Mark Scheme (Results) January 2015

Mark Scheme (Results)January 2015Pearson Edexcel International GCSE inChemistry (4CH0) Paper 2CPearson Edexcel Certificate inChemistry (4CH0) Paper 2C

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General Marking Guidance All candidates must receive the same treatment. Examiners mustmark the first candidate in exactly the same way as they mark thelast. Mark schemes should be applied positively. Candidates must berewarded for what they have shown they can do rather thanpenalised for omissions. Examiners should mark according to the mark scheme not accordingto their perception of where the grade boundaries may lie. There is no ceiling on achievement. All marks on the mark schemeshould be used appropriately. All the marks on the mark scheme are designed to be awarded.Examiners should always award full marks if deserved, i.e. if theanswer matches the mark scheme. Examiners should also beprepared to award zero marks if the candidate’s response is notworthy of credit according to the mark scheme. Where some judgement is required, mark schemes will provide theprinciples by which marks will be awarded and exemplification maybe limited. When examiners are in doubt regarding the application of the markscheme to a candidate’s response, the team leader must beconsulted. Crossed out work should be marked UNLESS the candidate hasreplaced it with an alternative response.

Questionnumber1 (a)AnswerAcceptRejectMarksD (a molecule)1(b)A (covalent)1(c)NH3H3N1Total 3 marks

Questionnumber2 (a)(i)Answer(solubility/it) increases as temperatureincreasesAcceptpositive correlation(ii)Rejectreferences toproportionalityMarks11(solid) B(b)M1 – solid/crystals would formM2 – (solid A) becomes less soluble (as thesolution cools) / solubility (of solid A)decreases (as temperature decreases)precipitate for solidgoes cloudy1reverse argument1Total 4 marks

Questionnumber3 (a)Expected AnswerAcceptM1 P – iron ore / haematiteignore iron(III) oxide/Fe2O3M2 Q - calcium silicateMarks2slag / CaSiO3(b)(c)Reject3M1- oxygenairIGNORE OO2M2 – watermoisture/H2O2

(d)M1 zinc corrodes/reacts instead of iron / fasterthan ironM2 iron corrodes/reacts instead of tin / fasterthan tinlack of comparison with other metal max 1 fromM1 and M2ignore references to tin rustingzinc loses electrons/isoxidised instead of ironzinc rusts (instead ofiron)3iron loses electrons/isoxidised instead of tinaccept reverseargumentsM3 correct reference to order of reactivity of allthree metalsTotal 10 marks

ectfermentationMarks1(to provide the) catalyst/enzyme/zymaseto increase the rate of thereaction1M1 (test) – flame testsuitable description of flame test2M2 (observation) – brick red / orange-redredcopper(II) ions:accept other suitable alkalisM1 (test) – (aqueous) sodium hydroxide /NaOHsuitable alternatives toprecipitate5all other coloursM2 (observation) – blue precipitateignore shades of blueM2 dep on M1 or near miss of formula, egNa(OH)2sulfate ions:(dilute) nitric acid / HNO3M1 (test) – (dilute) hydrochloric acid / HCl(aqueous) barium nitrate /Ba(NO3)2M2 (test) - (aqueous) barium chloride /BaCl2M3 (observation) – white precipitateM3 dep on M2 or near missReject sulfuricacid for M1 only

Questionnumber4 (c)AnswerM1 (pressure) – 60-70 atmM2 (catalyst) – phosphoric acid /H3PO4ignore references to concentration(d)M1 (Ʃ bonds broken) 348 412 360 ( 1120)Acceptany pressure or range within thisrangephosphoric(V) acid3231MarksReject2any other oxidationstate43186M2 (Ʃ bonds made) 612 463 ( 1075)M3 M1 – M2 / Ʃ bonds broken Ʃbonds madeM4( )45 (kJ/mol)Correct answer with no working scores4 45 (kJ/mol) scores 3Total 15 marks

Questionnumber5 (a)AnswerM1 temperature afterM2 temperature beforeM3 temperaturechange27.118.8( ) 8.3Acceptone trailing zeroRejectMarksmore than one trailingzero3Recorded temperatures correct but in wrong orderscores 1 for M1 and M2M3 csq on M1 and M2(b)M1 heat (energy) /thermal energy lost (to theatmosphere)ignore just energy lostM2 potassium hydroxide dissolves (very/too)slowlywater evaporates2potassium hydroxidedoes not completelydissolvepotassium hydroxide isimpureless than 3 g ofpotassium hydroxide isusedmore than 50 cm3 ofwater is usedTotal 5 marks

rangementof electrons in of electrons inatomionRejectMarks3Chargeon ion2.8.8(1) / 1K(1) / K 12.8.82 / 2S2 / S 2M1 – both arrangements correctM2 – charge on potassium ionM3 – charge on sulfide ion(b)(i)(ii)ions move/travel (to the electrodes)M1 (electrostatic) forces (of attraction) between (oppositelycharged) ionspositive for potassiumand negative for sulfidefor 1 markions are free to move /ions are mobileionic bonding / ionicbondselectrons freeto move13M2 are (relatively) strongM3 large amount of energy required to overcome the forces/ separate the ions from the latticebreak the bondsM2 dep on mention of forces (of attraction) or bondsMention of covalent bonds or intermolecular forces no M1Total 7 marks

Questionnumber7 (a)(b)AnswerH2S2O7 H2O 2H2SO4M132 (of S) 80 (of SO3) (tonnes or g)M2mass of SO3 M3 200 (tonnes)8032 80M2 csq on M1AcceptReject Marksmultiples and fractionsM1n(S) (n(SO3)) 500 000 (mol))180 x 10632(mol) ( 23M2 mass of SO3 M1 x 80 ( 200 000000 (g))M3 M2 106 / 200 (tonnes)M1n(SO2) M3 csq on M2Correct answer with no working scores 3(c)M1 64 (g) (of SO2) reacts with 12 (dm3) (ofO2)M2 (64 tonnes) reacts 12 x 106 (dm3) OR1.2 x 107 (dm3)M2OR𝐌𝟏264 x 10664(mol) ( 106 mol)2x 24 / 1.2 x 107 (dm3)M1 mass of oxygenM2 csq on M1accept 1.2 x 1010 cm3Correct answer with no working scores 2Total 6 marks

Questionnumber8AnswerM1 – add (aqueous) chlorine to (aqueous)KBrAcceptRejectMarks5yellow / brownredM3 – add (aqueous) bromine to (aqueous)KIred-brown / orangeyellowM4 - (solution) turns browncorrect ionic equationsM2 – (solution) turns orangeM5 – Cl2 2KBr Br2 2KClORBr2 2KI l2 2KBraccept Cl2 2KI I2 2KCl if chlorine is added topotassium iodideIgnore state symbolsTotal 5 marks

Questionnumber8AnswerAcceptRejectM1 – add (aqueous) bromine to (aqueous) KClM2 – no changeMarks5orange / yellow /brown solution/colourproduced only if it isclear that no reactionhas occurredredyellowM3 – add (aqueous) iodine to (aqueous) KBrM4 - no change / no changeIf this route is chosen then M5 cannot be scoredbrown / red-brown /orange solution/colourproduced only if it isclear that no reactionhas occurredTotal 5 marks

Questionnumber9 (a)(i)Answershifts to left(ii)shifts to the right(iii)impossible to know which shift is greater /impossible to know which change has thegreater effectAcceptmoves in the endothermicdirectionshifts to the side of the reactantsOWTTERejectMarks111moves in the exothermic directionshifts to the side of the productsOWTTEshifts to the side with fewer (gas)moles/moleculesOWTTEthe (two) effects are opposingone another(b)M1 – greater proportion of NO2more NO2 presentequilibrium shifts to left2M2 – (increase of) temperature has a greatereffect than(increase of) pressureTotal 5 marks

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Mark Scheme (Results) January 2015 Pearson Edexcel International GCSE in Chemistry (4CH0) Paper 2C . All the marks on the mark scheme are designed to be awarded. Examiners should always award full marks if deserved, i.e. if the . principles by which marks w