Mixed Questions Answers

Transcription

1 Mixed Questions Answers

2 hemistry - AQA GE Mark Scheme 200 June series Q Part Sub Part Marking Guidance Mark omments 2 a i Splitting/ breaking X / bond(s) using / by (adding) / with water 2 a ii M yellow NLY Splitting/ breaking the molecule / substance / compound using / by (adding) / with water M2 Ag + + I AgI (Ag + I ) 2 a iii M AgF silver fluoride is soluble / dissolves (in water) NT simply the reaction of / with water NT simply the addition or adding of water. NT the splitting of water Accept any halogen bond, but penalise other specified bonds 2 For M, penalise cream(y) white Ignore pale or light or dark (yellow) For M2, ignore state symbols 2 Accept silver flouride M2 No result no precipitate no (visible) change would occur colourless solution Mark independently Ignore reference to F bond breakage in M Ignore no reaction and nothing

3 hemistry - AQA GE Mark Scheme 200 June series 2 b The bond that takes less energy to break / the lower bond enthalpy (energy) / weaker bond means the precipitate / reaction / hydrolysis occurs faster / quicker /takes less time Insist on comparative on both bond strength and rate of reaction The bond that takes more energy / the higher bond enthalpy (energy) / stronger bond means the precipitate / reaction / hydrolysis occurs slower/ takes longer / takes more time 2 c i An electron pair donor 2 c ii Forms a covalent or co-ordinate or dative bond by donating a pair of electrons Answer must refer to an electron pair. redit lone pair Attracted does not equal donated Penalise M if covalent Na is used M must show an arrow from the lone pair of electrons on the oxygen atom of the negatively charged hydroxide ion to the central atom. M2 must show the movement of a pair of electrons from the Br bond to the Br atom. Mark M2 independently. NB The arrows here are double-headed 2 Penalise M2 for formal charge on or incorrect partial charges Penalise once only for a line and two dots to show a bond. Max mark for the wrong reactant Award mark only for -Br bond breakage if an S N mechanism is used. Do not penalise the use of sticks

4 hemistry - AQA GE Mark Scheme 200 June series 2 d i Structure of tertiary carbocation ( 3 ) 3 + or drawn out Insist on a full positive charge on the central atom. Penalise a bond to the positive charge. 2 d ii Tertiary carbocation / carbonium ion (from 2-bromo-2-methylpropane) is more stable (than the primary carbocation / carbonium ion) QoL Be lenient on vertical - bonds Ignore reference to the alleged relative stability of haloalkanes Primary carbocation / carbonium ion (from 2-bromo-2-methylpropane) is less stable (than the tertiary carbocation / carbonium ion)

5 hemistry - AQA GE Mark Scheme 200 June series Q Part Sub Part Marking Guidance Mark omments 5 a to neutralise stomach acidity Ignore milk of magnesia as an antacid redit suitable reference to indigestion / laxative / relief of constipation eases indigestion / heartburn 5 b i an electron acceptor NT an electron pair acceptor (readily) gains / accepts / receives electron(s) Ignore removes / takes away / attracts electrons 5 b ii Br 2 NLY Ignore bromine Apply the list principle 5 b iii 2 S e S S e S Ignore state symbols Ignore absence of negative charge on electron r multiples of equations

6 hemistry - AQA GE Mark Scheme 200 June series 5 c i (acid) catalyst catalyses (the reaction) Ignore provides + ions Accept phonetic spelling 5 c ii to speed up the reaction / increase the rate (of reaction) M must show an arrow from the double bond towards the atom of the bond on a compound with molecular formula for 2 S 4 (or accept 2 S 3 here) M could be to an + ion and M2 an independent bond break on a compound with molecular formula for 2 S 4 or 2 S 3 M2 M3 M4 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 4 M2 Ignore partial charges unless wrong M3 NT S 4 For M3, credit as shown or : S 3 NLY with the negative charge anywhere on this ion correctly drawn out with the negative charge placed correctly on oxygen Max 3 marks for wrong reactant Do not penalise the use of sticks

7 hemistry - AQA GE Mark Scheme 200 June series 5 c iii Primary o (alcohol) 5 c iv Displayed formula for ethanoic acid, 3 All the bonds must be drawn out and this includes the bond Ignore bond angles.

8 hemistry - AQA GE Mark Scheme 200 June series Q Part Sub Part 3 (a) (i) Marking Guidance Mark omments 3 ( 3 ) 2 must be branched and chiral not allow 3 7 Br 3 or Br or 2 Br allow 2 5 bonded to either way round 3 (a) (ii) elimination allow base elimination but penalise any other qualification 3 (a) (iii) Z-pent-2-ene or cis-pent-2-ene either Z or cis is necessary (allow Z-2-pentene or cis-2-pentene) 3 (b) (i) 3 (b) (ii) A 3 (b) (iii) B 3 (b) (iv) D 3 (c) allow 2 5 bonded via or with or without brackets around Z with or without hyphens must have both trailing bonds ignore brackets or n addition or radical or step or chain growth QL not additional

9 hemistry - AQA GE Mark Scheme 200 June series 3 (d) (i) 3 N M Br M2 allow M and M2 with ethyl groups missing M4 N M3 N 3 ethyl groups essential for M3 4 Allow SN, i.e M2 first then attack of N 3 on carbocation. Allow 2 5 in M3 bonded either way Allow with or without N 3 to remove + in M4, but lose mark if Br used. ignore + or unless wrong + on central instead of + loses M2 3 (d) (ii) excess N 3 ignore reflux allow conc ammonia in sealed tube 3 (d) (iii) Allow 2 5 bonded either way N NT 5 3 (e) (i) N (e) (ii) 3 3 N 3 3 NT ( 2 5 ) 2 N 3 which is tertiary with 3 peaks but its spectrum has no doublet.

10 EM2 - AQA GE hemistry 200 Mark Scheme January series Q Part Sub Part Marking Guidance Mark omments a i Reducing agent Reduce(s) (W 3 / tungsten oxide) electron donor to remove oxygen (from W 3 / tungsten oxide or to form water); a ii W W r multiples a iii ne from 2 is explosive flammable or inflammable easily ignited b i Addition (catalytic) hydrogenation Reduction b ii Geometric(al) cis/trans E Z E/Z Ignore reference to pressure or temperature Ignore electrophilic Penalise nucleophilic addition c i (If any factor is changed which affects an equilibrium), the position of equilibrium will shift / move / change/ respond / act so as to oppose the change. (When a system/reaction in equilibrium is disturbed), the equilibrium shifts / moves in a direction which tends to reduce the disturbance A variety of wording will be seen here and the key part is the last phrase and must refer to movement of the equilibrium. QoL 3

11 EM2 - AQA GE hemistry 200 Mark Scheme January series c ii M Statement of number of moles / molecules There are more moles / molecules (of gas) on the left / of reactants fewer moles / molecules (of gas) on the right./ products there are 4 moles / molecules (of gas) on the left and 2 moles / molecules on the right. 2 Ignore volumes for M Mark independently M2 Explanation of response / movement in terms of pressure Increase in pressure is opposed (or words to that effect) pressure is lowered by a shift in the equilibrium (from left) to right / favours forward reaction. d B(reactants) B(products) = Δ (M) Sum of bonds broken Sum of bonds formed = Δ (M) B( ) +½B(=) 2B( ) = 242 (M) B( ) = 242 ½(+496) + 2(+463) (this scores M and M2) B( ) = (+)436 (kj mol ) (M3) Award mark for M could stand alone Award full marks for correct answer. Ignore units. Two marks can score with an arithmetic error in the working. andidates may use a cycle and gain full marks. 4

12 EM2 - AQA GE hemistry 200 Mark Scheme January series Q Part Sub Part Marking Guidance Mark omments 6 a Functional group (isomerism) 6 b M Tollens (reagent) (redit ammoniacal silver nitrate a description of making Tollens ) (Ignore either AgN 3 or [Ag(N 3 ) 2 + ] or the silver mirror test on their own, but mark M2 and M3) M2 silver mirror black solid/precipitate (NT silver precipitate) M3 (stays) colourless or no change or no reaction M Fehling s (solution) or Benedict s solution (Ignore u 2+ (aq) or us 4 on their own, but mark on to M2 and M3) M2 Red solid/precipitate (redit orange or brown solid) M3 (stays) blue or no change or no reaction Mark on from an incomplete / incorrect attempt at the correct reagent, penalising M 6 c (Both have) = a carbonyl (group) 3 No reagent, E=0 Allow the following alternatives M (acidified) potassium dichromate(vi) (solution) M2 (turns) green M3 (stays) orange / no change M (acidified) potassium manganate(vii) (solution) M2 (turns) colourless M3 (stays) purple / no change For M3 Ignore nothing (happens) Ignore no observation 6 d i (Free-) radical substitution NLY Penalise (free) radical mechanism

13 EM2 - AQA GE hemistry 200 Mark Scheme January series 6 d ii Initiation l 2 2l First propagation l l Penalise absence of dot once only. Penalise incorrect position of dot on propyl radical once only. Penalise 3 7 once only Second propagation l l + l 3 7 l Termination (must make 6 4 ) or e M r = (for propane) M r = (for carbon dioxide) M a correct value for both of these M r values. M2 a statement or idea that two peaks appear (in the mass spectrum) two molecular ions are seen (in the mass spectrum). 2 Accept with the radical dot above / below / to the side of the last carbon. Use of the secondary free radical might gain 3 of the four marks Mark independently 2

14 Mark Scheme General ertificate of Education (A-level) hemistry Unit 2: hemistry In Action June 20 8(c) M 2( ) + 4(.00794) ) = M2 Ethene and or they have an imprecise M r of 28.0 / 28 Ethene and or they have the same M r to one d.p. These may be shown by two clear, simple sums identifying both compounds M ( 2 = 2 ) M4 Displayed formula 5 M must show working using 5 d..p.for hydrogen Penalise similar or close to, if this refers to the imprecise value in M2, since this does not mean the same For M3, accept 2 = For M4, all bonds must be drawn out including those on either side of the unit. Penalise sticks Ignore brackets around correct repeating unit but penalise n M5 Type of polymer = Addition (polymer) Penalise additional 2

15 EM4 Unit 4: Kinetics, Equilibria and rganic hemistry June 20 Question Marking Guidance Mark omments 4(a)(i) 2 N 2 N Allow N- or - N - 6 Mark two halves separately N 2 2 N 6 lose each for missing trailing bonds at one or both ends or error in peptide link or either or both of or on ends Not allow ( 6 2 ) Ignore n 4(a)(ii) M in polyamides - bonding M2 M3 in polyalkenes - van der Waals forces Stronger forces (of attraction) in polyamides r bonding is stronger (must be a comparison of correct forces to score M3) Penalise forces between atoms or van der Waals bonds Do not award if refer to stronger bonds

16 EM4 Unit 4: Kinetics, Equilibria and rganic hemistry June 20 4(b)(i) (nucleophilic) addition elimination Minus sign on N 2 loses M M2 3 2 l ( 3 )-N 2 M Not allow N 2 M3 ( 3 2 l 3 N M4 for 3 arrows and lp 3 2 N 3 4 M2 not allowed independent of M, but allow M for correct attack on + + rather than + on = loses M2 If l lost with = breaking, max for M M3 for correct structure with charges but lp on is part of M4 only allow M4 after correct/ very close M3 For M4, ignore N 3 removing + but lose M4 for l removing + in mechanism, but ignore l as a product 4(b)(ii) N-methylpropanamide Not N-methylpropaneamide 4(c) 2 S 3 Allow N- or - N - 2 N N 4(d)(i) 2-amino-3-hydroxypropanoic acid 2

17 EM4 Unit 4: Kinetics, Equilibria and rganic hemistry June 20 4(d)(ii) 2 or 2 or 2 allow 2 allow N 2 N 2 N 2 N 2 Must be salts of aspartic acid 4(d)(iii) Penalise use of aspartic acid once in d(iii) and d(iv) 2 allow 2 allow + N 3 don t penalize position of + on N 3 N 3 (l ) 4(d)(iv) Penalise use of aspartic acid once in d(iii) and d(iv) 2 allow 2 must show -N bond don t penalize position of + on N( 3 ) 3 N( 3 ) 3 (Br ) 3

18 Mark Scheme General ertificate of Education (A-level) hemistry Unit 2: hemistry in Action January 20 Question Marking Guidance Mark omments 9(a)(i) exan--ol NLY 9(a)(ii) omologous (series) NLY 9(a)(iii) Displayed formula for butan-2-ol All bonds must be drawn out including the bond Ignore bond angles 9(a)(iv) [] Require this whole equation as written or formulae drawn out Penalise sticks 9(a)(v) Displayed formula for butanone (credit possible enols, ethers and cyclic structures for 4 8 ) All bonds must be drawn out Ignore bond angles 2

19 Mark Scheme General ertificate of Education (A-level) hemistry Unit 2: hemistry in Action January 20 9(b) M q = m c ΔT calculation 75 x 4.8 x 8 M2 = 5852 (J) 5.85 (kj) 5.9 (kj) (This also scores M) M mol, therefore Δ = 70 (kjmol - ) Δ = 70.4 (kjmol - ) Δ = 200 (kjmol - ) 3 Award full marks for correct answer In M, do not penalise incorrect cases in the formula Ignore incorrect units in M2 Penalise M3 NLY if correct answer but sign is incorrect value is in J mol - If m = 5 x 0-3 if ΔT = 28, E and only allow one mark for correct mathematical formula for M If c = 4.8 (leads to 6734) penalise M2 NLY and mark on for M3 = 350 ( 347) 9(c)(i) M The enthalpy change (or heat change at constant pressure) when mol of a compound / substance / alcohol M2 is burned completely in oxygen burned in excess oxygen M3 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 / 298 K 3 For M3 Ignore reference to atmosphere 22

20 Mark Scheme General ertificate of Education (A-level) hemistry Unit 2: hemistry in Action January 20 9(c)(ii) M (could be scored by a correct mathematical expression) M Δ = Δ f (products) - Δ f (reactants) a correct cycle of balanced equations M2 = 4( 394) + 5( 286) ( 327) (This also scores M) M3 = 2679 (kj mol - ) 2680 (kj mol - ) Award mark NLY for (+) 2679 (+) orrect answer to calculation gains full credit redit mark if (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 2 marks (M and M2) If no AE, check for correct method; this requires either a correct cycle with 4 2 and 5 2 a clear statement of M which could be in words and scores only M 9(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 2 has one more - and two more - M2 This is about the reaction and bond breaking/making ombustion of each alcohol in the series breaks one more - and two more - compared with the previous one AND forms one more mol 2 and one more mol 2 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 2 N.B. If the first statement here for M2 is given, both marks score 23

21 Mark Scheme General ertificate of Education (A-level) hemistry Unit 2: hemistry in Action January 20 9(d)(ii) For the two marks M and M2 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. 2 24

22 Mark Scheme General ertificate of Education (A-level) hemistry Unit 4: Kinetics, Equilibria and rganic hemistry January 20 Question Marking Guidance Mark omments 4(a) 3-hydroxypropanoic acid allow 3-hydroxypropionic acid must be correct spelling 4(b)(i) must show trailing bonds or can start at any point in the sequence, e.g not allow dimer allow or ignore ( ) or n NB answer has a total of 6 carbons and 4 oxygens 4(b)(ii) condensation (polymerisation) Allow close spelling 4(c)(i) = or carbon-carbon double bond 4(c)(ii) must show ALL bonds including 4(c)(iii) must show trailing bonds allow polyalkene conseq on their c(ii) ignore n

23 Mark Scheme General ertificate of Education (A-level) hemistry Unit 4: Kinetics, Equilibria and rganic hemistry January 20 4(d) 2 3 allow N N allow 4(e)(i) In 4(e), do not penalise a slip in the number of carbons in the chain, but all must be bonded correctly 2 N 2 2 NB two carboxylate groups Allow Na or Na + but not covalent bond to Na allow N 2 4(e)(ii) 2 N In 4(e), do not penalise a slip in the number of carbons in the chain, but all must be bonded correctly NB two ester groups allow N 2 or + N N

24 Mark Scheme General ertificate of Education (A-level) hemistry Unit 4: Kinetics, Equilibria and rganic hemistry January 20 4(e)(iii) 3 N 2 2 In 4(e), do not penalise a slip in the number of carbons in the chain, but all must be bonded correctly allow anhydride formation on either or both groups (see below) with or without amide group formation 3 3 N (f) M phase or eluent or solvent (or named solvent) is moving or mobile M2 stationary phase or solid or alumina/silica/resin M3 separation depends on balance between solubility or affinity (of compounds) in each phase different adsorption or retention (amino acids have) different R f values (amino acids) travel at different speeds or take different times 3

25 Mark Scheme General ertificate of Education (A-level) hemistry Unit 2: hemistry in Action June 202 Question Marking Guidance Mark omments 3(a) 2a 5 F(P 4 ) 3 + 9Si aSi 3 + af P 3(b) M (P 4 =) 0 M2 ( 3 P 4 =) (+) 5 2 Accept Roman numeral V for M2 3(c) 2 S 4 M r = 2(.00794) (5.9949) and = or or or or 98. Both numbers required alculations not required 3 P 4 M r = 3(.00794) (5.9949) = or or or or (d)(i) A substance that speeds up a reaction alters / increases the rate of a reaction AND is chemically unchanged at the end / not used up. Both ideas needed Ignore reference to activation energy or alternative route. 3(d)(ii) The addition of water (QoL ) to a molecule / compound QoL- for the underlined words 9

26 Mark Scheme General ertificate of Education (A-level) hemistry Unit 2: hemistry in Action June 202 3(d)(iii) M 3 = () 3 ( 3 6 ) M2 propan-2-ol 2 For M insist on correct structure for the alcohol but credit correct equations using either 3 6 or double bond not given. 0

27 Mark Scheme General ertificate of Education (A-level) hemistry Unit 4: Kinetics, Equilibria and rganic hemistry June 202 Question Marking Guidance Mark Additional Guidance 4(a) M2 3 2 l M 3 methyl propanoate l M3 for structure M4 for 3 arrows and lone pair (N mark for name of mechanism) 4 M2 not allowed independent of M, but allow M for correct attack on + + rather than δ+ on = loses M2 If l lost with = breaking, max for M M3 for correct structure with charges but lp on is part of M4 only allow M4 after correct/very close M3 ignore l removing + 4(b)(i) pentane-,5-diol Second e and numbers needed Allow,5-pentanediol but this is not IUPA name 4(b)(ii) l l Must show ALL bonds 4(b)(iii) All three marks are independent M (base or alkaline) ydrolysis (allow close spelling) M2 δ+ in polyester M3 reacts with - or hydroxide ion Allow (nucleophilic) addition-elimination or saponification Not reacts with Na 4(c)(i) 3 Allow 3 or 3 2 7

28 Mark Scheme General ertificate of Education (A-level) hemistry Unit 4: Kinetics, Equilibria and rganic hemistry June 202 4(c)(ii) (nucleophilic) addition-elimination (nucleophilic) addition followed by elimination Both addition and elimination needed and in that order Do not allow electrophilic addition-elimination / esterification Ignore acylation 4(c)(iii) any two from: ethanoic anhydride is less corrosive less vulnerable to hydrolysis less dangerous to use, less violent/exothermic/vigorous reaction more controllable rxn does not produce toxic/corrosive/harmful fumes (of l) does not produce l less volatile 2 max NT ST List principle beyond two answers 4(d) 3 Allow or 2 4(e)(i) ester Do not allow ether Ignore functional group/linkage/bond 4(e)(ii) 2 or twelve (peaks) 8

29 Mark Scheme General ertificate of Education (A-level) hemistry Unit 4: Kinetics, Equilibria and rganic hemistry June 202 4(e)(iii) Allow a number or range within these limits Penalize extra ranges given Ignore units 4(f)(i) sulfuric acid sodium hydroxide 2 4 correct scores 2 hydrochloric acid ammonia X or blank ethanoic acid potassium hydroxide nitric acid methylamine X or blank 3 correct scores 2 or correct scores 0 4(f)(ii) Pink to colourless Allow red purple magenta instead of pink Do not allow clear instead of colourless 9

30 Mark Scheme General ertificate of Education (A-level) hemistry Unit 2: hemistry In Action June 203 Question Marking Guidance Mark omments 0(a)(i) M c(oncentrated) phosphoric acid / c(onc.) 3 P 4 c(oncentrated) sulfuric acid / c(onc.) 2 S 4 M2 Re-circulate / re-cycle the (unreacted) ethene (and steam) / the reactants pass the gases over the catalyst several / many times 2 In M, the acid must be concentrated. Ignore an incorrect attempt at the correct formula that is written in addition to the correct name. In M2, ignore remove the ethanol. redit re-use. 0(a)(ii) M (By Le hatelier s principle) the equilibrium is driven / shifts / moves to the right / L to R / forwards / in the forward direction M2 depends on a correct statement of M The equilibrium moves / shifts to oppose the addition of / increased concentration of / increased moles/ increased amount of water / steam to decrease the amount of steam / water Mark M3 independently M3 Yield of product / conversion increase ethanol increases / goes up / gets more 3 20

31 Mark Scheme General ertificate of Education (A-level) hemistry Unit 2: hemistry In Action June 203 0(a)(iii) M Poly(ethene) / polyethene / polythene / DPE / LDPE 2 M2 At higher pressures More / higher cost of electrical energy to pump / pumping cost ost of higher pressure equipment / valves / gaskets / piping etc. expensive equipment redit all converse arguments for M2 0(b) M for balanced equation 2 M2 for state symbols in a correctly balanced equation 2(s / graphite) (g) + ½ 2 (g) 3 2 (l) ( 2 5 ) Not multiples but credit correct state symbols in a correctly balanced equation. Penalise 2 6 but credit correct state symbols in a correctly balanced equation. 0(c)(i) M The enthalpy change / heat change at constant pressure when mol of a compound / substance / element M2 is burned / combusts / reacts completely in oxygen burned / combusted / reacted in excess oxygen M3 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 / 298 K 3 If standard enthalpy of formation E=0 For M3 Ignore reference to atmosphere. 2

32 Mark Scheme General ertificate of Education (A-level) hemistry Unit 2: hemistry In Action June 203 0(c)(ii) 0(d)(i) M B(reactants) B(products) = Δ Sum of bonds broken Sum of bonds formed = Δ B(-) + B(-) + B(-) + 5B(-) + 3B(=) (LS) 4B(=) 6B( ) (RS) = Δ M2 (also scores M) (42)+3(496) [LS = 479] (2060) (488) 4(805) 6(463) [RS = 5998] = Δ (3220) (2778) using only bonds broken and formed ( ) M3 Δ = 279 (kj mol ) Award mark for +279 andidates may use a cycle and gain full marks Reducing agent reductant electron donor to reduce the copper oxide 3 orrect answer gains full marks redit mark for (+) 279 (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 2 marks (M and M2) If no AE, check for a correct method; this requires either a correct cycle with 2 and 6 and 7 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 LS = 479 RS = 5998 Not reduction. Not oxidation. Not electron pair donor. 0(d)(ii) 3 22

33 Mark Scheme General ertificate of Education (A-level) hemistry Unit 2: hemistry In Action January 203 Question Marking Guidance Mark omments 8(a) M electrophilic addition 5 For M, both words required Accept phonetic spelling M2 must show an arrow from the double bond towards the atom of the Br molecule M3 must show the breaking of the Br bond M4 is for the structure of the secondary carbocation M5 must show an arrow from the lone pair of electrons on the negatively charged bromide ion towards the correct (positively charged) carbon atom NB These are double-headed arrows For the mechanism M2 Ignore partial negative charge on the double bond M3 Penalise partial charges on Br bond if wrong way and penalise formal charges Penalise once only in any part of the mechanism for a line and two dots to show a bond Maximum any 3 of 4 marks for the mechanism for wrong (organic) reactant wrong organic product (if shown) primary carbocation Accept the correct use of sticks 20

34 Mark Scheme General ertificate of Education (A-level) hemistry Unit 2: hemistry In Action January 203 Question Marking Guidance Mark omments 8(b) M Nucleophilic substitution 5 For M, both words required Accept phonetic spelling For the mechanism Penalise M2 if N 3 is negatively charged M2 must show an arrow from the lone pair of electrons on the nitrogen atom of an ammonia molecule to the correct atom M3 must show the movement of a pair of electrons from the Br bond to the Br atom. Mark M3 independently provided it is from their original molecule M4 is for the structure of the alkylammonium ion, which could be a condensed formula. A positive charge must be shown on/or close to, the N atom M5 is for an arrow from the N bond to the N atom Award full marks for an S N mechanism in which M2 is the attack of the ammonia on the intermediate carbocation NB These are double-headed arrows Penalise M3 for formal charge on of the -Br or incorrect partial charges on -Br Penalise M3 for an additional arrow from the Br to something else The second mole of ammonia is not essential for M5; therefore ignore any species here Penalise once only for a line and two dots to show a bond Maximum any 3 of 4 marks for the mechanism for wrong organic reactant wrong organic product if shown Accept the correct use of sticks 2

35 Mark Scheme General ertificate of Education (A-level) hemistry Unit 2: hemistry In Action January 203 Question Marking Guidance Mark omments 8(c) 8(d) M (addition) polymerisation poly-addition M2 poly(propene) / polypropene 2 Ignore additional redit polyprop--ene and polypropylene Penalise condensation polymerisation 3 M must show an arrow from the lone pair on the oxygen of a negatively charged hydroxide ion to a correct atom M2 must show an arrow from a correct bond adjacent to the Br bond to the appropriate bond. nly award if an arrow is shown attacking the atom of a correct - bond in M M3 is independent provided it is from their original molecule, but E=0 if nucleophilic substitution Award full marks for an E mechanism in which M3 is on the correct carbocation. NB These are double-headed arrows Penalise M if covalent K Penalise M3 for formal charge on of Br or incorrect partial charges on -Br. Ignore other partial charges Penalise once only in any part of the mechanism for a line and two dots to show a bond Maximum any 2 of 3 marks for wrong organic reactant Accept the correct use of sticks for the molecule except for the being attacked 22

36 MARK SEME A-LEVEL EMISTRY EM2 JUNE 204 Question Marking Guidance Mark omments 7(a)(i) M (ompounds / molecules with) the same structural formula M2 with atoms / bonds / groups arranged differently in space atoms / bonds / groups with different spatial arrangements / different orientation 2 Penalise M if same structure or different structural / displayed formula. Ignore references to same molecular formula or same empirical formula. Mark independently. 7(a)(ii) redit 3 redit 2 5 Penalise of 36

37 MARK SEME A-LEVEL EMISTRY EM2 JUNE 204 7(b) M Br 2 bromine (water) bromine (in l 4 / organic solvent) M2 Isomer : decolourised / goes colourless / loses its colour M3 Isomer 2: remains orange / red / yellow / brown / the same no reaction / no (observable) change reference to colour going to the cyclopentane layer Alternatives : potassium manganate(vii) M KMn 4 in acid M2 colourless M3 purple M KMn 4 in alkali / neutral M2 brown solid M3 purple 3 If M, has no reagent or an incorrect reagent, E=0 Ignore acidified. For M penalise Br (or incorrect formula of other correct reagent), but mark on. For M, it must be a whole reagent and/or correct formula. If oxidation state given in name, it must be correct. If manganate manganate(iv) or incorrect formula, penalise M, but mark on. redit for the use of iodine M iodine (solution / in KI) M2 colourless M3 (brown) to purple (credit no change) Ignore goes clear. Ignore nothing (happens). Ignore no observation. redit for the use of concentrated 2 S 4 M concentrated 2 S 4 M2 brown M3 no change / colourless No credit for combustion observations. 8 of 36

38 MARK SEME A-LEVEL EMISTRY EM2 JUNE 204 7(c)(i) (Both infrared spectra show an absorption in range) 620 to 680 (cm ) Ignore reference to other ranges (eg for or ). 7(c)(ii) The fingerprint (region) / below 500 cm will be different or its fingerprinting will be different different absorptions / peaks are seen (in the region) below 500 cm (or a specified region within the fingerprint range) Allow the words dip spike low transmittance as alternatives for absorption. QoL 7(d) All bonds must be drawn. Ignore bond angles. 9 of 36

39 MARK SEME A-LEVEL EMISTRY EM2 JUNE 204 7(e)(i) M Electrophilic addition 5 M both words needed. M2 must show an arrow from the double bond towards the atom of the Br molecule M3 must show the breaking of the Br bond M4 is for the structure of the tertiary carbocation M5 must show an arrow from the lone pair of electrons on the negatively charged bromide ion towards the positively charged carbon atom of either a secondary or a tertiary carbocation Penalise one mark from their total if half-headed arrows are used. M2 Ignore partial negative charge on the double bond. M3 Penalise incorrect partial charges on Br bond and penalise formal charges. Penalise M4 if there is a bond drawn to the positive charge. Penalise once only in any part of the mechanism for a line and two dots to show a bond. Max 3 of any 4 marks in the mechanism for wrong organic reactant or wrong organic product (if shown) or secondary carbocation. Max 2 of any 4 marks in the mechanism for use of bromine. Do not penalise the correct use of 'sticks. For M5, credit attack on a partially positively charged carbocation structure but penalise M4 NB The arrows here are double-headed 20 of 36

40 MARK SEME A-LEVEL EMISTRY EM2 JUNE 204 7(e)(ii) M Reaction goes via intermediate carbocations / carbonium ions M2 (scores both marks and depends on M) Tertiary carbocation / carbonium ion is more stable (than the secondary carbocation / carbonium ion) Secondary carbocation / carbonium ion is less stable (than the tertiary carbocation / carbonium ion) 2 M is a lower demand mark for knowledge that carbocations are involved. M2 is of higher demand and requires the idea that the secondary carbocation is less stable or the tertiary carbocation is more stable. Reference to incorrect chemistry is penalised. A carbocation may be defined in terms of alkyl groups / number of carbon atoms, rather than formally stated. 2 of 36

41 MARK SEME A-LEVEL EMISTRY EM2 JUNE 204 7(f) M Elimination 5 M credit base elimination but no other qualifying prefix. M2 must show an arrow from the lone pair on oxygen of a negatively charged hydroxide ion to a correct atom M3 must show an arrow from a correct bond adjacent to the Br bond to a correct bond. nly award if an arrow is shown attacking the atom of a correct adjacent bond (in M2) M4 is independent provided it is from their original molecule BUT penalise M2, M3 and M4 if nucleophilic substitution shown Award full marks for an E mechanism in which M2 is on the correct carbocation NB The arrows here are double-headed Penalise one mark from their total if half-headed arrows are used. Penalise M2 if covalent K Penalise M4 for formal charge on or Br of the Br bond or incorrect partial charges on Br Penalise M4 if an additional arrow is drawn from the Br of the Br bond to, for example, K + Ignore other partial charges. Penalise once only in any part of the mechanism for a line and two dots to show a bond. Max 2 of any 3 marks in the mechanism for wrong reactant or wrong organic product (if shown) or a correct mechanism that leads to the alkene 2-methylbut-2-ene redit the correct use of sticks for the molecule except for the being attacked. M5 hydroxide ion behaves as a base / proton acceptor / electron pair donor / lone pair donor Penalise M5 if nucleophile. 22 of 36

42 MARK SEME A-LEVEL EMISTRY EM2 JUNE 205 Question Marking Guidance Mark omments 8(a) P 3,3-dimethylbut--ene accept 3,3-dimethylbutene Q 3-chloro-2,2-dimethylbutane accept 2-chloro-3,3-dimethylbutane 2 Ignore absence of commas, hyphens and gaps Require correct spelling In Q, chloro must come before dimethyl 24 of 36

43 MARK SEME A-LEVEL EMISTRY EM2 JUNE 205 8(b) M Electrophilic addition 5 M both words required For the mechanism M3 Penalise incorrect partial charge on l bond and penalise formal charges Ignore partial negative charge on the double bond. M2 must show an arrow from the double bond towards the atom of l M3 must show the breaking of the l bond M4 is for the structure of the carbocation M5 must show an arrow from the lone pair of electrons on the negatively charged chloride ion towards the positively charged carbon atom on their carbocation. NB The arrows here are double-headed Maximum 3 of 4 marks for a correct mechanism using Br or the wrong organic reactant or wrong organic product (if shown) or a primary carbocation Penalise once only in any part of the mechanism for a line and two dots to show a bond redit the correct use of sticks For M5, credit attack on a partially positively charged carbocation structure, but penalise M4 25 of 36

44 MARK SEME A-LEVEL EMISTRY EM2 JUNE 205 8(c) M Nucleophilic substitution 5 For M, both words required. Accept phonetic spelling M2 must show an arrow from the lone pair of electrons on the nitrogen atom of an ammonia molecule to the correct atom M3 must show the movement of a pair of electrons from the l bond to the l atom. Mark M3 independently provided it is from their original molecule M4 is for the structure of the alkylammonium ion, which could be a condensed formula. A positive charge must be shown on, or close to, the N atom. M5 is for an arrow from the N bond to the N atom Award full marks for an S N mechanism in which M2 is the attack of the ammonia on the intermediate carbocation For the mechanism Penalise M2 if N 3 is negatively charged. Penalise M3 for formal charge on of the l or incorrect partial charges on l Penalise M3 for an additional arrow from the l to something else The second mole of ammonia is not essential for M5; therefore ignore any species here Penalise once only for a line and two dots to show a bond Maximum 3 of 4 marks for the mechanism for wrong organic reactant wrong organic product if shown NB These are double-headed arrows Accept the correct use of sticks 26 of 36

45 MARK SEME A-LEVEL EMISTRY EM2 JUNE 205 8(d) M (base) elimination M2 K Na M3 Must be consequential on a correct reagent in M2, but if incomplete or inaccurate attempt at reagent (e.g. hydroxide ion), penalise M2 only and mark on Any one from high temperature hot heat / boil under reflux concentrated alcohol / ethanol (as a solvent) / (ethanolic conditions) 3 M Dehydrohalogenation M3 not reflux alone M3 if a temperature is stated it must be in the range 78 o to 200 o Ignore pressure 8(e) M 3NaBr + 3 P 4 3Br + Na 3 P 4 4 M redit correct ionic species in the equation M2 and M3 S 2 and Br 2 identified M4 oncentrated sulfuric acid is an oxidising agent oxidises the bromide (ion) or Br or NaBr or Br is an electron acceptor In M2 and M3 the two gases need to be identified. If equations are used using sulfuric acid and the toxic gases are not identified clearly, allow one mark for the formulas of S 2 and Br 2 apply the list principle as appropriate but ignore any reference to Br the marks are for identifying the two gases either by name or formula 27 of 36

46 MARK SEME A-LEVEL EMISTRY EM2 JUNE 206 Question Answers Mark Additional omments/guidance 4a) AND alcohol IGNE hydroxy(l) 4b) A = butan-2-ol / 3 () 2 3 B = butan--ol / product from A / P is a ketone AND product from B / Q is an aldehyde If formulae given then must be unambiguous If both formula and name given then formula must match name for mark to be awarded Penalise reference to incorrect class of alcohol Type of Bond: = Must show all bonds in Isomer including bond 4c) Reagent: conc. 2 S 4 / conc. 3 P 4 If incorrect attempt at correct reagent, mark on Apply list principle for reagents and conditions marks conc required - may appear on conditions line NT (aq) For M3 even if seen on conditions line ALLW Reagent = Al 2 3 ondition = passing vapour over hot solid owtte onditions: 80 / igh temp / ot / Reflux / ALLW stated temp in range / K IGNE heat M4 dependent on correct reagent in M3 7 of 22

47 MARK SEME A-LEVEL EMISTRY EM2 JUNE 206 4d) i) S = aldehyde/ AND T = carboxylic// 2 T forms hydrogen bonds (which are) stronger than / need more energy to break than forces between molecules/imfs in S ora (or reverse argument) (No oxidation has occurred as..) If implication of breaking covalent bonds max M only 4d) ii (Still) contains peak at cm- due to /alcohol Does not contain peak at cm- due to /carboxylic acid Any 2 Must have wavenumber range (or value within range) and bond or functional group to score each mark. Does not contain peak at cm- due to = Total 3 8 of 22

48 MARK SEME A-LEVEL EMISTRY EM4 JUNE 206 Question Answers Mark Additional omments/guidance 3a(i) (2-)chloroethan (--) oyl chloride 2 not required but penalise - or other numbers at start. Ignore in ethanoyl Ignore hyphens, commas, spaces 3a(ii) l 2 l RN 2 l 2 R N l 4 M for arrow from lp on N to (or to space half way between N and ) If full amine drawn, ignore slips except in N 2 M2 for arrow from = bond to Not score M2 as an independent first step, but can allow M for attack on + produced If l lost at this stage, Max for M M3 for structure of ion including 2 charges M4 for 3 arrows and lp on - may be scored in two steps Ignore use of RN 2 to remove + in M4, but penalise use of l - 3b G nucleophilic substitution allow minor spelling errors e.g. nucleophyllic 3c A 9 8 of 20

49 MARK SEME A-LEVEL EMISTRY EM4 JUNE 206 3d M r = 234(.0) % = 9.4(0) 9.4 scores 2 marks 22 M2 = M 00 If M r = 234 not shown, can score M if their answer 234 = their no of 3e tertiary amine 3 o amine III o amine Ignore N- substituted 3f(i) If a given: E=0, can only score if answer given is b NTE there is N mark for b alone M lp on N b or on b Alternatives: M2 alkyl groups donate electron density or positive inductive effect or electron donating groups attached M3 (lp on N b ) more available or protonated amine stabilised or better lp donor/ + acceptor Ignore reference to nucleophiles M lp on N a or on a M2 lp or electrons (on N a ) delocalised into ring /towards in = M3 (lp on N a ) less available (to bond to + /accept proton) 3f(ii) Salt is ionic Independent marks (more) soluble (in blood/body fluids/water) Total 5 9 of 20

50 MARK SEME A-LEVEL EMISTRY EM4 JUNE 206 Question Answers Mark Additional omments/guidance 4a(i) 2(.0) Not 2.5 ignore working 4a(ii) l l Must be displayed and show + on relevant carbon Penalise extra dots or [ ] + penalise 37 l 4a(iii) [l 2 l] +. [ 35 l 2 ]. + [ 37 l] + Allow without brackets M for molecular ion M2 for both fragments with mass numbers Allow dot or + anywhere on formula 4b(i) l 2 Allow [l 2 ] + 4b(ii) 2 lm M3 M2 2 l M Arrow from inside hexagon to or + on on correct electrophile M2 Structure of intermediate horseshoe centred on ; + in intermediate not too close to (allow on or below a line from 2 to 6) M3 Arrow from bond to into ring Allow M3 arrow independent of M2 structure + on in intermediate loses M2 not M3 Ignore l - removing + (different from Qu3a(ii)) 0 of 20

51 MARK SEME A-LEVEL EMISTRY EM4 JUNE 206 4c reag ent water (Aqueous) silver nitrate Na followed by acidified silver nitrate (Water +) named indicator Named alcohol Na 2 3 or Na 3 ammonia P no reaction no reaction (or slow formation of ppt) no reaction (or slow formation of ppt) No colour change NV NV no reaction Do NT award No observation Q Steamy /misty/ white fumes white precipitate (immediately formed) white precipitate (immediately formed) Indicator turns to correct acid colour Fruity or sweet smell or misty fumes Fizzing or effervescence (not just gas produced) white smoke 4d(i) 2 4d(ii) ignore n and brackets ne unit only must have trailing bonds allow 2 Allow for = 4e(i) 2 2 ne unit only must have trailing bonds 3 ignore n and brackets of 20

52 MARK SEME A-LEVEL EMISTRY EM4 JUNE 206 4e(ii) PGA sutures react/dissolve/break down/are biodegradable/ are hydrolysed / attacked by water or nucleophiles /no need to remove Polypropene not biodegradeable/ not hydrolysed / not attacked by water/nucleophiles (Ester links have) polar bonds polypropene contains non-polar bonds ignore intermolecular forces Total 6 Question Answers Mark Additional omments/guidance 5a(i) 3 N N N N 3 N N 3 N N nly one molecule of each used 2 M for 2 amide links M2 2 and ( 3 ) Allow mark after one error 3 Dipeptide max Treat both trailing bonds missing as one error Ignore n ID details 2 of 20