GCE Chemistry B H433/02: Scientific literacy in chemistry Advanced GCE Mark Scheme for November 2020

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GCE Chemistry B H433/02: Scientific literacy in chemistry Advanced GCE Mark Scheme for November 2020 Oxford Cambridge and RSA Examinations GCE Chemistry B H433/02: Scientific literacy in chemist... ry Advanced GCE Mark Scheme for November 2020Oxford Cambridge and RSA Examinations 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, Functional Skills, Key Skills, Entry Level qualifications, NVQs and vocational qualifications in areas such as IT, business, languages, teaching/training, administration and secretarial skills. It is also responsible for developing new specifications to meet national requirements and the needs of students and teachers. OCR is a not-for-profit organisation; any surplus made is invested back into the establishment to help towards the development of qualifications and support, 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 requirements of the examination. It shows the basis on which marks were awarded by examiners. It does not indicate the details of the discussions which took place at an examiners’ meeting before marking commenced. All examiners are instructed that alternative correct answers and unexpected approaches in candidates’ scripts must be given marks that fairly reflect the relevant knowledge and skills demonstrated. Mark schemes should be read in conjunction with the published question papers and the report on the examination. © OCR 20202 Annotations Annotation Meaning Correct response Incorrect response Omission mark Benefit of doubt given Contradiction Rounding error Error in number of significant figures Error carried forward Level 1 Level 2 Level 3 Benefit of doubt not given Noted but no credit given Ignore3 Abbreviations, annotations and conventions used in the detailed Mark Scheme (to include abbreviations and subject-specific conventions). Annotation Meaning DO NOT ALLOW Answers which are not worthy of credit IGNORE Statements which are irrelevant ALLOW Answers that can be accepted ( ) Words which are not essential to gain credit __ Underlined words must be present in answer to score a mark ECF Error carried forward AW Alternative wording ORA Or reverse argumentQuestion Answer Mark AO element Guidance 1 a  1 1.1 ALLOW correct C–N bond circled 1 b i Correct 3D structure around chiral centre  correct mirror image  2 2.1 x 2 ALLOW any object and correct mirror image scores 1 mark ALLOW dotted wedges instead of dotted lines. ALLOW wedges for bonds in front of the plane of the paper ALLOW two ordinary lines as long as they are not 180o to each other. 1 b ii  1 1.1 DO NOT ALLOW NH3(+) IGNORE extra correct details on skeletal structure 1 b iii H2NCH(COOH)CH2COOH also formed  also CH3OH  hydrolysis of ester  3 3.2 x 3 ALLOW any unambiguous structures ALLOW NH3+ in formula of amino acid 1 c 1 1.1 ALLOW circles round NH2, NH and OH rather than the atoms separately ALL indicated atoms MUST be circled to score the mark NH O OH NH2 O O OCH3 CH2 C COOH NH2 Ph H C CH2 NH2 HOOC H Ph Ph O NH3 O + -H433/02 Mark Scheme November 2020 5 Question Answer Mark AO element Guidance  1 d Instantaneous (dipole)-induced dipole/id-id  1 2.5 ALLOW Van der Waals or London 1 e i place in solvent and allow solvent to rise up paper  solvent below level of spot  (dry and) use ninhydrin/locating agent/UV (light)  more than one spot indicates hydrolysis  4 1.2 3.3 1.2 3.4 ALLOW labelled diagrams to score MP1, 2 & 4 IGNORE use of water as solvent ALLOW matching spots from individual amino acids 1 e ii enzyme would be denatured /tertiary structure broken down so no reaction (AW) 1 3.1 1 e iii No difference to rate (AW) Aspartame/substrate zero order (when in excess)  2 3.1 x 2 ALLOW initially rate increases AND then becomes constant(AW) ALLOW all active sites occupied(AW) when aspartame in excess/at high concentration’ NH O OH NH2 O O OCH3H433/02 Mark Scheme November 2020 6 Question Answer Mark AO element Guidance 2 a i salt bridge  filter paper and potassium nitrate (solution)  2 3.4 x 2 ALLOW ion bridge ALLOW any Gr I /II nitrate solution 2 a ii 298 K/ 25oC  concentrations of solutions 1 mol dm–3  2 1.2 x 2 2 b i silver ions / Ag+  1 1.2 2 b ii From Cu to Ag AND Cu electrode potential is more negative/less positive  1 2.3 ALLOW Ag electrode is more positive/less negative ALLOW Cu is oxidised/loses electrons ALLOW Ag+ ions are reduced/accept electrons 2 c FIRST CHECK THE ANSWER ON ANSWER LINE If answer = 6.8 x 10–7 (mol dm–3) award 4 marks Eo = 0.46  Rearrange equation: 0.06 log[Ag+] = E – Eo  log [Ag+] = –6.17  [Ag+] = 6.8 x 10–7 (mol dm–3)  4 2.8 x 4 ALLOW 1 or more sf (0.06 in equation) ALLOW ecf throughout 2 d (i) Equation showing that IO3– reacts with Cu  2IO3– +12 H+ + 5Cu → I2 + 6H2O + 5 Cu2+ 2 2.8 x 2 Mark separately Second mark can be scored for reverse equation. ALLOW equilibrium sign IGNORE state symbols 2 d (ii) 2 3.3 x 2H433/02 Mark Scheme November 2020 7 Question Answer Mark AO element Guidance Pt/graphite electrode  IO3– and I2 and H+ in solution  2 d (iii) FIRST CHECK THE ANSWER ON ANSWER LINE If answer = 0.4 (mol dm-3) award 3 marks [I2] = 0.04  √0.04 = 0.2  [IO3–] = 0.4 (mol dm-3)  3 2.8 x 3 0.28.... (omission of factors of 2) scores 1 mark 0.56 and 0.2 score 2 marks ALLOW ecf from any statement that begins “[I2] =”H433/02 Mark Scheme November 2020 8 Question Answer Mark AO element Guidance 3 a ten electrons around P atom / eight electrons around P atom if clear that lone pair from P are used to form a dative covalent bond to one O atom  rest correct  2 2.5 x 2 IGNORE minus sign ALLOW ‘extra’ electron on single bonded O to be the same symbol or different from the rest of the electrons on that O. Must be clear that only five electrons are from P atom. 3 b mol P = 52 x 2/142 = 0.73 AND mol K = 34 x 2/94.2 = 0.72  Ratio is about 1:1 as in KH2PO4  2 2.6 x 2 ALLOW 52/142 = 0.365 AND 34/94.2 = 0.36 for MP1 3 c i HPO42– AND proton acceptor  1 1.1 3 c ii 7.2.....  1 1.2 3 c iii FIRST CHECK THE ANSWER ON ANSWER LINE If answer = 5.1.... award 2 marks [H+] (= √(6.2 x 10–8 x 1.0 x 10–3)) = 7.87 x 10–6 (mol dm–3)  pH = 5.1...  2 2.2 x 2 ALLOW ecf provided ‘[H+] =’ or ‘H+ =’ is shown AND value is > 10–7 and < 10–4 3 d NH4+ ⇌ NH3 + H+ OR NH4+ + H2O ⇌ NH3 + H3O+ Acid/ H+/ H3O+ (from KH2PO4) moves equilibrium (position) to left  2 2.7 x 2 ALLOW equilbrium the other way round (and the corresponding ‘right’ in MP2) H O P O H O OH433/02 Mark Scheme November 2020 9 Question Answer Mark AO element Guidance 3 e FIRST CHECK THE ANSWER ON ANSWER LINE If answer = 69 (g) award 4 marks Value of [H+]: 3.16 x 10–7 Rearrangement of eqn: [H2PO4–] = [H+] [HPO42–]/ Ka  [H2PO4–] = 3.16 x 10–7 x 0.1/ 6.2 x 10–8 OR 0.51  mass KH2PO4 = (0.51 x 136) = 69 (g)  4 2.8 x 4 ALLOW 2 or more sf ALLOW ecf throughout 3 f i Equilibrium will move to left (AW)  [H+] only restored/unchanged (AW) if [H2PO4–] is large  2 3.1 x 2 3 f ii (Student is correct (AW) AND) HCl strong (acid) so all reacts/dissociates/ionises  1 3.1 f iii FIRST CHECK THE ANSWER ON ANSWER LINE If answer = 0.7 award 2 marks [H+] (= 0.05 x 0.01/1000) = 5 x 10–7  pH change = 7 – 6.3 = 0.7  2 2.8 x 2 ALLOW ecfH433/02 Mark Scheme November 2020 10 Question Answer Mark AO element Guidance 4 a i (C=C) decolorises bromine water  (COOH/acid) will fizz with carbonate/appropriate colour with (named) indicator  2 1.2 x 2 ALLOW gas produced turns limewater cloudy(AW) if carbonate test used 4 a ii FIRST CHECK THE ANSWER ON ANSWER LINE If answer = 5 (cm3) award 3 marks conc maleic acid = (2.32/116) OR 0.02 (mol dm–3)  amt NaOH = 2 x 250 x 0.02/1000 OR 0.01 (mol)  vol NaOH = 1000 x 0.01/2 = 5  3 2.4 x 3 2.5 scores 2 marks ALLOW ecf Allow wrong answers (after ecf) to 2 or more sig figs. 4 b i CHO  1 1.2 ALLOW elements in any order b ii Z  butenedioic acid  2 1.1 x 2 ALLOW ‘butendioic acid’ c Description of groups being spatially different across C=C  Lack of free rotation of C=C /groups in a fixed position  2 1.2 x 2 ALLOW they are stereoisomers. d Loss of COOH/CO2H OR C3H3O2(+)/CHCHCOOH 1 2.6 e i COOH C C COOH H H HOOC C C COOH H H H H C C COOH HOOC H H+ + H+ + one for each arrow  2 2.5 x 2 One arrow must start) on the double bond and end pointing to H+(or to the bond being formed) The other arrow must start and end on the bonds shown. Other arrows are CON e ii (Electrophilic) Elimination 1 1.1H433/02 Mark Scheme November 2020 11 Question Answer Mark AO element Guidance e iii No, either of the Hs on the left C (of carbocation) could leave  some 2H/D would be incorporated  2 3.2 x 2 f O O O  1 2.1 g i Atom economies (98/170) = 58% AND (98/222) = 44%  Identifies butane/reaction 1 should be used because it has the larger atom economy/produces less waste  2 2.6 3.1 ALLOW 0.58 AND 0.44 g ii Benzene toxic/ more expensive/butane more available from cracking /doesn’t produce CO2 (ORA for reaction 2) 1 3.1 ALLOW ecf from (g)(i) eg butane more flammable g iii FIRST CHECK THE ANSWER ON ANSWER LINE If answer = 61 (kg) award 2 marks amt butane = 15000/24 = 625 mol  mass maleic anh = 625 x 98/1000 = 61(kg) (2sf)  2 2.8 x 2 61.3 or 61.2 score 1 Correct use of gas equation can score both marksH433/02 Mark Scheme November 2020 12 Question Answer Mark AO element Guidance h* Refer to marking instructions on page 5 of mark scheme for guidance on marking this question. Level 3 (5 – 6 marks) Correct structure/identity deduced and detailed evidence related to the structure is provided from each spectrum. There is a well-developed line of reasoning which is clear and logically structured. The information presented is relevant and substantiated. Level 2 (3 – 4 marks) Correct structure/identity deduced with detailed evidence from at least one spectrum. OR Structure/identity attempted with some correct evidence from a minimum of two spectra. There is a line of reasoning presented with some structure. The information presented is relevant and supported by some evidence. Level 1 (1 – 2 marks) Correct structure/identity deduced with no relevant evidence. OR Structure/identity not given or incorrect, but some correct evidence from at least one spectrum. There is an attempt at a logical structure with a line of reasoning. The information is in the most part relevant. 0 marks No response or nothing of value 6 3.1 x 4 3.2 x 2 Indicative scientific points may include: AO3.1 Analysis: IR: • C=O at 1700 • Broad OH 2500-3300 • COOH HNMR: • Three H environments • 1.2: Hs on C connected to C-H • 2.3: H on C connected to Cs with many Hs • 11.8 H in COOH CNMR: • Three C environments • two Cs in same environment • one C=O (at 183ish) • two C-C AO3.2 Evaluation: Compound A identified as 2-methylpropanoic acid Structure CH3CH(CH3)COOH presented in any unambiguous wayH433/02 Mark Scheme November 2020 13 Question Answer Mark AO element Guidance 5 a i Two Cls/chlorines/two Cl-/ chloride ligands are each -1  1 1.1 5 a ii 5d8 1 1.1 5 a iii Yes, it has an ion with an incomplete d subshell (in a compound)  1 1.1 5 b OR OR C C C C C HC H H H N N H H H H H H H H H H correct identification  full structural (with O- for first two) 2 1.1 x 2 5 c i guanine 1 1.1 5 c ii hydrogen (bond) 1 2.1 5 c iii (dative) covalent/ co-ordinate (bond)  (lone) pair on nitrogen donated to Pt  2 2.1 x 2 5 d i octahedral  1 2.1 ii 6  1 2.1 C C C C O C O C O O H H H H H H -- O C O C O O --H433/02 Mark Scheme November 2020 14 Question Answer Mark AO element Guidance 5 d iii Satraplatin also has ethanoate/ester/C=O groups/(4) O atoms (in addition to NH3 groups that cisplatin also has)  (These form more) H-bonds with water(ORA for cisplatin)  and (more than) compensate for ‘insoluble’ (AW) ring OR H-bonds broken in water  3 3.1 x 3 Oxygen MOLECULES is CON 5 e* Refer to marking instructions on page 5 of mark scheme for guidance on marking this question. Level 3 (5 – 6 marks) Considers disadvantages of cisplatin, with most examples of both toxicity and cell resistance. AND Identifies most examples of how new drugs attempt to overcome the disadvantages of cisplatin. There is a well-developed line of reasoning which is clear and logically structured. The information presented is relevant and substantiated. Level 2 (3 – 4 marks) Considers disadvantages of cisplatin, with some examples of both toxicity and cell resistance. OR Gives a detailed treatment of either toxicity OR cell resistance AND Attempts to provide examples of the ways new drugs attempt to overcome the disadvantages of cisplatin. There is a line of reasoning presented with some structure. The information presented is relevant and supported by some evidence. 6 3.1 x 3 3.2x 3 Indicative scientific points include: Disadvantages: toxicity • damaging to the kidneys/ gastrointestinal tract / nervous system. • targets all cells • difficulty of administration cell resistance • influx slower/method of entry slowed/prevented • efflux faster/method of exit accelerated • removed before it can act on DNA • improved cell repair mechanism • cancer cells evolve • improved methods of DNA repair New Drugs attempting to overcome disadvantages • carboplatin less toxic • satraplatin/picoplatin different structure and overcame resistance • formulae of some of above • bulky group in picoplatin helps overcome resistance • satraplatin soluble/ administered orallyH433/02 Mark Scheme November 2020 15 Question Answer Mark AO element Guidance Level 1 (1 – 2 marks) Considers disadvantages of cisplatin, with examples of toxicity OR cell resistance. OR Attempts to provide examples of the ways new drugs attempt to overcome the disadvantages of cisplatin There is an attempt at a logical structure with a line of reasoning. The information is in the most part relevant and correct. 0 marks No response or nothing of valueOCR (Oxford Cambridge and RSA Examinations) The Triangle Building Shaftesbury Road Cambridge CB2 8EA OCR Customer Contact Centre Education and Learning Telephone: 01223 553998 Facsimile: 01223 552627 Email: [email protected] [Show More]

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