Chemistry > EXAM > OCR-CHEMISTRY A H032/02: Depth in chemistry Mark Scheme for November 2020 (All)

OCR-CHEMISTRY A H032/02: Depth in chemistry Mark Scheme for November 2020

Document Content and Description Below

Oxford Cambridge and RSA Examinations GCE Chemistry A H032/02: Depth in chemistry Advanced Subsidiary GCE Mark Scheme for November 2020Oxford Cambridge and RSA Examinations OCR (Oxford Cambri... dge 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 2020Annotations 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 IgnoreAbbreviations, 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 argumentH032/02 Mark Scheme November 2020 Question Answer Marks AO element Guidance 1 (a) (i) Oxidised AND nickel has lost/donated two electrons  1 2.1 IGNORE reference to oxidation numbers (even if incorrect) (b) (i) FIRST CHECK ANSWER ON THE ANSWER LINE If answer = 43.6 (cm3) award 3 marks n(Ni) = 0.192 58.7 = 3.27… × 10–3 (mol)  n(HCl) = 3.27 × 10–3 × 2 = 6.54… × 10–3 (mol)  Volume HCl = 6.54 × 10–3 0.15 × 1000 = 43.6 (cm3)  3 SF required 3 1.1×1 2.4 ×2 ALLOW 3.27 × 10–3 up to calculator value of 3.270868825 × 10–3 ALLOW 6.54 × 10–3 up to calculator value of 6.541737649 × 10–3 (ii) Volume H2 = 3.27 × 10–3 × 24000 = 78.5 (cm3)  1 2.4 ×1 ALLOW ECF from incorrect n(Ni) from (b)(i) ALLOW 78.48 (cm3) (iii) Volume is the same  Mg is in excess OR Volume of H2 depends on HCl/HCl is limiting reagent  2 3.4 ×2H032/02 Mark Scheme November 2020 7 Question Answer Marks AO element Guidance (c)* 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) The candidate gives a clear description of all three tests with correct observations. AND Equations are mostly correct. AND Some fine detail included in answer. 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) The candidate describes all three tests with correct observations. OR Describes two tests with a few omissions. AND Includes at least one correct equation. 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) The candidate attempts to describe two tests and observations, but explanations are incomplete. OR Gives a thorough description and explanation of one of the tests and attempts one equation. 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 1.2 ×2 2.7 ×2 3.4 ×2 Indicative scientific points Tests for anions Carbonate test: Add HNO3(aq)/HCl(aq)/H2SO4(aq)/H+(aq) fizzing/ forms CO2(g) → Carbonate identified Sulfate test: Add Ba(NO3)2(aq) OR BaCl2(aq) White precipitate → Sulfate identified Bromide test Add AgNO3 (aq) Cream precipitate → Bromide identified Equations (ionic or full) IGNORE state symbols (even if wrong) Carbonate 2H+ + CO3 2– → CO2 + H2O OR 2H+ + NiCO3 → Ni2+ + CO2 + H2O OR 2HNO3 + NiCO3 → Ni(NO3)2 + H2O + CO2 OR 2HCl + NiCO3 → NiCl2+ H2O + CO2 OR H2SO4 + NiCO3→ NiSO4 + H2O + CO2 Sulfate Ba2+ + SO4 2– → BaSO4 OR Ba(NO3)2 + NiSO4 → BaSO4 + Ni(NO3)2 OR BaCl2 + NiSO4 → BaSO4 + NiCl2 Bromide Ag+ + Br– → AgBr OR 2AgNO3 + NiBr2 → 2AgBr + Ni(NO3)2 Fine Detail (NOT inclusive) Sequence of tests on samples Carbonate →Sulfate →Bromide Solubility of AgBr Soluble in concentrated ammonia State symbols in ionic or full equations e,g. • 2H+(aq) + CO3 2–(aq) → CO2(g) + H2O(l) OR 2H+( aq) + NiCO3(s) → Ni2+(aq) + CO2(g) + H2O(l) • Ba2+(aq) + SO4 2– (aq) → BaSO4(s) • Ag+(aq) + Br– (aq) →AgBr(s)H032/02 Mark Scheme November 2020 8 Question Answer Marks AO element Guidance 2 (a) (The enthalpy change) for complete combustion  of 1 mol (of substance)  2 1.1 ×2 ALLOW energy change for combustion in excess oxygen OR reacts in excess oxygen OR reacts completely in oxygen OR energy released during complete combustion OR energy change for combustion in excess air IGNORE energy required ALLOW element OR compound OR reactant DO NOT ALLOW atoms (b) FIRST CHECK ANSWER ON THE ANSWER LINE If answer = – 2680 (kJ mol–1) award 4 marks If answer = (+) 2680 (kJ mol-1) award 3 marks Energy released in J OR kJ = 200 × 4.18 × 20.0 = 16720 (J) OR 16.72 (kJ)  n(C6H12) = 0.525 84 = 0.00625 (mol)  Energy per mole = 16.72 0.00625 OR (–)2675.2 (kJ mol–1) ∆cH = – 2680 (kJ mol–1) Value to 3SF AND ‘–‘ sign  4 3.1 ×2 3.2 ×1 1.2 ×1 ALLOW 16700 J or 16.7 kJ up to calculator value of 16720 J (Must be at least 3 SF) ALLOW ECF from incorrect M(C6H12) or energy change IF energy released above rounded to 16700, Energy per mole = (–)2672 by ECF 3 marks ∆cH = – 2670 to 3SF 4 marks COMMON ERROR -7.02 (kJ mol-1) award 3 marks (c) (i) % uncertainty in temp. rise = 1 20 × 100 = 5%  % uncertainty in volume = 2 200 × 100 = 1% AND temp rise has greater % uncertainty  2 2.8 ×2 Award 1 mark if uncertainties are given as 0.05 AND 0.01 with correct statementH032/02 Mark Scheme November 2020 9 Question Answer Marks AO element Guidance (ii) Any two from: Heat released to the surroundings  Incomplete combustion OR incomplete reaction OR not everything burns  Non-standard conditions  2 3.2 ×2 ALLOW heat loss IGNORE reference to evaporation (iii) Less accurate due to greater heat losses  More accurate due to smaller % uncertainty in temperature change OR mass of fuel burnt  2 3.4 ×2 ALLOW less accurate due to evaporation of water ALLOW error for uncertainty ALLOW for both marks May not change as increase in temperature change OR increase in mass of fuel burned would decrease % uncertainty BUT may be outweighed by increased heat loss to surroundings OWTTEH032/02 Mark Scheme November 2020 10 Question Answer Marks AO element Guidance 3 (a) Ca: metallic bonding OR giant metallic lattice  Br2: simple molecular OR simple covalent  Induced dipole(–dipole) forces/interactions OR London forces  Conductivity linked to mobile electrons In Ca electrons are mobile OR electrons are delocalised OR electrons can move AND in Br2 charge carriers/electrons are not mobile  Melting point linked to bond strengths Metallic bonds are strong AND London forces are weak OR Metallic bonds need a large amount of energy to break AND London forces need little energy to break  5 1.1 ×2 2.1×1 3.2 ×2 ALLOW Metallic structure DO NOT ALLOW reference to molecules or intermolecular forces for calcium ALLOW ‘are molecules’ IGNORE • permanent dipole(–dipole) forces • IDID and LDF • van der Waals DO NOT ALLOW ‘free electrons’ for mobile electrons ALLOW comparison, e.g. • Metallic bonds are stronger than London forces OR • Metallic bonds need more energy to break than London forces  ALLOW intermolecular forces instead of London forces for this markH032/02 Mark Scheme November 2020 11 Question Answer Marks AO element Guidance (b) (i) Ca shown with either 8 or 0 electrons AND Br shown with 8 electrons with 7 crosses and 1 dot (or vice versa)  Correct charges on both ions  2 1.2 ×1 2.5 ×1 ALLOW separate Br– ions, i.e. For first mark, if eight electrons are shown around Ca, the ‘extra’ electrons around Br must match the symbol chosen for the electrons for Na. IGNORE inner shells Circles or brackets not required (ii) Atomic radius Ba has a greater atomic radius than Ca 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  3 1.1 ×1 2.3 ×2 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 BaH032/02 Mark Scheme November 2020 12 Question Answer Marks AO element Guidance (c) (i) Al2Se3 + 6H2O → 2Al(OH)3 + 3H2Se 1 2.6 ×1 (ii) H2O has hydrogen/H-bonds (between molecules)  H2Se has induced dipole(-dipole) interactions OR London forces  H-bonds are stronger (than other intermolecular forces) OR more energy needed to overcome H-bonds  3 1.1 ×2 2.1 ×1 ALLOW permanent dipole-dipole interactions (d) (i) Sodium bromate(V)  1 2.5 ×1 (ii) Br is oxidised AND reduced OR Br oxidation number is increased and decreased  Br is oxidised from 0 to +5  Br is reduced from 0 to –1  3 1.1 ×1 2.2 ×2 ALLOW same element is both oxidised and reduced ALLOW 1 mark if all 3 oxidation numbers are correct (even if oxidation/reduction incorrectly assigned)H032/02 Mark Scheme November 2020 13 Question Answer Marks AO element Guidance 4 (a) Bond angle 112–120º  Explanation Around N, there is a double bond, a single bond and a lone pair  Electron pairs repel  Seen anywhere 3 1.1 ×1 2.1 ×2 ALLOW 3 bonding pairs and 1 lone pair OR 2 bonding region and 1 lone pair ALLOW bonding pairs or lone pairs (b) (i) (Kc =) [NO]2[Cl2] [NOCl]2  1 1.2 ×1 DO NOT ALLOW curved brackets (ii) From equation, n(NO) is 2 × n(Cl2) OR Ratio NO:Cl2 is 2:1 1 3.1 ×1 Response MUST refer to stoichiometry of equation and compare molar ratio of both NO and Cl2 (iii) FIRST CHECK ANSWER ON THE ANSWER LINE If answer = √??. ???? = 1.1 (mol dm–3) award 2 marks [NOCl ]2 = [NO]2[Cl2] Kc OR 0.342 × 0.17 0.015 OR 1.3  [NOCl ] = √1.3 = 1.1 (mol dm–3)  2 2.6 ×2 ALLOW 1.1 up to calculator value of 1.144552314 ALLOW ECF from inverted Kc expression in b(ii) 2.9(478) x 10-4 1 mark 0.017(1691584) 2 marks (iv) As T increases, equilibrium (position) shifts to right AND (forward) reaction is endothermic  Equilibrium concentration of NO increases  2 2.5 ×2 ALLOW ‘favours the right’, for ‘shifts to right’ ALLOW moves to right in endothermic directionH032/02 Mark Scheme November 2020 14 Question Answer Marks AO element Guidance 5 (a) C, E AND F  Three correct alcohols → 2 marks Two correct alcohols → 1 mark 2 1.1 ×1 2.1 ×1 If >2 alcohols are shown lose 1 mark for each incorrect response (b) (CH3CH2CHOHCH3 +) 6O2 → 4CO2 + 5H2O  1 2.6 ×1 DO NOT ALLOW [O] (c) 2-methylbutan-2-ol  1 1.2 ×1 (d) (i) FIRST, CHECK THE ANSWER ON ANSWER LINE IF atom economy = 46.1(%) award 2 marks ---------------------------------------------------------------- Atom economy = Mr of (CH3)2CHCH2CH2OH Mr (CH3)2CHCH2CH2OH + Mr NaBr × 100 OR = 88 190.9× 100  = 46.1(%)  2 1.2 ×1 2.2 ×1 ALLOW Mr (CH3)2CHCH2CH2OH Mr (CH3)2CHCH2CH2Br + Mr NaOH × 100 ALLOW 46% up to calculator value (46.09743321) ALLOW ECF from incorrect Mr valuesH032/02 Mark Scheme November 2020 15 Question Answer Marks AO element Guidance (ii) ANNOTATE ANSWER WITH TICKS AND CROSSES ----------------------------------------------------------------------- Curly arrows 2 marks curly arrow from OH– to C atom of C−Br bond  dipole shown on C–Br bond, Cδ+ and Brδ−, AND curly arrow from C−Br bond to Br atom  IGNORE incorrect R groups for curly arrow marks IGNORE presence of Na+ but OH– needed i.e. Na+OH–can be allowed if criteria met ---------------------------------------------------------------------- Products 1 mark correct organic product AND Br–  IGNORE presence of Na+ but Br– needed i.e. Na+Br–can be allowed BUT NaBr does NOT show Br– NOTE: curly arrows can be straight, snake-like, etc. but NOT double headed or half headed arrows 3 2.5 ×1 1.1 ×1 2.5 ×1 1st curly arrow must • go to the C of C–Br AND • start from, OR be traced back to any point across width of lone pair on O of OH– • OR start from – charge on O of –OH ion (Lone pair NOT needed if curly arrow shown from O–) 2nd curly arrow must start from, OR be traced back to, any part of C–Br bond and go to Br --------------------------------------------------------------------- ALLOW SN1 mechanism for 2 curly arrow marks First mark Dipole shown on C–Br bond, Cδ+ and Brδ−, AND curly arrow from C−Br bond to Br atom  Second mark Curly arrow from OH– AND to correct carbocationH032/02 Mark Scheme November 2020 16 Question Answer Marks AO element Guidance Use curly arrow criteria in guidance above (iii) Nucleophilic substitution  1 1.1 ×1 (e) Rate slower with chloroalkane ORA  C–Cl bond is stronger than C–Br bond OR C–Cl bond has greater bond enthalpy OR more energy needed to break C–Cl bond  2 3.1 ×1 2.5 ×1 IGNORE reference to bond polarityH032/02 Mark Scheme November 2020 17 Question Answer Marks AO element Guidance (f) 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) The candidate gives thorough explanations of both spectra, and correctly identifies X and Y with a correct equation. 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) The candidate attempts all three scientific points but explanations are incomplete. OR Explains two scientific points thoroughly with few omissions. AND Attempts a feasible structure based on deduction from correct Mr. 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) The candidate gives a simple description based on at least two of the main scientific points. OR Gives a thorough description and explanation of one of the scientific points. 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 2.5 ×1 3.1 ×2 3.2 ×3 Indicative scientific points LOOK AT THE SPECTRA for labelled peaks Mass Spectrum • M+ or molecular ion of 86 • m/z = 43 shows CH3CO+ OR C3H7 + IR Spectrum • IR shows no broad absorption at 2500–3300 cm– 1 so no O–H bond AND not a carboxylic acid • IR shows absorption at 1700 cm–1 for C=O bond OR indicates a ketone/aldehyde present Identification and Equation • X must be a secondary alcohol, since refluxing a secondary alcohol with acidified potassium dichromate (VI) forms a ketone OR primary alcohol → carboxylic acid AND tertiary alcohol would not be oxidised. • X is (CH3)2CHCHOHCH3 OR compound E OR 3-methylbutan-2-ol • Y is (CH3)2CHCOCH3 OR 3-methylbutan-2-one Equation (CH3)2CHCHOHCH3 + [O] → (CH3)2CHCOCH3 + H2O OCR (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] www.ocr.org.uk For staff training purposes and as part of our quality assurance programme your call may be recorded or monitore [Show More]

Last updated: 1 year ago

Preview 1 out of 17 pages

Add to cart

Instant download

We Accept:

We Accept
document-preview

Buy this document to get the full access instantly

Instant Download Access after purchase

Add to cart

Instant download

We Accept:

We Accept

Reviews( 0 )

$9.00

Add to cart

We Accept:

We Accept

Instant download

Can't find what you want? Try our AI powered Search

OR

REQUEST DOCUMENT
59
0

Document information


Connected school, study & course


About the document


Uploaded On

Jun 24, 2021

Number of pages

17

Written in

Seller


seller-icon
QuizMaster

Member since 3 years

11 Documents Sold


Additional information

This document has been written for:

Uploaded

Jun 24, 2021

Downloads

 0

Views

 59

Document Keyword Tags

Recommended For You

Get more on EXAM »
What is Browsegrades

In Browsegrades, a student can earn by offering help to other student. Students can help other students with materials by upploading their notes and earn money.

We are here to help

We're available through e-mail, Twitter, Facebook, and live chat.
 FAQ
 Questions? Leave a message!

Follow us on
 Twitter

Copyright © Browsegrades · High quality services·