GCE 2002 June Series Chemistry Examiners' Reportdrbravochemistry.wikispaces.com/file/view/AQA-5421-6421-WRE-JUN… · GCE 2002 June Series ... covers the Advanced Extension Award

GCE 2002

June Series

Report on the Examination

Advanced Subsidiary/Advanced - (5421/6421)

Chemistry

� Advanced Subsidiary

� Advanced

Advanced Extension Award (AEA)

The report on this examination covers the Advanced Extension Award that AQA offers in Chemistry on behalf

of all awarding bodies

Further copies of this Report on the Examination are available from:

Publications Department, Aldon House, 39, Heald Grove, Rusholme, Manchester, M14 4NA

Tel: 0161 953 1170

or

download from the AQA website: www.aqa.org.uk

© Assessment and Qualifications Alliance 2002

COPYRIGHTAQA retains the copyright on all its publications. However, registered centres for AQA are permitted to copymaterial from this booklet for their own internal use, with the following important exception: AQA cannot givepermission to centres to photocopy any material that is acknowledged to a third party even for internal usewithin the centre.

Set and published by the Assessment and Qualifications Alliance.

The Assessment and Qualifications Alliance (AQA) is a company limited by guarantee, registered in England and Wales364473 and a registered Charity 1073334.Registered address Addleshaw Booth & Co., Sovereign House, PO Box 8, Sovereign Street, Leeds LS1 1HQ.AQA was formed by the merger of the Associated Examining Board (AEB)/Southern Examining Group (SEG) and theNorthern Examinations and Assessment Board (NEAB).Kathleen Tattersall, BA MEd Director General

Report on the Examination Advanced Subsidiary/Advanced - Chemistry

�� 3

CONTENTS

AS Units

Page No.

CHM1 Atomic Structure, Bonding and Periodicity ..............................4

CHM2 Foundation Physical and Inorganic Chemistry ........................6

CHM3/W Introduction to Organic Chemistry .............................................9

CHM3/C Internal Assessment ......................................................................12

CHM/P Practical Examination...................................................................16

A2 Units

Page No.

CHM4 Further Physical and Organic Chemistry ................................18

CHM5 Thermodynamics and Further Inorganic Chemistry ............21

CHM6/W Synoptic Assessment.....................................................................25

CHM6/C Internal Assessment ......................................................................26

CHM6/P Practical Examination...................................................................28

Advanced Extension Award

Page No.

Chemistry..........................................................................................29

Mark Ranges and Award of Grades ........................................................................32

Chemistry – Advanced Subsidiary/Advanced Report on the Examination

��4

Chemistry

Unit 1 CHM1 Atomic Structure, Bonding and Periodicity

General Comments

This paper proved to be slightly more difficult than the paper set in June last year.

Question 1

This question was answered well by many candidates and high marks were scored. In part (a) there

was some confusion between 5 decimal places and five significant figures. Candidates also had

difficulty handling powers of ten. Some candidates did not appear to understand part (b); they missed

the point and gave an answer suggesting that ammonia had more atoms. Answers to part (c) were

usually correct but a common error in the application of the formula n = PV/RT was a failure to

convert the pressure of 90.0 kPa into Pascals. Part (d) was answered well but fewer correct answers

to part (e) were seen. In part (e)(i) common mistakes were to use the wrong volume of sulphuric acid

solution and also to omit the factor of two when calculating the number of moles of ammonia from

the moles of sulphuric acid. In part (e) (ii) the Mr of ammonium sulphate was usually correct but

weaker candidates did not recognise that the number of moles of ammonium sulphate was the same as

the number of moles of sulphuric acid calculated in part (e) (i). In part (f) only the best candidates

gave a correct formula for magnesium hydroxide; a very common error was to give the incorrect

formula, MgOH.

Question 2

Most candidates gained high marks for this question. Parts (a) (i) to (iii) were usually correct but a

surprising number of the weaker candidates suggested that N→H represented a hydrogen bond. Full

marks for part (a) (iv) were seldom awarded. Despite the instruction about electron pairs in the

question, some candidates referred to repulsion between hydrogen atoms rather than between electron

pairs. Answers to parts (b) and (c) were of good quality.

Question 3

This question discriminated very effectively between good and weak candidates. Answers given by

the latter were often imprecise, contradictory and incomplete. In part (a) ionic and covalent bonding

were surprisingly frequent incorrect answers. Many answers to part (b)(i) did not display a clear

understanding of the distinction between the covalent intramolecular bonds and the van der Waals’

intermolecular bonding in iodine. In part (b)(ii) the iodine crystal was often described as ionic even

when ionic bonding was not mentioned in the previous part. In part (b)(iii) candidates frequently

suggested incorrectly that covalent bonds between iodine atoms must be broken. In part (c)(i) most

candidates gained one mark for mentioning hydrogen bonds but few drew a comparison between

those bonds and the weaker intermolecular forces in hydrogen chloride. In part (c)(ii) many

candidates did not answer the question. They referred to iodine and chlorine rather than to hydrogen

iodide and hydrogen chloride. Marks were lost frequently in part (d) because sodium chloride

molecules were mentioned, particularly in part (d)(ii). In part (e), despite reference in the question to

structure and bonding many candidates did not mention the macromolecular structure of graphite.


�� 5

Question 4

Group II chemistry continues to cause problems for candidates in CHM1 examinations. This question

was not answered well. The trends in parts (a) and (b) were generally known but the explanation for

the trend in melting points down Group II was rarely correct. The trend in part (c) was usually correct

but the equations were most often incorrect. Hydrogen was often omitted and an incorrect formula,

MgOH or Mg(OH)2, for the magnesium containing product was a common error. A correct answer to

part (e) was rarely seen. Candidates usually made no attempt or suggested incorrectly that the identity

of element M was barium. In part (f) most candidates scored only one mark for stating that beryllium

chloride is covalent. An explanation for the covalency was not usually attempted.

Question 5

Most candidates scored high marks for part (a) though the final part of the question, requiring an

explanation why isotopes have identical chemical properties, was more demanding. Part (b) was also

answered well though a considerable number of candidates wasted time by giving detailed but

irrelevant information about the operation of the various parts of a mass spectrometer. Candidates

were often imprecise about the information that can be obtained from a mass spectrum. Confusion

between mass/charge and atomic mass or relative atomic mass was common but did not incur a heavy

penalty.

Question 6

Marks awarded for this question were not as high as for question 5. There was some evidence that

candidates were short of time, particularly those who wrote irrelevant information about the operation

of the mass spectrometer in question 5. In part (a) the example of a p-block element and its electronic

configuration were more often correct than was an explanation of why elements are classified as

p-block. The meaning of the term periodicity was not understood well in part (b). Many candidates

considered that periodicity referred to trends down a Group. The remainder of part (b) discriminated

effectively between good and weak candidates. The latter sometimes stated trends in the wrong

direction and gave only partial explanations.


��6

Unit 2 CHM2 Foundation Physical and Inorganic Chemistry

General Comments

This examination proved to discriminate well. It contained some questions which required little more

than simple recall whilst others tested the ability of candidates to apply their knowledge and

understanding. Question 5, which required knowledge and understanding of the Maxwell-Boltzmann

curve, was well answered by almost all candidates. By contrast, question 8, which included a section

on the extraction and purification of iron, was not well answered even though most candidates would

have studied these processes as part of their GCSE course.

Question 1

The meaning of the term enthalpy change, required in part (a), was not well stated and whilst many

correctly referred to the heat energy change, most failed to state that this was measured at constant

pressure. Part (b) was well answered with many correct definitions of the term standard enthalpy of

formation of a compound though slightly fewer candidates gave a correct equation with state symbols

in section (ii). Hess’s Law was correctly stated by many candidates and it is particularly pleasing to

report that the calculation required in part (d) was very well done.

Question 2

It was disappointing to find many wrong equations for the reaction between silver nitrate and zinc in

part (a) especially as the use of silver nitrate solution to distinguish between halides ions forms part of

this module and the formula of zinc nitrate was given.

Parts (b) and (c) were well answered and, as part (d) was marked consequentially to answers given in

parts (a), (b) and (c), most candidates were also able to score full marks in part (d). Almost all

candidates stated correctly in part (e) that loss of heat energy was the reason why the experimental

value obtained was less than the correct value.

Question 3

In part (a) most candidates gave the correct oxidation state of sulphur in H2S and many also state that

Nal, or NaAt, would reduce concentrated sulphuric acid to H2S. Many also stated that its presence

can be recognised by a smell of bad eggs. Credit was also given to the few very good candidates who

gave alternative correct methods of recognising this gas using either an acidified solution of

potassium dichromate or a solution containing lead(II) ions.

Part (b) was not well done and and there were many speculative answers given in each section of this

question. Only the best candidates identified X in section (i) correctly as either HF or HCI. Sadly

some of these candidates then lost a mark when they gave an incorrect role to sulphuric acid in section

(iii). Candidates who stated incorrectly that X was HBr, HI or HAt were able to score one mark in

section (iii) if they stated the correct role of sulphuric acid in its formation.

Question 4

Sadly, candidates still confuse halogen molecules, halogen atoms and halide ions even though their

properties are very different. Candidates who gave incorrect species or made contradictory statements

were penalised. In part (a) only the very best candidates identified nitric acid as the reagent which

prevents interference by carbonate ions when silver nitrate is used to test for the presence of chloride

ions in aqueous solution. Sadly not even all of these were able to write an equation for the reaction of


�� 7

this acid with sodium carbonate. There were rather more correct answers given to parts (b) and (c)

but weak candidates found this question difficult.

Question 5

This question was well answered by most candidates. Candidates who lost marks usually made errors

in part (a). These errors included incorrect labelling of the axes of the Maxwell-Boltzmann curve

with temperature being the most common incorrect answer. The reason why this curve starts at the

origin also proved difficult and there were some incorrect answer to section (iii). Many candidates

scored full marks in part (b).

Question 6

Most candidates knew that a reducing agent accepts electrons in a redox reaction and that the

oxidation state of an uncombined element is zero. Many candidates also deduced correctly the

oxidation state of nitrogen in each of the three compounds given in part (c). The half-equations

required in part (d) proved rather more difficult and many candidates gave unbalanced equations,

often with electron transfer shown incorrectly. It was surprising to find that some candidates, who

had two correct half-equations, deduced an incorrect overall equation for the reaction.

Question 7

Almost all candidates knew why chlorine is added to drinking water. The equation for the reaction

which occurs when chlorine is bubbled into water proved much more difficult and there were many

incorrect answers. Although it was not essential for candidates to show this reaction as reversible,

candidates were required to recognise that the presence of chlorine imparts a green colour to the

solution; few did. In part (c) candidates were required to write an equation for the reaction of chlorine

with an excess of cold aqueous sodium hydroxide. Again this proved difficult with acids commonly

incorrectly shown as reaction products. Part (d) was, as expected, demanding. It is therefore pleasing

to report that a significant number of candidates were able to give a correct equation for the reaction

between iodine and sodium thiosulphate. Some of those who gave a correct equation for this reaction

had given an incorrect equation for the reaction between chlorine and potassium iodide. Candidates

who gave correct equations were often able to complete the calculation in section (iii) successfully.

Marks were often lost in this calculation by candidates who multiplied the number of moles of

chlorine by the relative atomic mass rather than the relative molecular mass of chlorine.

Question 8

Most candidates knew that coke and limestone are raw materials needed for the extraction of iron

from an iron oxide ore in a blast furnace but many failed to state that air is also necessary. Marks

were lost by candidates who failed to state that carbon, or carbon monoxide, act as a reducing agent in

the extraction process and by those who omitted to state that the reaction between carbon and oxygen

was exothermic. The role of limestone in the formation of slag was well known. The use of

magnesium to remove sulphur from impure iron was quite well known, as was the use of oxygen to

remove carbon but many lost a mark when they failed to state that the oxygen is blown through the

molten iron. The use of lime or limestone to remove the oxides of phosphorus, formed by a reaction

with oxygen, was not well known. Only the best candidates knew that sulphur is removed before

carbon and phosphorus because iron is oxidised in preference to sulphur. In this examination,

examiners allowed answers based on the formation of sulphur dioxide and either its toxicity or the

formation of acid rain in the atmosphere. Part (c) was generally well answered. Most candidates

were able to state a social benefit of recycling iron and knew that it could be separated from other

scrap using a magnet. Although most candidates were able to give one major factor in the cost of

recycling aluminium cans, rather less linked the much lower cost of recycling aluminium to the very

large amount of electrical energy necessary for its extraction from aluminium oxide.


��8

Question 9

This question was well answered. Many candidates in part (a) used Le Chatelier’s principle to predict

correctly the effect of increasing temperature and increasing pressure on the yield of hydrogen in the

given equilibrium reaction. Candidates who made the wrong prediction were able to score one mark

for each change if they stated correctly that the reaction was endothermic and that there was a

reduction in the number of moles of gas in the reaction as written. Part (b) was also well answered

but some candidates did not differentiate clearly between the equilibrium yield of hydrogen and the

amount of hydrogen produced in a given time.


�� 9

Unit 3(a) CHM3/W Introduction to Organic Chemistry

General Comments

The standard of much of the work seen by the examiners was good and high scores were not

uncommon, indicating that many candidates had, as last year, been well prepared for the examination.

There were, however, a significant number of poor scripts, suggesting that for these candidates

insufficient preparation had been made. The vast majority of candidates attempted all the questions,

however, there was some evidence that a small minority of candidates ran into time problems. In

questions that required a single response, for example the identity of alcohol D in question 3(d),

which could be either the name or the formula, or the requirement to quote a use for each product in

question 5, some candidates offered multiple answers. In such instances, an incorrect response would

cancel the mark earned for a correct response. It is strongly recommended that centres instruct their

candidates to adhere to the rubric of a question and only offer one response when a single response is

required. When answering questions which required a reaction mechanism to be “outlined”, very few

candidates this year chose to employ written prose rather than using a chemical equation with curly

arrows. This is a pleasing improvement on last year. There were still problems, however, associated

with the incorrect use of curly arrows. When showing the movement of an electron pair by the use of

a curly arrow, it is vital that the arrow is shown to start where the electron pair is found, either a bond

or a lone pair. It must also be drawn to the correct point to establish a new bond or onto an atom to

show the formation of an anion. Hydrogen atoms were omitted from some structures; in others, bonds

were shown between inappropriate atoms, for example, OH-CH2CH3, and C=OH for the aldehyde

functional group. There was still some use of correction fluid and a number of candidates wrote in

colours other than those specified on the front page. In particular candidates should be instructed not

to use red ink, as this conflicts with the colour used by the examiner.

Question 1

Many candidates were able to show some knowledge of the process of fractional distillation, however,

incomplete or confused answers were quite common. On the whole, part (a) was not well done.

Descriptions in which crude oil is heated and evaporated within the fractionating tower, with different

fractions being removed in sequence, were quite common. Many candidates misread the question and

wasted time explaining the variation in boiling point of different fractions, rather than concentrating

on the details of the process. Part (b) was fairly well answered but many candidates overlooked the

need to ‘use the data’ in their responses in order to identify shortfalls in supply which are met by

catalytic cracking. In part (b)(ii), some candidates quoted specific fractions, rather than identifying

different ‘types of product obtained by fractional distillation’ as required by the question. ‘Alkenes’

and ‘hydrogen’ were quite common errors. Part (c) was well done by many candidates but a

significant minority of attempts were poor. Radical mechanisms, the use of Al2O3 as catalyst and high

pressures, such as 7000kPa, were frequently seen. Some candidates offered no response.

Question 2

Parts (a)(i) and (ii) were generally well answered, although equations in (i) showing the reaction of

chlorine with substances such as methane, and equations in (ii) which contained such species as Cl·,

HCl·, Cl2· and H2, were not uncommon. There were rather more errors in (a)(iii), where equations

showing the mono-chlorination of methane, or which contained such species as CH2Cl3, CH2Cl· and

CH2Cl2· were quite common. It was not uncommon to see an equation for a termination step offered

as the second propagation step. Almost all candidates predicted an increase in rate in (a)(iv),

however, the explanations offered frequently lacked precision. Many vague references were seen to

increased numbers of radicals, radicals being formed faster, there being more kinetic energy available

or that the activation energy being altered by the more intense light. The better candidates correctly


��10

attributed the change in rate to an increased rate of production/concentration of chlorine radicals. The

equation in (b)(i) was usually correct, although balancing the equation was a problem for some

candidates. Carbon monoxide was usually correctly identified in (b)(ii) but once again, balancing the

equation proved to be beyond some candidates, while others used C2H6 or C15H32 in their equations.

This question discriminated quite well; full or high marks were quite often awarded, however, low

marks were not uncommon.

Question 3

Contrary to expectations, very few candidates were able to identify the planar carbon atoms in

2-methylbut-1-ene. The most common errors were to select the unsaturated carbon atoms alone or the

unsaturated carbons together with those in the ethyl group. In the mechanism, the curly arrow from

the double bond to the hydrogen atom was generally accurately drawn. To earn the mark for cleavage

of the H-O bond, candidates were required to draw a curly arrow from a clearly shown H-O bond to

the oxygen atom. However, the structure of the sulphuric acid molecule was frequently incorrectly

drawn, often showing the hydrogen bonded to the sulphur atom or showing the remainder of the

molecule as –SO4H, rendering this mark unavailable. The intermediate carbocation was often clearly

shown but the charge was sometimes omitted, shown as δ+ or positioned on the C1 carbon atom.

Weaker candidates frequently omitted the intermediate and so only the first two marks were available

to them. In part (c), many candidates suggested dilute sulphuric acid as a reagent for the reaction. As

the addition of water to the reaction mixture containing B would produce a dilute solution of sulphuric

acid, this answer was accepted. The use of concentrated sulphuric acid, or other mineral acids, was

not accepted. The requirement for the reaction mixture to be heated was quite well known, but some

candidates suggested unrealistically high temperatures for the reaction. Many candidates gave the

correct names of compounds C and D. The most common error in nomenclature was to name C as

2-methylbut-2-ol. Where this error was repeated in later compounds, an allowance was made. Better

candidates gave a clear explanation for the formation of compound C as the major product, but many

attempts were incomplete, in that they referred simply to a more stable carbocation, or incorrectly

identified one of the intermediates as a secondary carbocation. Incorrect explanations, in terms of the

relative stabilities of primary and tertiary halogenoalkanes, were also quite common.

Question 4

Part (a) was well answered and the majority of candidates correctly identified the type of alcohol in

(b)(i). Only a minority of candidates, however, were able to explain the resistance of the tertiary

alcohol to oxidation. Most attempts offered little more than a statement that tertiary alcohols are more

stable. References to the ‘carbonyl carbon’ were quite common. Valid arguments, based on the

absence of a hydrogen atom on the central carbon, were offered by some candidates. The structures in

(b)(ii) were frequently correct but duplicate structures showing a different orientation of a molecule

were not uncommon. Many candidates lost marks here due to incorrectly drawn bonds; the most

common error being to show a bond between a carbon atom and the hydrogen atom of the alcohol

group. In part (c)(i), ‘aldehyde’ was frequently correctly given as the type of product but it was not

unusual for a specific aldehyde, or other compound, to be quoted. Some candidates gave the correct

response of ‘aldehyde’, but then lost the mark by quoting, for example, propanal or pentanal. Many

candidates earned one mark for giving the structure of butanal in (c)(ii) but omitted to include [O] or

H2O in their equation and so lost the equation balancing mark. Equations showing a carboxylic acid

as the product were seen by some examiners. Part (c)(iii) was not well done. Although correct

answers were seen, common errors included quoting copper based products, suggesting ‘carboxylic

acid’ as the name or naming compounds that were not acids, for example, butanal. Some candidates

offered no response to this question. In part (d), an acceptable advantage was frequently seen but the

disadvantages were less precisely expressed, and the suggestion that ethene, rather than crude oil, was

a non-renewable resource was quite common. Part (e) was well done by the better candidates but it

was not uncommon to see a mechanism for the hydration of ethene into ethanol. Often, the


�� 11

dehydration step was omitted, as were the charges and the lone pair on the oxygen; also, incorrect

positioning of curly arrows was common.

Question 5

The level of knowledge shown by candidates in this question varied considerably. The reagent,

catalyst and hazards associated with the process were quite well known. In some instances, ethene

was quoted as the reagent, and a variety of inappropriate catalysts, such as nickel, platinum and

concentrated sulphuric acid, were seen. ‘Flammable’ and ‘explosive’ were considered to be examples

of one type of hazard and so earned a single mark. The second hazard mark was awarded for a

reference to the toxic nature of epoxyethane. Vague references to hazards, such as ‘harmful’ or

‘causes blisters’, earned no credit. There were many correct equations for the reaction of epoxyethane

with water, most candidates choosing to show the full ring structure of epoxyethane. It was not

uncommon, however, for the ring to carry a double bond, or to show CH3 groups. In the equation,

CH2CH2O was not accepted as an appropriate representation of epoxyethane. Again, poorly drawn

bonds between carbon and the OH group, where the bond clearly linked carbon and hydrogen atoms,

were quite common and resulted in the equation mark being withheld, unless a similar error had been

penalised earlier in the paper. The use of ethane-1,2-diol as an antifreeze was well known and widely

quoted. The use of ethane-1, 2-diol in the manufacture of polyesters also earned this mark but some

candidates suggested that ethane-1, 2-diol was Terylene and so earned no credit. The reaction with

ethanol was much less well done. Many candidates ignored the reference to excess epoxyethane in

the question and wrote equations showing a 1:1 mole ratio. Correct equations, showing the polymeric

product, were quite rare. In quoting an appropriate use for the product of this reaction, such

suggestions as brake fluids or plasticisers were often seen but the mark was frequently lost when a

candidate quoted an incorrect use, such as ‘solvent’, for the polymeric product.

Question 6

This question was often, but not universally, well done. The reaction types in part (a) were quite well

known, although it was quite common for the first type to be described as ‘nucleophilic substitution’.

Some candidates having quoted this as the type then went on to give the role of potassium hydroxide

as, for example, ‘oxidising agent’. ‘Nucleophilic substitution’ earned the mark for the type of

reaction but did not earn the mark for the role of potassium hydroxide. This mark was earned only by

a specific reference to the role being that of a nucleophile. Many candidates recognised the formation

of an alkene as being an elimination reaction but the role of potassium hydroxide as a base was less

well known. Most candidates correctly deduced the name and structure of the product in part (b).

Some candidates wasted time here by drawing the mechanism for the substitution reaction. The

polarity of the C-Br bond was frequently shown or described but the attraction of the partial positive

charge on the carbon atom for the hydroxide ion was less often seen. Better candidates described the

attack of a lone pair from the hydroxide ion on the δ+ carbon. Part (c) was well done by many

candidates and high scores were common. The mechanism was generally well known and clear

explanations for the formation of two structurally isomeric products were quite common. Successful

candidates either tackled the explanation by showing an alternative mechanism or by identifying the

possibility of proton removal at C1 or at C

3. Appropriate structures showing the cis/trans isomers of

but-2-ene were very common. Errors in the position and direction of curly arrows were quite

common and in some instances, the charge was omitted from the hydroxide ion. Some candidates,

mainly those who outlined an E1 mechanism, incorrectly explained the formation of structural

isomers in terms of the formation of different carbocations. Also, it was not unusual to see a

mechanism in which butan-2-ol was formed which then underwent dehydration.


��12

Unit 3(b) CHM3/C Internal Assessment

General Comments

Centres should once again be congratulated for their efforts in ensuring that the moderation scheme

ran smoothly and successfully. The standard of marking and the application of the appropriate criteria

were usually very good, and as a result relatively few adjustments were necessary during the

moderation process. The presentation and annotation of candidates' work was often of an excellent

standard. The really good work done by most centres in this regard is greatly appreciated by

moderators.

Judging by the number of centres using the exercises, the exemplar material issue 1 provided by AQA

continues to be popular. Centres are reminded that some updating of these exercises has taken place.

The marks awarded covered a similar range to those awarded in June 2001. Candidates continued to

have difficulties in Skill 4.

A small but significant number of centres have yet to come to terms with the new scheme. With the

aim of improving the internal assessment in these centres the following points are once again brought

to the attention of teachers:

• Many centres use their own exercises for assessment with great success. Problems sometimes

occur when the demand level of the exercise is inappropriate, or the centre does not provide the

candidate with enough information in the student instruction sheet to allow them to fulfil the

criteria for full marks. Any centre planning to produce their own practical exercise or modify an

existing exercise is strongly advised to submit a copy to their coursework adviser before using the

exercise.

• Major problems have sometimes arisen when centres have modified the exemplar marking

schemes. The modifications usually reduce the demand level of the exercise by removing some

of the more difficult scoring points without replacing them with appropriate alternatives. This

inevitably reduces the maximum mark available. Any centre planning to modify an exemplar

exercise is strongly advised to submit a copy to their coursework adviser before using the

exercise.

• A number of centres still use an Sc1 approach despite frequent warnings of its unsuitability.

Centres are again reminded that an Sc1 style exercise does not meet the current criteria. When an

exercise is used to assess several skills, the candidate must write a complete plan before the

practical work begins. Scale cannot be justified by trial experiments. Where appropriate, the

candidate may use hypothetical results, but the candidate must not use their own experimental

results in the plan. The section for each of the four skills must be submitted as a distinctly

separate item. An Sc1 exercise is almost certain to receive a significant mark reduction.

• Exercises may be marked according to the criteria as long as an appropriate commentary is

provided for each mark awarded, with the focus on the way in which the candidate's work

matches the criteria. Comments justifying the award of the mark for each skill must be provided

for the moderator.


�� 13

• Evidence suggests that a few centres carry out assessments without proper supervision.

Candidates with access to a very wide range of information sources may receive too much

guidance, limiting the maximum mark available. 2004 candidates will not be permitted to use

laboratory notebooks in practical assessments. If an exercise is not carried out under direct

supervision, the candidates' work should be annotated accordingly.

• Care should be taken with the use of ICT. Candidates should avoid downloading irrelevant

information from the internet or CD ROMs. Use of spreadsheets without any thought to the

precision of recording should also be avoided. If ICT is used by candidates to calculate

quantitative results, there needs to be clear evidence that the candidate can calculate the outcome

independently and can arrive at a judgement of the errors.

• Once again a small number of candidates failed to fulfil the minimum requirement of submitting

work taken from at least two modules, and suffered impoverished marks as a result. Centres are

reminded that the work submitted must cover at least two modules, thus the candidate's marks

which count towards the total cannot be taken from just one module. If, for example, a candidate

submits one mark per skill only, and all of the work is drawn from CHM1, the candidate will lose

the lowest of the four marks.

• Some centres continue to submit work which was more appropriate to the A2 assessment e.g. a

potassium manganate(VII) titration for CHM1 and The Enthalpy Change of Decomposition of

Sodium hydrogencarbonate exercise from the Exemplar booklet for CHM2. The use of these

exercises was not penalised but centres are reminded that work used in the AS assessment cannot

be re-submitted for assessment at A2.

• The standard of the annotation of scripts was very variable. Some centres provided detailed tick

lists for all the skills with little marking on the scripts; other centres provided annotated ticks on

scripts. Both methods are acceptable and greatly assist the moderation process. A minority of

centres provided little or no indication of where candidates had scored marks, this is unacceptable.

A summation at the end, showing the marks obtained for each of the specific criteria and how

these were then used to obtain the overall mark for a particular skill is very useful. This process

highlights those situations when marking rigorously according to the detailed mark scheme

undervalues the overall standard of a piece of work.

• A number of centres gave a zero score when the candidate had in fact made a little progress.

Centres are reminded that for any skill a score of 0 should only be awarded when a candidate

submits no useful work at all. If the candidate gains a few of the scoring points 1 mark must be

awarded.

• Centres are very strongly urged to attend the Teachers’ meetings which include coursework

standardising that will be held in the Autumn term. It is essential that centres are well informed

about moderation procedures and any changes that need to be made in the light of experience.

Skill 1 Planning

The standard of work seen was high. The sections on scale and use of results continue to be the most

demanding, with only the better candidates scoring highly in these areas. Centres are reminded that

they must not reduce the demand in these difficult areas if the candidate is to have access to the

highest marks. In particular :

• The planning exercise on pages 22-25 of the AQA Teachers' Guide illustrates the type of exercise

which is appropriate for a practical examination. The section on justification of scale is

undemanding for internal assessment and limits the maximum mark to 7.


��14

• A few centres continue to submit Exercise 6, The Identification of Alcohols, from the 1996

NEAB Exemplar booklet as a planning assessment. The demand level of this exercise under the

old scheme was only maintained by the inclusion of spectral analysis. As this is not feasible

under the new scheme the exercise is insufficiently demanding at AS level and is worth a

maximum of 5 marks. Centres are strongly advised not to use this exercise in the future.

• An acid-base titration where candidates are given reagent solutions and hence have limited

opportunity to justify scale.

Safety considerations were not always specific to the exercise in question. To earn the safety mark

candidates must consider the dangers posed by the reagents and products in the experiment, and

suggest appropriate precautions. Simply giving a list of standard precautions does not merit the

awarding of the safety mark.

Skill 2 Implementing

In general the standard of work seen varied widely; although most candidates scored some marks,

only the most accurate scored highly. Most centres used tick lists well and placed a suitable emphasis

on accuracy.

Once again a few centres submitted exercises where the manipulative skills required were limited :

• The hydrolysis of haloalkanes.

• The reaction of halides with silver nitrate or concentrated sulphuric acid.

• The percentage water in a hydrated salt.

Using this type of exercise limits the maximum available mark quite severely.

Centres are reminded that to achieve 8 marks it is essential that :-

• the candidate provides some written evidence of recording. In volumetric work the results must

be presented clearly and in full in the candidate's own table, and burette readings are recorded to

two decimal places. In an organic preparation masses and melting points must be presented

clearly and in full in the candidate's own table.

• the candidate's results are accurate, judged against a suitable target value. Centres must submit a

target value for accuracy clearly written on the tick list. Centres should not rely on literature

values but should use a teacher value or a class average. When the number of candidates is small

a teacher value is strongly advised.

A small number of centres insist on using inappropriate summative tick lists to arrive at the overall

skill assessment mark, treating the small number of points for accuracy as equivalent to the much

greater number of manipulative and recording points. When a simple scaling of the points scored to

marks is applied, failure to achieve an accurate result is often offset by the weight of manipulative and

recording points. To award high marks for an inaccurate result is completely unacceptable, and a

mark adjustment is inevitable. The maximum mark if accuracy is poor is 5.

Skill 3 Analysing

As expected the exercises seen were usually calculations of a titration experiment or an energetics

experiment involving graphs and calculations. These were usually well presented and error analysis

was covered very well. The only mark that was often missed was the precision mark. A few centres

attempted to analyse the results of observation or preparation exercises. The attempts were largely

unsuccessful as the depth of material available for analysis was too limited to compensate for the


�� 15

absence of precision and error analysis. Centres are strongly advised to used quantitative work for

this skill at AS level.

Skill 4 Evaluating

Evaluation was again the weakest area in terms of the level achieved in the student scripts and the

marking of the work. Centres often used an open-ended exercise and candidates answered in general

terms, making no specific reference to the data available. Candidates consequently struggled to score

high marks, mainly because they did not know what was expected rather than because of any lack of

ability. Structured exercises based upon a common set of data tended to be more candidate friendly,

and easier to mark accurately and consistently.

Centres are reminded that candidates must be encouraged to:

• Discuss the actual results objectively and comment on the quality of the results.

• Calculate a percentage error based on their final result and a given value, then compare this error

to the overall apparatus error calculated in the Analysing section.

• Identify the major weaknesses and areas for improvement in the experiment and suggest ways of

improving the accuracy. Candidates should be discouraged from writing an exhaustive list of all

possible sources of error, many of which are trivial or do not apply to the experiment in question.

The evaluation section of all of the exemplar exercises have been re-written and were distributed at

the Standardising meetings for practical work in Autumn 2001. Candidates found the new versions

much more accessible and centres are strongly advised to use them.

Administration

One or two centres submitted work several weeks after the deadline without any notification to the

moderator of the late submission. This is clearly unacceptable. Centres must make every effort to

comply with the deadlines. If circumstances make this impossible, they must advise the moderator

without delay.

Some centres submit all of the candidate's work rather than only those pieces which count towards the

final total. Where this is the case, centres must indicate clearly which pieces of work are to count, as

moderators can waste a good deal of time putting the sample in order. In future, to avoid the obvious

danger of mistakes being made, moderators will be instructed to send poorly prepared samples back to

the centre for sorting.

Notwithstanding this rather daunting list of comments, once again this was a very positive and

encouraging session for the new scheme. Centres are warmly commended for their efforts,

which are much appreciated by the moderator team.


��16

Unit 3(b) CHM3/P Practical Examination

General Comments

This examination discriminated effectively between able and less able candidates. Many good scripts

were seen, with a good number of high marks. Candidates found this year's paper more accessible

than Summer 2001 ( largely due to the Planning exercise ) and marks tended to be rather higher.

Exercise 1: Skill 2 Implementing

This was one of the easier exercises on the paper. Many candidates scored high marks, with a

significant number scoring full marks. The great majority of candidates scored the marks for

manipulative skills, completing the table and concordancy of titre values used in calculating the mean.

Most candidates also scored the mark awarded for precision of recording. As expected, the accuracy

of the candidates' results varied widely, but the majority of candidates scored at least one of the

marks.

Exercise 2: Skill 3 Analysing and Skill 4 Evaluating

This exercise differentiated markedly between able and less able candidates. The weakest candidates

failed to give correct answers to all but the simplest sections.

In the Analysing section the great majority of candidates scored marks for the reaction equation in

part 1 and the estimation of errors in part 6. A significant minority of candidates averaged all of the

titre values, rather than the concordant values, in part 2. Most candidates completed the calculations

successfully in parts 3 and 4, but a surprisingly large number of candidates could not calculate the

number of molecules of water of crystallisation in part 5. Weaker candidates scored no marks for the

calculation sections.

A significant number of better candidates failed to record results with appropriate precision. A

similar number of candidates failed to score the mark for nomenclature and terminology. Candidates

should be reminded that they are expected to explain calculations, including the calculation of the

average titre and the percentage errors in full, lay their work out logically and clearly, and use the

appropriate terminology correctly.

The Evaluating section of Exercise 2 proved once again to be the most difficult part of the paper.

Many candidates again answered in general terms, making no specific reference to the data available.

Only the most able candidates scored both marks when commenting on the consistency of the results

in part 1. Most candidates appreciated that the results were acceptably consistent, but few could

discuss the actual results objectively. Once again a surprisingly large number of candidates could not

calculate the percentage error in the experiment in part 2, while only the most able candidates could

relate this value to the apparatus error in part 3. Candidates did better in suggesting improvements to

the chemist's method of weighing out the sodium carbonate in part 4, although many tended to repeat

their first improvement rather than suggest two different improvements.

Exercise 3: Skill 1 Planning

This exercise was answered well by the majority of candidates who appeared familiar with the

required experiment. Few candidates ignored the information in the stem of the question and

described unworkable experiments involving a titration. However a surprising number of candidates

attempted to make a solution of zinc for the enthalpy change experiment, or attempted to measure the

initial temperature of the zinc rather than the copper(II) sulphate solution. The great majority of


�� 17

candidates scored the safety and apparatus points. However once again a disappointingly large

number of candidates could not justify their chosen scale, providing only trivial reasons for their

choice. Most candidates appreciated the basic method required, and could provide the necessary

detail. In the treatment of results, most candidates successfully plotted a cooling curve, described the

extrapolation of the graph and used the mc∆Τ formula. However many candidates could not clearly

describe how the experimental enthalpy change could be converted to a molar enthalpy change.


��18

Unit 4 CHM4 Further Physical and Organic Chemistry

General Comments

This was the first June paper on this unit and therefore the first A2 examination for many candidates.

After AS, some of the candidates found the questions difficult and there was some evidence that a few

candidates were short of time to finish the paper.

Question 1

This question on rate equations was answered well by most candidates even those who scored less

well elsewhere in the paper. In part (a) most candidates deduced the overall order correctly, but to

deduce that the order with respect to iodine was zero proved more difficult. Part (b) was well

answered by most students, but only the better candidates were able to gain both marks in part (c).

Many gave a general description of the role of a catalyst rather than the evidence that hydrogen ions

appear in the rate equation but not in the overall stoichiometric equation. The use of pH to show a

change of hydrogen ion concentration was understood by most candidates although some were unable

to convert a pH value into a hydrogen ion concentration. Full marks were available for correct use in

part (d) of an incorrect rate constant calculated in part (b).

Question 2

In part (a), naming the compound as butanedioic acid was found more difficult than expected, but

most candidates were able to write the correct expression for the equilibrium constant Kc. In part (c)

the number of moles of X was nearly always given correctly, those of water were usually correct, but

only the better candidates deduced the number of moles of methanol correctly. However, full marks

were available consequentially in the calculation in part (e) for use of the same values as stated in part

(c) in the same expression written in part (b). The units were frequently given correctly. Answers to

part (e) were often not expressed clearly. The reason that the volume is not required is that the

number of moles is the same on both sides of the equation, so the volume cancels in the expression for

Kc.

Question 3

Despite the fact that the first half of this question was similar to Question 5(a) in the Specimen paper

and that the answer to part (a) is given word for word in the final paragraph of section 13.6.5 in the

specification, only the better candidates scored highly in this question. In part (c) the type of

mechanism electrophilic substitution was required, not just the name “Friedel-Crafts” nor the more

general name “acylation”. The mechanism itself was known well by many candidates, although some

were careless where they drew the positive sign and the residual delocalisation in the intermediate

structure. Part (d) was found to be the most difficult part of the question and only the better

candidates could draw the correct structure for the product. On the other hand, most were able to

name addition polymerisation correctly and to draw the repeating unit of polystyrene.

Question 4

In part (a), the name 2-chloropropanoic acid was deduced correctly by most, but responses in part (b)

were often unclear. Candidates were expected to state, for instance, that the peak at δ1.72 was due to

the methyl group but was split into a doublet because of the single proton on the next carbon. Many

answers implied that the peak at δ1.72 was itself due to the single proton. Part (c) was usually well

answered. The mechanism in part (d) was well answered by the better candidates while others gained

the first two and the last marks despite difficulties with the structure of the substituted ammonium ion

and its loss of a proton to yield the amino acid.


�� 19

The effects of acid and of alkali on an amino acid were quite well answered although many did not

realise that both amine groups in lysine would be protonated in acidic conditions. The structure of the

dipeptide was answered much better than the similar question in the January CHM4 paper. A few

anhydride structures were again seen and allowed in place of the dipeptide.

Question 5

This question was found difficult by many candidates and some marks were lost by candidates who

did not read the question carefully. The second line of the question stated that P, Q and R were all

branched-chain molecules, but many answers included unbranched isomers. Part (b) was better

answered, but again the question asked for the reason a racemic mixture was formed and many

answers contained only a description of what a racemic mixture is. Part (c) was found to be difficult

and only the most able candidates gained all three marks here.

Question 6

This question was answered much better than the previous one. Most candidates were able to draw a

correct structure for ethyl propanoate and the mechanism was generally answered well. It is pleasing

to see that fewer candidates now start curly arrows at negative charges, but the part of the mechanism

showing the loss of a proton was still drawn correctly only by the better candidates. In part (c) most

were able to draw the structure of the acylium ion with m/z = 57 but many did not include it in a

correct equation. The two possible esters which form the fragment ion with m/z = 71 were well

known although some candidates drew the ion rather than the ester which produces it.

Question 7

This question was found difficult by many candidates. The synthetic route in part (a) ended with

butane-1,4-diamine and many candidates were able to deduce that Compound B was

NC–CH2CH2 –CN which would be reduced or hydrogenated to produce butane-1,4-diamine. To form

NC–CH2CH2 –CN in two steps from ethene was found more difficult. The use of hydrogen bromide or

even hydrogen were suggested as reagents with ethene by many candidates who forgot that a CN

group was required at both ends of the molecule. An appreciable number of candidates also wrote

equations and mechanisms in this question, when only reagents and structures were required. This

used up precious minutes of their exam time for no reward.

In part (b), the repeating unit of the polyamide was deduced well, although some candidates drew

nylon (6,6) rather than the polymer required. A brief statement to show that the chains were linked by

hydrogen bonding was then all that was required. Details of the secondary structure of peptides was

not necessary. Part (b) was worth 4 marks in total so candidates should be aware that they should

spend only about 4 minutes on their answer.

In part (c) many answers contained details of the type of polymerisation involved in the formation of

these polymers rather than the explanation that the non-polar polyalkenes are not attacked by

hydroxide ions and are therefore not hydrolysed.

Question 8

It is important that pH values are given to two decimal places; these two figures give the value to

the appropriate precision. The numbers before the decimal point only give the powers of ten involved

in the hydrogen ion concentration.

Three pH values were required in this question and answers to one decimal place only were penalised,

but only once on this occasion.


��20

The question involved three calculations of pH. First the pH of a solution of ethanoic acid was

required. This was usually well done even by candidates of moderate ability.

The second situation involved a buffer solution formed when some of the weak acid has been reacted

with alkali. This was done less well. Many candidates correctly calculated the number of moles of

acid used, the number of moles of hydroxide added and hence the number of moles of acid remaining.

However, these values were then too often used in a calculation which assumed only a weak acid was

present, as in the first part of the question rather than an acidic buffer solution. Although many

candidates still seemed unfamiliar with calculations of this type, there was a definite improvement in

the numbers gaining full marks compared with the January CHM4 paper.

The last part of the question involved finding the pH of the resulting solution of excess potassium

hydroxide produced when all the ethanoic acid is used up. This part was usually answered more

successfully than the second part.


�� 21

Unit 5 CHM5 Thermodynamics and Further Inorganic

Chemistry

General Comments

This was the first Unit 5 examination covering, in addition to Thermodynamics and Further Inorganic

Chemistry, Synoptic Assessment. Marks were awarded equally for these two components. Although

candidates taking this examination were, for the first time, required to complete a 2 hour examination

almost all were able to complete answers to all ten questions.

Although the synoptic assessment added to the difficulty of the paper, weaker candidates lost many

marks when answering questions on the content of Module 5.

Synoptic questions were set on inorganic, organic, physical and practical chemistry. As all questions

were compulsory, it was inevitable and expected, that almost all candidates would find some question

or questions difficult and lose some marks.

All questions were found to discriminate. Most candidates were able to score marks in the initial part

of each questions but, as the questions became more challenging, only the very best candidates were

able to score full marks. However, even very good candidates often lost at least one mark in each

question so that very few candidates scored more than 110 out of possible 120 marks. This was as

predicted for this paper which, for the first time, challenged candidates to answer compulsory

questions on the whole Specification.

Section A

Question 1

Part (a) was well answer by almost all candidates. Consequential marking enabled candidates who

had made a mistake in their calculation of the standard enthalpy or standard entropy change to score

marks in section (ii). Most candidates were able to write a correct equation for the reduction of

titanium(IV) chloride to titanium by either sodium or magnesium. Reduction by hydrogen was the

most common incorrect answer. The reason for the exclusion of air during this reduction was also

well known. Most candidates wrote a correct equation for the reaction of TiCl4 with water.

Question 2

This proved to be the most challenging question on the paper and candidates appeared unfamiliar with

the conventional representation of cells. In part (a) many candidates were able to calculate the e.m.f.

of the given cell but rather less gave a correct half-equation for the reaction occurring at the negative

electrode. Some gave the overall equation for the reaction whilst others gave incorrect half-equations.

Good candidates were able to deduce how a change in the concentration of Mg2+

ions would affect the

cell e.m.f. and gave correct explanations for this change. Credit was given to candidates who

correctly explained the effect of changing the concentration of Mg2+ ions even though the were unable

to link this to the change in the e.m.f of the cell. Part (c) was not well answered. Many candidates

failed to use the conventional representation of cells to deduce that, in this case, the cell e.m.f. was

negative and that the reaction would proceed spontaneously in the reverse direction with iron being

oxidised to Fe2+

ions.


��22

Question 3

Whilst many candidates linked the colour of transition-metal complexes to electron excitation in the

d sub-shell in answer to part (a), rather less stated that the required energy was absorbed from the

visible light. Some candidates stated incorrectly, that colour was due to the emission of visible light

energy. Part (b) was very well answered with most candidates scoring full marks. There were some

excellent outline plans given in part (c) but, although many were familiar with spectrophotometry,

many answers were vague and incomplete. The single most common error was failure to state that it

was necessary to add a suitable ligand to intensify the colour.

Question 4

Part (a) of this question was very well answered. Precipitate B was identified correctly by many

candidates as AgBr in part (b) but rather less went on to identify species C as [Ag(S2O3)2]3-

and write

an equation for its formation from silver bromide. The link between this reaction and photography

was recognised by many but not all realised that, by removing AgBr, the image was fixed. Species D,

required in part (c) was identified correctly as [Ag(CN)2]- by many candidates who also knew that

solutions containing this species are used in electroplating silver. In part (d) good candidates deduced

correctly that silver, in each of the given species, had a full d sub-shell since all the species were

colourless. Weaker candidates stated incorrectly that the lack of colour indicated a full outer shell.

Question 5

In part (a)(i) some candidates gave an equation for the reaction of CrCl3 with water rather than for the

hydrolysis of the hexaaqua ion. Candidates also lost this first mark if they gave an equation for the

reaction of the hexaaqua ion with a base other than water. The explanation of the greater acidity of

chromium(III) chloride solution when compared to chromium(II) chloride was generally well done

though weaker students based their answers only on charge rather than charge density. In part (b)

most candidates identified the green precipitate as chromium(III) hydroxide and the gas evolved as

carbon dioxide. The role of sodium hydroxide and sodium carbonate in the formation of the

chromium(III) hydroxide was less well known. Only the best candidates were able to write an

equation for the reaction between carbonate ions and aqueous chromium(III) ions. A surprisingly

large number of incorrect answers were given in part (c). Some candidates gave incorrect oxidising

agents whilst a significant number of others gave zinc and sulphuric acid as their incorrect answer.

Question 6

Many candidates stated correctly in part (a) that both electrons are supplied by one atom when a co-

ordinate bond is formed but some lost a mark when they failed to state that the bond formed is a

covalent bond. Part (b) was also well answered with only the weaker candidate failing to score full

marks. The term bidentate ligand was generally well understood although some candidates found

difficulty expressing their answer. Part (d) was similarly well answered. By contrast neither part (e)

nor part (f) were well done. Although there were some excellent answers to part (e), many candidates

failed to recognise that the same number and the same type of bond were being broken and made

when ammonia ligands are replace by ethane-1, 2-diamine. Some candidates gave incorrect answers

based on entropy rather than enthalpy change. Although most candidates would have been able to

state that each of the nitrogen atoms in ethane-1, 2-diamine had a lone electron pair only the very best

realised that (NH3CH2CH2NH3)2+

2Cl- would be formed when it reacts with an excess of hydrochloric

acid.


�� 23

Section B

Question 7

It was a delight so see so many fully correct answers to the unstructured equilibrium constant Kp

calculation set in part (a). Consequential marking enable candidates to score marks for partially

correct answers. Common errors included the use of square brackets in the expression for Kp,

incorrect calculation of the number of moles of PCl3 and Cl2 at equilibrium using 45% of the PCl5

remaining rather than dissociated. Part (b) proved to be unexpectedly difficult. Although the shape of

PCl5 molecules was often deduced correctly, the shape of PCl3 molecules was often given incorrectly

as trigonal planar. Some sketches of these structures were too vague to be awarded a mark. Only the

best candidates gave the correct formulae and shapes of the two ionic species present in solid PCl5.

Some made no attempt to answer this question whilst other answers had little logical explanation.

Question 8

Most candidates identified compound X correctly as ethane-1, 2-diol in part (a) but the reagents and

conditions required for its conversion into ethanedioic acid were less well known. The structure of

the ethanedioate ion, a bidentate ligand, was well known and good candidates were able to use this to

draw the structure of the cobalt-containing complex required in part (b). Good candidates also stated

correctly that the substitution reaction produced more molecules, or more disorder, and linked this to

an increase in entropy when the reaction occurred. The formula of ethanedioic acid was given in the

question and its reaction with 2NaOH indicated. Nevertheless, in part (c)(i) a large number of

candidates failed to sketch a pH curve for the titration showing two equivalence points even though

some gave equations for these two reactions. The acid-base calculation in part (c)(ii) required

application of the information given and was not marked consequentially to an incorrect equation

given in part (c)(ii). Candidates who failed to give the concentration of the enthanedioic acid to three

significant figures lost one mark. A disappointingly large number of candidates failed to state that

only half the original volume of sodium hydroxide solution would be required if sodium

hydrogenethanedioate of the same concentration had been used even though the formula of this

compound was given.

Question 9

The reaction between persulphate ions and iodide ions was well known and almost all candidates

stated correctly that the reaction has a high activation energy as these ions are both negative and repel

each other. Good candidates gave correct equations explaining the catalytic action of iron(II) ions but

a significant number of weaker candidates lost marks when they failed to balance these equations.

Many candidates completed their answer to part (a) by predicting correctly that the variable oxidation

states of the transition element vanadium would enable V3+(aq) to function as a catalyst for the

reaction whilst Mg2+

(aq) would not. The role of AlCl3 in the reaction between benzene and ethanoyl

chloride was well known by many candidates. Some, however, lost marks when they failed to show

the involvement of AlCl3 in the formation of the acylium intermediate and the reformation of AlCl3 at

the end of the reaction. Marks were lost by candidates who drew inaccurate structures in the organic

reaction mechanism. The link between the ability of AlCl3 to behave as a Lewis acid and accept a

lone electron pair was made by good students who then predicted correctly that FeCl3 would function

as a catalyst but NH4Cl would not. Marks in this section were not awarded to candidates who made

vague predictions.


��24

Question 10

This was a question on the oxides of Period 3 elements. In part (a) candidates were required to

identify two oxides, P and Q. Candidates who used the given information to correctly identify the

bonding present in the two oxides were awarded marks even when the oxides were then identified

incorrectly. Although many candidates identified P correctly as sodium oxide and gave a correct

equation for its reaction with water others lost marks when they attempted to explain the electrical

conductivity in terms of electron movement. Oxide Q was identified correctly as SO2 by many

candidates. Those who identified it as SO3 were penalised by the loss of one mark. Almost every

candidate stated correctly that hydroxide R was amphoteric. Most also identified it as aluminium

hydroxide. Although any correct equations for the reactions of this hydroxide with sodium hydroxide,

or hydroxide ions, and sulphuric acid, or hydrogen ions, were accepted, candidates often gave

unbalanced equations with incorrect species. Nevertheless there were many excellent answers which

scored full marks. Most candidates were unable to suggest a reason why R, aluminium hydroxide, is

insoluble in water. It was hoped that candidates would realise that a great deal of energy is needed to

break down the bonding in the hydroxide and that hydration would not supply sufficient energy for

this change to occur. In the event any sensible suggestion such as the hydroxide had strong covalent

bonds was accepted for the one mark.


�� 25

Unit 6(a) CHM6/W Snoptic Assessment

This paper produced a good spread of marks. Good candidates scored well and the paper was

effective at discriminating at all levels.

Questions 8, 12, 21, 23, 27, 29, 30, 33 and 38 proved to be relatively easy with a facility in the range

65% to 100%.

Questions 4, 18 and 28 proved to be difficult with a facility below 35%. In question 4, response B

was a notable distractor. Many candidates, even at this level, appear to consider incorrectly that the

formula of magnesium chloride is MgCl. In question 18 responses C and D were the main distractors.

Candidates appeared to have difficulty in recognising familiar reaction types involving unfamiliar

aromatic side-chains. In question 28 response B was a notable distractor, attracting almost twice as

many candidates as the correct answer A. The calculation of the pH value made this question difficult

and possibly time-consuming.

In addition to questions 4 and 28, question 35 also had a notable distractor, response A. Perhaps

candidates recognised correct colours in option (1) but failed to appreciate that, with KMnO4 in the

burette, the change would be from colourless to purple.

Questions 12 and 39 discriminated poorly. Question 12 had a fairly high facility of 68% but it

appeared that the question was very accessible to good and to weaker candidates. Question 39 had a

much lower facility of 42% but it appeared that response D was a distractor (facility 36%), perhaps

because candidates were not very familiar with tertiary amines.


��26

Unit 6(b) CHM6/C Internal Assessment

General Comments

Centres are congratulated for their efforts in introducing the new assessment scheme so smoothly and

successfully. The standard of marking and the application of the appropriate criteria were usually

very good, and as a result relatively few adjustments were necessary during the moderation process.

Centres had clearly benefited from their experience with the scheme last year.

The continuing difficulties encountered by candidates in Skill 4, together with the awarding of more

marks per skill, has meant that fewer candidates obtained maximum marks compared to the extension

modules in the legacy syllabus. Marks covered a wider range than in the legacy syllabus.

A small minority of centres continued to experience the same difficulties in meeting the requirements

of the scheme. Full details are given in the report for Unit 3(b). Rather than repeat the long list of

recommendations here, this report will concentrate on aspects which are particularly relevant to Unit

6(b).

• A significant number of centres used experiments based on exercises from the legacy exemplar

books. 1 The criteria for the new scheme do not match the criteria for the legacy syllabus. Some

centres successfully adapted these old exercises to the new scheme, and produced good work

which allowed the better candidate access to full marks. A small minority of centres simply used

the legacy exercises and marking schemes without change and then converted from a mark out of

5 to one out of 8. This was obviously unacceptable and invariably led to a downward adjustment

of marks being recommended.

• The two most commonly seen exercises were Experiment 14, Reactions of some Metal Ions, and

Experiment 17, Identification of an Organic Compound, both from the 1996 booklet. Reactions

of some Metal Ions is a traditional Skill 2 observation exercise involving familiar reactions of

some common transition metal ions. It matches the criteria with respect to recording and

observing but the exercises involve little in the way of manipulative skills. As the exercise stands

it does not give access to a score of 8 marks. In addition the legacy mark scheme credits the

observations only, and is therefore inappropriate.

• Identification of an Organic Compound is a Skill 3 exercise involving the use of spectra to

identify an organic compound. The mark scheme gives no credit to precision and errors and this

limits the maximum mark to 6. A version of this exercise, updated for the new scheme, was

distributed at the Standardising meetings for practical work held in Autumn 2001.

• Centres are reminded that the exercises from the current exemplar book2 were designed on the

assumption that candidates do not have access to notes or literature sources. In addition centres

must ensure that candidates do not receive help and guidance from any external source.

Supervisors should help a candidate who is in difficulty, and apply a suitable penalty if the help is

significant. This is the only guidance candidates should receive.

� 1 Exemplar Assessment Material for Practical Work (Issued November 1996 and February 1999)2 Guidance for Practical Work Exemplar Assessment Material (Issued June 2000)


�� 27

• The standard of the annotation of scripts was very variable indeed. Some centres provided brief,

vague mark schemes and scripts with virtually no annotation. This makes accurate moderation

much harder to achieve, especially when a centre is using its own exercises. To provide little or

no indication of where candidates have scored marks invites misunderstanding, maximises the

chances that errors will be made and is clearly unwise.

• A small number of centres insist on using inappropriate summative tick lists to arrive at the

overall skill assessment mark, presumably for the sake of convenience. Almost invariably all of

the scoring points are treated as equivalent when calculating the final mark. In addition the

numbers of points needed to score the highest marks are set generously low. As a result

candidates can score high marks without fully satisfying the criteria. They score enough “easy”

points to reach the required target, and their inability to complete the demanding sections of the

exercise are not properly penalised. This is completely unacceptable and will almost inevitably

result in a downward adjustment of marks.

• Evaluation was the weakest area in terms of the level achieved in the student scripts and the

marking of the work. Too many centres continued to use open-ended exercises and candidates

usually answered in general terms, making no specific reference to the data available. Centres

then tended to be too generous in marking this skill. Some centres asked candidates to evaluate

an organic preparation. The outcome was usually disappointing as the candidates did not have the

breadth of chemical knowledge or the insight needed to do this properly. Some centres allowed

candidates to evaluate their own results, without providing a suitable “correct” answer to the

problem. This again limits what the candidate can fairly be expected to achieve. There is no

doubt that structured exercises based upon a common set of data are more accessible; they are

also easier to mark accurately and consistently.

To reiterate, candidates must be encouraged to:

• Discuss the actual results objectively and comment on the quality of the results.

• Calculate a percentage error based on their final result and a given value, then compare this error

to the overall apparatus error calculated in the Analysing section.

• Identify the major weaknesses and areas for improvement in the experiment and suggest ways of

improving the accuracy. Candidates should be discouraged from writing an exhaustive list of all

possible sources of error, many of which are trivial or do not apply to the experiment in question.

The evaluation section of all of the exemplar exercises have been re-written and were distributed at

the Standardising meetings for practical work in Autumn 2001. Candidates found the new versions

much more accessible and centres are strongly advised to use them.

Notwithstanding this rather daunting list of comments, this was a very positive and encouraging first

session for the new scheme. Centres are once again warmly commended for their efforts.


��28

Unit 6(b) CHM6/P Practical Examination

General Comments

This examination discriminated effectively between able and less able candidates. Many good scripts

were seen though very high marks were rare.

Exercise One: Skill 2 Implementing

This was one of the easier exercises on the paper. Many candidates scored high marks, although

surprisingly few candidates scored full marks. The great majority of candidates scored the marks for

manipulative skills and completing the table, as well as obtaining most of the observations. A

significant number of candidates seemed unfamiliar with standard terminology. “Cloudy” and “clear”

were terms used frequently instead of “precipitate” and “colourless”. The observations when excess

of the reagent had been added were the most frequent omissions.

Exercise Two: Skill 3 Analysing and Skill 4 Evaluating

This exercise differentiated markedly between able and less able candidates. The weakest candidates

failed to give correct answers to all but the simplest sections.

In the Analysing section the great majority of candidates plotted the graph adequately, but lost a mark

because their line was not smooth or a best fit. Many candidates failed to meet the tolerance set for

the end point, and even more were unable to identify the correct half-equivalence points. The

conversion from a pKa value to the corresponding Ka value in part 3 proved too difficult for many

candidates.

The great majority of candidates scored the marks for the estimation of errors in part 5, but many

better candidates failed to record results with appropriate precision. A similar number of candidates

failed to score the mark for nomenclature and terminology. Candidates are expected to explain

calculations, including the calculation of the percentage errors, in full, lay their work out logically and

clearly, and use the appropriate terminology correctly.

The Evaluating section of Exercise 2 proved to be a more difficult part of the paper. The most

frequent error carried forward from the graph was the failure to identify the anomalous reading at

23.0 cm3. A surprisingly large number of candidates could not calculate the percentage error in the

experiment in part 1, or relate this value to the apparatus error in part 2. In part 3 candidates did better

in suggesting two improvements, although many tended to give a different version of their first

improvement rather than suggest a second different improvement.

Exercise Three: Skill 1 Planning

This exercise was answered well by the majority of candidates who appeared familiar with the

required preparation. Most candidates understood the basic principles of justifying their chosen scale,

but the scaling for a 75% yield caused many problems. The majority of candidates scored the method

and apparatus points, although a surprising number of candidates added water to the reaction mixture

at the initial stage, despite the clear warnings in the question introduction, rendering the experiment

unworkable. Many candidates could not accurately describe the recrystallisation process in detail,

while a similar number simply stated “recrystallise the impure aspirin” or omitted this section

completely. The great majority of candidates scored the safety points, although a small minority of

candidates then proceeded to describe an experiment which would be decidedly unsafe to carry out.


�� 29

Advanced Extension Award

General Comments

This was the first Advanced extension Award examination in chemistry targeted at the top 10% of

students taking Advanced level chemistry nationally. The remit given to the examiners included a

requirement to stretch the most able students by providing opportunities for them to demonstrate

greater depth of understanding than required at Advanced level.

The paper contained five questions; a short comprehension question, three longer questions linked to

topics in physical, inorganic and organic chemistry, and a free response essay question. Each of the

five questions in the examination discriminated effectively and produced a wide spread of marks.

There were some very good answers to each question but it was clear that not all candidates taking

the examination were amongst the top 10% of A level candidates.

Question 1 (15 marks)

Most, but certainly not all, candidates were able to write an equation for the formation of

phenylammonium hydrogensulphate from phenylamine and sulphuric acid in answer to part (a)(i).

The equation for the formation of 4-aminobenzenesulphonic acid from this salt, required in (a)(ii),

also caused problems for some candidates with an incorrect structure of the product being

disappointingly common.

The mechanism for the sulphonation of benzene by sulphur trioxide in part (b) proved more difficult

than expected. Common errors included beginning the mechanism by protonating the sulphur trioxide

and giving intermediates with incorrect charges and incorrect electron distributions.

Answers to part (c) varied greatly in quality. There were several easy points which almost all

candidates scored but only the better candidates realised that the sulphonation was reversible, that

isomer 2 was more stable than isomer 1 and that, as a consequence, isomer 1 would convert to isomer

2 at the higher temperature.


This question required clear logic and good basic mathematical skills. In part (a) most candidates

correctly stated the relationship between the partial pressure of each component, its mole fraction and

total pressure and gave a correct expression for Kp in terms of the two partial pressure. Only the better

candidates then went on to deduce an expression for Kp in terms of the number of moles of each

component and the overall pressure as required by the question. Candidates who managed to

complete this expression were usually able to use it to deduce the effect of change in overall pressure

and show that the change was consistent with Le Chatelier’s Principle. Part (a)(ii) was generally well

done with many candidates using the given expression to deduce how, in this case, Kp would change

with temperature and that this change was consistent with Le Chatelier’s Principle.

The calculation of the equilibrium constant Kp for the synthesis of ammonia using the given data was

generally well done and most of the better candidates scored full marks. The most common error was

a failure to deduce correctly the number of moles of each component. Consequential marking enabled

most of the marks to be awarded in these cases. In part (b)(ii) candidates were required to calculate

the pressure required to increase the equilibrium yield of ammonia to 50% at the same temperature.

This proved more difficult with errors again being most commonly made in the deduction of the

number of moles of each component. Nevertheless, the better candidates again frequently scored full

marks whilst consequential marking limited loss of marks for those who made mistakes.


��30

The calculation in part(c)(i) was well done and most candidates used the information given to deduce

correctly the pH of the ammonium nitrate solution. Marks were lost when incorrect equations were

given and the approximations made were not explained.

Part(c)(ii), was designed to be more difficult and so it proved. Most candidates scored just two marks

in this section with only the very best candidates scoring full marks.


The planning exercise in part (a) was well done by the better candidates most of whom began by

identifying copper(II) sulphate solution by its blue colour. Clear, logical planning then followed with

equations for the reactions occurring. Other candidates made all possible mixtures of the four

solutions, sometime tabulating the expected observations. Full marks were only awarded when a

clear plan was presented. Candidates who used an additional reagent lost the marks for the compound

identified by its use.

Most candidates were able to identify the potassium manganate(VII) as the oxidising agent in part

(b)(i). The half-equation for the reduction of manganate(VII) ions was well known but a significant

number of candidates gave an incorrect half-equation for the oxidation of hydroxide ions and an

incorrect overall equation for the reaction. Similarly in part (b)(ii), manganate(VII) ions were

identified correctly as causing the purple colour, but again the overall equation for the reaction of

manganate(VI) ions with an excess of acid was often incorrect.

Parts(c)(i) and (ii) were well answered. Most candidates scored full marks for the deduction of the

correct molecular formula. Many candidates then gave correct equations for the reaction of Na2O2

with water and carbon dioxide with almost all stating correctly why Na2O2 is used in submarines. The

calculation in part (c)(iii) was generally well done. Candidates who stated an incorrect mole ratio for

the reaction between H2O2 and Ce4+

and gave no half-equations for the reactions occurring were able

to score a maximum of two marks.

Many candidates gave a correct equation for the conversion of B, PF3Cl2, into the two pentahalides,

PF5 and PCl5 although some lost one mark when the equation was unbalanced. Many candidates

scored only one mark in part (d)(ii) when they identified compound C as P2F6Cl4 rather than as

PCl4+.PF6

-. Good candidates gave correct sketches of the shapes of the PCl4

+ and the PF6

- ions. Part

(d)(iii) was not marked consequentially to wrong answers in (d)(ii).


Although the better candidates wrote a correct equation for the reaction of sodium with ethanol as

required in part (a)(i), many weaker candidates found this very difficult even though the formula of

sodium ethoxide had been given. Surprisingly few stated correctly that sodium was a reducing agent

in this reaction. Only the better candidates gave a correct mechanism for the reaction of sodium

ethoxide with 2-bromopropane. Common errors included showing sodium covalently bonded to

oxygen, failure to show attack by an electron pairs on oxygen and a missing negative charge on the

ethoxide ion. Some candidates lost marks when they failed to state the role of sodium ethoxide in

substitution and elimination reactions. Marks were lost in part (a)(iii) as candidates did not explain

the link between the type the haloalkane, the reaction occurring and the stability of the intermediate

carbocations.

Not all the information given in part (b) was necessary for the identity of compounds A to F to be

deduced. Most candidates were able to identify A and B and many were also able to identify

compounds C and D. Almost all candidates deduced correctly the empirical formula of compound F

but only the very best were then able to use this information to deduce the formula of the diol E and


�� 31

the repeating unit of the polymer F.

In part (c)(i) almost all candidates were able to explain why the carbon-carbon bonds in benzene are

all the same length. However, few candidates realised that this explanation helped them to interpret

the enthalpy of hydration data given in part (c)(ii) and lead them to predict correct carbon-carbon

bond lengths in buta-1,3-diene. Failure to make this link led to a loss of one further mark in section

(iii). Most candidates were able to draw stereoisomers of 1,4-dichlorobuta-1,3-diene as required in

part (c)(iv) but candidates who, by repeating a structure, gave more than the three isomers lost marks.

Part (v) proved to be very difficult and most candidates were unable to deduce structures of isomers

with two chiral carbon atoms joined together. Very few candidates scored marks in this section.


Candidates were able to answer either question 5a, when a discussion of the melting/boiling point of

organic compounds was required or 5b, when a discussion of redox reactions was required.

5a

Most candidates elected to answer this question. Marks were awarded for a discussion covering non-

polar and polar molecules and hydrogen and ionic bonding. It is pleasing to report that there were

some very good, clearly presented and well structured answers covering each type of interaction

which were well illustrated with organic compounds. Almost all candidates discussed non-polar and

polar molecules and hydrogen bonding but many failed to consider ionic bonding. Some candidates

lost marks when they failed to illustrate their answer with organic compounds.

5b

After a brief explanation of the term redox, candidates were expected to give uses of redox reactions

in inorganic, organic and industrial chemistry. There were some excellent answers with examples

chosen from a wide range. Weaker candidates often failed to provide sufficient illustrations with no

examples under one or more of the required headings.


��32

Mark Ranges and Award of Grades

Unit/ComponentMaximum

Mark

(Raw)

Maximum

Mark

(Scaled)

Mean

Mark

(Scaled)

Standard

Deviation

(Scaled)

CHM1 90 90 50.3 18.7

CHM2 90 90 50.1 19.9

CHM3/W Written 75 75 38.1 17.6

CHM3/C Coursework 30 45 36.5 6.6

CH3C -- 120 74.6 21.9

CHM3/W Written 75 75 36.4 17.2

CHM3/P Practical Exam 30 45 29.6 8.1

CH3P -- 120 66.2 23.6

CHM4 90 90 40.5 20.4

CHM5 120 120 57.5 24.0

CHM6/W (OTQ) 40 60 32.6 10.4


CH6/P -- 90 58.1 12.3

CHM6/W (OTQ) 40 60 32.7 10.4


CH6/P -- 90 54.4 13.1

For units which contain only one component, scaled marks are the same as raw marks.


�� 33

CHM1 Atomic Structure, Bonding and Periodicity (12478 candidates)

Max.

markA B C D E

Scaled Boundary Mark 90 64 54 45 36 27

Uniform Boundary Mark 90 72 63 54 45 36

CHM2 Foundation Physical and Inorganic Chemistry (17937 candidates)

Max.

markA B C D E



CH3C Introduction to Organic Chemistry with Coursework (14704 candidates)

Max.

mark

A B C D E

Raw 75 52 44 37 30 23CHM3/W Boundary Mark

scaled 75 52 44 37 30 23

raw 30 26 23 20 17 14CHM3/C Boundary Mark

scaled 45 39 34 29 25 21

CHM3 Scaled Boundary Mark 120 91 79 67 55 44

CHM3 Uniform Boundary Mark 120 96 84 72 60 48

CH3P Introduction to Organic Chemistry with Practical Examination (2685 candidates)

Max.

mark

A B C D E

raw 75 52 44 37 30 23CHM3/W Boundary Mark

scaled 75 52 44 37 30 23

raw 30 22 19 16 14 12CHM3/P Boundary Mark

scaled 45 33 29 25 21 18

CHM3P Scaled Boundary Mark 120 85 74 63 52 41

CHM3 Uniform Boundary Mark 120 96 84 72 60 48


��34

CHM4 Further Physical and Organic Chemistry (7716 candidates)

Max.

markA B C D E



CHM5 Thermodynamics and Further Inorganic Chemistry (10994 candidates)

Max.

markA B C D E



CH6C Synoptic Assessment with Coursework (9471 candidates)

Max.

mark

A B C D E


scaled 60 42 37 32 28 24

raw 30 26 23 20 17 14CHM6/C Boundary Mark

scaled 30 26 23 20 17 14

CHM6C Scaled Boundary Mark 90 68 60 52 45 38

CHM6C Uniform Boundary Mark 90 72 63 54 45 36

CH6P Synoptic Assessment with Practical Examination (1526 candidates)

Max.mark

A B C D E


scaled 60 42 37 32 28 24

raw 30 22 19 17 15 13CHM6/P Boundary Mark

scaled 30 22 19 17 15 13

CHM6C Scaled Boundary Mark 90 64 57 50 43 37

CHM6C Uniform Boundary Mark 90 72 63 54 45 36


�� 35

Advanced Subsidiary award

Provisional statistics for the award (13858 candidates)

A B C D E

Cumulative % 25.9 43.6 60.3 75.4 87.8

Advanced award

Provisional statistics for the award (10805 candidates)

A B C D E

Cumulative % 30.7 52.4 71.7 86.0 95.2

Advanced Extension Award (AEA)

Provisional Statistics for the award (944 Candidates)

MaximumMark (Raw)

MaximumMark (Scaled)

Merit Distinction

Scaled Boundary Mark 160 160 74 95

Definitions

Boundary Mark: the minimum mark required by a candidate to qualify for a given grade.

Mean Mark: is the sum of all candidates’ marks divided by the number of candidates. In order to

compare mean marks for different components, the mean mark (scaled) should be expressed as a

percentage of the maximum mark (scaled).

Standard Deviation: a measure of the spread of candidates’ marks. In most components,

approximately two-thirds of all candidates lie in a range of plus or minus one standard deviation from

the mean, and approximately 95% of all candidates lie in a range of plus or minus two standard

deviations from the mean. In order to compare the standard deviations for different components, the

standard deviation (scaled) should be expressed as a percentage of the maximum mark (scaled).

Uniform Mark: a score on a standard scale which indicates a candidate’s performance. The lowest

uniform mark for grade A is always 80% of the maximum uniform mark for the unit, similarly grade

B is 70%, grade C is 60%, grade D is 50% and grade E is 40%. A candidate’s total scaled mark for

each unit is converted to a uniform mark and the uniform marks for the units which count towards the

AS or A-level qualification are added in order to determine the candidate’s overall grade.

Documents

GCE 2002 June Series Chemistry Examiners' Reportdrbravochemistry.wikispaces.com/file/view/AQA-5421-6421-WRE-JUN… · GCE 2002 June Series ... covers the Advanced Extension Award