GCE Chemistry A H032/02: Depth in chemistry Advanced Subsidiary GCE Mark Scheme for Autumn 2021

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GCE Chemistry A H032/02: Depth in chemistry Advanced Subsidiary GCE Mark Scheme for Autumn 2021 Oxford Cambridge and RSA Examinations GCE Chemistry A H032/02: Depth in chemistry Advanced Subsidia... ry GCE Mark Scheme for Autumn 2021Oxford 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 2021H032/02 Mark Scheme October 2021 6 1. 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 IgnoreH032/02 Mark Scheme October 2021 7 2. Abbreviations, annotations and conventions used in the detailed Mark Scheme (to include abbreviations and subject-specific conventions). Annotation Meaning / alternative and acceptable answers for the same marking point  Separates marking points 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 argumentH032/02 Mark Scheme October 2021 Question Answer Marks AO element Guidance 1 (a) (i) (Electrostatic) attraction between oppositely charged ions  1 AO1.1 IGNORE force IGNORE references to transfer of electrons (ii) Dot and cross 2  K shown with either 8 or 0 electrons AND S shown with 8 electrons with 2 crosses and 6 dots (or vice versa)  Charges Correct charges on K+ AND S2– ions  2 AO2.5  2 ALLOW separate K+ ions, i.e. If 8 electrons are shown around K, ‘extra electrons’ around S must match symbol chosen for electrons around K, e.g. Shell circles NOT needed IGNORE inner shell electrons K S 2 2 + K + K + S 2 2 K + S 2H032/02 Mark Scheme October 2021 Question Answer Marks AO element Guidance (b) Bonded pairs Electron pairs in covalent bonds shown correctly using dots and crosses in SF2 molecule  Lone pairs Lone pairs correct on S and 2 F atoms  2 AO2.5  2 Shell circles NOT needed IGNORE inner shells ALLOW Non-bonding electrons shown as unpaired (c) K2S: ionic bonds are strong OR has a giant ionic lattice  SF2: London forces/ dipole-dipole forces are weak  between molecules  3 AO1.1  2 AO1.2 ALLOW induced OR permanent dipole interactions ALLOW intermolecular forces are weak for 2 marks for SF2 IGNORE van der Waals forces, vdW (d) (i) Octahedral  90 o  2 AO1.1  2 (ii) SF6 has no overall dipole OR is non polar OR S–F bonds are strong OR SF6 has no lone pairs  1 AO2.1 Total 11 S F FH032/02 Mark Scheme October 2021 Question Answer Marks AO element Guidance 2 (a) A species with an unpaired electron  1 AO1.1 DO NOT ALLOW: species with one electron (b) Homolytic (fission)  1 AO1.1 (c)   2 AO2.5  2 ALLOW any combination of skeletal OR structural OR displayed formula as long as unambiguous (d) Structure of organic product  Complete balanced equation  2 AO2.5 AO2.6 ALLOW any combination of skeletal OR structural OR displayed formula as long as unambiguous, e.g. Total 6H032/02 Mark Scheme October 2021 Question Answer Marks AO element Guidance 3 (a) From colourless to pink  1 AO2.3 (b) (i) Titre: 18.50, 18.05, 18.20, 18.30  All titres with 2 DP and ending with ‘0’ OR ‘5’ 1 AO2.4 DO NOT ALLOW responses given to only 1 decimal place (ii) To estimate the titre  1 AO2.3 ALLOW ‘getting a rough idea of the titre’ (or similar wording) (iii) 18.25 cm3  1 AO2.4 (iv) % uncertainty = 18.05 0.1 × 100 = 0.55 %  1 AO2.4 ALLOW or incorrect mean ECF from incorrect subtraction in (b)(i) ALLOW calculation from other titre values (c) FIRST CHECK THE ANSWER ON ANSWER LINE If answer = 3 AND M = 132(,0)…. award 5 marks ----------------------------------------------------------------------- n(NaOH) = 18.25 × 0.240 1000 = 4.38 × 10–3  n(acid) in 25 cm3 = 4.38 × 10 2 –3 = 2.19 × 10–3 (mol)  n(acid) in 250 cm3 = 2.19 × 10–2 (mol)  M(acid) = 2.891 2.19 × 10–2 = 132(.0)…… (g mol–1)  M(CH2)n = 132 – 90 OR (132.0…. – 90) OR 42 (seen anywhere) AND n = 42 14 = 3   whole number required 5 AO2.8 ×4 AO3.2 ALLOW ECF throughout ALLOW ECF from (b)(iii) Answers should be to at least 3 significant figures for first 4 marks.H032/02 Mark Scheme October 2021 (d) The titre would be less  Glutaric acid would be less concentrated/more dilute  2 AO3.3  2 Total 12H032/02 Mark Scheme October 2021 Question Answer Marks AO element Guidance 4 (a) * Please refer to the marking instructions on page 4 of this mark scheme for guidance on how to mark this question. Level 3 (5–6 marks) Calculates CORRECT enthalpy change with correct signs for ∆H2 for reaction 2 AND ∆H1 for reaction 1. 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) Calculates a value of ∆H2 for reaction 2 from the: Energy change AND Amount in mol of MgCO3. 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) Processes experimental data to obtain the Energy change from mc∆T OR Amount in moles of MgCO3 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 no response worthy of credit. 6 AO3.1  4 AO3.2  2 Indicative scientific points may include: 1. Processing experimental data Energy change from mcΔT  Energy in J OR kJ Using 103.01 g or 100.0 g = 103.01 × 4.18 × 5.0 = 2152.909 (J) OR 2.153 (kJ) 3SF or more (2.152909 unrounded) OR 100.0 × 4.18 × 5.0 = 2090 (J) OR 2.09 (kJ) Amount in mol of MgCO3 n(MgCO3) = 4.215 84.3 = 0.0500 (mol) ---------------------------------------------- 2. ± value of ∆H2 for reaction 2 From m = 103.01 g = ± 0.0500 2.153 = ±43.06 (kJ mol–1) (–43.05818 unrounded) From m = 100.0 g = ± 0.0500 2.19 = ±41.8 (kJ mol–1) ---------------------------------------------- 3. CORRECT enthalpy changes for Reaction 1 and Reaction 2 with signs (using 103.01 g ONLY) Reaction 2 = –43.06 (kJ mol–1) 3SF or more with correct – sign Reaction 1 ∆H1 = ∆H2 – ∆H3 = –43.06 – (–136.1) = +93.04 (kJ mol–1) 3SF or more with correct – sign ALLOW omission of trailing zeroes, e.g. 93 for 93.0 NOTE: If 100 g used, ∆H is incorrect and L3 cannot be attained Total 6H032/02 Mark Scheme October 2021 Question Answer Marks AO element Guidance 5 (a) Kc = [CH3OH] [CO] × [H2]2  1 AO1.2 Multiplication sign is not required DO NOT ALLOW curved brackets (b) (i) FIRST CHECK THE ANSWER ON ANSWER LINE If answer = 1.4…….. (mol dm–3) award 2 marks ------------------------------------------------------------------------- [CH3OH] = 15.4 × 0.57 × 0.402  = 1.40448 (mol dm–3)  2 AO2.2  2 ALLOW ECF from incorrect expression in (a) ALLOW 1.4 up to calculator value of 1.40448 (ii) To the right  1 AO1.1 ALLOW towards the product/CH3OH (c) Less fossil fuel used  Reduction in CO2 (emissions)  2 AO3.2 2 ALLOW Less energy used (d) (i) d-block  1 AO1.1 (ii) 1s22s22p63s23p63d104s24p1  Look carefully at 1s22s22p63s23p6 – there may be a mistake 1 AO1.2 ALLOW 4s AND/OR 4p1 before 3d, e.g. 1s22s22p63s23p64s23d104p1 ALLOW 1s2 after answer prompt (ie 1s2 twice) ALLOW upper case D, etc and subscripts, e.g. …...4S23D8 DO NOT ALLOW [Ar] as shorthand for 1s22s22p63s23p6H032/02 Mark Scheme October 2021 Question Answer Marks AO element Guidance (e) Element A is silicon/Si  AND A large increase between the 4rd and 5th IE 5th electron is removed from shell closer to the nucleus OR there are 4 electrons in the outer shell  2 AO3.1 AO3.2 ALLOW an indication of a different shell (from removal of 5th electron) Total 10H032/02 Mark Scheme October 2021 Question Answer Marks AO element Guidance 6 (a) Best fit curve  Tangent drawn at approximately t = 50 s  Gradient calculated: 0.44 ± 0.2 (cm3 s–1)  3 AO1.2 AO2.4  2 DO NOT ALLOW interpolation (taking a direct reading from graph), answer must be derived from taking a gradient ALLOW ECF from incorrectly drawn tangent (b) Advantage: no loss of gas  Disadvantage: small loss in mass  2 AO3.4  2 IGNORE easier to set up (c) (i) FIRST CHECK THE ANSWER ON ANSWER LINE If answer = 0.41 (g) award 2 marks ---------------------------------------------------------------------------- n(Ba) = 0.26 87.6 OR 2.9……..  10–3 OR 3  10–3  mass Ba = 137.3  2.9.……..  10–3 = 0.41 g 2 DP required 2 AO3.3 2 ALLOW ECF from incorrect moles of Ba Calculator: 2.96803653  10–3 NOTE 3  10–3 also gives 0.41 g (ii) Steeper initial gradient AND levels off earlier  Same volume of gas produced  2 AO3.1  2H032/02 Mark Scheme October 2021 Question Answer Marks AO element Guidance (iii) Reactivity Ba is more reactive (than Sr)  Atomic radius Ba has a greater atomic radius (than Sr) OR Ba has more shells OR Ba has more shielding  Attraction Nuclear attraction is less in Ba OR (outer) electrons in Ba are less attracted (to nucleus) OR Increased distance / shielding in Ba outweighs increased nuclear charge  Ionisation energy Ionisation energy of Ba is less OR easier to remove (outer) electrons in Ba  4 AO1.1  4 Comparison required throughout ORA throughout For more shells, ALLOW higher energy level IGNORE more orbitals OR more sub-shells IGNORE ‘different shell’ or ‘new shell’ ALLOW Ba has less nuclear pull’ OR ‘Ba electrons are less tightly held’ IGNORE less effective nuclear charge’ IGNORE ‘nuclear charge’ for ‘nuclear attraction’ ALLOW easier to oxidise Ba Total 13H032/02 Mark Scheme October 2021 Question Answer Marks AO eleme nt Guidance 7 (a) Correct skeletal formulae for organic compounds  Complete balanced equation   2 AO2.5  2 Skeletal formulae needed for 1st marking point. For complete balanced equation, ALLOW any combination of skeletal OR structural OR displayed formula as long as unambiguous, e.g. (CH3)3COH + HCl  (CH3)3CCl + H2OH032/02 Mark Scheme October 2021 Question Answer Marks AO eleme nt Guidance (b) * Please refer to the marking instructions on page 4 of this mark scheme for guidance on how to mark this question. Level 3 (5–6 marks) Explains the purification steps with most fine detail. AND Calculates correct mass of 2-chloro-2-methylpropane, (CH3)3CCl 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) Describes some purification steps, with some detail. AND Calculates the mass of (CH3)3CCl with some errors. 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) Describes few purification steps. OR Attempts to calculate the mass of (CH3)3CCl with little progress. 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 no response worthy of credit. 6 AO1.2  2 AO2.7  2 AO3.3  2 Indicative scientific points may include: Main purification stages  Separating funnel to remove organic layer from aqueous layer  Anhydrous salt to dry organic layer  Distillation to purify the product Fine detail  Organic layer is the top layer  Name of a drying agent e.g. anhydrous MgSO4 or CaCl2  Collect fraction at 50 ºC IGNORE washing with carbonate/water not in spec. Calculation of mass of (CH3)3CCl  n((CH3)3COH) = 7.70 74.0 = 0.10405 (mol)  expected n((CH3)3CCl) = 0.10405 × 76 100 = 0.0791 (mol)  expected mass = 0.0791 × 92.5 = 7.315 g ALLOW 7.31–7.32 for small slip/rounding Using mass  Theoretical mass (CH3)3CCl = 7.70  92.5 74.0 = 9.625 g  Mass of (CH3)3CCl = 9.625  100 76 = 7.315 gH032/02 Mark Scheme October 2021 Question Answer Marks AO eleme nt Guidance NOTE: Incorrect inverse ratio of 100 76 gives:  0.10405 × 76 100 = 0.137 (mol)  Mass = 92.5  0.137 = 12.7 g (c) (i) Butan-2-ol  1 AO1.2 (ii) (CH3)2CHCH2OH +2[O] → (CH3)2CHCOOH + H2O B as reactant: (CH3)2CHCH2OH  (CH3)2CHCOOH as product  Correct equation with 2[O] and H2O  3 AO2.5  2 AO2.6 ALLOW any combination of skeletal OR structural OR displayed formula as long as unambiguous If structure of B is a different primary or secondary alcohol, ALLOW ECF for product and equation Total 12OCR (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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