Question Answer Mark Guidance 1 (a) (i) 4 Please use annotations (rate) molecules/particles in smaller volume OR increases concentration

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Stuart Alexander
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1 ERRY ILL TUITIN R (SALTERS) EMISTRY A2 PAPER 28 MARK SEME 1 (a) (i) 4 Please use annotations (rate) molecules/particles in smaller volume R increases concentration ALLW molecules/particles closer together Use of other particles (eg atoms) Ns first mark (only) IGNRE reactants (for particles ) ALLW less [or smaller] space [or area] (iii) greater frequency of collision (yield) fewer moles/molecules/particles on RS(ora) equilibrium (posn): moves to right / moves to products R moves to oppose change a lot of energy/electricity (needed for compressor) R thick pipes/strong materials/materials to withstand high pressure needed (forward) reaction exothermic (ora) equilibrium position: moves to oppose (change) AW R moves in endothermic direction/to endothermic side (ora) yield decreases / less methanol formed NT just more collisions ; the answer must imply frequency IGNRE chance/likelihood of collision NT atoms (N first mark but not second) RS can be implied by equilibrium shift (eg equilibrium shifts to right as there are fewer molecules scores both marks) right can be implied by greater yield Mark separately ALLW abbreviations of equilibrium and equilibria equilibrium moves to side with fewer molecules(etc) scores 1 1 ALLW specialised plant, specialist equipment (but not just plant, equipment ) IGNRE safety precautions 3 IGNRE references to rates ALLW left side is endothermic (ora) this is the QW link point (but mark separately with ecf from first marking point) must say equilibrium position [or abbreviations or equilibria ] ALLW moves to left / moves towards reactants (ora) if first marking point scored Mark separately no ecf 1

2 ERRY ILL TUITIN R (SALTERS) EMISTRY A2 PAPER 28 MARK SEME (iv) [ 3 ]/[] [ 2 ] 2 1 must have square brackets. IGNRE state symbols terms in divisor may have dot or x between them, NT + (v) 1000 dm 6 mol 2 2 ALLW 1030 or more sf ALLW standard form ALLW ecf from (a)(iv) unless plus sign used ALLW mol 2 dm 6 R (mol dm 3 ) 2 R (dm 3 mol 1 ) 2 or ecf from (a)(iv) (b) (i) 240 (2x131) 198 = Award one mark for: +220 (with sign) 89 (factor of 2 missing) correct evaluation of expression opposite with one S o wrong 91000/T = 220 R T = 91000/220 T = ALLW ecf from b(i) ALLW ecf for second mark for correct evaluation of an expression: x/t = y only (eg T = 0.41 scores one mark) ALLW 2 or more sf ( ) NT rounding errors Negative values score no marks (c) (i) distil acid(ified) dichromate 2 IGNRE heat NT reflux mark separately ALLW sulfuric/sulphuric acid AND potassium/sodium dichromate ALLW dichromate(vi) ALLW correct formulae for these (or dichromate ion) ALLW small spelling errors IGNRE conc(entrated) 2

3 ERRY ILL TUITIN R (SALTERS) EMISTRY A2 PAPER 28 MARK SEME methanol: has no (=) around 1700 R (-) at / / methanal has no (-) at / / / above 3000 / 2950 R (=) at methanoic acid has ( ) at R (=) at Please annotate For each compound, one mark for the wavenumber range Mark any correct range for each compound first and IGNRE other ranges, even if they have small errors (eg for ) IGNRE units of wavenumber ranges IGNRE correct but irrelevant peaks (eg ) ompounds must be named to score (i.e. not just alcohol ) ALLW indistinguishable methanol / methanal from context related to one correct range as above = related to one correct range as above (iii) 3 / none none proton+shift relative no + splitting (iv) Data suggests M r = 92, which is double expected (AW) (two) molecules of methanoic acid must be joined diagram showing hydrogen bonding of two molecules with two hydrogen bonds: IGNRE atoms with no bond (eg ) or descriptions (eg alcohol ) IGNRE = 4 IGNRE bonds (eg 3 ) in type of proton ALLW hydroxyl for but IGNRE methyl IGNRE units for chemical shift ALLW singlet, unsplit 1, no etc in splitting Second pair of marking points dependent on chemical shift value (not type of proton ) 3 ALLW volume is half expected half a mole of gas ALLW any reference to hydrogen bonding between molecules (or on diagram) This diagram scores mpts 2 and 3 3

4 ERRY ILL TUITIN R (SALTERS) EMISTRY A2 PAPER 28 MARK SEME (d) (i) 2 ALLW 3 IGNRE bond angles IGNRE other correct non-full structural formulae methyl methanoate Mark separately no ecf from wrong formula to name or vice-versa ester has permanent (dipole) permanent dipole methanol has hydrogen bonding more energy needed in methanol (ora): to break (bonds) R to separate (molecules) 3 no abbreviations ALLW small spelling errors ALLW third mark even if wrong imb are given, but not covalent bonds (iii) sodium methanoate 1 ALLW methanoate ion but not sodium methanoate ion ALLW formate for methanoate Total 35 4

5 ERRY ILL TUITIN R (SALTERS) EMISTRY A2 PAPER 28 MARK SEME 2 (a) (i) 1s 2 2s 2 2p 1 1 ALLW any size numerals and capital letters NT subscripts 1 bond angles not important B (iii) trigonal (planar) three groups of electrons / three electron pairs / three areas of electron density electrons: repel and get as far away from each other as possible R move to minimise repulsion 3 ALLW triangular / triangle / (bond angle) 120 First marking point must match diagram ALLW ecf from number of pairs in a for second mark, but not first 3 rd marking point must be in terms of electrons (not bonds/atoms etc) repelling but can be scored for any electron pairs or just electrons NT repel as much as possible (b) (i) 2 / two 1 it is useful for/works/good model for: many/most (simple) molecules/compounds/structures/ substances 1 utility AND many/most/ generally (works) AW (c) (i) ability of atom to attract AW electrons in a (covalent) bond 2 ALLW bonded/ bonding electrons, shared pair for bond -1, +1, 0, +1 Both NT numbers alone; signs after numbers: no mark on first occasion, then allow as ecf 5

6 ERRY ILL TUITIN R (SALTERS) EMISTRY A2 PAPER 28 MARK SEME (d) (i) (27.6 x 100/279.6) = 9.87 % 2 ALLW 2 or more sf ( ) much waste R uneconomical / inefficient / unprofitable R little useful product must imply a lot of waste not just waste no ecf from a medium or large miscalculated atom economy IGNRE reference to the size of the number ALLW second mark only if atom economy is less than 40% ionic + Na 3 Mark separately ALLW eight electrons on sodium (all dot or all cross) ALLW without square brackets (signs must be there) two electrons (dot-cross) on hydrogen rest correct shared electron diagram scores no diagram marks (e) (i) B F 2 B F B 2 3 correct completely correct 2 IGNRE state symbols (= g) 2 sf (150g) 3 ALLW ecf on the mole ratio from equation in e(i) correct answer (to any sf) scores two marks regardless of working ALLW different answers if intermediate rounding to 2 sf occurs (eg 0.91 from 25/27.6) ALLW answers based on 2 sf A r for B (11) [ > 145] ALLW intermediate rounding (even to 1sf) any number to 2 sf resulting from a shown correct evaluation scores this mark (iii) BF 3 R 2 1 IGNRE names ALLW B 2 F 6 Total 23 6

7 ERRY ILL TUITIN R (SALTERS) EMISTRY A2 PAPER 28 MARK SEME 3 (a) (i) 3 o 3 (As 4 ) 2 2 ALLW 3 or 3 ALLW with some/all correct charges shown (eg o 2+ 3(As 4 ) 3 2) ecf from first to second mark 3d 7 1 ALLW capital letter and/or subscript or full size 7. (b) (i) Blue It reflects blue only/most R it does not reflect any other colours 2 reflects blue only scores both marks ALLW absorbs all other colours R absorbs red, not blue ALLW high/good reflectance for reflects ALLW violet or purple for blue if in the context of absorbing beyond blue, (not blue/red mix) second mark depends on first cobalt A d-orbitals / d-subenergy levels are split B electrons are excited R electrons move to higher energy levels absorbing (visible) light / red light / colour D EITER E = hv / frequency (absorbed) proportional/corresponds (AW) to energy difference AW R complementary colour reflected/transmitted 5 Please use annotations mark first mpt separately ALLW cobalt(ii), cobalt ion do not award mpt A if it appears to be a consequence of electrons being excited Max 2 from A-D if electrons falling and emitting light mentioned QW only award mpt if mpt B scored Mpt D - must be E (not just E ) unless supported by words ALLW complimentary ALLW ecf from (b)(i) on actual colours absorbed/reflected 7

8 ERRY ILL TUITIN R (SALTERS) EMISTRY A2 PAPER 28 MARK SEME (c) Electrons fall (to lower energy-levels) light of specific frequency/colour emitted / ( )E = hv cobalt/elements has/have: own (set of) energy levels R different energy gaps 3 Please use annotations an be scored from energy-level diagram provided only downward lines are shown (or labelling is clear) some idea of certain frequency of light needed, not just light 2 nd mpt must be in context of emission (or absorption followed by emission) ALLW other elements have their own (different) energy levels ALLW from a diagram of two sets of energy levels Mark independently (d) (i) idea that substrate fits/binds/bonds/forms enzymesubstrate complex with active site / has complementary shape to active site idea that this ability is lost when shape changed idea that substrate fitting (etc) goes on to cause a reaction (ora) 3 QW substrate must be used (somewhere) and spelled correctly to score first mark can score first mpt here as well ALLW substrate broken down arsenic combines/binds AW with S groups (on dimercaprol) (arsenic has) less effect on enzyme / (arsenic) does not combine AW (so much) with enzyme / allows (normal) substrate to bind / does not inhibit enzyme 2 ALLW smalt for arsenic ; must mention S groups Mark separately (iii) one from: what is a safe dose? relative toxicity compared with arsenic 1 Total 19 8

9 ERRY ILL TUITIN R (SALTERS) EMISTRY A2 PAPER 28 MARK SEME 4 (a) Z the groups/chains/hydrogens are on the same side/one side... of the (carbon-carbon) double bond 1 ALLW link between Z and cis (b) (i) instantaneous (dipole) induced dipole 1 ALLW small spelling errors if the sense is clear ALLW Van der Waals (ignore spelling) NT abbreviations Molecules/chains can pack/ line up/ fit... more closely intermolecular bonds/forces are stronger (ora) 3 must be a comparison ALLW any named imb IGNRE more bonds ALLW more area for imb ; ALLW stronger forces between chains (c) (i) more energy required to break/melt (ora) + I 2 I I reacting with one mole of I 2 formula of product ALLW breaking of anything except covalent bonds 2 ALLW any product formula that indicates one iodine on each carbon atom ( atoms need not be shown) IGNRE hydrogens on organic molecules electrophile 1 (iii) (g I 2 ) shown somewhere (253.8 x 100/282) = 90.0 (iv) answer to c(iii) 0 2 ALLW ecf from wrong equation in (c)(i) ALLW 254 ALLW ecf orrect answer (or answer with ecf from wrong equation) scores both marks despite working. (45 similarly scores 1 mark) ALLW 90 ALLW ecf from wrong M r for I 2 2 IGNRE grams 9

10 ERRY ILL TUITIN R (SALTERS) EMISTRY A2 PAPER 28 MARK SEME (d) 3 Please add annotations any three from the following: hydrogen bonds are broken in water ALLW abbreviations of inter-molecular bonds ALLW just hydrogen bonds in water id-id bonds / a small number of hydrogen bonds are broken in oleic acid id-id bonds / pd-id bonds / (a small number of) hydrogen bonds are made between oleic acid and water more energy required to break bonds than make them (AW) ALLW it for oleic acid to score third bullet, must have correct imb AND idea of between acid and water ALLW more bonds broken than made R bonds broken stronger than bonds made (ora) ALLW wrongly named imb for last bullet (e) 4 R R R ALLW any unambiguous formulae (not molecular for organics) except that ester groups must be full structural Mark separately 3 R ester group correct (even if wrong way round) triglyceride formula formulae of products 3 2 and 3 R Total 19 10

11 ERRY ILL TUITIN R (SALTERS) EMISTRY A2 PAPER 28 MARK SEME 5 (a) 1 ALLW any order of atoms (b) (compound X:) 3 any unambiguous representation of structure ALLW any anhydride formed between 2 molecules of maleic/fumaric for 1 st mark need to rotate = high energy needed ALLW restricted rotation of = (c) (i) 2 / two 1 (each chiral centre/carbon gives rise to a) non superimposable mirror image one isomer common to both AW 2 can score from diagrams (d) (i) A + + A 1 NT with square brackets ALLW reversed State symbols must be (aq) if present A + + A conjugate acid conjugate base (iii) [ + ] = (K a x 0.1) (= 9.6 x 10 3 ) p = ALLW with square brackets here. IGNRE state symbols 2 either working R correct answer scores first mark, must say + =... or [ + ] =... to score ALLW 2.0 or more decimal places ( 2 and 2.01 score 1 mark) ALLW ecf from a stated [ + ] ( [ + ] =... or + =...) 11

12 ERRY ILL TUITIN R (SALTERS) EMISTRY A2 PAPER 28 MARK SEME F335 Mark Scheme January 2012 (iv) [ + ] = [A ] / all + comes from acid/a 4 Please add annotations ALLW + = A initial [A] = equm [A] (AW) second (is more inaccurate) since p low / Ka high / acid quite strong (AW) ALLW concentration of A is the same R very small amount of dissociation (e) (i) appreciable amounts of A (compared with initial amount) will react (AW) maintains p / little change in p when small amount of acid or alkali added add + /acid moves equm (posn) to left/towards reactants R add /alkali moves equm (posn) to right [A ] large (AW) [ + ] = K a x 0.5 R 2[ + ] = K a R [ + ] = 4.65 x 10 4 p = Please add annotations Mark second and third independently from first second mark depends on mention of acid or alkali both acid and alkali need to be mentioned for third mark ALLW alkaline for alkali IGNRE base weak acid/ alkali Ns third marking point. ALLW ecf from equation in (d)(i) (eg if reversed) ALLW reservoir of A 2 either working R answer scores first mark, must say + =... or [ + ] =... to score orrect p scores both marks ALLW 3.3 or more sf; D NT ALLW ecf unless [ + ] = K a x 2 is shown or implied, when 1 mark can be awarded for 2.7(3...) (f) (i) ALLW 2.7 or more sf Total

2854 Chemistry (Salters) June Mark Scheme

2854 Chemistry (Salters) June Mark Scheme 854 hemistry (Salters) June 004 Mark Scheme The following annotations may be used when marking: X = incorrect response (errors may also be underlined) ^ = omission mark bod = benefit of the doubt (where