2854 Chemistry (Salters) June Mark Scheme

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1 854 hemistry (Salters) June 004 Mark Scheme

2 The following annotations may be used when marking: X = incorrect response (errors may also be underlined) ^ = omission mark bod = benefit of the doubt (where professional judgement has been used) ecf = error carried forward (in consequential marking) con = contradiction (in cases where candidates contradict themselves in the same response) sf = error in the number of significant figures Abbreviations, annotations and conventions used in the Mark Scheme: / = alternative and acceptable answers for the same marking ; = separates marking points NT = answers not worthy of credit ( ) = words which are not essential to gain credit (underlining) = key words which must be used ecf = allow error carried forward in consequential marking AW = alternative wording ora = or reverse argument

3 Question Expected Answers Marks a i nitrogen dioxide/ nitrogen(iv) oxide nothing else a ii Manufacture of fertilizers/explosives/dyes can be named ones. Making must be implied Named lab use, eg nitration of benzene b +4 (allow x +4) +5 () each max if plus signs missing or signs after numbers. ALLW Roman numerals. c i Increases () mark separately; More molecules/particles collide (); (with) energy greater than activation enthalpy/energy (ignore barrier )() successful collisions can score second mark only. c ii (forward) reaction exothermic (ora) (); equilibrium (position) moves to oppose change/in endothermic direction (); lower yield () must follow some correct reasoning (which can be in (c)(i)) Apart from this, c(i) and c(ii) must be answered in the correct places to score. d this temperature a compromise/balance (AW)(); between rate and yield (); e i Kp = p N 4 /pn () for mathematical expression N 4 /N whatever symbols () for indicating partial pressures correctly. Ignore ( ), allow p N. Mark separately e ii atm () ecf from expression but NT concentration units ALLW atmos, atmospheres, /atm. e iii pn4 = Kp x pn = 8.7 x 0.60 =. () sig figs () mark separately provided SME working f Be, B,, F Any two (Names [allow small mis-spellings] or symbols [must be correct]) ALLW names or correct formulae of oxides. g i two from: toxic/ poisonous/ specific effect (eg respiratory problems); (gives rise to) acid rain/ causes corrosion of metal/stone; (photochemical) smog/ more ozone; NT depletes ozone greenhouse gas /global warming g ii recycled/used again/some reference to using it in Equation.. h i negative, fewer (gas) molecules on right h ii positive, exothermic/ negative/reference to /T h iii positive() because the reaction goes/ is spontaneous() mark separately S = 0 for an equilibrium scores ()

4 i i complete reaction (with water)/fully dissociated/ almost fully dissociated/ K a > i ii N (ignore +aq ) give + ( ) + ()+ N () or reaction with to i iii p = lg[ + ] stated or implied () = lg (0.05) =. ()

5 a alkene, alcohol/hydroxy(l) NT hydroxide or carbon-carbon double bond b Five marks from: mass spectroscopy: Mr /(relative) molecular mass/ molar mass (IGNRE total mass)(); from M + peak/peak of highest mass /molecular/parent ion (AW) () must follow from first marking point. Fragments (from other peaks) () 5 i.r: (max four points) = () at (cm )() ALLW descriptions of groups () at (cm )() eg alkene etc a () at (cm )() within range if qualified alkane or alkene () with appropriate range () ( or ) If nothing scored above for bonds, allow: i.r. identifies bonds/ functional groups () If nothing scored for absorptions allow general statement about absorption values () QW sentences, logical, words from list below used correctly (or plurals, verbs), QW sentences, logical, words from list below used correctly (or plurals, verbs) molecular/molar mass; peak; molecular/parent ion; fragment; bond; absorption

6 c i (R) c ii R δ δ+ N R N + Idea of N attacking carbonyl carbon*/polarisation of = () Intermediate with () not Rest of detail correct () (partial charges optional) not single arrows here. * can be N here but then do not award third marking point. R N d i peaks () : (AW) () d ii 7/ ()7 (allow ()8 ) orrect number of atoms (4 or 9) (); correct group(s) at end(s) (if first mark scored)() e A cis (); B trans (). one mark for correct words the wrong way round. f Three from Receptor site(s) ALLW active site; will have a certain/specific shape; Pheromone molecule must fit/ If pheromone is not correct shape it will not be detected/ smelled; Bonding/ imf / binding occurs; pheromone fitting site triggers response (AW); g i bromine/br Allow aqueous bromine g ii, alcohol, hydroxy(l) g iii heat/reflux (); (Aqueous )Na (); mark separately. Extra reagents negate second mark.

7 a i carbon: 0 (); hydrogen: 6 (); a ii A 09 (); B 0 (); (both ± 4, angle sign not required) b Side-effects/suggested specific side-effect/ only active for a short time/ toxic Not very effective (or molecular descriptions implying this but NT that it is ineffective) c i Three from (can be obtained from a labelled diagram) each carbon atom has four outer shell electrons; but only uses three to form bonds; six electrons; shared by/evenly spread/distributed over the carbon atoms/ conjugated; form rings (of electrons); above and below (plane of) molecule; plus NE from: all bonds equal in length; undergoes substitution (rather than addition reactions); more stable (AW); planar; c ii l (); All(); eat/reflux/no water () mark separately Max for reagent marks if extra reagents added. 4 c iii electrophilic c iv Four from the following points. A*oloured substances absorb (certain frequencies of )visible light; B (when) electrons excited (to higher energy-level); more highly delocalised molecules(aw) need less energy to excite electrons; D* (burimamide/ metiamide/ benzene ) do not absorb in visible/ are colourless they absorb in u.v./at higher frequency/ energy; E energy level difference measures frequency absorbed/ E = hv; F visible light has lower energy than u.v. 4 * if neither A nor D scored, can award A/D for idea of molecules absorbing e-m radiation or light. If emission mentioned, max. d N N S N N double bond may be included or not but N atom must not be. Accept if drawn on metiamide structure N N

8 4 a i a a + 4 a ii Amount a = 000/00 (= 0 moles) (); Mass a = 0ecf x 56 = 560 g () + 4 b xx a xx x x x xx () each. a may have no electrons. xygen may have all same symbol (dot or cross) If all other detail correct but no charges shown, award (). Square brackets optional. ALLW charges on symbols or inner shells if correct A - ionisation enthalpies/energies () 4 c i B - (g) () - enthalpy (change) of formation (of a) () ALLW enthalpy (change) of combustion of calcium/a st and nd Ea = ( 49) () = +() 609 () kj 4 c ii mol ecf on sign; ecf on number, provided all quantities used in calculation. 609, 609 score () 4 d i Energy + a (g) + (g) lattice enthalpy () a() (aq) enthalpy of hydration/ solvation of ions/ separate ions () Line above solid line and correctly labelled (as shown or separate ions) () 4 a() (s) Enthalpy (change) of solution () Allow for enthalpy and accepted symbols, eg LE 4 d ii increase down Group 4 e i 0.0 mol dm () one mark for 0.06 mol dm 4 e ii K w = [ + ] [ ] stated or implied (); [ + ] = 0 4 /0.0 =. x 0 (mol dm ) ecf from (e)(i)(); (6.6 x 0 from 0.06) p = lg(. x 0 ) =.5 ecf (); (. from 6.6 x 0 ) 4 e iii a() + l al + compounds (); balancing tied to first mark () 4 e iv Amount a() = 0 x 0.05/000 (=.5 x 0 4 mol) () Amount l = twice this (.0 x 0 4 mol) ecf from ratio in equation, even if equation unbalanced Volume l =.0 x 0 4 x 000/0.0 = 5.(0 )cm () (ecf 7.5(0)cm from : ratio)

9 4 f Five from the following points. A lays have a layer structure/ exist as sheets; B Water /ions can penetrate layers; Layers/surface are/is negatively charged; D Because of /Al replacing Si (ALLW Si 4 4 ); E + ions held by negative charge; F alcium ions push out hydrogen ions by ion exchange; G Equilibrium effect; hydrogen ions for one calcium ion; I a + held more tightly since doubly charged QW Accurate spelling, punctuation and grammar (one spelling mistake allowed) 5

10 5 a A sample (of ointment) (); ALLW ointment as gas 4 B detector (); column (); ALLW tube with description of contents D oven /heater () 5 b (retention) time 5 c i allow this group attached to chain 6 carbon atoms (no - hydrogens shown, nor dots () 6th carbon can be part of ; skeletal detail, provided no other groups are present () 5 c ii alkene NT = 5 c iii ends in -ol / anol 5 c iv hydrolysis 5 d glycerol residue correct () ester correct and full structural () but can score this mark(not previous one) if rather than. carbon chains() (allow dots and - hydrogens shown if penalised in 5(c)(i)) D NT award third mark if other substituents on chain, though double bonds allowed.

2850 Chemistry (Salters): Chemistry for Life. January Mark Scheme

2850 Chemistry (Salters): Chemistry for Life. January Mark Scheme 850 Chemistry (Salters): Chemistry for Life January 004 Mark Scheme The following annotations may be used when marking: X = incorrect response (errors may also be underlined) ^ = omission mark bod = benefit