Regional network meetings – spring 2016 OCR GCE Chemistry A (H032/H432)

OCR GCE Chemistry B (Salters) (H033/H433)

Chemistry A (H032/H432) website: http://www.ocr.org.uk/qualifications/as-a-level-gce-chemistry-a-h032-h432-from-2015/ Chemistry B (Salters) (H033/H433) website: http://www.ocr.org.uk/qualifications/as-a-level-gce-chemistry-b-salters-h033-h433-from-2015/ For more information on the OCR Science qualifications: - follow us on twitter: @ocr_science - check out our science webpages: http://www.ocr.org.uk/qualifications/by-subject/science/ - join our community: http://www.ocr.org.uk/community/ - find out about the Practical Endorsement: http://www.ocr.org.uk/positiveaboutpractical

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Level of response questions

Example Level of Response question:

[6]

AS Chemistry A

Specimen Paper 2, q5(c)

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Example student response 1:

Thedehydrationreactionelimanatesthe–OHgroupandaHatomfromthe

adjacentcarbon.Thisformsstructuralisomerswiththedoublebondin

eitherthe1or2position.Thereforebothpent‐1‐eneandpent‐2‐eneare

formed.

Pent‐2‐enealsohastwostereoisomers,acis/Zisomerwiththepriority

groupsonthesamesideofthedoublebondandatrans/Eisomerwiththe

prioritygrouponoppositesidesofthedoublebond.Thisisduetothepi

andsigmabondsfixingthegroupssothereislimitedrotationaboutthe

doublebond.

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Example student response 2:

TheOHgrouponpentan‐2‐olcancombinewithahydrogenononeofthe

carbonsnexttoittoformamoleculeofwater.Anewbondthenforms

betweenthe2carbonstoformanalkenegroup.Thiscanformpent‐1‐ene

orpent‐2‐enedependingonwhethertheOHgroupcombineswiththeHon

carbon1or3.

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Maths skills in chemistry

Example 1

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AS Chemistry A

Specimen Paper 2, q7

Many of the marks in this question are considered ‘Level 2 maths’ because the question involves problem solving, devising the strategy to answer the question and selecting equations to use.

The question explicitly prompts candidates to determine the molar mass. They are given values for a mass, volume of gas, pressure and temperature.

There is no equation that connects molar mass with the data provided, so candidates need to realise 2 things:

Using the data in the question, they can calculate the amount of A using the ideal gas equation.

The molar mass can then be calculated using n = m/M.

As a general principle, if pressure and temperature values are given in the question, this is a strong signal that the ideal gas equation will be required.

The calculation then proceeds as follows:

n =

366314.8

1076110100 63

= 0.0250 mol

Three marks are available for this part of the calculation, in recognition of the range of skills involved:

rearranging the equation

conversion of units

substituting values into the equation

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calculating the value for n.

The next step of the calculation is:

M = 1.15 / 0.0250 = 46.0 g mol–1

There is 1 mark for this step, encompassing both the rearrangement of the equation and the calculation.

The final mark is for determining the most likely identity of the alcohol and drawing the structure. This involves realising that this is ethanol, any many routes could be followed to determine this. As the main skills are more ‘chemical’ than ‘mathematical’, this mark does not contribute to the assessment of mathematical skills on the paper.

Example 2

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AS Chemistry B (Salters)

Specimen Paper 2, q1(f)(i)

This question incorporates mathematical skills, but also assesses the practical skills of experimental design, including an appreciation of aspects of the titration method. It is an AO3 question, as candidates have to interpret and evaluated new information – including a less familiar way of describing a concentration – in order to design a practical procedure.

Being able to start on this question hinges on the appreciation that, in a titration, the concentrations of the two solutions involved should be approximately equal.

This establishes the goal that the final NaOH concentration in the diluted drain cleaner should be about 0.300 mol dm–3.

To know how much of the drain cleaner to dilute, first the concentration of the drain cleaner in mol dm–3 must be calculated.

The question provides the information that 50 g NaOH are dissolved in 100 cm3. From here, candidates can either first convert this to g / dm–3, or work out the amount of substance that 50 g NaOH equates to. Either way, to get to amount from mass, n = m/M needs to be used at some point.

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Using the former route

concentration = 500 g / dm–3

n = 500 / 40.0 = 12.5

concentration = 12.5 mol / dm–3

This is the first mark, incorporating conversion of units, looking up an Mr value and solving an equation.

The next mark is for working out how many times the solution needs to be diluted to create a solution of approximately 0.300 mol dm–3.

12.5 / 0.300 = 41.666666…

To calculate the volume required to dilute in 1000 cm3 then requires

1000 / 41.67 = 24.0 cm3

for the final mark.

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Practical planning skills in chemistry

The previous maths example was also an example of an experimental design question where candidates had to adapt their knowledge of titration procedures to an experiment that they will probably not have carried out themselves.

Other questions may be much closer to actual experience, or focus more on standard procedures, such as the following example. This is still classified as AO3 as it involves evaluating the information provided and deciding how each half-cell should be constructed.

[4]

A Level Chemistry A

Specimen Paper 1, q21(a)(i)

The paper offers space for drawing the setup.

1 mark is available for each half-cell, naming correct solution and electrode.

1 mark is for depicting a complete circuit, including voltmeter, wires and salt bridge.

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1 mark is for mentioning correct standard conditions.

As with the drain cleaner example above, other questions may require candidates to apply their understanding of certain procedures to a particular problem.

[4]

A Level Chemistry B (Salters)

Specimen Paper 2, q1(e)

Candidates would be highly unlikely to have studied this particular reaction. However, they are asked to apply their understanding of rates experiments and the nature of the compounds involved to comment on the practical procedures used here.

Level of response questions - commentary

Example student response 1:

This is a Level 3 response and has been awarded all 6 marks.

The candidate recognises that a hydrogen atom can be eliminated from a carbon

atom on either side of the C–OH group. The candidate then describes how this

elimination leads to formation of two structural isomers, with pent-2-ene having two

stereoisomers.

All three isomers are shown as correct diagrams and are correctly named as cis or

trans.

The candidate shows their understanding of E/Z isomerism in terms of priority

groups and their existence from limited rotation about the double bond.

While there is mis-spelling of a technical term (elimanates), this does not

substantially interfere with the communication of the chemical concept, so award of

the higher mark within the Level is still appropriate.

This is an excellent response that is clear and logically structured throughout.

Example student response 2:

This is a Level 1 response and has been awarded 2 out of 6 marks.

The candidate has described in detail the elimination of water linked to the loss of an

H atom from either side of the C–OH group, leading to the structural isomers pent-1-

ene and pent-2-ene. The structures and names of these isomers are correct.

Although this description shows communication at Level 3, the candidate has not

identified that pent-2-ene would be formed as a mixture of E and Z stereoisomers.

This omission restricts the candidate to Level 1. The answer could therefore be

improved by discussing the formation of and reason for the two stereoisomers

formed by pent-2-ene (see previous commentary).

Spec changes in A Level Chemistry A

This document gives a detailed overview of changes to the letter of the specification. Many of the points detailed below are minor in practice; much of the detail explicitly included in the reformed qualification will already frequently have been taught as a matter of course.

There are some specification statements that are no longer included, but which are not detailed here, as the understanding would still be required to effectively cover the specification content. E.g. where certain facts were required to be ‘stated’, now they are incorporated into explanations of phenomena.

Content from the outgoing specification (H034/H434) which is not in the reformed specification (H032/H432):

1.3.2(d) Thermal decomposition of Group 2 carbonates.

2.1.2(b)(h–j) Hydrocarbons as fuels.

2.1.3(j) Specific uses of alkenes.

2.2.1(b,d) Industrial production and uses of alcohols.

2.2.2(e–g) Uses of CFCs.

2.2.3(d)(ii) Use of mass spectrometry to identify elements.

2.3.2(d)(ii–iv) Specific aspects of catalysts.

Most of topics 2.4.1, Chemistry of the Air and 2.4.2, Green Chemistry.

4.1.1(h) Uses of phenols.

4.1.3(e) Uses of esters.

4.1.3(f–i) Fatty acids.

4.2.1(b,c) Details of amino acid chemistry.

4.2.2(e,h) Uses, and specifics of degradability, of polyesters and polyamides.

4.2.3(c–f) Chiral synthesis.

4.3.1(g,h) GC-MS.

4.3.2(h) MRI

5.2.3(k–p) Hydrogen fuel cells.

5.3.1 Cobalt examples (replaced with chromium and manganese).

5.3.1(m–o) Kstab.

Module 1: A new module that describes the practical skills that will be assessed in the examinations, and (for A Level only) through the Practical Endorsement.

Module 2: 2.1.2(a) Addition of formulae for OH–, Ag+, Zn2+.

2.1.3(a) Addition of term ‘molar gas volume’ (= 24.0 g mol–1) at RTP.

Note: ‘RTP’ does not correspond to defined values for temperature and

pressure. If specific values are given, the ideal gas equation must be used.

2.1.3(e) The ideal gas equation.

2.1.4(a) Addition of formula of ethanoic acid.

2.1.4(b) Qualitative explanation of strong/weak acids (now required at AS)

2.1.4(c) Neutralisation reaction.

2.1.4(e) Non-structured titration calculations (now required at AS).

2.2.2(d) Understanding of covalent bonding in terms of electrostatic

interaction between electrons and nuclei.

2.2.2(i) Interpretation of Pauling electronegativity values.

2.2.2(k) Intermolecular forces terminology. Use:

o Induced dipole–dipole interactions (or London forces)

o Permanent dipole–dipole interaction.

Do not use ‘Van der Waals’ forces to describe specifically induced dipole–

dipole interactions; IUPAC defines the term more generally.

Module 3: 3.1.1(c) Periodic trend in ionisation energy to include small decreases e.g.

between Be and B, and N and O.

3.1.1(e) Graphene.

3.1.2(b) Reactions of Group 2 elements with dilute acids.

3.1.4(a) Testing for presence of CO32–, SO4

2– and NH4+.

3.2.1(d) Addition of terms ‘standard states’ and ‘enthalpy change of

neutralisation’; definition required for the latter (now required at AS).

3.2.2(d) Homogeneous and heterogeneous catalysts.

3.2.3 Equilibrium

o (a) Addition of concentrations of reactants and products not changing

as a characteristic of dynamic equilibrium.

o (c) Explanation of effect of a catalyst on position of equilibrium.

o (f,g) Kc (now required at AS): expressions for Kc, calculation of value of

Kc (not units), other calculations only involving equilibrium

concentrations (not initial concentrations), meaning of magnitude of Kc.

Module 4:

4.1.1(c) Terms alkyl group, aliphatic, alicyclic, aromatic.

4.1.3(c) Cahn–Ingold–Prelog priority rules for naming E/Z isomers.

4.1.3(e) Explanation of reactivity of alkenes.

4.1.3(i) Markownikoff’s rule.

4.1.4(d,e) Azo dyes.

4.3.1(e) Substitution of alcohols with halide ions.

4.2.2(e) Mechanism of ozone breakdown by CFCs.

4.2.3(a) Purification techniques for organic liquids.

4.2.3(b,c) Synthetic routes (now required at AS).

Note: esterification of alcohols is no longer AS content – now in Module 6.

Module 5:

5.1.1(a) Addition of term ‘overall order’.

5.1.1(f) The relationship k = ln 2/t1/2.

5.1.1(k) The Arrhenius equation.

5.1.2 Kp: terms ‘mole fraction’ and ‘partial pressure’, expressions and

calculations as for Kc; practical techniques not required

5.1.3(a) Monobasic, dibasic and tribasic acids.

5.1.3(h) Limitations of approximations to Ka.

5.1.3(j) Formation of buffers from excess of weak acid and a strong alkali.

5.1.3(n) Explanation of indicator colour changes in terms of HA/A– shift.

5.2.2(f) Limitations of using G to predict feasibility, in terms of kinetics.

5.3.1(e) Examples of four-fold coordination.

5.3.1(h) [Cr(NH3)6]3+ from [Cr(H2O)6]

3+.

5.3.1(j) Addition of Mn2+ and Cr3+ and complexation with ammonia.

5.3.1(k) Colour changes in redox reactions.

5.3.2(a) Qualitative tests for transition metal ions.

Module 6:

6.1.1(c) Nomenclature for aromatic compounds.

6.1.1(d) Friedel–Crafts reaction.

6.1.1(i) Reaction of phenol with dilute nitric acid.

6.1.1(k,l) Directing effects in electrophilic substitution of aromatics.

6.1.2(b,c) Nucleophilic addition of carbonyls with HCN.

6.1.3(e,f) Acyl chlorides.

6.2.2(b) Structures of primary and secondary amides.

6.2.4 Carbon–carbon bond formation in synthesis.

6.2.5(a) Purification techniques for organic solids.

6.3.1(b) Use of external calibration curves to determine concentrations in gas

chromatography.

6.3.2(c) Prediction of NMR spectra.

Spec changes in A Level Chemistry B

Content from the outgoing specification (H035/H435) which is not in the reformed specification (H033/H433) The following are no longer specifically included in the specification, which means that recall will not be expected. Note that many of these may still form useful teaching contexts. Application of understanding in unfamiliar contexts will still be required.

EL(h,i,k) Radioactive decay and use of radioactive isotopes.

EL(s) Mendeleev and the periodic table.

EL(t) Time-of-flight mass spectrometers.

DF(k) Specific examples of catalysts and catalysed processes.

DF(m,u–w) Crude oil and fractional distillation, octane number, improvement

of fuels.

ES(l) Successive ionisation enthalpy.

ES(q,r) Risks and uses of fluorine, bromine and iodine.

A(i) Gases of the atmosphere.

A(l,r) Evidence for ozone depletion and ‘hole’.

A(p) Uses of CFCs and alternatives.

A(w,x) Evidence for effect of greenhouse gases; approaches to controlling

CO2 emissions.

PR(c,n,o) Solubility, uses, properties and terminology of polymers.

WM(l,m,o) Drug development.

MR(b,c) Properties of polymers.

TL(r) DNA analysis.

TL(s) Industrial importance of enzymes.

SS(k) Corrosion protection.

SS(l) Recycling of iron and steel.

SS(m) Extraction and purification of metals.

AI(p) Improvements in food production.

CD(g) Use of ionic liquids.

CD(l) Identification of materials in paintings.

O(a) Explanation for certain physical properties of water.

O(o) Environmental aspects of CO2.

Content included in the reformed specification (H033/H433) which was not present in the outgoing specification (H035/H435): Points detailed below are those which are either new to the specification, or have switched between being assessed at AS or A (formerly A2) Level. This document does not give a detailed overview of topics that have moved between storylines.

Module 1: A new module that describes the practical skills that will be assessed in the examinations, and (for A Level only) through the Practical Endorsement.

Elements of life: EL(b) Water of crystallisation.

EL(e) Shapes of s and p orbitals.

EL(k) Effect of lone pairs on bond angles.

EL(o) Names and formulae of Cu2+, Zn2+, Pb2+, Fe2+, Fe3+.

EL(p) Reactions of Group 2 elements with oxygen.

EL(r) Charge density & relation to thermal stability of Group 2 carbonates.

EL(s,t) Solubility of ionic compounds, colours of precipitates, tests for ions,

making salts.

EL(w) c = , flame tests.

Developing fuels: DF(a) Ideal gas equation.

DF(b) and bonds.

DF(c) Note use of dashed wedges rather than dotted lines for bonds into the

paper.

DF(d) Enthalpy change of neutralisation.

DF(l) Terms ‘functional group’ and ‘homologous series’.

DF(m,n) Nomenclature of cycloalkanes; combustion of cycloalkanes and

alkenes.

Note: Entropy is no longer introduced at AS – it is included in the A Level course in Oceans (O). Elements from the sea:

ES(b) Explanation of processes in extracting halogens from the sea (no

recall).

ES(d) Recognition of oxidising and reducing agents (now required at AS).

ES(f) Use of oxidation states to balance redox equations; iodine–thiosulfate

titrations.

ES(k) Solubility of silver halides in ammonia.

ES(l,m) Preparation and properties of hydrogen halides.

ES(n) Use of chlorine in sterilisation of water.

ES(p,q) Kc (now required at AS): expressions, calculations (not using initial

concentrations at this point), meaning of size of Kc, use of Kc to explain effect

of changing concentrations.

Note: Consideration of industrial processes is no longer introduced at AS – it is included in the A Level course in The chemical industry (CI). The ozone story:

OZ(f) The Boltzmann distribution.

OZ(p) Use of ‘half curly arrows’ in radical mechanisms.

Note: The greenhouse effect is no longer introduced at AS – it is included in the A

Level course in Oceans (O).

What’s in a medicine:

WM(a) Phenols, acid anhydrides, esters (now required at AS) – formulae only,

nomenclature at A Level.

WM(c) Properties of phenols (now required at AS).

WM(d) Esterification of alcohols (now required at AS).

WM(e) Recrystallisation and TLC (now required at AS).

WM(g) Principles of green chemistry (now required at AS, no quoting of

principles required).

WM(i) The M+1 peak in mass spectra.

The chemical industry:

CI(c) Graphical methods in kinetics.

CI(d) Arrhenius equation.

CI(h) Kc calculations involving initial concentrations.

CI(j) Tests for nitrate(V) and ammonium.

Polymers and life:

PL(c) RNA.

PL(k) Naming nylon structures.

PL(s) Carbon-13 NMR.

Oceans:

O(c) Dependence of lattice enthalpy and enthalpy change of hydration on

charge density.

O(h) Solubility product.

Developing metals:

DM(j) Recall of structure of ethanedioate.

Colour by design: CD(i) Fehling’s and Tollens’.

Chemical literacy

 

Version 1 1 © OCR 2016

 

Useful information for OCR A Level Chemistry teachers

Contact with the OCR science team

PASS@ocr.org.uk Practical Endorsement queries, comments or ideas for practical activities ocrgce.science@ocr.org.uk – the existing (and continuing) address for general queries twitter @OCR_science OCR Community http://www.ocr.org.uk/community/ see updates from the science team,

collaborate with your colleagues and discuss education and assessments. Available from the open access qualification webpages Chemistry A http://www.ocr.org.uk/qualifications/as-a-level-gce-chemistry-a-h032-h432-from-2015/  Chemistry B http://www.ocr.org.uk/qualifications/as-a-level-gce-chemistry-b-salters-h033-h433-from-2015/ 

Full AS and A Level Specifications Qualification summary brochure Full set of AS and A Level Sample Assessment Materials (SAMs) The Scheme of Work Builder Delivery Guides Topic Exploration Packs and Transition Guides Lesson Elements Candidate exemplars (Level of Response exam questions with commentary) Multiple-choice topic tests Teacher guides to content mapping and planning Qualification factsheet, for use at 6th form open evenings etc. Links to OCR-endorsed textbooks.

Available from Interchange – password protected https://interchange.ocr.org.uk/

A full set of AS practice papers and mark schemes for Chemistry A and Chemistry B Suggested activities for each of the 12 Practical Activity Groups (PAGs) The Practical Endorsement PAG Tracker spreadsheet Chemistry Practical Skills Handbook Chemistry Maths Skills Handbook Practical planning support document.

Other useful OCR webpages http://www.ocr.org.uk/qualifications/by-subject/science/ The science homepage, with links to all our science qualifications, team info, newsletters, videos and more, plus a link to www.ocr.org.uk/positiveaboutpractical with videos and links explaining aspects of the Practical Endorsement. http://www.ocr.org.uk/ocr-for/teachers/ Contains links to useful information including free, termly, teacher networks (to see listings and book yourself in http://www.ocr.org.uk/ocr-for/teachers/teacher-networks/). Training www.cpdhub.ocr.org.uk Upcoming face to face courses and online webinars plus resources from CPD sessions which have previously run. Downloadable ‘Reviewing the external assessment’ presentations reviewing past examination series at question level (for legacy specs, but still largely relevant to new qualifications).