The table below compares the CT values of different disinfectants necessary to achieve 99% inactivation of two types of bacteria, listed as A and B.

(i) Deduce the oxidation state of chlorine in the following disinfectants.

(ii) From the data on CT values, justify the statement that bacterium B is generally more resistant to disinfection than bacterium A.

(iii) CT values can be used to determine whether a particular treatment process is adequate. Calculate the CT value, in mg min dm⁻³, when 1.50 × 10⁻⁵ g dm⁻³ of chlorine dioxide is added to a water supply with a contact time of 9.82 minutes.

(iv) From your answer to (a) (iii) and the data in the table, comment on whether this treatment will be sufficient to inactivate 99% of bacterium A.

CT values are influenced by temperature and by pH. The table below shows the CT values for chlorine needed to achieve 99% inactivation of a specific bacterium at stated values of pH and temperature.

(i) With reference to the temperature data in the table, suggest why it may be more difficult to treat water effectively with chlorine in cold climates.

(ii) Sketch a graph on the axes below to show how the CT value (at any temperature) varies with pH.

(iii) Comment on the relative CT values at pH 6.0 and pH 9.0 at each temperature.

(iv) Chlorine reacts with water as follows:

Cl₂ (g) + H₂O (l) $\rightleftharpoons$ HOCl (aq) + HCl (aq)

HOCl (aq) $\rightleftharpoons$ OCl⁻ (aq) + H⁺ (aq)

Predict how the concentrations of each of the species HOCl (aq) and OCl⁻ (aq) will change if the pH of the disinfected water increases.

Despite widespread improvements in the provision of safe drinking water, the sale of bottled water has increased dramatically in recent years. State one problem caused by this trend.

i

HOCl: +1
AND
ClO₂: +4

Accept “I” and “IV” but not “1+/1” and “4+/4” notations.

ii

«most» CT values are higher for «bacterium» B
OR
«generally» higher dosage needed for «bacterium» B 

Accept converse arguments. Accept “concentration” for “dosage”

iii

«CT = 1.50 × 10^–5 × 10³ mg dm^–3 × 9.82 min =» 1.47 × 10^–1 «mg min dm^–3»

iv

lower than CT value/minimum dosage/1.8 × 10^–1 «mg min dm^–3»
AND
no/insufficient

Accept “concentration” for “dosage”.

i

higher CT value at lower temperature
OR
higher dosage «of chlorine» needed at low temperature

Accept “effectiveness decreases at lower temperature”.
Accept “concentration” for “dosage”.
Accept converse arguments.

ii

labeled axes ( y: CT and x: pH)
AND
curve with increasing gradient 

Do not accept axes the wrong way round.
Accept a linear sketch.

iii

values at pH 9.0 approximately 3 times values at pH 6.0
OR
increase in CT values in same ratio 

The exact ratio is 2.9 times
Do not accept just “increase in value”.

iv

[HOCl] decreases AND [OCl⁻] increases

plastic disposal/pollution
OR
plastic bottles use up petroleum/non-renewable raw material
OR
chemicals in plastic bottle can contaminate water
OR
«prolonged» storage in plastic can cause contamination of water
OR
plastic water bottles sometimes reused without proper hygiene considerations

Accept other valid answers.
Accept economic considerations such as “greater production costs”, “greater transport costs” or “bottled water more expensive than tap water”

Calculate the percentage uncertainty of the volume of the aqueous sodium hydroxide.

Suggest how the precision of this measurement could be improved.

«$\frac{0.5}{25.0}\times 100$» = 2 «%»

[1 mark]

pipette/pipet «rather than a measuring cylinder»

Accept “using a burette/buret”.

Accept “using a volumetric/measuring flask”.

Do not accept “use of a more precise measuring cylinder”.

[1 mark]

Suggest why aspirin is slightly soluble in water. Refer to section 37 of the data booklet.

Formulate an equation for the conversion of aspirin to a more water soluble derivative.

A student prepares aspirin from salicylic acid in the laboratory, extracts it from the reaction mixture, ensures the sample is dry and determines its melting point.

Suggest why the melting point of the student’s sample is lower and not sharp compared to that of pure aspirin.

Organic molecules can be characterized using infrared (IR) spectroscopy.

Compare and contrast the infrared peaks above 1500 cm⁻¹ in pure samples of aspirin and salicylic acid using section 26 of the data booklet.

The pharmaceutical industry is one of the largest producers of waste solvents.

State a green solution to the problem of organic solvent waste.

presence of «large» benzene/arene ring AND non-polar/hydrophobic
OR
presence of «large» benzene/arene ring AND cannot form H-bond with water

contain COOH/carboxyl/–OH/hydroxyl «and ester group» AND polar/hydrophilic
OR
contain COOH/carboxyl/–OH/hydroxyl «and ester group» AND can form H-bonds with water

Accept “phenyl” for “benzene ring”.

Accept "carboxylic acid" for "carboxyl".

Do not accept "alcohol" for "hydroxyl".

[2 marks]

OR
C₆H₄(OCOCH₃)COOH + NaOH → C₆H₄(OCOCH₃)COONa + H₂O

Charges (O^– and Na⁺) not necessary to score the mark.

Accept net ionic equation.

Accept any strong base in place of NaOH.

[1 mark]

«student’s» sample impure

lattice disrupted/not uniform «due to presence of impurities»
OR
fewer interparticle/intermolecular forces «due to presence of impurities»

Accept converse arguments.

[2 marks]

One similarity:
peak at 2500–3000 «cm^–1»/peak due to O–H/hydroxyl in carboxylic acids
OR
peak at 1700–1750 «cm^–1»/peak due to C=O/carbonyl
OR
peak at 2850–3090 «cm^–1»/peak due to C–H of arene

One difference:
peak at 3200–3600 «cm^–1» in salicylic acid/ peak due to O–H in phenol in salicylic acid
OR
«two» peaks at 1700–1750 «cm^–1» in aspirin AND one peak «in the same area» in salicylic acid

Accept “peak at 1600 cm^–1 for arene/benzene ring” – not in the data booklet.

Accept “2500–3600 cm^–1 «overlapping absorptions of two O–H» in salicylic acid”.

Accept “stronger/broader/split peak at 1700–1750 cm^–1 in aspirin”.

[2 marks]

«use of» alternative solvents such as supercritical/liquid CO₂
OR
use of water «as solvent»
OR
solvent-free reactions «for example, polymerization of propene»
OR
solid-state chemistry
OR
recycle «waste» solvents
OR
catalysis that leads to better/higher yield
OR
reducing number of steps

Do not accept political/regulatory solutions.

“catalysis” not sufficient for mark.

[1 mark]

Suggest why a non-polar solvent was needed.

State one reason why the mixture was not heated strongly.

Non-polar solvents can be toxic. Suggest a modification to the experiment which allows the evaporated solvent to be collected.

Suggest one source of error in the experiment, excluding faulty apparatus and human error, that would lead to the following:

oil is non-polar «and dissolves best in non-polar solvents»
OR
oil does not dissolve in polar solvents ✔

Do not accept “like dissolves like” only.

solvent/oil is flammable
OR
solvent/oil must be kept below its flash point
OR
oxidation/decomposition of oil
OR
mixture has a low boiling point ✔

Accept “to prevent evaporation of oil”.

distillation «instead of evaporation» ✔

Accept “pass vapour through a condenser and collect liquid”.

Do not accept “condensation” without experimental details.

Experimental mass greater than actual mass of oil in crisps:
other substances «in the crisps» are soluble in the solvent
OR
not all the solvent evaporates ✔

Experimental mass less than actual mass of oil in crisps:
not all oil dissolved/extracted ✔

Accept “oil evaporated” OR “oil burned/decomposed” OR “oil absorbed by the filter” OR “assumption «all oil dissolved» was wrong” for M2.

Do not accept examples of human errors OR faulty apparatus.

A well answered question where replies used all the alternatives provided. Very few candidates limited their answer to "like dissolves like" and while this expression was used most student elaborated with higher quality answer. Some common incorrect responses included students talking about dissolving the crisps (chips) or indicating the oil was a polar compound.

Another correctly answered question. As accepted by notes many candidates scored by stating "to prevent evaporation of oil". This resulted in the same argument scoring twice as often used for 1d as well. Some students incorrectly indicated the problem was to prevent the evaporation of the solvent which was the point of this step in the experiment. This could indicate a general lack of understanding of experimental methods.

A bit disappointing as the number of correct answers were substantially lower than expected. Many students responded using a fume hood or other method to remove the solvent. Once again this indicates a general misunderstanding about experimental methods.

Even weak candidates scored at least one point and often both. One common pitfall was to invert the arguments or provide answers excluded by the stem. A frequent incorrect answer was identification of faulty apparatus and human error which was specifically excluded in the question.

Suggest how the end point of the titration might be estimated from the graph.

volume «found by extrapolation of the two best fit lines» required to give the highest temperature
OR
extrapolate «two best fit» lines to the point where they meet

Accept “where lines through the points meet”.

Accept “at maximum temperature”.

Accept “at 35 cm³ of HCl”.

[1 mark]

Explain how the concentration may be calculated in this way.

Heat losses would make this method less accurate than the pH probe method. Outline why the thermometric method would always give a lower, not a higher, concentration.

Suggest how heat loss could be reduced.

State one other assumption that is usually made in the calculation of the heat produced.

Suggest why scientists often make assumptions that do not correspond to reality.

Outline why the thermochemical method would not be appropriate for 0.001 mol$$dm⁻³ hydrochloric acid and aqueous sodium hydroxide of a similar concentration.

heat change/evolved can be calculated from the «maximum» temperature increase and the mass of solution
OR
q = mcΔT

heat «evolved» gives the number of moles «of both acid and alkali present when neutralisation occurs»
OR
$n=\frac{q}{\mathrm{\Delta }{H}_{neut}}$

volume «of acid and the volume of alkali required to just neutralise each other» can be used to calculate the concentration«s of both»
OR
$\left[\text{NaOH}\right]=\frac{n}{V}$

[2 marks]

smaller temperature increase/ΔT
OR
heat released would «appear to» be less

amount of substance/n calculated is smaller

[2 marks]

using «expanded» polystyrene cup
OR
insulating beaker
OR
putting a lid on beaker

Do not accept calorimeter by itself.

Accept any other reasonable suggestion.

[1 mark]

«specific» heat capacity of the beaker/container/thermometer is ignored
OR
density of the solutions is assumed as 1.00 g$$cm^–3/same as water
OR
specific heat capacity of the solutions is assumed as 4.18 J g^–1$$K^–1/same as water

Accept “reaction goes to completion”.

Accept “reaction is conducted under standard conditions”.

Accept “no evaporation occurs”.

Accept any other relevant valid assumption.

Do not accept “heat is not released from other reactions”.

[1 mark]

allows simple theories to be applied to real life situations
OR
enables us to start to understand complex situations
OR
gives answers that are accurate to the required order of magnitude
OR
simplifies the calculations involved

Do not accept “to simplify the situation” without further detail.

Accept “errors do not have a major impact on the results”.

[1 mark]

temperature rise would be too small «to be accurately measured»

Accept “heat released would be too small «to be accurately measured»”.

[1 mark]

Dose response curves are determined for each drug.

Outline the significance of range “a”.

Suggest the type of reaction used to convert morphine to codeine.

State and explain the action of opiates as painkillers.

«measures» therapeutic window/margin «of a drug»
OR
range of doses that produce a therapeutic effect without causing toxic effects

Accept “difference between ED₅₀/minimum effective/therapeutic dose «for 50% of population» AND TD₅₀ /toxic dose «for 50% of population»”.

Do not accept “therapeutic index”.

Do not accept “lethal/fatal dose” as this is not LD₅₀.

[1 mark]

«nucleophilic» substitution/S_N

Accept “methylation”.

[1 mark]

work directly on opioid/pain receptors «in brain»

suppress pain impulses in brain/CNS

resemble endorphins/enkephalins/natural chemical painkillers «produced in the brain and spinal cord»

Do not award mark for “resemble hormones”.

[2 marks]

The following graph represents world energy consumption by type for the years 1988–2013.

Estimate the percentage of energy consumption which did not directly produce CO₂ in 2013.

O₂ is consumed in producing CO₂ for electricity generation. The graph shows the relationship between the world’s electricity generation and CO₂ production between 1994 and 2013.

Calculate the mass, in million tonnes, of oxygen gas ultimately found in CO₂ which is consumed in generating 18$$000 terawatts of electricity using the equation given for the best fit line. Give your answer to 2 significant figures.

Assume coal is the only energy source.

The equilibrium expression for O₂ exchange between the atmosphere and ocean is O₂(g) $\rightleftharpoons$ O₂(aq). Identify one factor which shifts the equilibrium to the right.

Factors such as photosynthesis and respiration are excluded so that APO is influenced by oceanic changes only. Suggest why the seasonal cycles from Alert station and Cape Grim observatory are different.

The change in APO O₂/N₂ ratio, per meg, is measured relative to an O₂/N₂ reference.

$$\mathrm{\Delta }\text{(}{\text{O}}_{\text{2}}\text{/}{\text{N}}_{\text{2}}\text{)}=\left(\frac{{({\text{O}}_2/{\text{N}}_2)}_{\text{sample}}}{{({\text{O}}_2/{\text{N}}_2)}_{\text{reference}}}-1\right)\times {10}^6$$

Calculate the APO Δ(O₂/N₂) value for an oxygen concentration of 209$$400 ppm assuming that any change in N₂ concentration is negligible. Reference values for O₂ and N₂ are 209 460 and 790 190 ppm respectively.

Suggest a reason for the general negative gradient of the APO curve given in (c).

«$\frac{\sum (\text{renewables}+\text{hydroelectricity}+\text{nuclear)}}{\text{total}}$»

«$\left(\frac{8800-7200}{12600}\right)\times 100=$» 13 «%»

Accept range of “11–16%”.

[1 mark]

«18000 = 0.54x – 2000»
x = 37037 «million tonnes of CO₂»
«$\frac{32.00}{44.01}$ x 37037 = 26930»
27000/2.7 x 10⁴ «million tonnes of O₂»

Accept “37000 «million tonnes of CO₂»” for M1.

Award [2] for correct final answer with two significant figures.

Award [1] for non rounded answers in range 26903–26936 «million tonnes of O₂».

[2 marks]

increase in «atmospheric» pressure
OR
increase in [O₂(g)]/concentration of O₂(g)
OR
decrease in [O₂(aq)]/concentration of O₂(aq)
OR
decrease in temperature

Accept “increase in volume of oceans «due to polar ice cap melting»” OR “consumption of O₂ in oceans/O₂(aq)
«by living organisms»”.

State symbols required for oxygen concentration.

[1 mark]

summer in one station while winter in other
OR
stations are at different latitudes

oxygen dissolves better in colder water

Accept “opposite seasons «in each hemisphere»”.

Do not accept “different locations with different temperatures” OR “stations are in different hemispheres”.

[2 marks]

«$\text{(}\frac{209400}{209460}-1\text{)}\times {10}^6$ =» − 286.5 «per meg»

The nitrogen cancels so is not needed in the calculation.

Negative sign required for mark.

[1 mark]

decrease in [O₂]/concentration of O₂
OR
increasing combustion of fossil fuels «consumes more O₂ so [O₂]/concentration of O₂ decreases»
OR
warmer oceans/seas/water «as oxygen dissolves better in colder water»
OR
deforestation

Accept “decrease in level of O₂”.

Accept "increasing CO₂ production «consumes more O₂ so [O₂]/concentration of O₂ decreases»".

Do not accept “decrease in amount of O₂” OR “increase in greenhouse gases”.

[1 mark]

Estimate the lowest freezing point of water that can be reached by adding sodium chloride.

Estimate the percentage by mass of NaCl dissolved in a saturated sodium chloride solution at +10 ºC.

Calculate the percentage of water by mass in the NaCl•2H₂O crystals. Use the data from section 6 of the data booklet and give your answer to two decimal places.

Suggest a concern about spreading sodium chloride on roads.

–21 «ºC»

28 «%»

Accept any specific answer in the range 27 to 29 «%».

M_r = 94.48

«$2\frac{\left(1.01\times 2+16.00\right)}{94.48}\times 100=$» 38.15 «%»

Award M2 only if answer is to 2 decimal places.

Award [2] for correct final answer.

Award [1 max] for 38.10 %.

rust/corrosion «of cars and bridges»
OR
waste of important raw material
OR
soil/water salination/pollution «from run off»
OR
erosion of/damage to the road surface
OR
specific example of damage to the ecosystem
OR
«outdoor» temperatures may go below effective levels for NaCl «to lower freezing point» so NaCl could be wasted
OR
roads can refreeze causing hazards

Do not accept “tyre damage”.

Do not accept “economic issues” OR “environmental issues” unless specified (eg accept “increase in costs for local councils road budgets” but not “cost” alone).

Do not accept “makes roads more slippery”.

List the data the student would need to collect in this experiment.

Explain why this experiment might give a low result for the molar mass of butane.

Suggest one improvement to the investigation.

mass/m of lighter before AND after the experiment

volume of gas/V_gas «collected in the cylinder»

«ambient» pressure/P «of the room»

temperature/T

Accept “change in mass of lighter”.

Accept “weight” for “mass”.

Do not accept just “mass of lighter/gas”.

Accept “volume of water displaced”.

Do not accept “amount” for “volume” or “mass”.

[4 marks]

Any two of:

pressure of gas not equalized with atmospheric/room pressure

too large a recorded volume «of gas produces a lower value for molar mass of butane»
OR
cylinder tilted

difficult to dry lighter «after experiment»
OR
higher mass of lighter due to moisture
OR
smaller change in mass but same volume «produces lower value for molar mass of butane»

using degrees Celcius/°C instead of Kelvin/K for temperature

Accept “vapour pressure of water not accounted for” OR “incorrect vapour pressure of water used” OR “air bubbles trapped in cylinder”. Do not accept “gas/bubbles escaping «the cylinder»” or other results leading to a larger molar mass.

Accept “lighter might contain mixture of propane and butane”.

Do not accept only “human errors” OR “faulty equipment” (without a clear explanation given for each) or “mistakes in calculations”.

[2 marks]

record vapour pressure of water «at that temperature»
OR
equalize pressure of gas in cylinder with atmospheric/room pressure
OR
tap cylinder before experiment «to dislodge trapped air»
OR
collect gas using a «gas» syringe/eudiometer/narrower/more precise graduated tube
OR
collect gas through tubing «so lighter does not get wet»
OR
dry lighter «before and after experiment»
OR
hold «measuring» cylinder vertical
OR
commence experiment with cylinder filled with water

Accept “adjust cylinder «up or down» to ensure water level inside cylinder matches level outside”.

Accept “repeat experiment/readings «to eliminate random errors»”.

Accept “use pure butane gas”.

[1 mark]

Below are the IR spectra of two plastics (A and B); one is PETE, the other is low density polyethene (LDPE).

Deduce, giving your reasons, the identity and resin identification code (RIC) of A and B using sections 26 and 30 of the data booklet.

Describe the difference in their structures.

Explain why the difference in their structures affects their melting points.

A RIC: 1 AND B RIC: 4

ALTERNATIVE 1:
«only» PETE contains carbonyl/C=O/ester/COO groups
carbonyl groups absorb at 1700–1750 «cm^–1»

ALTERNATIVE 2:
LDPE contains more C–H bonds «than PETE»
C–H bonds absorb at 2850–3090 «cm^–1»

For either, accept specific frequencies in these ranges (eg 1735 «cm^–1» or 2900 «cm^–1»).

[3 marks]

HDPE less branched
OR
LDPE more branched

Accept “no branching in HDPE AND branching in LDPE”.

[1 mark]

HDPE «polymer» chains/molecules can pack together more closely «than LDPE chains»
OR
HDPE «polymer» chains/molecules have a higher contact surface area «than LDPE chains»

stronger intermolecular/dispersion/London/van der Waals’ forces in HDPE AND higher melting point

Accept converse arguments.

[2 marks]

Infrared (IR) spectra can be used to distinguish between various types of plastics. Some simplified IR spectra are given here.

Explain, with a reference to molecular structure, which two of the plastics can not be distinguished by IR spectroscopy.

HDPE AND LDPE «have similar IR»

both are polyethene/polyethylene
OR
only branching differs
OR
same bonds
OR
same bending/stretching/vibrations

Accept “water bottle AND water bottle cap” for M1.

[2 marks]

Annotate the balanced equation below with state symbols.

CaCO₃(__) + 2HCl(__) → CaCl₂(__) + CO₂(__) + H₂O(__)

Neither method actually gives the initial rate. Outline a method that would allow the initial rate to be determined.

Deduce, giving a reason, which of the two methods would be least affected by the chips not having exactly the same mass when used with the different concentrations of acid.

State a factor, that has a significant effect on reaction rate, which could vary between marble chips of exactly the same mass.

Justify why it is inappropriate to record the uncertainty of the mean as ±0.01 s.

If doubling the concentration doubles the reaction rate, suggest the mean time you would expect for the reaction with 2.00 mol dm⁻³ hydrochloric acid.

Another student, working alone, always dropped the marble chips into the acid and then picked up the stopwatch to start it. State, giving a reason, whether this introduced a random or systematic error.

CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + CO₂(g) + H₂O(l)

Accept “CO₂(aq)”.

[1 mark]

measure the volume of gas at different times «plot a graph and extrapolate»

OR

measure the mass of the reaction mixture at different times «plot a graph and extrapolate»

Accept other techniques that yield data which can be plotted and extrapolated.

[1 mark]

method 2 AND marble is in excess «so a little extra has little effect»

OR

large chips AND marble is in excess «so a little extra has little effect»

OR

method 2 AND HCl is limiting reagent «so a little extra marble has little effect»

OR

large chips AND HCl is limiting reagent «so a little extra marble has little effect»

Accept, as a reason, that “as the mass is greater the percentage variation will be lower”.

[1 mark]

surface area

OR

purity «of the marble»

Accept “shape of the chip”.

[1 mark]

variation of individual values is much greater «than this uncertainty»

OR

«uncertainty» does not take into account «student» reaction time

[1 mark]

«$\frac{121.96\text{ s}}{2}$ = 60.98 s» = 61 «s»

[1 mark]

systematic AND always makes the time shorter «than the actual value»

OR

systematic AND it is an error in the method used «not an individual measurement»

OR

systematic AND more repetitions would not reduce the error

Accept, as reason, “it always affects the value in the same direction” OR “the error is consistent”.

[1 mark]

Outline two properties a substance should have to be used as liquid-crystal in a liquid-crystal display.

Describe how the structures of LDPE and HDPE affect one mechanical property of the plastics.

One of the two infrared (IR) spectra is that of polyethene and the other of polytetrafluoroethene (PTFE).

Deduce, with a reason, which spectrum is that of PTFE. Infrared data is given in section 26 of the data booklet.

Many plastics used to be incinerated. Deduce an equation for the complete combustion of two repeating units of PVC, (–C₂H₃Cl–)₂.

Any two of:

ability to form a LC phase

chemically stable

«LC phase that is» stable over suitable temperature range 

polar

OR

being able to change orientation with applied electric field

rapid switching speed «responds to changes of voltage quickly»

Accept “ability of molecules to transmit light under certain conditions” OR “rodshaped molecules” OR “stable to light/not light sensitive”.

[Max 2 Marks]

branching in LDPE prevents close packing «of chains»

LDPE is more flexible/less rigid

OR

LDPE has lower «tensile» strength

Do not accept “difference in density”.

Award [1 max] for stating “branching in LDPE AND little/no branching in HDPE”.

B AND absence «of absorption of» C–H at 2850–3090 «cm^–1»

OR

B AND presence of «absorption of» C–F at 1000–1400 «cm^–1»

(–C₂H₃Cl–)₂ (s) + 5O₂ (g) → 4CO₂ (g) + 2H₂O (l) + 2HCl (g)

correct species in reactants and products

balanced

Accept “(–C₂H₃Cl–)₂ (s) + 5.5O₂ (g) → 4CO₂ (g) + 3H₂O (l) + Cl₂ (g)”.

Award M2 only if M1 correct.

Draw the dipeptide represented by the formula Ala-Gly using section 33 of the data booklet.

Deduce the number of ¹H NMR signals produced by the zwitterion form of alanine.

Outline why amino acids have high melting points.

peptide bond

order of amino acids

Accept zwitterion form of dipeptide.

Accept a condensed structural formula or a skeletal structure.

Penalize missing hydrogens or incorrect bond connectivities once only in Option B.

[2 marks]

3

[1 mark]

form zwitterions

«strong» ionic bonding

OR

«strong» ionic lattice

OR

«strong» electrostatic attraction/forces

Do not accept hydrogen bonding or IMFs for M2.

[2 mark]

Outline why the initial reaction should be carried out under a fume hood.

Deduce the equation for the relationship between absorbance and concentration.

Outline how a solution of 0.0100 mol dm⁻³ is obtained from a standard 1.000 mol dm⁻³ copper(II) sulfate solution, including two essential pieces of glassware you would need.

The original piece of brass weighed 0.200 g. The absorbance was 0.32.

Calculate, showing your working, the percentage of copper by mass in the brass.

Deduce the appropriate number of significant figures for your answer in (d)(i).

Comment on the suitability of using brass of this composition for door handles in hospitals.

If you did not obtain an answer to (d)(i), use 70 % but this is not the correct answer.

Suggest another property of brass that makes it suitable for door handles.

Copper(II) ions are reduced to copper(I) iodide by the addition of potassium iodide solution, releasing iodine that can be titrated with sodium thiosulfate solution, Na₂S₂O₃ (aq). Copper(I) iodide is a white solid.

4I⁻ (aq) + 2Cu²⁺ (aq) → 2CuI (s) + I₂ (aq)

I₂ (aq) + 2S₂O₃²⁻ (aq) → 2I⁻ (aq) + S₄O₆²⁻ (aq)

Deduce the overall equation for the two reactions by combining the two equations.

Suggest why the end point of the titration is difficult to determine, even with the addition of starch to turn the remaining free iodine black.

NO₂/NO/NO_x/HNO₃/gas is poisonous/toxic/irritant ✔

Accept formula or name.

Accept “HNO₃ is corrosive” OR “poisonous/toxic gases produced”.

Accept “reaction is harmful/hazardous”.

Slope (gradient):

40 ✔

Equation:

absorbance = 40 × concentration

OR

y = 40x ✔

Accept any correct relationship for slope such as $\frac{1.00}{0.025}$.

Award [2] if equation in M2 is correct.

dilute 1.00 cm³ «of the standard solution with water» to 100 cm³

OR

dilute sample of standard solution «with water» 100 times ✔

«graduated/volumetric» pipette/pipet ✔

volumetric flask ✔

Accept any 1 : 100 ratio for M1.

Accept “mix 1 cm³ of the standard solution with 99 cm³ of water” for M1.

Do not accept “add 100 cm³ of water to 1.00 cm³ of standard solution” for M1.

Accept “burette/buret” for M2.

Accept “graduated/measuring flask” for M3 but not “graduated/measuring cylinder” or “conical/Erlenmeyer flask”.

concentration of copper = 0.0080 «mol dm^–3» ✔

mass of copper in 250.0 cm³ = «0.0080 mol dm^–3 × 0.2500 dm³ × 63.55 g mol^–1 =» 0.127 «g»

OR

mass of brass in 1 dm³ = «4 × 0.200 g =» 0.800 g AND [Cu2+] = «0.0080 mol dm^–3 × 63.55 g mol^–1 =» 0.5084 g dm^–3 ✔

«% copper in this sample of brass $=\frac{0.127}{0.200}\times 100=$» 64 «%»

OR

«% copper in this sample of brass $=\frac{0.5084}{0.800}\times 100=$» 64 «%» ✔

Accept any value in range 0.0075–0.0085 «mol dm^–3» for M1.

Accept annotation on graph for M1.

Award [3] for correct final answer.

Accept “65 «%»”.

two ✔

Do not apply ECF from 1(d)(i).

«since it is greater than 60%» it will reduce the presence of bacteria «on door handles» ✔

resistant to corrosion/oxidation/rusting

OR

low friction surface «so ideal for connected moving components» ✔

Accept “hard/durable”, “«high tensile» strength”, “unreactive”, “malleable” or any reference to the appearance/colour of brass (eg “gold-like”, “looks nice” etc.).

Do not accept irrelevant properties, such as “high melting/boiling point”, “non-magnetic”, “good heat/electrical conductor”, “low volatility”, etc.

Do not accept “ductile”.

2I⁻ (aq) + 2Cu²⁺ (aq) + 2S₂O₃²⁻ (aq) → 2CuI (s) + S₄O₆²⁻ (aq)

correct reactants and products ✔

balanced equation ✔

M2 can only be awarded if M1 is correct.

precipitate/copper(I) iodide/CuI makes colour change difficult to see

OR

release of I₂/iodine from starch-I₂ complex is slow so titration must be done slowly ✔

State and explain how the graph would differ if 1 mol$$dm⁻³ sulfuric acid had been used instead of 1 mol$$dm⁻³ hydrochloric acid.

graph would peak/maximum at 17.5 cm³
OR
smaller volume of acid «needed to reach equivalence» 

sulfuric acid is dibasic/diprotic

higher temperature would be reached

Accept “gradient/slope «of graph» is greater/steeper” for M1.

Accept “one mole of sulfuric acid neutralizes two moles of NaOH” for M2.

[2 marks]

Deduce, giving a reason, the group of elements in the periodic table most likely to undergo sublimation.

Describe the density trend across periods 4 and 5 of the periodic table.

Suggest, with a reason, whether the lanthanoids or actinoids of the f-block would have the higher density.

Compare the ease of oxidation of s-block and d-block metals to their melting points and densities. Use section 25 of the data booklet.

Sketch how the first ionization energies of elements vary with their atomic radius.

group 18/noble gases  [✔]

smallest difference between melting and boiling points
OR
weakest intermolecular forces «in that period»  [✔]

Note: Accept “group 17/halogens”.

density increases «to a maximum in the transition elements» AND then decreases  [✔]

actinoids AND density increases down all groups «due to large increase in atomic mass for small increase in atomic volume»
OR
actinoids AND «much» greater atomic mass with similar type of bonding
OR
actinoids AND density «of actinoids» atomic number 90 to 95 is greater than corresponding lanthanoids  [✔]

Note: Accept “actinoids AND on graph actinoids have «much» greater density than lanthanoids”.

Alternative 1:
«metals with» low densities oxidize easier  [✔]

«metals with» low melting points oxidize easier [✔]

Alternative 2:
in s-block «metals with» high densities oxidize easier
OR
in s-block «metals with» low melting points oxidize easier [✔]

in d-block «metals with» low densities oxidize easier
OR
in d-block «metals with» low melting points oxidize easier [✔]

Note:  Award [1 max] for “s-block metals more easily oxidized” OR “s-block metals have lower melting points” OR “s-block metals have lower densities”.

Accept “have greater activity” for “oxidize easier”.

  [✔]

Note: Accept any negative sloping line.

Do not award mark if line touches either axis.

Some candidates appeared to be unfamiliar with the term “sublimation”. Whilst most students correctly identified the noble gases as the group most likely to sublime there were a variety of other answers. Many students referred to “low melting and boiling points” rather than identifying the difference between these as the key factor.

Most students realised that density peaks around the middle of each of these periods, though a significant minority seemed unaware of the significance of “periods” and just reported the overall general increase in density.

Poorly answered. Some students seemed unaware of the terms “lanthanoids” and “actinoids”. Many others just stated the actinoids because they had greater atomic masses, without adding that the bonding, and hence the volume occupied by each atom, would be similar to the lanthanoids. Others responded in terms of the given data, but this required rather more justification than just stating “as can be seen from the graph”.

Almost all candidates gained some credit on this question and many obtained full marks. Students were generally aware that s-block elements are more reactive than d-block ones and hence are more easily oxidised. Many correctly linked this to lower melting points and densities. Often a causal relationship was implied (more reactive because of their low density/mp) but this was not penalised. A significant minority of students referred to only one of the physical properties; not reading the question fully?

Most students sketched a negative correlation between IE and radius, but then many lost the mark by drawing a line that met an axis; it is not possible for either to have a value of zero.

State an equation for the reaction of magnesium hydroxide with hydrochloric acid.

Suggest two variables, besides the time of reaction, which the student should have controlled in the experiment to ensure a fair comparison of the antacids.

Calculate the uncertainty in the change in pH.

The student concluded that antacid B was the most effective, followed by A then C and finally D. Discuss two arguments that reduce the validity of the conclusion.

Mg(OH)₂ (s) + 2HCl (aq) → MgCl₂ (aq) + 2H₂O (l)

Accept full or net ionic equation.

Any two from:

volume «of HCl»

concentration «of HCl»/[HCl]

temperature «of HCl»

mass of antacid/tablets

size of antacid particles/tablets

OR

surface area of antacid «particles»/tablets

Accept “number of tablets/different doses”.

Do not accept “same pH meter” OR “initial pH” OR “concentration of antacid/[antacid]”.

A variable must be given so do not accept answers such as “stirring”, “whether tablets are whole or crushed” etc.

[Max 2 Marks]

(±) 0.04

OR

(±) 0.03

Any two of:

uncertainty «(±)0.04/(±)0.03» means A and C cannot be distinguished

each measurement was conducted once

stomach pH should not be raised a lot «so antacid B is not necessarily effective»

mass/number of tablets/dose «of antacid» used was not controlled

actual environment in stomach is different

Accept “amount of tablets” for “dose”.

Do not accept “nature/composition of tablets differs”.

Accept an answer such as “time frame is too short since some antacids could be long-acting drugs if they contain a gelatinisation/delaying agent” but not just “time frame is too short since some antacids could be long-acting drugs”.

[Max 2 Marks]

Draw a best-fit line on the graph.

Determine the initial rate of reaction of limestone with nitric acid from the graph.

Show your working on the graph and include the units of the initial rate.

Explain why the rate of reaction of limestone with nitric acid decreases and reaches zero over the period of five days.

Suggest a source of error in the procedure, assuming no human errors occurred and the balance was accurate.

Justify this hypothesis.

The student obtained the following total mass losses.

She concluded that nitric acid caused more mass loss than sulfuric acid, which did not support her hypothesis.

Suggest an explanation for the data, assuming that no errors were made by the student.

best-fit smooth curve ✔

NOTE: Do not accept a series of connected lines that pass through all points OR any straight line representation. 

tangent drawn at time zero ✔
g day⁻¹ ✔
0.16 ✔

NOTE: Accept other reasonable units for initial rate eg, mol dm⁻³ s⁻¹, mol dm⁻³ min⁻¹, g s⁻¹ OR g min⁻¹.

M3 can only be awarded if the value corresponds to the correct unit given in M2.
Accept values for the initial rate for M3 in the range: 0.13 − 0.20 g day⁻¹ OR 1.5 × 10⁻⁶ g s⁻¹ − 2.3 × 10⁻⁶ g s⁻¹ OR 7.5 × 10⁻⁸ − 1.2 × 10⁻⁷ mol dm⁻³ s⁻¹ OR 4.5 × 10⁻⁶ − 6.9 × 10⁻⁶ mol dm⁻³ min⁻¹ OR 9.0 × 10⁻⁵ − 1.4 × 10⁻⁴ g min⁻¹ OR a range based on any other reasonable unit for rate.

Ignore any negative rate value.
Award [2 max] for answers such as 0.12/0.11 g day⁻¹, incorrectly obtained by using the first two points on the graph (the average rate between t = 0 and 1 day).
Award [1 max] for correctly calculating any other average rate.

acid used up
OR
acid is the limiting reactant ✔

concentration of acid decreases
OR
less frequent collisions ✔

NOTE: Award [1 max] for "surface area decreases" if the idea that CaCO₃ is used up/acts as the limiting reactant” is conveyed for M1.

Do not accept “reaction reaches equilibrium” for M2.

surface area not uniform
NOTE: Accept “acids impure.

OR
limestone pieces do not have same composition/source
NOTE: Accept “«limestone» contains impurities”.

OR
limestone absorbed water «which increased mass»

OR
acid removed from solution when limestone removed
NOTE: Accept “loss of limestone when dried" OR "loss of limestone due to crumbling when removed from beaker”.

OR
«some» calcium sulfate deposited on limestone lost

OR
pieces of paper towel may have stuck to limestone

OR
beakers not covered/evaporation

OR
temperature was not controlled ✔

sulfuric acid is diprotic/contains two H⁺ «while nitric acid contains one H⁺»/releases more H⁺ «so reacts with more limestone»
OR
higher concentration of protons/H⁺ ✔

NOTE: Ignore any reference to the relative strengths of sulfuric acid and nitric acid.
Accept “sulfuric acid has two hydrogens «whereas nitric has one»”.
Accept "dibasic" for "diprotic".

calcium sulfate remained/deposited on limestone «in sulfuric acid»
OR
reaction prevented/stopped by slightly soluble/deposited/layer of calcium sulfate ✔

NOTE: Answer must refer to calcium sulfate.

Identify the independent and dependent variables in this experiment.

The ice bath is used at equilibrium to slow down the forward and reverse reactions. Explain why adding a large amount of water to the reaction mixture would also slow down both reactions.

Suggest why the titration must be conducted quickly even though a low temperature is maintained.

An additional experiment was conducted in which only the sulfuric acid catalyst was titrated with $\mathrm{NaOH}\hspace{0.17em}\left(\mathrm{aq}\right)$. Outline why this experiment was necessary.

Calculate the percentage uncertainty and percentage error in the experimentally determined value of $K_{\mathrm{c}}$ for methanol.

Comment on the magnitudes of random and systematic errors in this experiment using the answers in (e).

Suggest a risk of using sulfuric acid as the catalyst.

Independent variable:
chain length OR number of carbon «atoms in alcohol»
AND
Dependent variable:
volume of $\mathrm{NaOH}$ OR $K_c$/equilibrium constant OR equilibrium concentration/moles of ${\mathrm{CH}}_3\mathrm{COOH}$ ✔

dilution/lower concentrations ✔

less frequent collisions «per unit volume» ✔

Accept “lowers concentration of acid catalyst” for M1. M2 must refer to increase in activation energy or different pathway.

Do not accept responses referring to equilibrium.

equilibrium shifts to left
OR
more ethanoic acid is produced «as ethanoic acid is neutralized»
OR
prevents/slows down ester hydrolysis ✔

Accept “prevents equilibrium shift” if described correctly without direction.

to determine volume/moles of $\mathrm{NaOH}$ used up by the catalyst/sulfuric acid «in the titration»
OR
to eliminate/reduce «systematic» error caused by acid catalyst ✔

Do not accept “control” OR “standard” alone.

Percentage uncertainty:
$«\frac{0.4\times 100}{6.5}=»6«\%»$ ✔

Percentage error:
$«\frac{6.5-5.3}{5.3}=»23«\%»$ ✔

Award [1 max] if calculations are reversed OR if incorrect alcohol is used.

Any two:

large percentage error means large systematic error «in procedure» ✔

small percentage uncertainty means small random errors ✔

random errors smaller than systematic error ✔

Award [2] for “both random and systematic errors are significant.”

corrosive/burns/irritant/strong oxidizing agent/carcinogenic
OR
disposal is an environmental issue
OR
causes other side reactions/dehydration/decomposition ✔

Do not accept just “risk of accidents” OR “health risks” OR “hazardous”.

Well answered. Students mostly identified (alcohol) chain length as the independent variable and K_c at the dependent. For the latter [ethanoic acid] at equilibrium was another popular choice with some students neglecting to clarify "equilibrium" which was needed for the mark. This evidences an issue already identified in the Internal assessment that very often students only identify the processed variables. The proportion of students referring to volume of NaOH was too low for expectations.

A significant number of students scored at least one mark, usually the first and many both. Weaker students lost the second mark by referring to less collisions instead of less frequent collision or other words to this effect. Very few students referred to more diluted catalyst and of those even less were able to provide an adequate explanation in terms of the increased Ea. Many students tried to answer this question in terms of equilibrium instead of kinetics. There were also several responses that replied as if the dilution would only occur for part of the reaction or individual reactants instead of the entire solution.

Not well answered and of the few students that replied correctly most referred to preventing equilibrium shift and few candidates identified the direction of the shift. It was rather common to see answers where Le Chatelier's principle was stated without any attempt in adapting it to the context. Very few students described the specific equilibrium shift that could occur during the titration, changing the results.

Some students achieved on mark. Many answers referred simple to "control" or "standard" underlining the lack of some skills as also identified in the Internal assessment. Once again very few students had the specific details necessary to explain why this separate titration was needed in their response to receive a mark.

Many students scored both points and others at least one. Weaker students inverted the calculations.

Of the many students that obtained the mark most did through the first alternative and a lesser percentage through the third. Many students were unable to relate their calculations from 2e (percentage error and percentage uncertainty) to systematic error and random error. They either compared the calculations to incorrect errors or in some cases did not discuss the errors at all. Once again this points to a general lack on experimental understanding.

Most students received a mark for this question base on specific hazards. Very few students related disposal to environmental issues which isn't surprising as this is often missed in the Internal Assessment. Weaker students provided vague answers related to health issues which did not receive a mark. Some students misunderstood the question.

Determine from the graph the rate of reaction at 20 s, in cm³ s⁻¹, showing your working.

Outline, with a reason, another property that could be monitored to measure the rate of this reaction.

Examine, giving a reason, whether the rate of lead dissolving increases with acidity at 18 °C.

Describe one systematic error associated with the use of the gas syringe, and how the error affects the calculated rate.

Identify one error associated with the use of an accurate stopwatch.

tangent drawn to curve at t = 20 s  [✔]

slope/gradient calculation  [✔]

0.35 «cm³ s^–1»  [✔]

Note: Accept values in the range 0.32–0.42 «cm³ s^–1».

ALTERNATIVE 1
colour  [✔]

Br₂/reactant is coloured «Br^– (aq)/product is not»  [✔]

Note: Do not accept “changes in temperature” or “number of bubbles”.

ALTERNATIVE 2
conductivity  [✔]

greater/increased concentration of ions in products  [✔]

ALTERNATIVE 3
mass/pressure  [✔]

gas is evolved/produced  [✔]

Note: Do not accept “mass of products is less than mass of reactants”.

ALTERNATIVE 4
pH  [✔]

methanoic acid is weak AND HBr is strong
OR
increase in [H⁺]  [✔]

no AND experiment 7/beer has lowest rate and intermediate acidity/pH
OR
no AND experiment 6/orange juice has fastest rate but lower acidity/higher pH than experiment 5/lemonade
OR
no AND experiment 6/orange juice has highest rate and intermediate acidity/pH   [✔]

Note: Accept no AND any comparison, with experimental support, that concludes no pattern/increase with acidity.
eg: “rate of Pb/lead dissolving generally decreases with acidity as tap water has highest rate (after orange juice) while lemonade (lower pH) has lower rate”.

ALTERNATIVE 1
gas may leak/be lost/escape
OR
plunger may stick/friction «so pressure is greater than atmospheric pressure»
OR
syringe may be tilted «up» so plunger moves less «with gravity acting on plunger»
OR
CO₂ dissolved in water  [✔]

calculated rate lower  [✔]

ALTERNATIVE 2
syringe may be tilted «down» so plunger moves more «with gravity acting on plunger»
OR
syringe is held in hand so gets warmer and gas expands  [✔]

calculated rate higher [✔]

Note: Calculated rate is lower or higher must be stated for M2.

Do not accept “scale on syringe is inaccurate”, “errors in reading syringe”, or “bubbles in syringe”.

human reaction time/delay «starting/stopping the stopwatch»  [✔]

Note: Do not accept “inaccurate stopwatch”.

This question was challenging for many students. Quite a few candidates did draw a tangent line at 20s for 1 mark, show a slope/gradient calculation of the line for 1 mark, and had a reasonable final value for the final mark. Some candidates only found the average rate by finding the ratio of the value at that data point and received one mark (16/20=0.80 cm³ s^-1). Candidates also received one mark if they had a correct answer with no work since the question clearly asked students to show their work.

The reaction rate was originally monitored by measuring the volume of CO₂ produced. Students needed to propose another method for this reaction, with a reason, that could be used to measure the rate. There were several possible correct answers and most students received at least one mark with many receiving both marks. The most common incorrect answer involved changes in temperature.

This question required students to recognize the rate of lead dissolving did not increase with acidity and to refer to data in the table for the reason. Some students did not refer to data in the table and did not receive the mark because they did not have a reason, other students compared the rate of lead dissolving with temperature increasing which did not answer the question.

This question was asking about a systematic error. There were several possible correct answers for the error, but students also needed to clearly identify a specific error and if the rate increased or decreased for the second mark. Many students confused this with the concept of a random error and identified the uncertainty of reading the syringe which is incorrect. Teachers need to reinforce the concept of systematic versus random errors.

This question was well answered by most candidates although some students did not read the question clearly and commented on the stopwatch having problems or not being accurate.

Sketch a graph that would support the student’s hypothesis.

Suggest what the correlation coefficient of −0.9999 indicates.

State the equation of the straight line obtained using the data.

Outline how current flows in the sodium chloride solution.

OR

OR

Correct labels of axes required for mark.

Accept d^–1 instead of $\frac{1}{d}$.

Accept I^–1 instead of $\frac{1}{I}$.

Plot of I vs d should not be linear.

negative correlation

OR

model/prediction matches results

OR

99% of variance accounted for

I = – 0.001631 d + 0.09939

OR

y = – 0.001631 x + 0.09939

Accept correctly rounded values for m and b in equation.

Do not accept “y = mx + b”.

ions move «across electrolyte»

Compare and contrast the structures of oseltamivir and zanamivir, stating the names of functional groups.

Deduce the wavenumber of one absorbance seen in the IR spectrum of only one of the compounds, using section 26 of the data booklet.

Suggest one ethical consideration faced by medical researchers when developing medications.

One similarity:

both contain amido «group»

One difference:

oseltamivir contains ester «group» AND zanamivir does not
OR
oseltamivir contains amino «group» AND zanamivir does not «but contains a guanidino group»
OR
zanamivir contains carboxyl «group» AND oseltamivir does not
OR
zanamivir contains «several» hydroxyl «groups» AND oseltamivir does not
OR
oseltamivir contains ester «group» AND zanamivir contains carboxyl «group»
OR
oseltamivir contains ester «group» AND zanamivir contains «several» hydroxyl «groups»

Accept “both contain ether «group»” OR “both contain alkene/alkenyl «group»” OR “both contain carbonyl «group»” OR “both contain amino/amine «group»”. Latter cannot be given in combination with second difference alternative with respect to amino group.

Accept “amide/carboxamide/carbamoyl” for “amido”.

Accept “amine” for “amino”.

Accept “carboxylic acid” for “carboxyl”.

Accept “hydroxy/alcohol” for “hydroxyl”, but not “hydroxide”.

[2 marks]

1050–1410
OR
1620–1680
OR
1700–1750
OR
2500–3000
OR
3200–3600
OR
2850–3090
OR
3300–3500 «cm^–1»

[1 mark]

«negative» side-effects of medication on patient/volunteers
OR
effects on environment «from all materials used and produced»
OR
potential for abuse
OR
drugs may be developed that are contrary to some religious doctrines
OR
animal testing
OR
risk to benefit ratio
OR
appropriate consent of patient volunteers

[1 mark]

Draw a section of isotactic polychloroethene (polyvinylchloride, PVC) showing all the atoms and all the bonds of four monomer units.

The infrared (IR) spectrum of polyethene is given.

Suggest how the IR spectrum of polychloroethene would differ, using section 26 of the data booklet.

Identify a hazardous product of the incineration of polychloroethene.

Explain how plasticizers affect the properties of plastics.

Suggest why the addition of plasticizers is controversial.

correct bonding  [✔]

Cl atoms all on same side and alternate  [✔]

Note: Continuation bonds must be shown.

Award [1 max] if less than or more than four units shown.

Accept a stereo formula with all atoms and bonds shown.

«strong additional» absorption at 600–800 «cm^–1»  [✔]

Any one of:
HCl  [✔]

Cl₂ [✔]

dioxins [✔]

C [✔]

CO [✔]

Any two of:
embedded/fit between chains of polymers  [✔]

prevent chains from forming crystalline regions [✔]

keep polymer strands/chains/molecules separated/apart [✔]

increase space/volume between chains [✔]

weaken intermolecular/dipole-dipole/London/dispersion/instantaneous dipoleinduced dipole/van der Waals/vdW forces «between chains» [✔]

increase flexibility/durability/softness [✔]

make polymers less brittle [✔]

leach into foodstuffs/environment
OR
«unknown» health/environmental consequences [✔]

Note: Accept “plasticizers cannot be recycled”.

Quite a few candidates scored at least one mark although most either scored both or none for this polymer structure.

Almost all students who attempted this question received the mark for identifying the correct absorption band.

This was a well answered question, with most candidates identifying at least one method plasticizers affect the properties of plastic.

Many students received a mark for this question although some did not because their answers were too vague.

Suggest why a high-octane number fuel is preferable.

Reforming reactions are used to increase the octane number of a hydrocarbon fuel.

Suggest the structural formulas of two possible products of the reforming reaction of heptane, C₇H₁₆.

The ¹H NMR spectrum of one of the products has four signals. The integration trace shows a ratio of the areas under the signals of 9 : 3 : 2 : 2.

Deduce the structural formula of the product.

low knocking/auto-ignition
NOTE: Do not accept “pre-ignition”.
OR
more efficient fuel
NOTE: Accept “less CO₂ emissions since knocking engine uses more fuel «to produce the same power»”.
OR
high compression
OR
more power extracted
OR
more air going into engine / turbocharging
OR
less engine damage ✔

Any two of:

NOTE: Accept skeletal formulas or full or condensed structural formulas.
Accept any other branched cycloalkane that contains 7 carbons.
Do not accept any alkenes.
Penalise missing hydrogens or bond connectivities once only in Option C.
Accept hydrogen as the second product if the first product is toluene or a cycloalkane.

NOTE: Accept a skeletal formula or a full or condensed structural formula.
Penalise missing hydrogens or bond connectivities once only in Option C.