kpa / bar and specified T / 98 K For M Ignore reference to atmosphere Page 6 of
(e) M Σ B (reactants) Σ B (products) = ΔH Sum of bonds broken Sum of bonds formed = ΔH B(C C) + B(C=) + 6B(C H) + 4B(=) (LHS) 6B(C=) 6B( H) (RHS) = ΔH M (also scores M) (48)+805+6(4)+4(496) [LHS = 5957] (696) (47) (984) 6(805) 6(46) [RHS = ( ) 7608] = ΔH (480) (778) using only bonds broken and formed (55 680) M ΔH= 65 (kj mol ) Candidates may use a cycle and gain full marks. Correct answer gains full marks Credit mark for (+) 65 (kj mol ) For other incorrect or incomplete answers, proceed as follows check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication / addition error; this would score marks (M and M) If no AE, check for a correct method; this requires either a correct cycle with 4, C and H a clear statement of M which could be in words and scores only M Allow a maximum of one mark if the only scoring point is LHS = 5957 (or 55) RHS = 7608 (or 680) Award mark for + 65 Page 7 of
(f) For the two marks M and M, any two from heat loss or not all heat transferred to the apparatus or heat absorbed by the apparatus or (specific) heat capacity of the apparatus not considered incomplete combustion / not completely burned / reaction is not complete The idea that the water may end up in the gaseous state (rather than liquid) reactants and / or products may not be in standard states. MBE data refers to gaseous species but the enthalpy of combustion refers to liquids in their standard states / liquid propanone and liquid water in standard states MBE do not refer to specific compounds MBE values vary with different compounds / molecules are average / mean values taken from a range of compounds / molecules Apply the list principle but ignore incomplete reasons that contain correct chemistry Ignore evaporation Ignore faulty equipment Ignore human error Not enough simply to state that MBE are mean / average values [5] M5. (a) Any correct skeletal formula (both H groups must be shown) (b) M Displayed formula of correct product Incorrect organic product CE=0 Must be displayed formula but can be shown separately or in the equation M Balanced equation Allow any correct structural formula (or molecular formula C H 4 ) for product in balanced equation Allow any correct formula of propane-,-diol (including its molecular formula C H 8 ) Page 8 of
(b) CH CH H + H CH CH + 4H + + 4e (c) M flask with condenser vertically above it (without gaps between flask and condenser) Distillation diagram CE = 0 Condenser must have outer tube for water that is sealed at top and bottom; condenser must have two openings for water in/out (that are open, although these openings do not need to be labelled) Penalise M if apparatus is sealed (a continuous line across the top and/or bottom of the condenser is penalised) M flask and condenser labelled Allow condensing tube for condenser label (d) (e) Form small(er) bubbles or prevent large bubbles Any one of these four structures: Allow any correct structural / displayed / skeletal formula For reference: Carbon Carbon aldehyde alcohol carboxylic acid alcohol aldehyde ketone alcohol ketone [7] M6. D M7. (a) A mixture of liquids is heated to boiling point for a prolonged time Vapour is formed which escapes from the liquid mixture, is changed back into liquid and returned to the liquid mixture Any ethanal and ethanol that initially evaporates can then be oxidised [] (c) Mixture heated in a suitable flask / container A labelled sketch illustrating these points scores the marks Page 9 of
With still head containing a thermometer Water cooled condenser connected to the still head and suitable cooled collecting vessel Collect sample at the boiling point of ethanal (d) Cooled collection vessel necessary to reduce evaporation of ethanal Hydrogen bonding in ethanol and ethanoic acid or no hydrogen bonding in ethanal (e) Intermolecular forces / dipole-dipole are weaker than hydrogen bonding Reagent to confirm the presence of ethanal: Add Tollens reagent / ammoniacal silver nitrate / aqueous silver nitrate followed by drop of aqueous sodium hydroxide, then enough aqueous ammonia to dissolve the precipitate formed Add Fehling s solution Warm M and M can only be awarded if M is given correctly Result with Tollen s reagent: Silver mirror / black precipitate Result with Fehling s solution: Red precipitate / orange-red precipitate Reagent to confirm the absence of ethanoic acid Add sodium hydrogencarbonate or sodium carbonate Page 0 of
Allow (CH ) CHCCH Allow (CH ) C=CHCH Allow (CH ) CHCH=CH Result; no effervescence observed; hence no acid present M5 can only be awarded if M4 is given correctly Reagent; add ethanol and concentrated sulfuric acid and warm Result; no sweet smell / no oily drops on the surface of the liquid, hence no acid present [6] M8. (a) -methylbutan--ol (b) (c) Elimination (d) (e) (f) Position C B A Page of
Allow (CH ) C(H)CH CH Allow (CH ) CCH H (g) (h) [9] Page of
Page of