Oxford Cambridge And RSA - PMT
PMTOxford Cambridge and RSAGCEChemistry AUnit F325: Equilibria, Energetics and ElementsAdvanced GCEMark Scheme for June 2015Oxford Cambridge and RSA Examinations
PMTOCR (Oxford Cambridge and RSA) is a leading UK awarding body, providing a wide range ofqualifications to meet the needs of candidates of all ages and abilities. OCR qualificationsinclude AS/A Levels, Diplomas, GCSEs, Cambridge Nationals, Cambridge Technicals,Functional Skills, Key Skills, Entry Level qualifications, NVQs and vocational qualifications inareas such as IT, business, languages, teaching/training, administration and secretarial skills.It is also responsible for developing new specifications to meet national requirements and theneeds of students and teachers. OCR is a not-for-profit organisation; any surplus made isinvested back into the establishment to help towards the development of qualifications andsupport, which keep pace with the changing needs of today’s society.This mark scheme is published as an aid to teachers and students, to indicate the requirementsof the examination. It shows the basis on which marks were awarded by examiners. It does notindicate the details of the discussions which took place at an examiners’ meeting before markingcommenced.All examiners are instructed that alternative correct answers and unexpected approaches incandidates’ scripts must be given marks that fairly reflect the relevant knowledge and skillsdemonstrated.Mark schemes should be read in conjunction with the published question papers and the reporton the examination.OCR will not enter into any discussion or correspondence in connection with this mark scheme. OCR 20152
PMTF3251.Mark SchemeThese are the annotations, (including abbreviations), including those used in scoris, which are used when markingAnnotationMeaning of annotationBenefit of doubt givenContradictionIncorrect responseError carried forwardIgnoreNot answered questionBenefit of doubt not givenPower of 10 errorOmission markRounding errorError in number of significant figuresCorrect response3June 2015
PMTF3252.Mark SchemeAbbreviations, annotations and conventions used in the detailed Mark Scheme (to include abbreviations and subject-specific conventions).AnnotationDO NOT ALLOWMeaningAnswers which are not worthy of creditIGNOREStatements which are irrelevantALLOWAnswers that can be accepted()Words which are not essential to gain creditUnderlined words must be present in answer to score a markECFError carried forwardAWAlternative wordingORAOr reverse argument3.June 2015The following questions should be annotated with ALL annotations to show where marks have been awarded in the body of the text:1(d)3(b)(i)3(b)(iv)4(e)(iii)5(b)(ii)7(b)4
PMTF325Mark SchemeQuestion111Marks( )5 For equations, IGNORE any state symbols; ALLOW ------------------------------------------Any correct equation for a reaction catalysed by a transitionelement, compound or ionANDtransition element, compound or ion (by formula or name) (a)(b)(c)Answer(i)June 20151GuidanceALLOW 5 OR V OR Cr5 EXAMPLESN2 3H2 2NH3 (allow ) AND Fe/iron oxide12SO2 O2 2SO3 (allow ) AND V2O5/Pt2CO 2NO 2CO2 N2 AND Pt/Pd/Rh/AuEquation for any alkene H2 alkane AND Ni/Pt/PdC6H6 Cl2 C6H5Cl HCl AND Fe/FeCl3/Fe3 C6H6 Br2 C6H5Br HBr AND Fe/FeBr3/Fe3 2H2O2 2H2O O2 AND MnO2For other examples, CHECK with TLALLOW lone pairs for electron pairsDonates two electron pairs (to a metal ion)ANDforms two coordinate bonds (to a metal ion) 1NOTE: Metal ion not required as Ni3 is in the questionALLOW dative (covalent) bonds for coordinate bondsTWO is only needed once, e.g.Donates two electron pairs to form coordinate bondsDonates electron pairs to form two coordinate bonds1(c)(ii)C3H10N2 1(c)(iii)MARK NCH2CH2CH2NH2 1ALLOW in any orderIGNORE structureALLOW correct structural OR displayed OR skeletalformula OR mixture of the above (as long asunambiguous)ALLOW H2NCH2CH(CH3)NH2 OR H2NCH(CH2CH3)NH2ALLOW secondary or tertiary diamines or mixtureEach N OR each NH2 OR amine group has a lone pair/electronpairOR lone pairs shown on N atoms in structure 5IGNORE complex ion2For other examples, CHECK with TL
PMTF325Mark SchemeQuestionAnswerJune 2015Marks1(c)(iv)6 1(c)(v)3–D diagrams of BOTH optical isomers required for the markGuidance1In this part, Charge AND Square brackets NOT requiredIGNORE N or attempts to draw structure of bidentateligandNiNiANDOther orientations possible but all follow same principlewith 2nd structure being a mirror image of the first 16
PMTF325Mark SchemeQuestion1(d)AnswerJune 2015MarksFULL ANNOTATIONS MUST BE USED THROUGHOUTALLOW some reactions for Cu2 and some for Co2 ALLOW equilibrium signs in all equationsIGNORE any incorrect initial coloursIGNORE state symbolsIGNORE an incorrect formula for an -------------------------------------- ALLOW [Cu(H2O)6]2 2OH– Cu(OH)2(H2O)4 2H2OQuality of written communicationObservation must be linked to the correct reactionREACTIONS OF AQUEOUS Cu2 --------------------------- REACTION OF Cu2 with NaOH(aq)Correct balanced equationCu2 (aq) 2OH–(aq) Cu(OH)2(s) state symbols not requiredALLOW full or ‘hybrid’ equations,e.g. Cu2 2NaOH Cu(OH)2 2Na [Cu(H2O)6]2 2OH– Cu(OH)2 6H2OObservationblue precipitate/solid 1(d)Guidance24 2NaOH Cu(OH)2 Na2SO4ALLOW any shade of blueCuSOIGNORE initial precipitation of Cu(OH)2REACTION OF Cu2 WITH excess NH3(aq)IGNORE [Cu(NH3)4]2 Correct balanced equation[Cu(H2O)6]2 4NH3 [Cu(NH3)4(H2O)2]2 4H2O ALLOW royal blue, ultramarine blue or any blue colourthat is clearly darker than for [Cu(H2O)6]2 Observationdeep/dark blue (solution) 2DO NOT ALLOW deep blue precipitate for observation1(d)2 REACTION OF CuWITH HCl(aq)IGNORE mention of different concentrations of HClCorrect balanced equation[Cu(H2O)6]2 4Cl– [CuCl4]2– 6H2O Observationyellow (solution) 2ALLOW CuCl42– i.e. no brackets OR Cu(Cl)42–ALLOW [Cu(H2O)6]2 4HCl [CuCl4]2– 6H2O 4H IGNORE Cu2 4Cl– CuCl42–ALLOW green–yellow OR yellow–greenDO NOT ALLOW yellow precipitate for observation7
PMTF325Mark SchemeQuestion1(d)AnswerJune 2015MarksGuidanceFULL ANNOTATIONS MUST BE USED THROUGHOUTALLOW some reactions for Cu2 and some for Co2 ALLOW equilibrium signs in all equationsIGNORE any incorrect initial coloursIGNORE state symbolsIGNORE an incorrect formula for an -------------------------------------- ALLOW [Co(H2O)6]2 2OH– Co(OH)2(H2O)4 2H2OQuality of written communicationObservation must be linked to the correct reactionREACTIONS OF AQUEOUS Co2 --------------------------- REACTION OF Co2 with NaOH(aq)Correct balanced equationCo2 (aq) 2OH–(aq) Co(OH)2(s) state symbols not requiredObservationblue precipitate/solid 2ALLOW full or ‘hybrid’ equations,e.g. Co2 2NaOH Co(OH)2 2Na [Co(H2O)6]2 2OH– Co(OH)2 6H2O41(d) 2NaOH Co(OH)2 Na2SO4ALLOW any shade of blueCoSOIGNORE changes in colour over timeIGNORE initial precipitation of Co(OH)2REACTION OF Co2 WITH excess NH3(aq)Correct balanced equation[Co(H2O)6]2 6NH3 [Co(NH3)6]2 6H2O ALLOW any shade of brown or yellow1(d)Observationbrown/yellow (solution) REACTION OF Co2 WITH HCl(aq)2DO NOT ALLOW brown/yellow precipitate for observationIGNORE mention of different concentrations of HClCorrect balanced equation[Co(H2O)6]2 4Cl– [CoCl4]2– 6H2O Observationblue (solution) 2ALLOW CoCl42– i.e. no brackets OR Co(Cl)42–ALLOW [Co(H2O)6]2 4HCl [CoCl4]2– 6H2O 4H IGNORE Co2 4Cl– CoCl42–ALLOW any shades of blueDO NOT ALLOW blue precipitate for observationTotal814
PMTF325Mark SchemeQuestion2(a)AnswerJune 2015MarksNote: rate and [NO] are any correct pair of readings fromthe graph,The [NO] below are the most commonly seen.For these [NO] values, these are the ONLY rates allowedNOTE: First 3 marks are ONLY available from an expressionusing [NO]2Units are marked Using values ON THE CURVE in CORRECT expression1markUse of any two correct values for rate and [NO] from graphe.g. for 5.0 10–4 and 4.2 10–4,4.2 10–4k (2.0 10–2) (5.0 10–4)2[NO]1.0 10–42.0 10–43.0 10–44.0 10–45.0 10–46.0 10–47.0 10–4OR 4.2 10–4 k (2.0 10–2) (5.0 10–4)2 ------------------------Calculation of k 2 marksFOR 1 MARKk calculated correctly from values obtained from graphBUT NOT in standard form AND/OR more than 2 SF6.0 10–4e.g. k (2.0 10–2) (6.0 10–4)2 83673k5.0 1041.0 1057.5 1048.8 1048.3 1048.4 1048.4 1048.3 1048.4 104NOTE: IGNORE any numbers used from -------------------------------- SPECIAL CASES that ALLOW ECF for calculation of kfrom ONLY ONE of the following (2 marks)1. Powers of 10 incorrect or absent in initial k expression2. [H2]2[NO] used instead of [H2][NO]23. Any value within 0.2 of actual values from --------------------49rate0.1 10–4 to0.2 10–40.6 10–4 to0.7 10–41.5 10–42.7 10–44.2 10–46.0 10–48.2 10–4IF OTHER values are given, mark using the sameprinciple. If any doubt, contact TL.OR FOR 2 MARKSk calculated correctly from values obtained from graphAND in standard form AND TO 2 SFe.g. k 83333.33 gives 8.3 104 ---------------------- UNITS FOR 1 MARK:dm6 mol–2 s–1 GuidanceALLOW units in any order, e.g. mol–2 dm6 s–1
PMTF325Mark SchemeQuestion2(b)AnswerJune 2015MarksGuidance(i)ALLOW 1 mark for two upward sloping curves starting atoriginAND upper curve labelled H and lower curve labelled LHLrateNOTE: ALLOW some leeway for lines starting from origin0,0ALLOW straight line not drawn with ruler,i.e. is a straight line rather than a curve[H2(g)]One straight upward line AND starting at 0,0 2(b)2(c)(ii)2nd straight upward line starting at 0,0 and steeperANDSteeper line labelled H OR less steep line labelled L 2increases 1MARK ---------------------------------------------ALLOW similar labelling as long as it is clear which line iswhichALLOW curve touching y axisALLOW curve touching x axis[H2(g)]0,0timeDownward curve ALLOW Two half lives are the sameHalf life is constant 2IGNORE ‘regular’ half life (not necessarily the same)10
PMTF325Mark SchemeQuestionAnswerJune 2015MarksGuidance2(d)(i)H2 N2O N2 H2O 1ONLY correct answerDO NOT ALLOW multiples2(d)(ii)Steps 1 AND Step 2 together give 2NO H2 1ALLOW Step 1 AND Step 2 together give species in sameratio as in rate equationALLOW rate-determining step/slow step for Step 2ALLOW H2 reacts with N2O2 which is formed from 2NONOTE: The response must link Step 1 with Step 2Steps can be referenced from the species in each stepTotal1111
PMTF325Mark SchemeQuestionAnswer3(a)(i)5 mol/molecules (of gas) forms 3 mol/molecules (of gas) 3(a)(ii)FIRST, CHECK THE ANSWER ON ANSWER LINEIF answer ( )131 (J K–1 mol–1) , award 2 ----------------------–164 (186 2 206) – (4 S 238)OR4 S 164 (186 2 206) – 238 –1June 2015Marks1GuidanceALLOW reaction forms fewer moles/moleculesIF stated, numbers of molecules MUST be correctIGNORE comments related to GOR disorder (even if wrong)NOTE: IF any values are omitted, DO NOT AWARD anymarks. e.g. –164 may be missing–1S ( )131 (J K mol ) 2ALLOW FOR 1 mark–131 wrong final sign49 wrong sign for 16479.5 no use of 2524 no division by 438 wrong sign for 186–75 wrong sign for 206250 wrong sign for 238Any other number:CHECK for ECF from 1st marking point for expressionsusing ALL values with ONE error onlye.g. one transcription error:, e.g.146 for 16412
PMTF325Mark SchemeQuestion3AnswerJune 2015Marks(a) (iii) NOTE: DO NOT ALLOW answer to 3(a)(ii) for G --------------------------------------------- G calculation: 2 marksALLOW G correctly calculated from 3 SF up to calculatorvalue of –185.128 G –234 – 298 –0.164 –185 (kJ mol–1) IGNORE units (even if wrong) –185 subsumes 1st mark)Guidance2ALLOW working in J, ie: G –234000 – 298 –164 –185000 (J mol–1) ALLOW 1 mark for use of 25 OR mixture of kJ and J,e.g. G –234 – 25 –0.164 –229.9 G –234 – 298 –164 48638Feasibility comment for negative G answer: 1 mark(Forward) reaction is feasible / spontaneousAND G 0 / H – T S 0 3(a) (iv)1( G ) –234 – 1427 164 0 (calculator 0.028(kJ) OR 28 (J)) ALLOW ECF if calculated value for G is veThen ‘correct’ response for 3rd mark would benot feasible/not spontaneous AND G 0 / H – T S 0ALLOW (When G 0)1000T 234 1427 K OR 234000 1427 K 0.1642nd mark only available if 1st mark has been awarded2(Above 1427K/1154ºC), reaction is not feasible/not spontaneous OR 1427 K is maximum temperature that reaction happens 164For 2nd mark, IF G is ve from (a)(iii)ALLOW ECF for:Above 1427 K, reaction is feasible / spontaneousOR 1427 K is minimum temperature that reaction happensIGNORE LESS feasibleIGNORE comparisons of the signs of T S and H,e.g IGNORE T S is more negative than H13
PMTF325Mark SchemeQuestion3(b)(i)AnswerJune 2015MarksGuidanceFIRST, CHECK THE ANSWER ON ANSWER LINEIF answer 57.6 dm3 mol–1, award 6 marksIF answer 57.6 with incorrect units, award 5 ---------------------Equilibrium amounts in mol2 MARKSn(SO2) 0.180 (mol) ALL 3 correct: n(O2) 0.090 (mol) ANY 2 correct: n(SO3) 0.820 (mol)FULL ANNOTATIONS NEEDEDEquilibrium concentrations (moles 4)ALLOW ECF from incorrect moles of SO2, O2 AND SO2IF there is an alternative answer, check to see if there isany ECF credit possible using working --------------- 1 MARKSO2 0.720 (mol dm–3)AND O2 0.360 (mol dm–3)AND SO3 3.28 (mol dm–3) ALL three concentrations required for this markALLOW ECF from incorrect concentrationsCalculation of Kc and unitsKc [SO3 ]22[SO2 ] [O2 ]OR3 MARKS3.282 (0.720)2 (0.360)NO ECF for numerical value with a square missing 57.6 dm3 mol–1 6At least 3SF is requiredFor Kc, ALLOW 3 significant figures up to calculator valueof 57.64746228 correctly roundedFor units, ALLOW mol–1 dm3DO NOT ALLOW dm3/molALLOW ECF from incorrect Kc expression for bothcalculation and unitsCOMMON ERRORS0.02943 marks units markfrom SO2 0.820, O2 0.410, SO3 0.180 (mol)3(b)(ii) (Pressure) decreases AND fewer molecules/moles 114For fewer moles, ALLOW 3 mol 2 molALLOW more moles of reactants
PMTF325QuestionMark SchemeAnswerJune 2015Marks3(b) (iii) H is negative / ’– ‘ / –ve AND yield of SO3 decreases 3(b) (iv) IGNORE le Chatelier ---------------------------------------Each marking point is independent1GuidanceIGNORE exothermic and endothermicFULL ANNOTATIONS NEEDEDKcKc does not change (with pressure/ concentration) ALLOW Kc only changes with temperatureIF 1st marking point has been awarded, IGNOREcomments about ‘Kc decreasing’ or ‘Kc increasing’ andassume that this refers to how the ratio subsequentlychanges. i.e DO NOT CON 1st marking point.Comparison of conc terms with more O2[O2]/concentration of oxygen is greaterOR denominator/bottom of Kc expression is greater IGNORE O2 is greater/increasesQWC: yield of SO3 linked to Kc(Yield of) SO3 is greater/increasesANDnumerator/top of Kc expression is greater/increases ALLOW(Yield of) SO3 is greater/increasesANDto reach/restore Kc value 3Total1519
PMTF325Mark SchemeQuestion4(a)4(b)AnswerJune 2015MarksGuidance Proton/H donorANDPartially dissociates/ionises FIRST, CHECK THE ANSWER ON ANSWER LINEIF answer 13.7(0), award 2 -----------------------------------1.00 10 –14OR 2(.00) 10–14 (mol dm–3) [H ] 0.5(00)pH –log 2(.00) 10–14 13.7(0) 1For pOH method:,ALLOW pOH –log[OH–] 0.3(0) (calculator 0.301029995)2ALLOW pH 14 – 0.3 13.7 ALLOW 13.7 up to calculator value of 13.69897 correctlyrounded.4(c)(i)(Ka )[H ] [C2H5COO – ] [C2H5COOH]1ALLOW ECF from incorrect [H (aq)] provided that pH 7[H ] [A – ][H ]2ORIGNORE[HA][C2H5COOH]ALLOW [H3O ] for [H ]IGNORE state symbols16
PMTF325Mark SchemeQuestion4(c)(ii)AnswerJune 2015MarksFIRST, CHECK THE ANSWER ON ANSWER LINEIF answer 2.9(0), award 3 -----------------------------------–3[C 2H5COOH] 0.12(0) mol dm [H ] K a [C2H5COOH] GuidanceALLOW HA for C2H5COOH and A– for C2H5COO–1.35 10 5 0.12(0)ALLOW ECF from incorrectly calculated [C2H5COOH]OR 1.27 10–3 (mol dm–3) ALLOW 1.27 10–3 to calculator value of 1.272792206 10–3 correctly roundedpH –log 1.27 10–3 2.9(0) 3NOTE: The final two marks are ONLY available from attempteduse of Ka AND [C2H5COOH]ALLOW 2.9(0) 10–3 to calculator value of 2.895242493correctly roundedALLOW use of quadratic equation which gives sameanswer of 2.90 from 0.120 mol -----------------------------COMMON ERRORS (MUST be to AT LEAST 2 DPunless 2nd decimal place is 0)pH 2.59 2 marks–log (1.35 x 10–5 0.480) Original conc17pH 5.79 2 marks–log(1.35 x 10–5 0.120)No pH 5.19 1 mark–log (1.35 x 10–5 0.480)Original conc, no pH 4.87 0 marks–log(1.35 x 10–5) 4.87–log Ka
PMTF325Mark SchemeQuestionAnswerJune 2015Marks4(d)(i)2C2H5COOH Na2CO3 2C2H5COONa CO2 H2O 14(d)(ii)H OH– H2O 14(e)(i)pH –log 1.35 10—5 4.87 14(e)(ii)Added ammoniaC2H5COOH removes added NH3/alkali/baseOR C2H5COOH NH3 / OH– OR NH3/alkali reacts with/accepts H OR H NH3 OR H OH– GuidanceIGNORE state symbols and use of equilibrium signFOR CO2 H2O ALLOW H2CO3ALLOW C2H5COO–Na OR C2H5COO– Na BUT BOTH and – charges must be shownALLOW NaC2H5COOALLOW C2H5COOH OH– C2H5COO– H2OIGNORE state symbolsONLY correct answerDO NOT ALLOW 4.9(Question asks for 2 DP)ALLOW use of HA/weak acid/acid for C2H5COOH;ALLOW use of NH4OH for NH32Equlibrium C2H5COO– OR Equilibrium right ALLOW A– for C2H5COO–ASSUME that equilibrium applies to that supplied in thequestion, i.e. IGNORE any other equilibria18
PMTF325Question4Mark SchemeAnswerJune 2015Marks(e) (iii) CHECK WORKING CAREFULLY AS CORRECT NUMERICALANSWER IS POSSIBLE FROM WRONG VALUES ALLOW HA and A– throughoutAmount of Mg(1 mark)6.075n(Mg) 24.3 0.25(0) mol ons (2 marks)GuidanceFULL ANNOTATIONS MUST BE ------------------------------- For n(Mg), 1 markALLOW ECF for ALL marks below from incorrect n(Mg)ECF ONLY available from concentrations that have subtracted 0.50 OR 0.25 from 1 for [C2H5COOH] added 0.50 OR 0.25 to 1 for [C2H5COO–]i.e.For moles/concentration 1 mark (1 mark lost)1. n (C2H5COOH) 0.75 AND n(C2H5COO–) 1.252. n(C2H5COOH) 0.50 AND n(C2H5COO–) 1.253. n(C2H5COOH) 0.75 AND n(C2H5COO–) ------------------------------ ALLOW ECF ONLY for the following giving 1 additionalmark and a total of 3 marks0.751. [H ] 1.35 10–5 1.25 pH –log 8.1 10–6 5.09n(C2H5COOH) 1.00 – (2 0.25) 0.50 (mol) (C2H5COO–) 1.00 (2 0.25) 1.50 (mol) -------------------------------------n[H ] and pH(1 mark)0.50 ] 1.35 10–5 1.50 OR 4.5 10–6 (mol dm–3)[H4pH –log 4.5 10–6 5.35 2 dp required 0.502. [H ] 1.35 10–5 1.25 pH –log 5.4 10–6 5.27NOTE: IF there is no prior working,0.50ALLOW 4 MARKS for [H ] 1.35 10–5 1.50 AND pH 5.350.753. [H ] 1.35 10–5 1.50 pH –log 6.75 10–6 5.17IF the ONLY response is pH 5.35, award 1 mark ONLYAward a maximum of 1 mark (for n(Mg) 0.25 mol) for:pH value from Ka square root approach (weak acid pH)pH value from Kw /10–14 approach (strong base -----------------------------------ALLOW alternative approach based on Henderson–Hasselbalch equation for final 1 mark1.50.5pH pKa logOR pKa – logpH 4.87 0.48 5.35 ALLOW –log Ka for pKa0.51.5Total1619
PMTF325Mark SchemeQuestion5(a)AnswerJune 2015MarksGuidance(i)Fe2 (g) 2I-(g)Fe (g) 2I(g) e– Correct species AND state symbols required for eachmarks ALLOW e for e–TAKE CARE: In top left box, e– may be in centre ofresponse and more difficult to see than at end.Fe(g) 2I(g) There is only ONE correct response for each lineFrom the gaps in the cycle, there is NO possibility of anyECFFe(s) I2(s) 4Mark each marking point independently20
PMTF325Mark SchemeQuestion5(a)(ii)Answer(The enthalpy change that accompanies)the formation of one mole of a(n ionic) compoundfrom its gaseous ions (under standard conditions) Award marks as follows.1st mark: formation of compound from gaseous ions2nd mark: one mole for compound onlyJune 2015MarksGuidance2IGNORE 'Energy needed' OR ‘energy required’ALLOW one mole of compound is formed/made from itsgaseous ionsALLOW as alternative for compound: lattice, crystal,substance, solidIGNORE: Fe2 (g) 2I–(g) FeI 2(s)(Part of cycle)DO NOT ALLOW 2nd mark without 1st markALLOW 1 mark for absence of ‘gaseous’ only, i.e.the formation of one mole of a(n ionic) compoundfrom its ions (under standard conditions) DO NOT ALLOW any marks for a definition for enthalpy change offormation BUT note the two concessions in guidanceALLOW 1 mark for Hf definition with ‘gaseous’:the formation of one mole of a(n ionic) compoundfrom its gaseous elements (under standard conditions) 21
PMTF325Mark SchemeQuestion5AnswerJune 2015Marks(a) (iii) FIRST, CHECK THE ANSWER ON ANSWER LINEIF answer –2473 (kJ mol–1) award 2 -----------------------–(–113) 416 (2 107) 759 1561 (2 –295) HLE(FeI2)OR HLE(FeI2) –113 – ( 416 (2 107) 759 1561 (2 –295) )OR –113 – 2360 – 2473 (kJ mol–1)2GuidanceIF there is an alternative answer, check to see if there isany ECF credit possible using working below.See list below for marking of answers from ---------------------- ALLOW for 1 mark: 2473wrong sign–2661107 and –295 used instead of 2 107 and2 –295–2366 107 used instead of 2 107–2768–295 used instead of 2 –295–3653wrong sign for 295–2247wrong sign for 113–1641wrong sign for 416–2045wrong sign for 2 107–955wrong sign for 750 649wrong sign for 1561–3653wrong sign for 2 –295Any other number:CHECK for ECF from 1st marking point for expressionswith ONE error onlye.g. one transcription error: e.g. 461 instead of 4165(b)(i)Fe2 : 1s22s22p63s23p63d6 Br–: 1s22s22p63s23p63d104s24p6 2ALLOW 4s before 3d, ie 1s22s22p63s23p64s23d104p6ALLOW 1s2 written after answer prompt (ie 1s2 twice)ALLOW upper case D, etc and subscripts, e.g. .4S23D1ALLOW for Fe2 .4s0DO NOT ALLOW [Ar] as shorthand for 1s22s22p63s23p6Look carefully at 1s22s22p63s23p6 – there may be amistake22
PMTF325Mark SchemeQuestion5(b)AnswerJune 2015MarksGuidanceFULL ANNOTATIONS NEEDED(ii)With Cl2 AND Br2 AND I2products are Fe2 (AND halide ion)FeCl2 AND FeBr2 AND FeI2 ALLOW products within equations (even if equations arenot balanced)IF stated, IGNORE reactantsOREvidence that two electrode potentials have been compared for atleast ONE reaction, e.g. Fe –0.44 AND Cl2 1.36e.g. Iron has more/most negative electrode potentialALLOW response in terms of positive ‘cell reactions’,e.g Fe Cl2 Fe2 2Cl– E ( )1.80 VIGNORE comments about reducing and oxidising agentsand electrons3With Cl2 AND Br2,products are Fe3 (AND halide ion)FeCl3 AND FeBr3 5(c)ALLOW correct multiples throughoutALLOW equilibrium signs in all equationsBOTH EQUATIONS REQUIRE IONS PROVIDED IN QUESTIONORReaction 1: 2 marks1st mark for ALL CORRECT speciese.g.: Fe2 NO3– H Fe3 NO H2OFor 1st mark, IGNORE e– present2nd mark for CORRECT balanced equation3Fe2 NO3– 4H 3Fe3 NO 2H2O -------------------------------Reaction 2: 1 mark2 NO [Fe(H2O)5NO]2 H2O 2O)6][Fe(HTotal23316Check carefully for correct charges
PMTF325Mark SchemeAnswerQuestion6(a)June 2015MarksEoredoxsystemMostnegativeEALL 3 correct for 1 markCLeastnegativeD1 6(b)(i)6(b)(ii)pH 0 1GuidanceALLOW ORA, ieAg redox system (D) has more positive E / less negative EH redox system is more negative(e.g. has a more –ve E OR less ve E OR is –ve electrode)OR H redox system releases electrons(May be in equation, e.g. H2 2H 2e–) ALLOW equilibrium signIGNORE H is more reactive ORAEquilibrium shifts to increase [H ] OR H OR standard hydrogen equation shifts to increase [H ] OR H 6(b) (iii) H2 2Ag 2Ag 2H 2IGNORE direction of equilibrium shift1ALLOW multiplese.g. ½H2 Ag Ag H State symbols NOT requiredALLOW equilibrium sign6(c)(i)–AND Base 2CNH2OAcid 1 HCNAcid 2 OH–Base 1 1State symbols NOT requiredALLOW CNH and HO– (i.e. any order)ALLOW 1 and 2 labels the other way around.ALLOW ‘just acid’ and ‘base’ labels throughout if linked bylines so that it is clear what the acid-base pairs are.24
PMTF325Mark SchemeQuestion6(c)(ii)Answer June 2015Marks–GuidanceALLOW Acid reacts with/removes OH– ions (to form HCN)ALLOW CNH (i.e. any order)H reacts with CN OR HCN formsOR equation: H CN– HCN (ALLOW )OR CN– accepts a proton/H OR equilibrium shifts right AND CN– is removed 1IGNORE other equilibrium comments6(d)(i)Fuel reacts with oxygen/oxidant to give electrical energy/voltage 16(d)(ii)ethanol is a liquid OR is less volatileOR ethanol is easier to store/transport/stored more safelyOR hydrogen is explosive/more flammableOR ethanol has more public/political acceptance 16(d) (iii) C2H5OH 3O2 2CO2 3H2O 16(d) (iv) O2 4H 4e– 2H2O 125ALLOW named fuel. e.g. hydrogen/H2; ethanol;methanol, etcALLOW fuel cell requires constant supply of fuel ANDoxygen/an oxidantOR fuel cell operates continuously as long as a fuel ANDoxygen/an oxidant are addedIGNORE ‘reactants’ ‘products’ and comments aboutpollution and efficiencyAssume that ‘it’ refers to ethanolALLOW ORA throughoutIGNORE ethanol has a higher boiling pointIGNORE H2 is a gasIGNORE 'produces no CO2' OR less pollutionIGNORE comments about efficiencyIGNORE comments about biomass and renewableCorrect species AND balancing neededALLOW multiplesALLOW C2H6O for formula of ethanolIGNORE state symbolsCorrect species AND balancing neededALLOW multiples, e.g. 3O2 12H 12e– 6H2O –2 2H 2e H2OALLOW e (ie no –½Osign)ALLOW O2 2H2O 4e– 4OH–OR 3O2 6H2O 12e– 12OH–IGNORE state symbols
PMTF325Mark SchemeQuestion6(d)(v)Answeroxidation: C from –2 to 4reduction: O from 0 to –2June 2015Marks’ ’ sign not required GuidanceALLOW 2– and 4 ALLOW C2– C4 2ALLOW 0 and 2–ALLOW O0 O2–ALLOW 1 mark if correct oxidation numbers shown forBOTH C and O but wrong way around(ie C on reduction line and O on oxidation line)IGNORE O2 reducedIGNORE any reference to electron transfer(not in question)Total2613
PMTF325Mark SchemeQuestion7(a)AnswerJune 2015MarksGuidanceEquations can be in either orderALLOW multiples throughoutIGNORE state symbolsNa2O H2O 2NaOH ALLOW Na2O H2O 2Na 2OH–DO NOT ALLOW equations with uncancelled species.e.g. Na2O 2H2O 2NaOH H2ONaFeO2 2H2O Fe(OH)3 NaOH 2ALLOW 2NaFeO2 H2O Fe 2O3 2NaOH –OR2 H2O Fe 2O3 2Na 2OH 2NaFeO27
PMTF325Mark SchemeQuestion7(b)AnswerJune 2015MarksFULL ANNOTATIONS MUST BE USEDFIRST, CHECK THE ANSWER ON ANSWER LINEIF answer 33.7%, award 6 marks.IF there is an alternative answer, check to see if there is any ECFcredit possible using working ----------------------amount S2O32– used 0.1000 GuidanceIF a step is omitted but subsequent step subsumesprevious, then award mark for any missed stepWorking: at least 3 SF throughout until final % markBUT ignore trailing zeroes, ie for 0.490 allow ------------ 25.501000 2.550 10–3 (mol) ECF answer above 2amount I2 2.550 10–3 21.275 10–3 (mol) amountCrO42– 2/3 1.275 10–3 OR 1.275 10–3 1.5ECF answer above 1.5 8.5(00) 10–4 (mol) ECF answer above 40amount CrO42– in original 1000 cm3 40 8.5(00) 10–4 3.4(00) 10–2 mol 3 Mass of Cr/Cr6–2in ore 52.0 3.4(00) 10 g1.768 g 1.768 percentageCr in ore 1005.25ECF answer above 52.0IMPORTANT: The last two marks are ONLY available byusing 52.0 for ----------------------Common ECFs:0.8% x 40 missing5 marks (scaling error) 33.7% 0.84%x 40 missing 4 marks (scaling error and 2 DP)MUST be to one decimal place (in the question)33.68%5 marks (2 DP)16.8%5 marks (divide Cr somewhere by 2)144.9%; 72.5% 4 marks (Final 2 marks unavailable)Use of M(Fe(CrO2)2) 223.8 instead of M(Cr).28
PMTF325Mark SchemeQuestionAnswerJune 2015MarksGuidanceALLOW multiples and equilibrium signs throughoutIGNORE state symbols throughout(c)Overall:2–4–3 – 3I 4H2O Cr 1½ I2 8OH e.g. 2CrO42– 6I– 8H2O 2Cr 3 3I2 16OH–ALLOW equation using H . i.e.2–3I– 8H Cr 3 1½ I2 4H2OCrO 42– OR 2CrO4 6I– 16H 2Cr3 3I28H2O CrOHalf
Oxford Cambridge and RSA Examinations . PMT. OCR (Oxford Cambridge and RSA) is a leading UK awarding body, providing a wide range of qualifications to meet the needs of candidates of all ages and abilities. OCR qualifications include AS/A Levels, Diplomas, GCSEs, Cambridge Nationals, Cambridge Technicals,
Marten van Dijk RSA Laboratories Cambridge MA marten.vandijk@rsa.com Ari Juels RSA Laboratories Cambridge MA ari.juels@rsa.com Alina Oprea RSA Laboratories Cambridge MA alina.oprea@rsa.com Ronald L. Rivest MIT Cambridge MA rivest@mit.edu Emil Stefanov UC Berkeley Berkeley CA emil@berke
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MS Excel – PMT Function(WS, VBA) In Excel, the PMT function returns the payment amount for a loan based on an interest rate and a constant payment schedule. The syntax for the PMT function is: PMT( interest_rate, number_payments, PV, [FV], [
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Each RSA number is a semiprime. (A nu mber is semiprime if it is the product of tw o primes.) There are two labeling schemes. by the number of decimal digits: RSA-100, . RSA Numbers x x., RSA-500, RSA-617. by the number of bits: RSA-576, 640, 704, 768, 896, , 151024 36, 2048.
Oxford Cambridge and RSA. 2 OCR 2018 Answer all the questions. SECTION A . OCR is part of the Cambridge Assessment Group; Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.
Oxford Cambridge and RSA Please write clearly in black ink. Do not write in the barcodes. . OCR is part of the Cambridge Assessment Group; Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a
Changes in Oracle Providers for ASP.NET in ODAC 12c Release 4 xiv Changes in Oracle Providers for ASP.NET Release 11.2.0.2 xiv Changes in Oracle Providers for ASP.NET Release 11.2.0.1.2 xv 1 Introduction to Oracle Providers for ASP.NET 1.4 Connecting to Oracle Database Cloud Service 1-1 1.1 Overview of Oracle Providers for ASP.NET 1-1 1.2 Oracle Providers for ASP.NET Assembly 1-4 1.3 System .
