Cambridge Ordinary Level

5070 Chemistry November 2024

Principal Examiner Report f or Teachers

CHEMISTRY

Paper 5070/11
Multiple Choice

Question Question Question Question

Key Key Key Key
Number Number Number Number

1 B 11 D 21 B 31 A

2 B 12 A 22 D 32 D

3 C 13 B 23 A 33 D

4 D 14 C 24 C 34 C

5 A 15 A 25 B 35 A

6 C 16 C 26 A 36 C

7 B 17 D 27 B 37 A

8 A 18 A 28 D 38 B

9 B 19 D 29 B 39 C

10 C 20 D 30 C 40 A

General comments

Questions 16, 30 and 36 were f ound to be easy. Questions 6, 7, 8, 21, 33, 34 and 39 were f ound to be
more challenging. There was evidence of guessing in Questions 6, 21, 33 and 34.

Comments on specific questions

The choice of options in the following items shows where candidates who performed less well overall, unless
specif ied, have gaps in their knowledge, skills and/or understanding:

Question 3

Some candidates chose option D rather than the key, option C. These candidates may have thought of X
and Y in terms of familiar examples such as sodium and oxygen or calcium and chlorine. This would then
make statement 3 incorrect.

Question 6

This item was answered well by candidates who performed well overall. Other candidates either did not know
how to work out the answer or perhaps guessed their answer as all of the options were selected.

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Question 7

More candidates chose option D rather than the key, option B. These candidates may have attempted to
balance the charge using the potassium ions with one (rather than three) sulf ate ion(s) and ignoring the
chromium ion.

Question 8

There was some evidence that better performing candidates chose option B rather than the key, option A.
These candidates did not appreciate that it is possible for elements to have an Ar with a whole number and
also to have isotopes.

Question 15

There was some evidence that better performing candidates chose option D rather than the key, option A.
These candidates incorrectly linked larger particle size with an increase in the rate of reaction.

Question 21

There was some evidence of guessing f or this question and also some evidence of better perf orming
candidates choosing option D rather than the key, option B. The two salts in option D can be made f rom the
listed reagents. These candidates did not appreciate that these two salts can then be reacted with the
original reagents to make two further salts by precipitation reactions to give the key B. Option A was also
chosen by some candidates but includes a salt which cannot be made.

Question 33

There was some evidence of guessing with both options A and C chosen. There was also some evidence of
better performing candidates choosing option A rather than the key, D. Option A was chosen by more
candidates than the key. Learning objective 11.5.6 requires candidates to understand how bromine adds
across the double carbon-carbon bond. It is clear that this is not well understood by some candidates.

Question 34

There was some evidence of guessing and some evidence that better perf orming candidates choosing
option D rather than the key, option C. Candidates choosing option D had the correct stoichiometry, but did
not take into account the oxygen present in the ethanol molecule.

Question 39

Option D was chosen by more candidates than the key, option C. These candidates ignored the statement,
given twice, that the chromatogram was of coloured dyes, theref ore use of a locating reagent is
unnecessary.

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 Cambridge Ordinary Level
5070 Chemistry November 2024
Principal Examiner Report f or Teachers

CHEMISTRY

Paper 5070/12
Multiple Choice

Question Question Question Question

Key Key Key Key
Number Number Number Number

1 A 11 D 21 D 31 C

2 D 12 C 22 C 32 C

3 C 13 A 23 B 33 A

4 D 14 B 24 A 34 C

5 B 15 D 25 D 35 B

6 C 16 B 26 D 36 B

7 C 17 A 27 C 37 A

8 C 18 B 28 B 38 B

9 A 19 A 29 D 39 D

10 B 20 C 30 B 40 D

General comments

Questions 3 and 8 were f ound to be easy. Questions 1, 24, 30, 34, 37 and 40 were f ound to be more
challenging. There was evidence of guessing in Questions 24 and 37.

Comments on specific questions

The choice of distractor in the following items shows where candidates who perf ormed less well overall,
unless specif ied, have gaps in their knowledge, skills and/or understanding:

Question 1

Candidates choosing option D incorrectly thought that gas particles will form ‘layers’ dependent on the mass
of the particles in the gas.

Question 2

More candidates chose option B rather than the key, option D. Candidates incorrectly thought that simple
molecules had to be elements and did not consider the simple molecules referenced in the syllabus, such as
water and ammonia.

Question 4

More candidates chose option A rather than the key, option D. Candidates only used data on the x-axis.

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Question 6

Options A and D were chosen by over 40% of candidates, including some candidates who perf ormed well
overall. They incorrectly thought that aqueous and solid sodium chloride conducts electricity by the
movement of electrons.

Question 9

Options B and D were popular incorrect choices. There was also some evidence of guessing. Perhaps
candidates thought this item required them to calculate the formula masses of each compound rather than
the quicker route of multiplying the number of moles of the compound by the number of O atoms in the
f ormula.

Question 17

Candidates choosing option C correctly identif ied which experiment was carried out at the higher
temperature, but did not correctly link the volumes of P and Q in the graphs to the stoichiometry in the
equation.

Question 18

Options C and D were chosen by over half of candidates. They did not understand that the rate of the
f orward and reverse reactions is the same at equilibrium.

Question 24

There was evidence of guessing and all in the options were chosen. Candidates did not have a good
understanding of LOs 7.3.1–7.3.3, preparation of salts.

Question 30

Option C was a popular incorrect response. Metal M would be extracted from its ore by heating with carbon,
but the column header is ‘possible method of extraction of M f rom MO’. Candidates need to read the
question caref ully.

Question 34

Option B was chosen by over 40% of candidates, including some candidates who perf ormed well overall.
Candidates might not have considered the isomer propyl methanoate.

Question 37

More candidates chose option C rather than the key, option A. Candidates did not, or could not, deduce the
equation f or the f ermentation reaction f or glucose.

Question 40

Options A and B were chosen by over 70% of candidates, including some candidates who perf ormed well
overall. The f irst statement may have steered candidates towards options A and B, but they needed to use
all the inf ormation given to deduce the correct answer, option D.

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 Cambridge Ordinary Level
5070 Chemistry November 2024
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CHEMISTRY

Paper 5070/21
Paper 2 Theory

Key messages

• Candidates need more practice constructing balanced equations and ionic equations.
• Many candidates did not understand the term structural f ormula.
• Many candidates drew structures containing 5- or 3- valent carbon atoms, 1-valent oxygen atoms and
2-valent nitrogen atoms.
• Candidates need to read questions carefully so that they answer what is being asked e.g. Question 5
(b)(ii) where the change was more concentrated acid and Question 5 (c) where the question asked f or
the answer to two signif icant f igures.
• Candidates need practice in drawing accurate reaction pathway diagrams.
• Many candidates did not know the reactions in the blast f urnace.
• Good practice is to show working out in calculations such that error carried f orward marks can be
awarded were available.

General comments

Candidates were generally well prepared f or this examination and appeared to have suf f icient time to
complete the paper as only some of the more demanding questions were omitted.

Many gave detailed explanations for questions whilst others stated answers rather than explaining them.

Candidates f ound using and understanding chemical terminology quite dif f icult.

Practical techniques used in salt preparation and identif ication of an ion proved challenging.

Comments on specific questions

Question 1

(a) (i) Most candidates chose the correct atom. All of the other responses were seen occasionally.

(ii) The majority of candidates knew the flame colour of H. D was the most popular incorrect response.

(iii) Candidates f ound this a little challenging. All atoms were seen with E and H being the most
common incorrect responses.

(iv) Many candidates confused the uses of carbon and chlorine, hence a popular response was G.

(v) Almost all candidates chose the correct atom.

(b) Almost all candidates deduced the correct numbers of protons and neutrons. A small number
reversed the numbers or gave 53 as the number of neutrons.

Question 2

(a) (i) The meaning of redox was well known with many candidates appreciating that these occurred
simultaneously. Oxidation or reduction, gain of oxygen, loss of electrons and citing only reduction
were the most common incorrect responses.

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(ii) Candidates found this very challenging. Incorrect responses included repeating the equation by
naming the substances involved i.e. iron oxide becomes iron or carbon monoxide becomes carbon
dioxide and oxygen removed f rom iron instead of iron ions. Those t hat appreciated that CO
removed oxygen often did not include it being removed from the iron oxide or that electrons were
added to the iron ions.

(b) The most common errors were a double headed arrow or an upwards arrow f or H. Common
incorrect responses included endothermic reaction pathways, activation energy arrow f rom
products to the top of the energy hump and imprecise arrows that were either too long or too short.

(c) The blast furnace was not well known. Many thought that calcium carbonate reacted with the sand
or with the impurities and many equations gave silicon dioxide as SiO or SiO4. A significant number
omitted the question.

(d) The properties of transition elements were quite well known. The most common incorrect
responses included they are coloured (rather than their compounds are coloured), more reactive or
citing general metallic properties such as malleability, ductility and conduction of electricity which
also apply to Group I metals.

(e) (i) Candidates f ound this dif f icult. Many thought the equilibrium moved to the lef t. Those that
appreciated the equilibrium moved to the right of ten omitted gas in their explanation.

(ii) Candidates found this very challenging and a significant number omitted the question. Those that
considered the equilibrium discussed decreasing the pressure, not appreciating that an equilibrium
would still exist and so pure iron would still not be obtained. The most successf ul responses
realised that the system needed to be open; very f ew went on to explain that the equilibrium would
then be driven completely to the right.

(f) Candidates f ound this extremely challenging. Common errors included Fe 3SO4, FeSO4, FeS,
FeSO, Fe and FeO. Those that gave the correct f ormulae of ten did not balance the equation.

Question 3

(a) Candidates found this quite difficult with many labelling the test-tube or the positive symbol on the
power supply. Many omitted the question.

(b) Many candidates discussed electrons rather than ions or delocalised ions rather than mobile ions.

(c) (i) Over half of candidates knew the correct product. Sodium and H+ were the most common incorrect
responses.

(ii) Candidates f ound this quite challenging. Common incorrect responses included adding the
electrons to the chloride ion, Cl – → Cl + e–, Cl – + e– → Cl and ionising a chlorine molecule.

(d) The property of graphite was quite well known. Common incorrect responses included low melting
point, low boiling point, hard, giant structure, contains delocalised electrons and conducts
electricity.

(e) Over half of candidates named the product correctly. Hydrogen was the most common incorrect
response; oxygen, chlorine and sodium hydroxide were also quite common.

Question 4

(a) About half of the candidates could name one characteristic with a third naming two. Same physical
properties, same molecular formula, same chemical formula and repetition of the characteristics in
the stem were common incorrect responses.

(b) (i) Almost all candidates gave a correct explanation. A small number of incorrect responses were
seen, including not all the bonds used and does not contain a f ull amount of hydrogen.

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5070 Chemistry November 2024
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(ii) Candidates found this a little challenging as structural formula was not well understood. C 4H8 was
the most common incorrect response.

(iii) Candidates f ound drawing a displayed f ormula quite dif f icult. The most common incorrect
responses included 3- and 5- valent carbon atoms; many did not include a double carbon-carbon
bond.

(c) (i) The use of kerosine was well known. Use as a fuel and use in aircraft/jets were both insufficient on
their own. A small number of uses of other fractions were seen including cooking gas, lubricant and
road surf acing.

(ii) Candidates found this quite challenging and often gave an incorrect f ormula for at least one of the
products. Those that gave correct products often did not balance the equation. A small number
omitted the question.

(d) (i) Many candidates appreciated the product to be HCl but gave the name incorrectly as hydrochloric
acid rather than hydrogen chloride. Hydrogen was also a common incorrect response.

(ii) Ultraviolet light was quite well known. Incorrect responses included high pressure, catalyst (of ten
named), constant temperature and absence of oxygen.

(e) (i) Most candidates performed well. Common errors included not breaking the C=C double bond,
miscounting the number of C-H bonds both broken and made and the most common error being
reversing the f inal subtraction.

(ii) The colour change was quite well known. The most common error was reversing the colour
change.

Question 5

(a) State symbols were well known. Solid f or copper chloride was the most common incorrect
response; aqueous f or water was also seen.

(b) (i) Many candidates showed either a steeper curve or the same f inal mass. Incorrect responses
included lines above the one on the paper and of ten drawn as a straight line f rom 200.0 g to
6 minutes, or a line ending at a lower mass.

(ii) Many candidates misread the original experiment which added large pieces of copper( II) carbonate
to the acid. Hence, they assumed the large pieces of copper(II) carbonate was the change and so
discussed the effects of surface area rather than the increased acid concentration. Those that did
appreciate that concentration had been increased discussed more particles rather than more
crowded particles and more collisions rather than increased f requency of collision.

(c) Many candidates calculated the volume correctly but then did not give their answer to two
significant figures. Common errors included not using the stoichiometry in the equation and using
0.5 as the number of moles of acid rather than its concentration. Those that did not use the
stoichiometry of ten also did not give their answer to two signif icant f igures.

(d) (i) The test f or copper(II) ions with aqueous ammonia was not well known. White, green and cream
precipitates and colourless solution were often seen for the first part and insoluble f or the second
part.

(ii) Candidates found this quite difficult. The most common responses were 2 and +2. Other incorrect
responses included 0, –1, 1 and +3.

(e) Candidates continue to find describing salt preparations difficult. Many did not appreciate that an
acid and alkali were reacting in solution and so did not use titration. The small number that did
titrate the solutions did not repeat the mixing with the titration volumes but without the indicator.
Many thought one of the reagents was solid and so f iltered to obtain the solution of ammonium
chloride. Some candidates then gained partial credit by evaporating the solution to saturation,
cooling and drying. Many incorrectly heated or evaporated to dryness. A small number thought
incorrectly that the product was a precipitate and so filtered washed and dried.

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Question 6

(a) (i) Whilst many candidates discussed electrons , the majority discussed no f ree or delocalised
electrons which were not creditworthy unless their lack of movement was also mentioned.

(ii) Many candidates gave a correct property. Incorrect responses included coloured compounds,
strong and a discussion of its bonding and structure.

(b) Intermolecular forces were not well known. Few bonds, weak bonds and weak covalent bonds
were popular incorrect responses. Some answers showed poor use of terminology such as weak
intermolecular f orces between atoms. Simple covalent was insuf f icient.

(c) Most candidates drew a correct dot and cross diagram f or disulf ur dichloride

(d) The majority of candidates calculated either the number of moles of disulf ur dichloride or the
number of moles of water. A significant number calculated both. The more successf ul candidates
used the stoichiometry of the equation to show water being in excess. Some candidates did not
calculate moles but compared the masses and so gained no credit.

(e) (i) Acid rain, respiratory issues or irritation were well known. Non-creditworthy responses included
climate change, greenhouse gas, toxic and disease causing. Depletion of ozone was incorrect.

(ii) Candidates f ound this challenging. Incorrect responses included: plant more trees, reduce
livestock, use a catalytic converter, use filters, do not burn sulfur, more ef f icient engines and less
f actories or f actory waste.

Question 7

(a) (i) Naming the ester was quite well known. The most common incorrect response was propyl
methanoate. Alcohols and acids were also quite popular.

Candidates found drawing the ester more difficult. Many drew an acid, had –O at the end of the
molecule, had a 5-valent carbon atom, had an alcohol and a ketone group or just an alcohol.

(ii) Both parts were quite well known. The f irst part was better known; incorrect responses included
reversible reaction, receiving protons and electron donor. For the second part , f ully ionised and
partially dissolved were common responses.

(iii) Candidates deduced the products quite well; hydrogen was very well known. Common incorrect
responses included salt, magnesium oxide, water, propanol and ethanol.

(iv) The particulate structure of a solid was well known. For movement , non-creditworthy responses
included slow, no movement and f ixed.

For separation, non-creditworthy responses included closer, fixed, small and a description of being
heated. A small number described how the particles could be separated.

(b) (i) Candidates found this very difficult and a signif icant number omitted the question. The linkages
of ten had an extra O or H in them sometimes with 5-valent carbon atoms, 1-valent oxygen atoms
and 2-valent nitrogen atoms; each contained totally different atoms or the boxes had a + between
them. The ends of the molecule occasionally had continuation bonds.

(ii) Polymer was not well defined. In place of large molecule, common non-creditworthy responses
included a molecule, a substance and a polymer. In place of ‘many monomers’, a large number of
responses referred to ‘making f rom one or more monomers’ or ‘f rom monomers’. A signif icant
number described the breakdown of a polymer rather than polymerisation.

(iii) The dif f erence between polymerisations was quite well known. Non-creditworthy responses
included condensation polymers react with water, condensation polymers have a double bond,
addition polymers have a double bond, addition polymers use only one monomer, addition polymer
has ester or amide linkages and condensation polymers are natural.

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 Cambridge Ordinary Level
5070 Chemistry November 2024
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CHEMISTRY

Paper 5070/22
Theory

Key messages

• Candidates found aspects of polymers and polymerisation quite challenging , in particular drawing a
polymer.
• Candidates must use the names of particles with clarity so that it is clear within an answer if the particle
involved is an atom, molecule or ion.
• Candidates found aspects of organic chemistry demanding and were often unable to name or draw the
correct organic products of a reaction. In particular, candidates did not always know how to draw the
ester linkage.
• Candidates need to check that blank spaces within the question paper are actually spaces and not the
answer spaces where either calculations, drawings or labels should be written.

General comments

Candidates appeared to have sufficient time to complete all the examination paper. Candidates were of ten
able to interpret and explain given data in questions.

In quantitative questions, some candidates did not always show sufficient working out so it was not always
possible to award error carried f orward marks.

Candidates often found balancing equation difficult of ten because they wrote down incorrect f ormulae so
making the balancing impossible.

Comments on specific questions

Question 1

This question was about the atomic structure of some elements.

(a) Most candidates followed the rubric and gave the letter of the electronic conf iguration rather than
the symbol or name of the element.

(i) Most candidates identif ied the noble gas.

(ii) Most candidates identif ied the electronic conf iguration f or aluminium.

(iii) Many candidates identif ied the element in Group V of the Periodic Table.

(iv) Many candidates identif ied the element in Period 3 of the Periodic Table.

(v) Many candidates were able to identif y the correct element.

(b) Most candidates deduced the number of protons and the number of neurons. The most common
misconception was to give the number of neutrons as 51.

Question 2

This question was about iron.

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 Cambridge Ordinary Level
5070 Chemistry November 2024
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(a) (i) Many candidates did not associate burning carbon with the release of thermal energy to maintain
the temperature within the blast furnace. The most common misconception was to produce carbon
monoxide.

(ii) Many candidates were able to state one adverse effect of carbon monoxide. The most common
answers ref erred to carbon monoxide being toxic or poisonous. Some candidates tried to explain
why carbon monoxide is poisonous in terms of its effect on the oxygen carrying capacity of blood.
Some candidates did not mention blood and merely referred to reduced oxygen transport within the
body. This was not considered to be sufficient to be awarded credit. Another misconception was
that carbon monoxide causes global warming. A common answer was that carbon monoxide
caused respiratory or breathing problems without specif ying why.

(iii) Candidates often did not balance the equation. Other candidates did not appreciate that carbon
dioxide was the second product of the reaction.

(b) The best answers gave two equations, either symbol or word equations, describing the thermal
decomposition of calcium carbonate and the reaction of calcium oxide with silicon( IV) oxide. A
common misconception was that calcium carbonate itself reacts with silicon( IV) oxide to form slag.
Other candidates did not appreciate that slag is formed rather than removed by calcium oxide. A
signif icant proportion of candidates did not answer this question.

(c) Candidates were often able to state two suitable properties. The most common properties were
that transition elements were of ten catalysts, have variable oxidation numbers, f orm coloured
compounds, are hard and have a high density. Only a small proportion of the candidates gave a
dif f erence in chemical properties such are Group I elements are more reactive.

(d) Some candidates only explained one method of rust protection and this was of ten sacrif icial
protection. For sacrificial protection, although many answers stated that zinc was more reactive
than iron, they did not explain that zinc reacts, instead of iron, with water and oxygen. A common
misconception was that zinc rusts rather than zinc corrodes. When explaining the barrier method ,
many candidates did not specify that the barrier does not allow contact between oxygen and water.

(e) A significant proportion of the candidates predicted that the position of equilibrium changed and did
not appreciate the number of moles of gaseous reactants equals the number of moles of gaseous
products.

(f) Candidates f ound this question very challenging. The f ormula of iron( II) chloride and iron(III)
chloride were often incorrect and as a result the equation could not be balanced. Typical incorrect
f ormulae included Fe2Cl and Fe2Cl 3. Many candidates identif ied the third product as water.

Question 3

This question was about the electrolysis of dilute sulf uric acid.

(a) Many candidates were not able to recall the def inition f or the term electrolysis. Only the best
answers appreciated that electrolysis involves the decomposition of an aqueous or molten ionic
compound using electricity. Typical answers did not mention ionic compounds in their answers.

(b) A significant proportion of candidates did not answer this question. Common misconceptions
involved labelling the test-tube or the sulf uric acid in the test-tube.

(c) (i) Many candidates gave hydrogen as the product. Some gave oxygen and others sulf ur dioxide.

(ii) Many candidates could not construct the correct ionic half -equation. Some candidates wrote the
equation the wrong way around; others used oxide ions losing electrons rather than hydroxide ions.
Electrons were often missing or on the incorrect side of the equation. A signif icant proportion of
candidates did not answer this question.

(d) Candidates gave a variety of names of elements, many of which were metals that react with dilute
sulf uric acid. Carbon was also a common incorrect answer. Some candidates did choose a suitable
element such as platinum.

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 Cambridge Ordinary Level
5070 Chemistry November 2024
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Question 4

This question was about alkanes and alkenes.

(a) Many candidates stated two correct characteristics of a homologous series. The most common
characteristics were the same chemical properties or physical properties that showed an
observable trend. The physical property trend was often given as a specif ic example such as the
boiling points increased down a homologous series.

(b) (i) Many candidates recognised the significance of butane having single carbon-carbon bonds but
of ten forgot to mention that all these carbon-carbon bonds were single bonds. Candidates were
more likely to mention that butane does not have any double bonds , which earned f ull credit.

(ii) Many candidates gave the molecular f ormula C 4H10 rather than the structural f ormula
CH3CH2CH2CH3.

(c) (i) A common misconception was to ref er to a f eedstock f or animals rather than f or the chemical
industry. Other incorrect uses included f uels f or ships and aeroplanes.

(ii) Candidates found this question challenging because they often did not write the correct formula f or
propane or ethene, or included other hydrocarbons as products. Some candidates gave extra
reactants in addition to nonane. A significant proportion of candidates did not answer this question.

(d) (i) Many candidates recognised that the reaction was an example of substitution. Some candidates
ref erred to chlorination and this was also given credit. Other candidates ref erred to displacement
but this was not credited .

(ii) Candidates often gave imprecise answers that referred to the ultraviolet light providing energy but
they did not ref er to either providing the activation energy or the energy needed to break the
chlorine-chlorine bond.

(iii) The best answers gave the correct answer of −122 kJ / mol supported by clear working out. The
working out allowed the award of error carried f orward marks and was best organised as :
• Bond broken with the associated energy change.
• Bond f ormed with the associated energy change.
• Enthalpy change being the difference between these two energy changes (energy to break
bonds minus the energy to f orm bonds).

A signif icant proportion of candidates did not answer this question.

(e) Candidates often used the explanation that reactants were added to describe an addition reaction
rather than appreciating that there was only one product or that no other molecule was lost in the
reaction.

Question 5

This question was about the reaction between zinc and dilute hydrochloric acid.

(a) Many candidates wrote the correct state symbols. A common error was to have the zinc chloride as
a solid or a liquid. Some candidates wrote the state symbols in upper case rather than lower case.

(b) (i) The best answers appreciated that the slope or gradient of the graph decreases with time.
Descriptions of the line for example curving until it becomes straight were not suf f icient f or the
award of credit.

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(ii) Many candidates referred to changes in the kinetic energy or speed of the particle, which was not
relevant since there was no change in temperature. The best answers appreciated that during the
reaction the concentration of the hydrochloric acid decreased and then gave explanations that
related to particle collisions. These answers appreciated that as time increased the particles
became less crowded and the collision f requency decreased.

(iii) As in (ii), many candidates referred to the kinetic energy of the particles and the speed of particles
and did not mention the increase in surface area when powdered zinc is used. The best answers
appreciated that the collision frequency between particles increased and there were more exposed
particles on the surf ace of the zinc.

(c) A significant proportion of the candidates calculated the correct volume of hydrogen gas although
some of these candidates quoted the answer to three significant figures rather than two signif icant
f igures. The best answers worked out the number of moles of hydrochloric acid, used this to work
out the number of moles of hydrogen and finally used the molar volume of hydrogen to calculate
the volume of hydrogen. Some candidates did not use the stoichiometric equation to use the
correct link between number of moles of hydrochloric acid with the number of moles of hydrogen.

(d) Many candidates were not awarded f ull credit since the two energy changes on their diagrams
were not suf f iciently clear. Candidates should be advised to use an arrowhead on the energy
change lines making sure the arrowhead is in the correct direction and start the line f rom the
correct energy level. Double headed arrows should be avoided since they do not show the direction
of the energy change.

Some candidates muddled up the position of the reactants and products both in terms of height
and horizontal position in the diagram.

(e) Some candidates recalled the correct observations f or aqueous zinc ions. The appearance of a
white precipitate was the most common observation but some candidates did not appreciate that
the precipitate dissolves in excess aqueous ammonia to give a colourless solution.

(f) Candidates found this question quite challenging and often these candidates f ocused on making
the aqueous zinc chloride rather than how crystals were made f rom the aqueous zinc chloride.
Answers often mentioned filtering but it was unclear if this was filtering off excess zinc or filtering off
crystals of zinc chloride. In the same way, candidates often described heating to get a saturated
solution without specifying what was being heated the reaction mixture or the filtrate af ter f iltering.

The best answers described:

• f iltering the reaction mixture to get aqueous zinc chloride
• heating the aqueous zinc chloride to get a saturated solution
• cooling the saturated solution to get crystals and drying the crystals with f ilter paper.

A significant proportion of the candidates heated the f iltrate to dryness ; this was not given any
credit.

Question 6

This question was about boron nitride and hydrazine.

(a) The idea that boron nitride has a giant structure was well known although some candidates thought
that it was an ionic compound rather than a covalent compound. Candidates of ten mentioned
strong bonds, but other candidates mentioned strong bonds between bonds or between molecules.
A common misconception was to ref er to intermolecular f orces.

(b) Many candidates referred to a lack of mobile electrons, although some candidates just referred to a
simple molecular structure.

(c) Candidates found drawing the dot-and-cross diagram very challenging. Common misconceptions
included drawing a double or triple bond between the nitrogen atoms, having no lone pairs on the
nitrogen atoms or including extra electrons around the hydrogen ato ms.

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(d) (i) Some candidates could deduce the oxidation number of nitrogen in ammonia. Some of these
candidates also showed their working out even though this was not needed.

(ii) Candidates often ignored the instruction in the question and ref erred to electron gain or electron
loss. Other candidates only explained there was either no oxidation or no reduction. Only the best
answers appreciated that the oxidation number of nitrogen did not change during the reaction.

(e) Candidates used a variety of different methods to show that boron oxide was in excess. Most of the
approaches involved some or all of these f our steps:
• calculating the number of moles of boron oxide
• calculating the number of moles of magnesium
• using the stoichiometric relationship between moles of boron oxide and moles of magnesium
• comparing moles or mass needed with actual moles or mass .

The best answers showed working out rather than just a set of unrelated calculations. Some
candidates calculated the mass of boron oxide that reacts with the provided magnesium to show
that some boron oxide would remain unreacted. Other candidates calculated the mass of
magnesium needed to react with the provided boron oxide to show there was not enough
magnesium.

Question 7

This question was about esters and polyesters.

(a) (i) Some candidates recognised that the f ormula shown was a general f ormula.

(ii) Only a small proportion of the candidates deduced that the value of n was 5. Numbers between 1
to 4 were also common incorrect answers. Some candidates gave the f ormula of the ester with
n = 5 and this was given f ull credit.

(b) Many candidates attempted to draw a displayed f ormula but a signif icant proportion of the
candidates did not draw an ester. Only a small proportion of candidates drew butyl ethanoate.

(c) (i) Many candidates found this question challenging because they could not draw the ester linkage
between repeat units. The ester linkage often included extra carbon, hydrogen or oxygen atoms.
Most candidates did not draw the correct continuation bonds at both ends of the structure.

(ii) Candidates of ten named condensation polymerisation.

(d) Candidates found this question challenging and often described recycling and the use of physical
processes. The idea of cracking or thermal decomposition of polymers to make monomers and
subsequent repolymerisation was rarely mentioned in answers. A signif icant proportion of the
candidates did not answer this question.

(e) (i) Candidates were often able to name at least two products of the reaction; water and carbon dioxide
were the most likely correct answers. Some candidates named sodium ethanoate as just ‘salt’.

(ii) Candidates of ten described the separation of particles in a liquid as well as the arrangement.
Comments about the separation of particles were ignored. Answers of ten ref erred to a random
arrangement or a disordered arrangement. In terms of the motion, the best answers ref erred to
particles sliding over each other. Random motion was also accepted. It was not suf f icient just to
ref er to the particles being f ree to move.

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 Cambridge Ordinary Level
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CHEMISTRY

Paper 5070/31
Practical Test

Key messages

• Candidates should lay out their workings f or calculation questions clearly, with indications of what is
being calculated at each stage. By working in this way, candidates may be eligible to get an ‘error carried
f orward’ mark f rom a question, even when they have made an error.
• Candidates should note that a solid disappearing is as valid an observation as bubbles appearing. They
should also make sure that when f ormulae are written that they are correct.
• While most candidates gave a successf ul method f or the planning question, some missed out the
accuracy section and should be sure that they carefully read and respond to the whole of the question
stem.

General comments

In most cases, candidates were well practised in carrying out the titration practical and in perf orming
calculations with their determined volume. A common area that could be improved was the reading and
understanding of the question stem. There were instances when taking a bit more time reading the question
f irst would have benefitted candidates. This was relevant in Question 1(e) when candidates were asked to
give their answer to three significant figures, and in Question 3 when asked to discuss the accuracy of their
method.

Comments on specific questions

Question 1

(a) Successful candidates carefully carried out four titrations, giving initial and final burette readings to
one decimal place and then correctly calculated the volume of X used. The highest achieving
candidates obtained at least one volume that was within 0.2 cm3 of the Supervisor’s average
volume. Candidates who were slightly less accurate, but still had a volume which was within
0.3 cm3 of the Supervisor’s average volume, still got some credit f or their accuracy.

(b) Candidates were required to tick the ‘best two’ titration results f rom Table 1.1 and to explain their
choice. Most candidates correctly chose their closest two values and explained this in the answer.
Some candidates seemed to not understand that the ‘best’ values meant those that were closest
together and instead ticked which ones used the least ethanedioic acid.

(c) In this question candidates were required to use their ticked values to calculate the average volume
of ethanedioic acid needed. Some candidates calculated an average of all the values, rather than
just their ticked values.

(d) Candidates were asked to calculate the number of moles of sodium hydroxide, Y, in this question.
All the inf ormation required (the volume and concentration of NaOH(aq)) was given in the question.
Many candidates gave the correct answer of 0.02 moles.

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(e) The question stem told the candidates, ‘One mole of ethanedioic acid is neutralised by two moles
of sodium hydroxide’ and asked them to use their answers to (c) and (d) to calculate the
concentration of ethanedioic acid. Successful candidates used the ratio provided to recognise that
they would need to halve the number of moles that they calculated for NaOH, so they divided their
answer f rom (d) by 2. They then divided that answer by their average volume f rom (c) in dm3. The
question stem also asked that candidates, ‘Give your answer to three signif icant f igures’. Several
candidates did not give their answer to three signif icant f igures, even though they had done the
calculation correctly. Candidates should be reminded to follow the guidance of the question stem,
as they will not achieve f ull credit if they do not give answers to the precision requested.

(f) (i) Candidates were given the formula of ethanedioic acid and the mass of ethanedioic acid (6.3 g) in
100 cm3 of the aqueous solution. They were asked to calculate the relative f ormula mass of
ethanedioic acid using their answer from (e). There were various acceptable methods to get this
answer. One correct method, which some successful candidates used, was to multiply their answer
of the concentration from (e) by 0.1, giving the number of moles in 100 cm3. They then divided the
mass, 6.3 g, by this number of moles to give the relative molecular mass. Candidates who
incorrectly calculated the number of moles in the first step were still able to receive an error carried
f orward mark, if they clearly indicated that they were dividing 6.3 g by their number of moles.
Candidates should be encouraged to lay out their answers to calculations clearly, indicating what
the calculated values refer to e.g. number of moles, mass, concentration etc. so that error carried
f orward marks are accessible.

(ii) Using their answer to (f)(i) candidates were asked to deduce the value of n (the number of moles of
water in the f ormula of the hydrated compound). Successf ul candidates calculated the Mr of
C2H2O4 then subtracted this value from their answer to (f)(i). This gave an intermediate value which
was divided by 18 (the Mr of H2O) to give the f inal answer.

(g) Candidates were asked why the conical f lask in the titration is placed on a white tile. Many
candidates correctly stated that it is to see the colour change more clearly. It should be noted that
all three parts of this statement were needed. Some candidates just mentioned seeing the colour,
but the important part of a titration is the endpoint, when the colour changes. Others omitted the
colour and just said ‘the change’ but they needed to say what type of change they were looking for.
Finally, some did mention the colour change, but did not say how the white tile would help. The
colour change would be visible without the tile, the key point is that the colour change could be
seen more easily, or more clearly.

(h) Most candidates successf ully stated that a measuring cylinder is not used in this experiment
because it is not accurate, or not precise enough.

Question 2

In (a), (b) and (c), candidates were asked to carry out tests on solid P. They were instructed to record
observations, test and identif y any gases evolved and to describe the gas tests used.

(a) This involved the candidates adding dilute hydrochloric acid to a sample of P in a boiling tube. Most
candidates successfully noted that there was effervescence and that when the gas was tested by
bubbling it through limewater. The limewater became cloudy indicating the presence of carbon
dioxide. The better perf orming candidates also recognised that the solid had disappeared.

(b) (i) To one half of the mixture from (a) candidates were asked to add aqueous sodium hydroxide drop
by drop, then in excess. Most candidates were able to identify that a white precipitate was f ormed,
which was soluble in excess. Some candidates also correctly noted that it left a colourless solution.

(ii) Candidates were asked to add aqueous ammonia drop by drop and then in excess. Most
candidates correctly identif ied a white precipitate which was soluble in excess.

(c) Most candidates correctly identif ied the cation and anion in solid P as zinc and carbonate.
Candidates should be reminded to make full use of the ‘Notes for use in qualitative analysis’ at the
back of the paper. They should also be reminded that if f ormulae are written then they must be
correct. This question just asked candidates to ‘identif y’ the ions, so a name was perf ectly
acceptable. If a candidate did write f ormulae, they could check them in the ‘Notes f or use in
qualitative analysis’.

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(d) Candidates were asked to carry out a flame test on solution Q. They should have noted that there
was a lilac f lame.

(e) (i) Candidates were instructed to add nitric acid to solution Q in a test-tube. Most candidates were
successf ul in recognising that there was no observable change.

(ii) To the test-tube from (e)(i), candidates were asked to add aqueous silver nitrate and to record their
observations. Most candidates were successful in this question and recorded a yellow precipitate.

(f) Most candidates correctly identified the cation and anion in solution Q as potassium and iodide.
Candidates should be reminded to make full use of the ‘Notes for use in qualitative analysis’ at the
back of the paper. They should also be reminded that if f ormulae are written then they must be
correct. This question just asked candidates to ‘identif y’ the ions, so a name was perf ectly
acceptable. If a candidate did write f ormulae, they could check them in the ‘Notes f or use in
qualitative analysis’.

Question 3

In the question stem, candidates were told that argentan is an alloy containing zinc, nickel and copper. They
were told that zinc and nickel react with dilute hydrochloric acid, but that copper does not. Using this
inf ormation, they were asked to plan an investigation to f ind the percentage by mass of copper in a
powdered sample of argentan.

Although most candidates answered this question to a high level, some candidates did not appreciate that
the zinc, nickel and copper were in an alloy and described a method as if they were using three separate
powders.

Candidates were asked to consider the apparatus needed, the methods and measurements, accuracy and
the calculation.

Apparatus: Better performing candidates not only gave a suitable piece of apparatus to use for their reaction,
e.g. beaker or conical f lask but also clearly stated that they would carry out their reaction in it. If the
apparatus was simply listed, but its use not described, then the candidates did not get credit f or the
‘apparatus’ section.

Method to use and measurements to take: The best responses described how to weigh the argentan sample,
add hydrochloric acid to the sample, f ilter the unreacted copper and then re-weigh the copper. Some
candidates missed out the initial weighing step, or when filtering they stated they were removing the zinc and
nickel.

Accuracy: Better performing candidates described that hydrochloric acid should be in excess, or that the
reaction should continue until ef f ervescence ends. They described washing and drying the copper af ter
f iltering it and recognised that they should repeat the investigation and calculate an average. Of the f our
bullet points, the accuracy statement was the one that was most frequently missed out. Candidates should
be advised to re-read their answer and consider if they have met all the bullet points. Successful candidates
made rough notes next to the question stem, so they did not f orget to cover any of the required areas.

Calculation: Most candidates successfully gave an acceptable calculation to obtain the percentage by mass
of copper in argentan.

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 Cambridge Ordinary Level
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CHEMISTRY

Paper 5070/32
Practical Test

Key messages

It is crucial that candidates have as much practical experience as possible bef ore doing a practical
examination. Practice at titrations improves candidates’ accuracy and practicing the f lame test makes
candidates familiar with the colours seen. Doing experiments with coloured solutions helps candidates
identif y the colours of precipitates f ormed.

Comments on specific questions

Question 1

Candidates generally f ound (d)–(f) dif f icult. Some candidates omitted one or more of these parts.

(a) Most candidates were able to do four titrations and record their results. A signif icant number of
candidates did not show all figures to one decimal place, particularly when the value is 0.0. The
accuracy of titration results was quite variable with some candidates being a long way f rom the
Supervisor values. It is important that appropriate Supervisor values are provided as the accuracy
of candidates’ titrations are marked with ref erence to these.

(b) There were a wide range of answers to this part with some ticks appearing in apparently random
places. However, many candidates recognised that they needed to select the two values that were
identical, within 0.2 cm3 of each other or the two closest values. Some candidates did not follow the
instructions correctly and ticked either one value or more than two values.

(c) Most candidates could calculate a correct average of their ticked values. Some candidates
calculated an average of all f our values.

(d) A common error was to use the value of 24 or 24000 in the calculation, presumably because they
were thinking of the volume of one mole of gas at room temperature and pressure. Another
common error was to try to use an Mr or Ar value.

(e) Very f ew candidates achieved full credit. Some candidates multiplied their answer to (d) by two
instead of dividing by two from the molar ratio in the equation. Candidates who obtained a correct
answer f rom their data sometimes did not express it to three significant figures as was specif ically
required in the question. This was particularly the case when the candidate’s answer came to a
value where the second or third significant figure was a 0. Candidates were awarded partial credit if
they did an incorrect calculation but expressed their answer correctly to three signif icant f igures.

(f) This question was more difficult because less structure was given to the calculation and candidates
needed to do a three-step calculation to gain full credit. Many candidates correctly determined the
molar mass but then did not know how to use it in the rest of the calculation. The mark scheme
shows one method f or the calculation, but credit was given f or any correct method.

(g) Many candidates correctly described the idea of needing to mix the contents

(h) Many candidates realised that this increased the accuracy of the titration by avoiding overshooting
the end-point. The most common error was to write about the ease of seeing the colour change.

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Question 2

(a) It is important that candidates gain experience in doing f lame tests and recognising the colours
rather than simply using the quantitative analysis notes. In particular, they need to be able to
distinguish between the yellow of sodium, the flame colour of calcium which, in practice, is much
more red than orange and the very distinct red obtained f rom lithium ions.

It is essential that an appropriate piece of apparatus that produces a pale blue/colourless f lame is
provided f or this test. A spirit burner is not suitable.

Many candidates described the colour as orange.

(b) Error carried forward was applied to this part and candidates were given credit f or choosing a
suitable ion based on their observation of the colour. Equally, if they had written sodium but had not
obtained a yellow colour f or the f lame test then sodium ions would not gain credit.

This general principle is applied throughout Question 2.

(c) Most candidates were able to do this test correctly although many did not describe their
observations fully. Some candidates thought they had identified carbon dioxide as the gas evolved.

(d) Those candidates who had obtained suitable results were generally able to identif y the anion ,
although some thought it was ammonium or ammonia.

(e) Many candidates answered this by referring to the difficulty of identifying a gas by its smell rather
than addressing the hazards associated with this method.

(f) Most candidates obtained a green precipitate, although some described it as white. Candidates
need to be aware that it sometimes requires a large quantity of sodium hydroxide to be sure that
excess has been added. With the chromium ion, the precipitate should have dissolved quite easily.
Many candidates did not describe the green solution f ormed when the precipitate dissolved.

(g) This was generally done well, although as in (e) some candidates thought the precipitate was
white.

(h) Most candidates realised there was no change when nitric acid was added.

Observing a white precipitate in a green solution is difficult. Candidates should be encouraged to

always leave a precipitate to stand for a f ew minutes before recording their observations so that the
precipitate settles. This makes it easier to see the colour. Given the nature of the test, candidates
should have known that if a precipitate is formed, it is likely to be either white, cream or pale yellow.

The most common error was to state that the precipitate was green.

(i) The expected answers were chromium(III) and chloride, but award of credit was dependent on the
observation candidates had made. Conclusions should always be based on experimental
observations.

Question 3

Candidates continue to f ind the planning question quite dif f icult. The quality of the answers was very
variable. Most candidates made an attempt at an answer, but many did not address all of the bullet points in
the question. Candidates cannot gain f ull credit unless they write about all of these points.

Some candidates misunderstood the question and thought they had been provided with separate samples of
zinc and copper.

Some candidates did not gain credit because they described a completely inappropriate method such as
distillation or using a magnet. Some candidates suggested electrolysis as a method and gained some credit.
Using a method which involved collecting and measuring the volume of hydrogen gas was completely
acceptable but few of the candidates who chose this method were able to describe it appropriately or knew
how to use the data to obtain the percentage of zinc.

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Those candidates who described an appropriate method often did not write about techniques that ensured
accuracy and/or did not show how to use the data they collected to calculate the percentage of zinc.
Calculation of the percentage of copper instead of zinc was quite common.

A very common mistake was for candidates to add the acid to the Muntz, filter the mixture but then go on to
suggest that if they evaporated the f iltrate they would then obtain zinc crystals.

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 Cambridge Ordinary Level
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CHEMISTRY

Paper 5070/41
Alternative to Practical

Key messages

• Candidates should be encouraged to pay attention to the command word used in questions. For
example, Question 1 included a ‘describe’ command word, which was not always recognised by
candidates.
• Candidates should lay out their workings f or calculation questions clearly, with indications of what is
being calculated at each stage. By working in this way, candidates may be eligible to get an ‘error carried
f orward’ mark, even when they have made an error.
• Candidates could have increased their marks on Question 3 by careful reading of the question stem, or
of the ‘Notes f or use in qualitative analysis’.
• While most candidates gave a successf ul method f or the planning question, some missed out the
accuracy section and ensure they caref ully read the whole of the question stem.

General comments

Candidates showed much greater awareness of the use of ‘Notes f or use in qualitative analysis’ this year
than in previous examination series. The questions which involved referencing those sheets were generally
well answered. It was more noticeable this year that questions which involved candidates ref lecting on
practical techniques that they should be familiar with, such as how to read the scale on a burette, or how to
carry out a f lame test were less successf ully answered f or many of the candidates. It was evident in
Question 1 that candidates remembered to give burette readings to one decimal place. A common area that
could be improved was the reading and understanding of the question stem. There were instances when
taking a bit more time reading the question first would have benefitted the candidates. This was relevant in
Question 1(b) when asked to ‘describe the products’, Question 2(e) when candidates were asked to give
their answer to three significant f igures, and in Question 4 when asked to discuss the accuracy of their
method.

Comments on specific questions

Question 1

(a) Most candidates recognised that the apparatus labelled L and M were electrodes and that a
suitable material from which they are made is carbon or graphite. Some candidates recommended
the use of a non-inert metal, which would not be suitable.

(b) Candidates should be encouraged to take time to understand what the question stem is asking for.
The candidates were asked to, ‘Describe the appearance of the products at L and M’. A number of
candidates named the products of lead and bromine, but did not describe their appearance. A
suitable answer would have been to describe a shiny, grey solid or liquid (due to the molten state of
the lead) at the cathode and an orange-brown gas at the anode.

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(c) This question asked candidates to, ‘Explain why the lamp goes out’ when the teacher stops heating
and allows the lead(II) bromide to cool. Successf ul candidates realised that the molten lead( II)
bromide would solidify as it cooled. The best answers also explained that current would no longer
f low because ions in the lead(II) bromide would no longer be able to move. Two common
misconceptions were evident in the answers of candidates. Some candidates thought that the
power f or the lamp was coming from heating, rather than from the power supply. Another common
misconception was that electrons were no longer able to move in the solidif ied lead( II) bromide,
rather than ions.

Question 2

(a) Candidates should have completed initial and f inal burette readings on the table, by using the
burette readings shown in Fig. 2.1. They should then have used those readings to give the volumes
of ethanedioic acid added, 20.9 cm3, 20.5 cm3 and 19.9 cm3. Most candidates gave the correct
values f or initial and final readings, although there were some who were reading the burette values
f rom the bottom upwards, rather than from the top down, for example giving a reading of 22.9 cm3
rather than 21.1 cm3 f or the final reading of titration 1. It would be very useful for candidates to have
regular practise of reading burette scales, either physically, or using diagrams as were used in this
question. Candidates should also be reminded that they need to take guidance f or how many
decimal places to use from what is already shown on the table. In this case, the values on the table
were to one decimal place, so candidates should have given their values to one decimal place also.
This includes writing 0.0 cm3 rather than 0 cm3. Most candidates successf ully calculated the
volumes used based on their values.

(b) Candidates were required to tick the ‘best two’ titration results f rom Table 2.1, which they had
completed in (a). Some candidates seemed to not understand that the ‘best’ values meant those
that were closest together. The correct answer was to tick titrations 3 and 4 as their values were
the closest, only 0.2 cm3 apart.

(c) In this question, candidates were required to use their ticked values to calculate the average
volume of ethanedioic acid needed. Some candidates calculated an average of all the values,
rather than just their ticked values. The expected answer was 20.0 cm3.

(d) Candidates were asked to calculate the number of moles of sodium hydroxide in this question. All
the inf ormation required (the volume and concentration of NaOH(aq)) was given in the question.
Many candidates gave the correct answer of 0.02 moles.

(e) The question stem told the candidates, ‘One mole of ethanedioic acid is neutralised by two moles
of sodium hydroxide’ and asked them to use their answers to (c) and (d) to calculate the
concentration of ethanedioic acid. Successful candidates used the ratio provided to recognise that
they would need to halve the number of moles they calculated f or NaOH, so they divided their
answer f rom (d) by 2. They then divided that answer by their average volume f rom (c) in dm3. The
question stem also asked that candidates, ‘Give your answer to three signif icant f igures’. Some
candidates did not give their answer to three signif icant f igures, even though they had done the
calculation correctly. Candidates should be reminded to follow the guidance of the question stem,
as they will not achieve f ull credit if they do not give answers to the precision requested. The
expected answer was 0.500 mol / dm3.

(f) (i) Candidates were given the formula of ethanedioic acid and the mass of ethanedioic acid (6.3 g) in
100 cm3 of the aqueous solution. They were asked to calculate the relative f ormula mass of
ethanedioic acid using their answer from (e). The expected answer was 126. There were various
acceptable methods to get this answer. One correct method, which several successf ul candidates
used, was to multiply their answer of the concentration from (e) by 0.1, giving the number of moles
in 100 cm3. They then divided the mass, 6.3 g, by this number of moles to give the relative
molecular mass. Candidates who incorrectly calculated the number of moles in the f irst step were
still able to receive an error carried forward mark, if they clearly indicated they were dividing 6.3 g
by their number of moles. Candidates should be encouraged to lay out their answers to
calculations clearly, indicating what the calculated values ref er to e.g. number of moles, mass,
concentration etc. so that error carried f orward marks are acc essible.

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(ii) Using their answer to (f)(i) candidates were asked to deduce the value of n (the number of moles of
water in the f ormula of the hydrated compound). Successf ul candidates calculated the Mr of
C2H2O4 then subtracted this value from their answer to (f)(i). This gave an intermediate value which
was divided by 18 (the Mr of H2O) to give the f inal answer. The expected answer was 2.

(g) Candidates were asked why the conical f lask in the titration is placed on a white tile. Many
candidates correctly stated that it is to see the colour change more clearly. It should be noted that
all three parts of this statement were needed. Some candidates just mentioned seeing the colour,
but the important part of a titration is the endpoint, when the colour changes. Others omitted the
colour and just said ‘the change’ but they needed to say what type of change they were looking for.
Finally, some did mention the colour change, but did not say how the white tile would help. The
colour change would be visible without the tile, the key point is that the colour change could be
seen more easily, or more clearly.

(h) Most candidates successf ully stated that a measuring cylinder is not used in this experiment
because it is not accurate, or precise enough.

Question 3

(a) (i) The majority of candidates were able to describe how a gas is passed through limewater. This
question could have been answered with a description, a diagram or both. When a diagram was
drawn, some candidates did not draw the delivery tube going into the limewater. In successf ul
diagrams it was clear that the delivery tube was entering the limewater.

(ii) Candidates were required to give two observations from test 1. Test 1 involved the addition of a
white powder, Y, into excess dilute acid. Candidates could see in Table 3.1 that a colourless
solution forms and limewater becomes milky. They needed to give two observations in addition to
those. Most candidates recognised that carbon dioxide was produced. However, just stating that a
gas, or carbon dioxide, is produced is not an observation. The candidates needed to clearly state
what they would see. Therefore, they could say they would see fizzing, effervescence, or bubbling,
which were the most common correct statements. Candidates should also recognise that the solid
would disappear, or dissolve.

(iii) Most candidates correctly identif ied the gas as carbon dioxide.

(iv) Most candidates successfully identified the anion as a carbonate. Candidates should recognise that
the ‘Notes for use in qualitative analysis’ pages at the back of the question paper are there to be
ref erred to.

(v) Candidates were asked to use the results f rom test 2 to identif y the acid used in test 1. Test 2
involved the addition of nitric acid and barium nitrate. A white precipitate was observed. Using the
‘Notes for use in qualitative analysis’, candidates should have identified that the test described in
test 2 is a test for sulfate ions. In (a)(iii), the only anion in solid Y was identified as a carbonate, so
the sulf ate ion must have come from the acid which was used in step 1, hence the correct answer
is sulf uric acid. Most candidates successf ully identif ied the acid.

(vi) Several dif f erent ions were given by candidates as the answer f or this question. Successf ul
candidates used the ‘Notes for use in qualitative analysis’ and recognised that the cation in Y must
be zinc, Zn2+. Candidates should be reminded that for any of the ‘identify’ questions, any f ormulae
that they give must be correct. If they are unsure, they can copy how it is written from the ‘Notes for
use in qualitative analysis’.

(b) (i) This question asks candidates to state why it is not correct that Z contains Cu2+ ions. The start of
(b) states that, ‘Solution Z is colourless’. Better performing candidates recognised that Cu2+ ions
are blue, and that solution Z is colourless. Other candidates got conf used by talking about the
colours of precipitates in the ‘Tests for aqueous cations’, which was irrelevant, they simply had to
state that Cu2+ ions would not be colourless.

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(ii) Successful candidates clearly stated the procedure for completing a flame test. They stated that a
wire or splint should be placed in solution Z, then held in a blue Bunsen burner f lame and the
colour of the f lame (lilac) observed. Some candidates seemed not to have had experience of
completing a f lame test and, although they got the ‘lilac f lame colour’ f rom the ‘Notes f or use in
qualitative analysis’, they were not able to describe the process.

(iii) This question asked candidates to describe a test to identif y which Group VII ion is present in Z.
Successful candidates consulted the ‘Notes for use in qualitative analysis’ and clearly stated that
nitric acid and silver nitrate should be added and the colours of the precipitates observed. The best
responses linked the precipitate colours to the Group VII ions, white for chloride, cream for bromide
and yellow for iodide. Other responses incorrectly referred to the gas test for chlorine. Candidates
should ensure they caref ully read both the question and the notes sheets in order to give the
correct tests.

Question 4

In the question stem, candidates were told that argentan is an alloy containing zinc, nickel and copper. They
were told that zinc and nickel react with dilute hydrochloric acid, but that copper does not. Using this
inf ormation, they were asked to plan an investigation to f ind the percentage by mass of copper in a
powdered sample of argentan.

Although most candidates answered this question to a high level, some candidates did not appreciate that
the zinc, nickel and copper were in an alloy and described a method as if they were using three separate
powders.

Candidates were asked to consider the apparatus needed, the methods and measurements, accuracy and
the calculation.

Apparatus: Better performing candidates not only gave a suitable piece of apparatus to use for their reaction,
e.g. beaker or conical f lask but also clearly stated that they would carry out their reaction in it. If the
apparatus was simply listed, but its use was not described, then the candidates did not get credit f or the
‘apparatus’ section.

Method to use and measurements to take: The best responses described how to weigh the argentan sample,
add hydrochloric acid to the sample, f ilter the unreacted copper and then re-weigh the copper. Some
candidates missed out the initial weighing step, or when filtering they stated that they were removing the zinc
and nickel.

Accuracy: Better performing candidates described that hydrochloric acid should be in excess, or that the
reaction should continue until ef f ervescence ends. They described washing and drying the copper af ter
f iltering it and recognised that they should repeat the investigation and calculate an average. Of the f our
bullet points in Question 4, the accuracy statement was the one that was most f requently missed out.
Candidates should be advised to re-read their answer and consider carefully if they have met all of the bullet
points. Successful candidates made rough notes next to the question stem, so they did not f orget to cover
any of the required areas.

Calculation: Most candidates successfully gave an acceptable calculation to obtain the percentage by mass
of copper in argentan.

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 Cambridge Ordinary Level
5070 Chemistry November 2024
Principal Examiner Report f or Teachers

CHEMISTRY

Paper 5070/42
Alternative to Practical

Key messages

There continues to be evidence that candidates are answering questions based more on theoretical
knowledge than from practical experience. It is important that candidates have as much opportunity as
possible to do experiments, see equipment and make observations f or themselves.

General comments

Overall, candidates showed a good understanding.

Comments on specific questions

Question 1

(a) Most candidates realised that sulfuric acid is required to make copper sulf ate. A f ew suggested
other acids and some clearly did not understand the reaction and suggested other compounds.

(b) (i) Many candidates did not know the name of an evaporating dish. Some simply called it a dish or a
bowl and a few suggested completely inappropriate pieces of apparatus such as a conical f lask or
volumetric f lask.

(ii) Stating that the candidate stops heating when the solution becomes saturated was insuf f icient. A
description of an observation was required. Better perf orming candidates described a way of
testing for saturation and others wrote about crystals appearing or the volume of the solution
decreasing. A few candidates misunderstood the experiment and wrote about heating to dryness.

(iii) Very f ew candidates gained full credit. Many candidates incorrectly suggested that the evaporating
dish will break or wrote about safety issues but did not specifically mention the issue of the solid
spitting out of the dish. Some candidates thought that copper(II) sulf ate was f lammable. Some
candidates stated that the water bath provides more gentle heat or words to that effect but very few
wrote about the need to f orm hydrated crystals and to avoid the f ormation of the anhydrous
product.

(iv) Most candidates realised the last step was drying the crystals. A f ew candidates incorrectly dried
the crystals and then washed them again.

Question 2

Candidates generally f ound (d)–(f) dif f icult. Some candidates omitted one or more of these parts.

(a) Most candidates were able to read the diagrams of the burette correctly. A signif icant number of
candidates did not show all figures to one decimal place, particularly when the value is 0.0. A f ew
candidates read the scale incorrectly and some thought that the initial reading was 50.0 cm3.

(b) There were a wide range of answers to this part with some ticks appearing in apparently random
places. However, many candidates recognised they needed to select the two values that were
closest together and within 0.2 cm3 of each other. Some candidates did not f ollow the instructions
correctly and ticked either one value or more than two values.

© 2024
 Cambridge Ordinary Level
5070 Chemistry November 2024
Principal Examiner Report f or Teachers

(c) Most candidates could calculate a correct average of their ticked values. Some candidates
calculated an average of all f our values.

(d) A common error was to use the value of 24 or 24000 in the calculation, presumably because they
were thinking of the volume of one mole of gas at room temperature and pressure. Another
common error was to try to use an Mr or Ar value.

(e) Very f ew candidates gained f ull credit. Some candidates multiplied their answer to (d) by two
instead of dividing by two f rom the molar ratio in the equation. Candidates who obtained the
answer of 0.200 often did not express it to three significant figures as was specif ically required in
the question. Candidates were awarded partial credit if they did an incorrect calculation but
expressed their answer correctly to three signif icant f igures.

(f) This question was more difficult because less structure was given to the calculation and candidates
needed to do a three-step calculation to gain full credit. Many candidates correctly determined the
molar mass but then did not know how to use it in the rest of the calculation. The mark scheme
shows one method f or the calculation, but credit was given f or any correct method.

(g) Many candidates correctly described the idea of needing to mix the contents.

(h) Many candidates realised that adding dropwise increased the accuracy of the titration by avoiding
overshooting the end-point. The most common error was to write about the ease of seeing the
colour change.

Question 3

(a) (i) There was a f airly even spread of marks f rom 0–3 f or this question. Most candidates knew the
f lame turned yellow or that they needed to observe the colour of the f lame. Some candidates
realised they needed to dip a suitable piece of apparatus into the solution or use a spray to
introduce the solution into the flame. Some candidates thought that the flame would change colour
if they heated the solution in a test tube. Few candidates stated that a blue Bunsen f lame was
needed or that the air-hole should be open.

(ii) Most candidates performed well on this question as is expected, as they are given the quantitative
analysis notes. A few candidates incorrectly thought that the question required them to test f or
oxygen gas. Most candidates who did not gain full credit omitted some of the detail f rom the test.

(b) (i) Most candidates identified the cation. A few candidates wrote chromium without the oxidation state.
The oxidation state is given on the quantitative analysis notes and should be used even though
candidates are not expected to be aware of other oxidations states f or chromium.

(ii) Many candidates were aware of the need to add dilute nitric acid. Some suggested adding acid but
without saying that it need to be nitric acid. Common errors were to name a wrong acid or suggest
adding excess silver nitrate.

(iii) Most candidates correctly stated chloride or gave a correct f ormula f or a chloride ion. Some
candidates said it was chlorine or a chlorine ion, which was unacceptable. A f ew candidates
suggested sulf ate.

(iv) Many candidates got this correct but a signif icant number automatically wrote that a white
precipitate was formed based on the test that was used. They had not taken note of the f act that
their answer to (iii) was the only anion present. A few candidates said that a colourless solution
was f ormed. Although this is often the case in negative sulf ate tests, here the solution is green.

(v) Many candidates correctly described effervescence but some simply stated that carbon dioxide is
f ormed. This is a conclusion and not an observation.

Question 4

Candidates continue to f ind the planning question quite dif f icult. The quality of the answers was very
variable. Most candidates made an attempt at an answer, but many did not address all of the bullet points
in the question. Candidates cannot gain f ull credit unless they write about all of these points.

© 2024
 Cambridge Ordinary Level
5070 Chemistry November 2024
Principal Examiner Report f or Teachers

Some candidates misunderstood the question and thought they had been provided with separate samples of
zinc and copper.

Some candidates did not gain credit because they described a completely inappropriate method such as
distillation or using a magnet. Some candidates suggested electrolysis as a method and gained some credit.
Using a method which involved collecting and measuring the volume of hydrogen gas was completely
acceptable but few of the candidates who chose this method were able to describe it appropriately or knew
how to use the data to obtain the percentage of zinc.

Those candidates who described an appropriate method often did not write about techniques that ensured
accuracy and/or did not show how to use the data they collected to calculate the percentage of zinc.
Calculation of the percentage of copper instead of zinc was quite common.

A very common mistake was for candidates to add the acid to the Muntz, filter the mixture but then go on to
suggest that if they evaporated the f iltrate they would then obtain zinc crystals.

Some answers were excellent with candidates addressing seven or eight of the marking points to gain the
maximum six marks.

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