(i) Draw the structure of 2-methylpropene.

(ii) Deduce the repeating unit of poly(2-methylpropene).

Deduce the percentage atom economy for polymerization of 2-methylpropene.

(i) Suggest why incomplete combustion of plastic, such as polyvinyl chloride, is common in industrial and house fires.

(ii) Phthalate plasticizers such as DEHP, shown below, are frequently used in polyvinyl chloride.

With reference to bonding, suggest a reason why many adults have measurable levels of phthalates in their bodies.

i

OR
H₂C=C(CH₃)₂

ii

OR
−CH₂C(CH₃)₂−

Continuation bonds needed for mark.
No penalty if square brackets present or “n” appears after the bracket/formula.

«same mass of product as reactant, thus» 100«%»

Accept “less than 100%” only if a reason is given (eg, the catalyst is not converted into the product, or other reasonable answer).

i

due to stability of plastics/strong covalent bonds
OR
low volatility preventing good mixing with oxygen «gas»
OR
lack of/insufficient oxygen
OR
plastics are often parts of devices with non-combustible components «which mechanically prevent the combustion of plastic components»
OR
PVC already partly oxidised «because some C–H bonds are replaced with C–Cl bonds», so it cannot produce enough heat for complete combustion
OR
many industrial/household materials contain additives that reduce their flammability/act as flame retardants

ii

weakly bound to the PVC/no covalent bonds to PVC/only London/dispersion/instantaneous induced dipole-induced dipole forces between DEHP and PVC AND leach/evaporate «from PVC» to atmosphere/food chain
OR
has low polarity/contains non-polar hydrocarbon chains AND fat-soluble/deposits in the fatty tissues
OR
has unusual structural fragments/is a xenobiotic/difficult to metabolise AND stays in the body for a long time

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]

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.

Calculate the charge, in coulombs, passed during the electrolysis.

$\left(\text{current }I=\frac{\text{charge }Q}{\text{time }t}\right)$

Calculate the amount, in mol, of electrons passed using section 2 of the data booklet.

Calculate the mass of indium deposited by one mole of electrons.

Calculate the number of moles of electrons required to deposit one mole of indium. Relative atomic mass of indium, A_r=114.82.

Deduce the charge on the indium ion and the formula of indium sulfate.

«0.300A × 9.00 × 10³ s =» 2.70 × 10³ «C»

«mol e⁻ = $\frac{2700\text{C}}{96500\text{C}\text{mo}{\text{l}}^{-1}}$ =» 2.80 × 10⁻² «mol»

«$\frac{1.07\mathrm{g}}{0.0280\mathrm{m}\mathrm{o}\mathrm{l}}$=» 38.2 «g»

«$\frac{114.82\text{g}}{38.2\text{g}\text{mo}{\text{l}}^{-1}}$ e⁻ =» 3.01/3.00 «mol e⁻»

In³⁺ /3+ AND In₂(SO₄)₃

Do not accept “+3/3”

Magnesium oxide, MgO, and silicon carbide, SiC, are examples of ceramic materials. State the name of the predominant type of bonding in each material.

Predict the predominant type of bonding for a binary compound AB in which the electronegativity of both atoms is low. Use section 29 of the data booklet.

MgO: ionic AND SiC: covalent

Accept “covalent network/network covalent” for “covalent” but not just “network”.

metallic «bonding»

Explain these properties of carbon nanotubes.

Alloying metals changes their properties. Suggest one property of magnesium that could be improved by making a magnesium–CNT alloy.

Pure magnesium needed for making alloys can be obtained by electrolysis of molten magnesium chloride.

© International Baccalaureate Organization 2020.

Write the half-equations for the reactions occurring in this electrolysis.

Calculate the theoretical mass of magnesium obtained if a current of $3.00 \mathrm{A}$ is used for $10.0$ hours. Use charge $\left(Q\right)=current(I )\times time(t )$ and section 2 of the data booklet

Suggest a gas which should be continuously passed over the molten magnesium in the electrolytic cell.

Zeolites can be used as catalysts in the manufacture of CNT. Explain, with reference to their structure, the high selectivity of zeolites.

Experiments have been done to explore the nematic liquid crystal behaviour of CNT. Justify how CNT molecules could be classified as nematic.

Excellent strength: defect-free AND rigid/regular 2D/3D ✔

Excellent conductivity: delocalized electrons ✔

Accept “carbons/atoms are all covalently bonded to each other” for M1.

Any of:
ductility ✔
strength/resistance to deformation ✔
malleability ✔
hardness ✔
resistance to corrosion/chemical resistance ✔
range of working temperatures ✔
density ✔

Do not accept “conductivity”.

Anode: $2{\mathrm{Cl}}^{-}\to {\mathrm{Cl}}_2\left(\mathrm{g}\right)+2{\mathrm{e}}^{-}$ ✔

Cathode: ${\mathrm{Mg}}^{2+}+2{\mathrm{e}}^{-}\to \mathrm{Mg}\left(\mathrm{l}\right)$ ✔

Accept $C{l}^{-}\to C{l}_2\left(g\right)+e^{–}$.

Award [1 max] for correct equations at incorrect electrodes.

$«Q=I\times t=3.00\times 10.0\times 3600=»108 000 \mathrm{C}$ ✔

$«\frac{Q}{F}=\frac{108 000 C}{96 500 C {\mathrm{mol}}^{-1}}=»1.12«\mathrm{mol} {\mathrm{e}}^{-}»$ ✔

$«\frac{1.12 \mathrm{mol}}{2}=0.560 \mathrm{mol} \mathrm{Mg}»$
$«m=0.560 \mathrm{mol}\times 24.31 \mathrm{g} {\mathrm{mol}}^{-1}=»13.6«\mathrm{g}»$ ✔

Award [3] for correct final answer.

argon/$\mathrm{Ar}$/helium/$\mathrm{He}$ ✔

Accept any identified noble/inert gas.
Accept name OR formula.

Do not accept “nitrogen/$N_2$“.

pores/cavities/channels/holes/cage-like structures ✔

«only» reactants with appropriate/specific size/geometry/structure fit inside/go through/are activated/can react ✔

Accept “molecules/ions” for “reactants” in M2.

rod-shaped molecules
OR
«randomly distributed but» generally align
OR
no positional order AND have «some» directional order/pattern ✔

Accept “linear” for “rod-shaped”.

This was a very popular option with approximately 34% of candidates attempting Option B. Many students appeared well prepared for this option. Some candidates continue to provide answers with a heavy Biology bias that often make them lose valuable points.

This was a very popular option with approximately 34% of candidates attempting Option B. Many students appeared well prepared for this option. Some candidates continue to provide answers with a heavy Biology bias that often make them lose valuable points.

This was a very popular option with approximately 34% of candidates attempting Option B. Many students appeared well prepared for this option. Some candidates continue to provide answers with a heavy Biology bias that often make them lose valuable points.

This was a very popular option with approximately 34% of candidates attempting Option B. Many students appeared well prepared for this option. Some candidates continue to provide answers with a heavy Biology bias that often make them lose valuable points.

This was a very popular option with approximately 34% of candidates attempting Option B. Many students appeared well prepared for this option. Some candidates continue to provide answers with a heavy Biology bias that often make them lose valuable points.

This was a very popular option with approximately 34% of candidates attempting Option B. Many students appeared well prepared for this option. Some candidates continue to provide answers with a heavy Biology bias that often make them lose valuable points.

This was a very popular option with approximately 34% of candidates attempting Option B. Many students appeared well prepared for this option. Some candidates continue to provide answers with a heavy Biology bias that often make them lose valuable points.

Outline the two distinct phases of this composite.

Thermoplastic composites are increasingly replacing thermosets.

Suggest one advantage of thermoplastic polymers over thermosets.

Explain how thermoplastics, such as polyvinylchloride, PVC, can be made more flexible by the addition of phthalate ester plasticizers.

Explain why phthalates are replaced by other plasticizers in the production of plastics.

carbon fibre reinforcing phase ✔

«in a» matrix phase of epoxy ✔

Award [1 max] for “reinforcing phase «embedded» in a matrix”.

can be recycled
OR
can be reformed when hot
OR
high impact/chemical/abrasion resistance ✔

Any three of:

plasticizers embed/fit between «polymer» chains ✔

keep polymer strands/chains/molecules separated/apart ✔

weaken intermolecular/London/dispersion/attractive/forces/instantaneous induced dipole-induced dipole/forces «between chains» ✔

prevent chains from packing closely/forming regular packing/structure ✔

Accept “van der Waals/vdW” for “London”.

Any two of:

readily released into environment
OR
have weak intermolecular forces «rather than covalent bonds between chains» ✔

get into biological systems by ingestion/inhalation ✔

interrupt endocrine systems
OR
affect release of hormones
OR
effect development of male reproductive system ✔

considered carcinogenic
OR
can cause cellular damage ✔

can cause early puberty in females ✔

can cause thyroid effects ✔

can cause asthma ✔

Do not accept just “are a health concern”.

Approximately 1% of the candidates this session attempted this option so feedback on this section by question is not possible due to the minimal number of scripts available for marking. The students that did attempt this option did not perform very well with several of them leaving some questions unanswered.

Approximately 1% of the candidates this session attempted this option so feedback on this section by question is not possible due to the minimal number of scripts available for marking. The students that did attempt this option did not perform very well with several of them leaving some questions unanswered.

Approximately 1% of the candidates this session attempted this option so feedback on this section by question is not possible due to the minimal number of scripts available for marking. The students that did attempt this option did not perform very well with several of them leaving some questions unanswered.

Approximately 1% of the candidates this session attempted this option so feedback on this section by question is not possible due to the minimal number of scripts available for marking. The students that did attempt this option did not perform very well with several of them leaving some questions unanswered.

Explain, with reference to their structure, the great selectivity of zeolites as catalysts.

Nanocatalysts play an essential role in the manufacture of industrial chemicals.

(i) Describe the high pressure carbon monoxide (HIPCO) method for the production of carbon nanotubes.

(ii) Outline one benefit of using nanocatalysts compared to traditional catalysts in industry.

pores/cavities/channels/holes/cage-like structures

«only» reactants with appropriate/specific size/geometry fit inside/go through/are activated/can react

Accept “molecules/ions” for reactants.

i

iron«0»«penta»carbonyl/Fe(CO)₅ catalyst decomposes
OR
Fe(CO)₅ (g) → Fe(s) + 5CO(g)
OR
metal nanocatalyst/clusters/particles formed «in situ»

Accept “cobalt-molybdenum/Co-Mo/CoMo” as a catalyst

2CO(g) → CO₂(g) +C(s) 

Accept “conversion of CO molecules into CNTs/ SWNTs” for M2.

ii

higher efficiency per unit mass/volume of the catalyst «due to higher surface to mass/volume ratio»
OR
greater selectivity «due to metal nanoclusters/surface topology/pore size»
OR
higher stability of the catalyst «due to lower tendency to aggregation»
OR
reduced cost of the catalyst/product/chemicals «as precious metals can be replaced with nanocatalysts made of inexpensive materials»

Accept “high conversion efficiency”.

Accept specific examples such as use of nanocatalysts in fuel cells/catalytic converters «leading to reduced use of Pt/Rh/Pd».

Accept “nanocatalysts often operate under milder conditions «so less energy consumption involved/so promotes principles of green chemistry»”.

Accept “lower energy consumption” OR “reduced carbon footprint” OR “reduced global warming”.

Accept “nanocatalysts often have long lifetimes «so more economical».

Accept “some nanocatalysts have enzyme mimicking activities”.

State the major advantage that nanoparticles have in these applications.

Suggest why nanoparticles need to be handled with care.

large surface area

[1 mark]

«potentially» explosive
OR
small size/large surface area could give dangerously fast reactions
OR
unknown health effects
OR
potentially toxic
OR
immune system/allergy concerns

Do not accept just “dangerous/poisonous/toxic”.

Accept other valid concerns.

[1 mark]

Catalysts reduce the activation energy. Outline how homogeneous catalysts are involved in the reaction mechanism.

Suggest why it is important to know how catalysts function.

Antimony and its compounds are toxic, so it is important to check that the catalyst is removed from the final product. One technique to detect antimony is Inductively Coupled Plasma Mass Spectroscopy (ICP-MS).

Outline the nature of the plasma state and how it is produced in ICP-MS.

combine with reactants to form a «temporary» activated complex/intermediate
OR
consumed in one reaction/step AND regenerated in a later reaction/step

[1 mark]

can modify/improve the catalyst/reaction «by making logical predictions»
OR
science relies on models to understand physical reality

Accept other reasonable, relevant answers.

Accept "to predict/select

[1 mark]

electrons AND positive ions «in gaseous state»

high frequency/alternating current passed through argon
OR
«oscillating» electromagnetic/magnetic field
OR
high frequency radio waves

Accept “gas” instead of “argon”.

[2 marks]

State why lanthanum cannot be produced by reducing its oxide with carbon.

Calculate the current (I), in A, required to produce 1.00 kg of lanthanum metal per hour. Use the formula $Q(C)=I(A)\times t(s)$ and sections 2 and 6 of the data booklet.

too high/higher than carbon in the reactivity series
OR
carbon/C is a weaker reducing agent than lanthanum/La

Accept “lanthanum is more reactive than carbon”.

Accept “lanthanum is a weaker oxidizing agent than carbon”.

Accept converse arguments.

[1 mark]

amount of La «$=\frac{1000\text{ g}}{138.91\text{ g}\text{mo}{\text{l}}^{-1}}$» = 7.20 «mol»

Q «= 7.20 mol x 3 x 96$$500 C$$mol^–1» = 2.08 x 10⁶ «C»

I «$\frac{2.08\times {10}^6\text{ C}}{60\times 60\text{ s}}$» = 579 «A»

Award [3] for “578 «A»” (from premature rounding) or “579 «A»”.

[3 marks]

State equations for the formation of iron nanoparticles and carbon atoms from Fe(CO)₅ in the HIPCO process.

Outline why the iron nanoparticle catalysts produced by the HIPCO process are more efficient than solid iron catalysts.

Discuss one possible risk associated with the use of nanotechnology.

Fe(CO)₅ (g) → Fe (s) + 5CO (g)

2CO (g) → C (s) + CO₂ (g)

large surface area «on which carbon nanotubes form»

unknown health effects
OR
unknown effect on immune systems
OR
unknown environmental effects
OR
greater inflammatory response
OR
lung damage/toxicity
OR
hazardous effect on biodiversity
OR
risk of explosion

Do not accept vague responses.

Catalysts can take many forms and are used in many industrial processes.

Suggest two reasons why it might be worth using a more expensive catalyst to increase the rate of a reaction.

Any two of:

greater selectivity

higher efficiency

longer life expectancy

OR

not easily poisoned

easier to recover

low«er» environmental impact

large range of conditions/temperatures/pressures supported

lower energy costs

increase in yield «per unit time» offsets cost of catalyst

[Max 2 Marks]

In a catalytic converter, carbon monoxide is converted to carbon dioxide. Outline the process for this conversion referring to the metal used.

Nickel is also used as a catalyst. It is processed from an ore until nickel(II) chloride solution is obtained. Identify one metal, using sections 24 and 25 of the data booklet, which will not react with water and can be used to extract nickel from the solution.

Deduce the redox equation for the reaction of nickel(II) chloride solution with the metal identified in (b)(i).

Another method of obtaining nickel is by electrolysis of a nickel(II) chloride solution. Calculate the mass of nickel, in g, obtained by passing a current of 2.50 A through the solution for exactly 1 hour. Charge (Q) = current (I) × time (t).

carbon monoxide/CO adsorbs onto palladium/Pd

bonds stretched/weakened/broken
OR
«new» bonds formed
OR
activation energy/E_a «barrier» lowered «in both forward and reverse reactions»

products/CO₂ desorb «from catalyst surface»

[3 marks]

Fe/iron
OR
Zn/zinc
OR
Co/cobalt
OR
Cd/cadmium
OR
Cr/chromium

Accept “Mn/manganese”.

[1 mark]

Ni²⁺(aq) + Fe(s) → Ni(s) + Fe²⁺(aq)
OR
Ni²⁺(aq) + Zn(s) → Ni(s) + Zn²⁺(aq)
OR
Ni²⁺(aq) + Co(s) → Ni(s) + Co²⁺(aq)
OR
Ni²⁺(aq) + Cd(s) → Ni(s) + Cd²⁺(aq)
OR
Ni²⁺(aq) + Cr(s) → Ni(s) + Cr²⁺(aq)

Accept “3Ni²⁺(aq) + 2Cr(s) → 3Ni(s) + 2Cr³⁺(aq)”.

Do not penalize similar equations involving formation of Fe³⁺(aq), Mn²⁺(aq) OR Co³⁺(aq).

Ignore Cl⁻ ions.

Accept correctly balanced non-ionic equations eg, “NiCl₂(aq) + Zn(s) → Ni(s) + ZnCl₂(aq)” etc.

Do not allow ECF from (b)(i).

[2 mark]

$n\text{(}{\text{e}}^{-}\text{)}$ «$=\frac{2.50\text{ A}\times 3600\text{ s}}{96500\text{ C}\text{mo}{\text{l}}^{-1}}$» = 0.09326 «mol»
OR
$n\text{(Ni)}$ «$=\frac{0.09326\text{ mol}}{2}$» = 0.04663 «mol»

$m\text{(Ni)}$ «= 0.04663 mol x 58.69 g$$mol^–1» = 2.74 «g»

Award [2] for correct final answer.

[2 marks]

State the two distinct phases of a composite.

Identify the methods of assembling nanocomposites by completing the table.

Explain how the structure of plasticizers enables them to soften PVC.

Suggest a reason why nanoparticles can better anchor plasticizers in the polymer.

reinforcing «phase»

«embedded in» matrix «phase»

[2 marks]

Award [2] for all 4, [1] for 2 or 3 correct.

[2 marks]

Any three of:

contain a polar group «which locks into the polymer»

a non-polar group «which weakens the forces between chains»

embedded between chains of polymers

«plasticizer molecules» fit between chains

«plasticizer molecules» prevent chains from forming crystalline regions

«plasticizer molecules» keeps strands/chains/molecules separated

«plasticizer molecules» increase space/volume between chains

weakens intermolecular/dipole-dipole/London/dispersion/instantaneous induced dipole-induced dipole/van der Waals/vdW forces

Do not accept “«plasticizer molecules» “lower density” or “softer”.

[3 marks]

more places «for plasticizers» to bond
OR
increased surface area

[1 mark]

Outline the composition of an alloy and a composite.

Outline why an alloy is usually harder than its components by referring to its structure.

At present, composite fillings are more expensive than amalgam fillings.

Suggest why a patient might choose a composite filling.

Explain how Inductively Coupled Plasma (ICP) Spectroscopy could be used to determine the concentration of mercury in a sample of dental filling.

Alloy:
mixture of metal with other metals/non-metals

OR

mixture of elements that retains the properties of a metal

Composite:
reinforcing phase embedded in matrix phase

Award [1 max] for implying “composites only have heterogeneous/nonhomogeneous compositions”.

[Max 2 Marks]

difference in ionic/atomic radius prevents layers sliding over each other

Accept “difference in diameter/packing of cations prevents layers sliding over each other”.

concern about Hg poisoning
OR
«composite» is white «so looks more like tooth»
OR
galvanic response potential exists
OR
local allergic potential
OR
less damage/destruction of healthy tooth tissue
OR
long term corrosion requires replacement
OR
gradual darkening of tooth

Accept other correct responses.

Any three of:

sample injected into argon «plasma»

atoms «of sample» are excited/ionised

OR

electrons are promoted

electrons drop back/recombine with ions AND emit photons of characteristic energies/wavelengths/frequencies

total number of photons is proportional to concentration of element

actual concentration found from calibration/standard curve

Accept "graph/plot" for “curve”.

[Max 3 Marks]

Two important properties of a liquid crystal molecule are being a polar molecule and having a long alkyl chain. Explain why these are essential components of a liquid crystal molecule.

Metal impurities during the production of LCoS can be analysed using ICP-MS. Each metal has a detection limit below which the uncertainty of data is too high to be valid. Suggest one factor which might influence a detection limit in ICP-MS/ICP-OES.

Polar molecule:
«orientation of molecule» influenced by electric field/«applied» voltage/«applied» potential «difference»/«applied» current
OR
can be switched on and off

Long alkyl chain:
prevent close packing of molecules
OR
molecules can align
OR
reduces the melting point of the liquid crystal/LC «phase making liquid at room temperature»

Accept “makes molecule rod-shaped” for M2.

[2 marks]

inability to replicate calibrations below certain levels
OR
variation in methodology
OR
variation between machines calibrated with the same samples
OR
variation in plasma torches
OR
different detection limits for MS AND OES
OR
interference from solvents/other chemicals
OR
inability to produce pure standards
OR
chance that low signal AND blank are same

[1 mark]

Discuss, in terms of its structure, why an aluminium saucepan is impermeable to water.

State the name given to a material composed of two distinct solid phases.

State one physical property of HDPE that will be affected by the incorporation of carbon nanotubes.

Describe how carbon nanotubes are produced by chemical vapour deposition (CVD).

State the property of carbon nanotubes that enables them to form a nematic liquid crystal phase.

«close packed» lattice of metal atoms/ions

no spaces for water molecules to pass though the structure

[2 marks]

composite

[1 mark]

melting point

OR

permeability

OR

density

OR

conductivity

OR

elasticity/stiffness

OR

brittleness/flexibility

OR

«tensile» strength

Accept “colour/transparency”.

[1 mark]

Any three of:

hydrocarbon/carbon-containing gas/compound

mixed with inert gas

heat/high temperature

«transition» metal catalyst

hydrocarbon/carbon compound decomposes to form carbon «nanotubes»

nanotubes form on catalyst surface

Accept “ethanol” or specific hydrocarbons.

Accept “N₂”, “H₂”, “NH₃” or specific inert gases.

Accept temperature or range within 600–800 °C.

Accept specific metals such as Ni, Co or Fe.

[3 marks]

rod shaped molecules

[1 mark]

Both of these are thermoplastic polymers. Outline what this term means.

Compare and contrast the structures of HDPE and LDPE.

State one way in which a physical property of HDPE, other than density, differs from that of LDPE as a result of this structural difference.

The production of HDPE involves the use of homogeneous catalysts. Outline how homogeneous catalysts reduce the activation energy of reactions.

Trace amounts of metal from the catalysts used in the production of HDPE sometimes remain in the product. State a technique that could be used to measure the concentration of the metal.

Suggest two of the major obstacles, other than collection and economic factors, which have to be overcome in plastic recycling.

Suggest why there are so many different ways in which plastics can be classified. HDPE can, for example, be categorized thermoplastic, an addition polymer, having Resin Identification Code (RIC) 2, etc.

soften/melt when heated

OR

can be melted and moulded

Accept “low melting point” OR “can be moulded when heated”.

[1 mark]

both have «long» hydrocarbon chains

OR

both have chains comprising CH₂ units

HDPE has little/no branching AND LDPE has «more» branching

Accept “CH₂–CH₂ units”.

Accept “HDPE more crystalline”.

[2 marks]

HDPE is more rigid/less flexible

OR

HDPE has a higher melting point

OR

HDPE has greater «tensile» strength

Accept “HDPE has lower ductility”.

[1 mark]

form «temporary» activated complexes/reaction intermediates

Accept “consumed in one reaction/step AND regenerated in a later reaction/step”.

Accept “provides alternative mechanism”.

[1 mark]

inductively coupled plasma/ICP spectroscopy using mass spectroscopy/mass spectrometry/MS/ICP-MS

OR

inductively coupled plasma/ICP spectroscopy using optical emission spectroscopy/OES/ICP-OES

Accept “atomic absorption/aa spectroscopy” or “MS/massspectroscopy/mass spectrometry”.

[1 mark]

Any two of:

many types «of plastics» exist

OR

«plastics» require sorting «by type»

«plastics» need to be separated from non-plastic materials

OR

«often» composites/moulded on/bound to non-plastic/other components

Accept other valid factors such as thermal decomposition of some plastics, production of toxic fumes, etc.

[2 marks]

«different classifications are appropriate for» different properties/applications/purposes

[1 mark]

ICP-OES/MS can be used to analyse alloys and composites. Distinguish between alloys and composites.

ICP-MS is a reference mode for analysis. The following correlation graphs between ICP-OES and ICP-MS were produced for yttrium and nickel.

Each y-axis shows concentrations calculated by ICP-OES; each x-axis shows concentrations for the same sample as found by ICP-MS.

The line in each graph is y = x.

Discuss the effectiveness of ICP-OES for yttrium and nickel.

Identify the purpose of each graph.

Calculate, to four significant figures, the concentration, in μg kg⁻¹, of vanadium in oil giving a signal intensity of 14 950.

Vanadium(V) oxide is used as the catalyst in the conversion of sulfur dioxide to sulfur trioxide.

SO₂(g) + V₂O₅(s) → SO₃(g) + 2VO₂(s)

$\frac{1}{2}$O₂(g) + 2VO₂(s) → V₂O₅(s)

Outline how vanadium(V) oxide acts as a catalyst.

Alloy:

mixture of metal with other metals/non-metals

OR

mixture of elements that retains the properties of a metal

Composite:

reinforcing phase embedded in matrix phase

Award [1 max] for implying “composites only have heterogeneous/nonhomogeneous compositions”.

[2 marks]

effective for yttrium «but less/not for nickel»

points on nickel graph do not lie on «y = x» line

OR

cannot be used for low concentrations of nickel

OR

concentration of nickel is lower than recorded value

Accept “ICP-OES is more accurate for lower yttrium concentrations than higher concentrations” for M1.

Accept [Ni] and [Y] for concentrations of nickel and yttrium.

Accept “detection limit for yttrium is lower than for nickel” for M2.

Award [1 max] for “more accurate for yttrium at lower concentrations AND nickel at higher concentrations”.

[2 marks]

Graph 1: determines wavelength of maximum absorption/maximum intensity «for vanadium»

Graph 2: determines absorption of known concentrations «at that wavelength»

OR

estimates [V]/concentration in a sample using «the signal» intensity

Do not accept just “determines maximum wavelength/λ_max” for M1.

Do not accept “calibration curve” for M2.

[2 marks]

«14 950 = 392.19x + 147.62»

x = 37.74 «μg kg^–1»

Answer must be given to four significant figures.

Do not accept values obtained directly from the graph.

[1 mark]

vanadium reduced in first reaction AND oxidized in second reaction

OR

V₂O₅ oxidizes SO₂ in first reaction AND VO₂ reduces O₂ in second reaction

OR

vanadium returns to original oxidation state «after reaction»

provides an alternative reaction pathway/mechanism «with a lower activation energy» ✔

Do not accept “reactants adsorb onto surface AND products desorb”.

Accept “oxidation number” for “oxidation state”.

[2 marks]

Sketch four repeating units of the polymer to show atactic and isotactic polypropene.

State the chemical reason why plastics do not degrade easily.

Compare two ways in which recycling differs from reusing plastics.

Civilizations are often characterized by the materials they use.

Suggest an advantage polymers have over materials from the iron age.

Do not accept syndiotactic (alternating orientation of the CH₃ groups), eg,

for M1 or M2.

Accept any correct atactic ordering of CH₃ groups.

Penalize missing hydrogens or incorrect bond connectivities once only.

Accept skeletal structures.

Ignore continuation bonds, brackets and “n” indices in structures.

[2 marks]

strong covalent bonds

Accept “moisture cannot get inside the plastic matrix, and bacteria cannot live without moisture, so they cannot attack the polymer chains”.

Accept “bacteria lack the enzymes required to break down the hydrocarbon chains”.

[1 mark]

Any two of:

Recycling: shredded/melted/reformed AND Reuse: used in its current form

recycling is more energy intensive «than reusing»

recycling degrades the quality of plastic but reusing «typically» does not

recycling breaks down original product to form a new product whereas reuse extends product life

[2 marks]

more pliable/flexible materials

OR

more durable/non-corrosive/longer-lasting materials

OR

greater variety of materials

OR

lower density

OR

can be clear/translucent

Accept “more adaptable”.

Do not accept just “more useful”.

[1 mark]

State the source of carbon for MWCNT produced by arc discharge and by CVD.

Discuss three properties a substance should have to be suitable for use in liquid crystal displays.

Arc discharge:

graphite electrode

OR

hydrocarbon solvent

CVD:

gaseous hydrocarbons

Accept “carbon electrode”.

Accept specific examples of suitable hydrocarbon solvents (eg, methyl benzene/toluene OR cyclohexane).

Accept specific examples of suitable gaseous hydrocarbons (eg, methane, ethane, ethyne/acetylene) OR carbon monoxide OR carbon dioxide.

[2 marks]

Any three from:

chemically stable AND does not «chemically» degrade over time

stable over range of temperatures AND to avoid «voltage/random shift» fluctuations ✔

polar AND influenced by an electric field

strong intermolecular forces AND allow molecule to align in specific orientations ✔

rapid switching speed/low viscosity AND change orientation «quickly» when electric field is applied/reversed

Award [1 max] for identifying three correct properties without any discussion or incorrect interpretation of suitability.

Accept “voltage” for “electric field”.

[3 marks]

Outline why this type of classification is not entirely satisfactory by using magnesium diboride, MgB₂, as an example. Refer to sections 8 and 29 of the data booklet.

Structures of poly(methyl acrylate), PMA, and Bakelite^® are shown.

Suggest, giving reasons, which is the thermoplastic polymer and which is the thermosetting polymer.

In an incomplete combustion of the polyvinyl chloride, PVC, it was found that hydrogen chloride, carbon monoxide, carbon dioxide, and water vapour were released.

Formulate an equation for this reaction using the formula of the PVC repeating unit.

A zeolite is an alternative catalyst for this reaction.

Explain how zeolites act as selective catalysts.

Identify another advantage of using a zeolite instead of concentrated sulfuric acid.

Repeating units of several polymers are listed.

The infrared (IR) spectrum of one of these polymers is shown.

Deduce, giving a reason, the name of this polymer and its Resin Identification Code (RIC), using sections 26 and 30 in the data booklet.

$\mathrm{\Delta }\chi$ = 0.7 AND average $\mathrm{\Delta }\chi$ = 1.7 ✔

bonding between metallic and ionic

OR

more than one type of bonding present

OR

bond type difficult to determine as close to several regions/several types/named bonding types «eg ionic and covalent etc.»

OR

bond is mostly covalent «based on % covalent scale on diagram»

OR

bond has « $\frac{0.7}{3.2}\times 100=$» 22% ionic character ✔

Accept “EN” for “$\chi$".

Accept “bond is ionic but close to several regions/several types/other named bonding type(s) (eg covalent, metallic and covalent etc.)”.

Do not accept just “bond is ionic”.

Accept any value for % ionic character in range 15–24% or % covalent character in range 76–85%.

Thermoplastic polymer:

PMA AND «weak» intermolecular/IMFs/London/dispersion/van der Walls/vdW/dipole-dipole forces «between layers/chains»

OR

PMA AND no/few cross-links «between layers/chains» ✔

Thermosetting polymer:

Bakelite^® AND «strong» covalent bonds «between layers/chains»

OR

Bakelite^® AND extensive cross-links «between layers/chains» ✔

Do not accept “hydrogen bonding” for M1.

Award [1 max] for correct reasons for both polymer classes even if named polymers are incorrectly classified.

CH₂CHCl (s) + 2O₂ (g) → HCl (g) + CO (g) + CO₂ (g) + H₂O (g)

OR

CH₂CHCl (s) + O₂ (g) → HCl (g) + 2CO (g) + H₂O (g) AND 2CO (g) + O₂ (g) → CO₂ (g) ✔

Accept any correctly balanced equation that includes the products specified.

pores/cavities/channels/holes/cage-like structures «in zeolites» have specific shape/size ✔

only reactants «with appropriate size/geometry» fit inside/go through/are activated/can react ✔

does not require corrosive acid/«concentrated» sulfuric acid/H₂SO₄

OR

zeolite can be recycled «more easily»

OR

product can be «more» easily separated from a zeolite «than from sulfuric acid»

OR

minimal/less impact on environment

OR

synthesis of specific isomers as products ✔

Name and reason:

PET/PETE AND peak for C=O «at 1700–1750 cm^–1» ✔

RIC:

1 ✔

Accept “PET/PETE AND peak for C–O «at 1050–1410 cm^–1»” for M1.

Accept “PET/PETE AND peak(s) for COO” for M1.

Accept name or abbreviation for polymer.

No ECF for M2.

State the type of particle present in the plasma formed.

An unknown antacid sample has a lead ion concentration of 0.50 μg dm^‒3.

Calculate the concentration of lead ions in the sample in mol dm^‒3.

Electrolysis is used to obtain lead from Pb²⁺ (aq) solution.

Determine the time, in hours, required to produce 0.0500 mol lead using a current (I) of 1.34 A. Use section 2 of the data booklet and the equation, charge (Q) = current (I) × time (t, in seconds).

positive ions/cations/Pb²⁺

OR

free electrons ✔

Accept “ions” OR “charged species/particle”.

[Pb²⁺] = 0.50 × 10^‒6/5.0 × 10^–7 «g dm^–3» ✔

[Pb²⁺] «$=\frac{0.50\times {10}^{-6}\text{g}\text{d}{\text{m}}^{-3}}{207.20\text{g}\text{mo}{\text{l}}^{-1}}$» = 2.4 × 10^‒9 «mol dm^‒3» ✔

Award [2] for correct final answer.

«Faraday’s constant, F = 9.65 × 10⁴ C mol^‒1 and 1 A = 1 C s^–1»
Q «= 0.0500 mol × 2 × 96500 C mol^‒1» = 9650 «C» ✔

t «$=\frac{Q}{I}=\frac{9650\text{C}}{1.34\text{C}{\text{s}}^{-1}}\approx 7200\text{s}$ so $\frac{7200\text{s}}{60\times 60\text{s}{\text{h}}^{-1}}$» = 2.00 «hours» ✔

Award [2] for correct final answer.

Outline two observations that he could have made.

The structure of biphenyl nitrile is shown.

Describe, giving a reason, a feature of the molecular structure, other than its polarity, that allows biphenyl nitrile to show liquid crystal behaviour.

Arc discharge, consisting of two inert metal electrodes in a liquid solvent, is one method of producing carbon nanotubes (CNTs).

Predict, giving a reason, the electrode at which the solvent cyclohexane, C₆H₁₂, will decompose to form CNTs.

Any two of:

cloudy/foggy/hazy phase «at first melting point» ✔

clear liquid phase «at second melting point/higher temperature» ✔

two «different» melting points

OR

new phase observed over a wide temperature range ✔

Accept “exhibit both liquid and solid properties at the same time” for M3.

ALTERNATIVE 1:

«bulky/long» C₅H₁₁/R/alkyl «group/chain» AND prevents molecules from packing closer together «to form solid state» ✔

ALTERNATIVE 2:

biphenyl «fragment»/two benzene rings/two aromatic rings AND «makes molecule» rigid/rod-shaped ✔

Accept “rigid/rod-shaped molecule, so aligns with other molecules” for ALTERNATIVE 2.

«average» oxidation state of C in C₆H₁₂/cyclohexane = –2 AND in CNTs = 0

OR

oxidation state of C in CNTs is higher than in C₆H₁₂/cyclohexane

OR

loss of H’s/hydrogens ✔

«oxidation at» anode/positive/+ «electrode» ✔

Accept “oxidation number” for “oxidation state”.

Determine the type of bond present in SbBr₃, showing your method. Use sections 8 and 29 of the data booklet.

Lanthanum has a similar electronegativity to group 2 metals. Explain, in terms of bonding and structure, why crystalline lanthanum bromide is brittle.

polar covalent

average electronegativity «= $\frac{1}{2}$(3.0 + 2.0)» = 2.5 AND electronegativity difference «= 3.0 – 2.0» = 1.0

[2 marks]

ionic bonding
OR
electrostatic forces between ions

«slight» movement brings ions of same charge adjacent to each other «causing the crystal to break»
OR
«slight» movement results in repulsion between layers «causing the crystal to break»

[2 marks]

Describe the structure and bonding of a carbon nanotube.

Structure:

Bonding:

Suggest one application for carbon nanotubes.

Structure:
giant covalent/network covalent  [✔]

Note: Accept “cylindrical/tube shaped”.

Bonding:
each carbon covalently bonded to 3 other carbons
OR
each bond has order of 1.5

Note: Accept “has delocalized electrons” OR “has sp² hybridization”.

Any one of:
3D electrodes  [✔]
catalysts [✔]
biosensors [✔]
molecular stents [✔]
body armour [✔]
synthetic muscles [✔]
micro transistors/circuitry/capacitors/electrodes [✔]
reinforcing phase in a matrix/composite material «such as concrete» [✔]
micro antenna [✔]
stealth technology [✔]
water/air filtration [✔]
solar cells [✔]
tennis racquets [✔]
microelectronic circuits [✔]

Note: Do not accept just general answerssuch as “medicine” or “defence”.

Most students were aware that nanotubes have a tubular structure, but answers to the bonding were rarely detailed enough to gain the second mark.

Only a few students gained this mark and they usually gave the use of nanotubes for a reinforcing.

State the name of the functional group which allows the molecule to be responsive to applied electric fields.

Explain the effects of very low and high temperatures on the liquid-crystal behaviour of this molecule.

Low temperature: 

High temperature:

nitrile  [✔]

Note: Accept “cyano".

Low temperature:
intermolecular forces prevent molecules moving AND solid/«normal» crystal formation  [✔]

High temperature:
«above a critical temperature» disrupts alignment of molecules AND behaves as fluid/liquid  [✔]

Note: Accept “weak intermolecular forces break AND behaves as fluid/liquid”.

A few students correctly named the nitrile group as being the one responsible for the polarity of the liquid crystal molecule.

Very poorly answered with candidates failing to link the change in liquid crystal properties to changes in molecular motion.

Outline two differences between heterogeneous and homogeneous catalysts.

Suggest, giving a reason, how elastomers used for the tyre tread can increase the traction between the tyre and the road.

Tyre fires emit trace quantities of polychlorinated dibenzofurans and polychlorinated dibenzo-p-dioxin.

Outline, using section 31 of the data booklet, why polychlorinated dibenzofuran is not classed chemically as a dioxin but considered “dioxin-like”.

The trace quantities of dioxins from tyre fires are rarely inhaled and instead settle on the ground.

Describe why this is a health concern.

Any two of:
heterogeneous catalyst is in different phase than reactants AND homogeneous catalyst in same phase  [✔]

homogeneous catalysts chemically change/react and are reformed at end of reaction
OR
reactants adsorb onto heterogenous catalyst and products desorb  [✔]

heterogeneous catalysts are more easily removed than homogenous catalysts [✔]

heterogeneous catalysts can function at higher temperatures [✔]

homogeneous catalysts are «generally» more selective [✔]

homogeneous catalysts offer a broader range of reactions [✔]

Note: Accept “state” for “phase”.

Accept “heterogeneous catalyst provides a surface to activate reaction”.

elastomers bend under force «and return to original form when force is released»
OR
elastomers make tyre more flexible  [✔]

allows greater contact with road  [✔]

does not contain heterocyclic ring with 2 oxygen atoms
OR
middle ring has only 1 oxygen atom  [✔]

produces similar toxic effects to dioxins  [✔]

Note: Accept “does not contain dioxin ring” for M1.

taken up by plants, which are eaten by animals «and then further dispersed»
OR
passed on in food chain  [✔]

Note: Accept “do not break down and can be remobilised as dust”.

Many students were aware of the fundamental difference between homogeneous and heterogeneous catalysts, but only a few could identify another difference to obtain full marks.

Whilst some students realised that elastomers would increase the area of road in contact, hardly any linked this to their fundamental property of deforming under stress.

This was a question that highlighted a perennial problem; students appearing to know the answer but not having sufficient command of the English language to express it accurately. A number did identify similar toxic effects as the reason for being “dioxin like”.

Only a few students linked this to the toxin entering the food chain.

Aluminium is produced by the electrolysis of a molten electrolyte containing bauxite.

Determine the mass, in g, of aluminium produced by the passage of a charge of 1.296 × 10¹³ C. Use sections 2 and 6 of the data booklet.

ratio of electrons : aluminium ions = 3 : 1

amount Al «$\frac{1.296\times {10}^{13}\text{ C}}{96500\text{ C mo}{\text{l}}^{-1}\times 3}$ » = 4.48 × 10⁷ «mol»

mass Al «= 4.48 × 10⁷ mol × 26.98 g mol^–1» = 1.21 × 10⁹ «g»

Award [3] for correct final answer.

[3 marks]

Identify the type of bonding in lithium hydride, using sections 8 and 29 of the data booklet.

Explain why lithium is paramagnetic while lithium hydride is diamagnetic by referring to electron configurations.

Suggest why ICP-OES does not give good quantitative results for distinguishing ⁶Li from naturally occurring lithium.

Suggest a better method.

Lithium is obtained by electrolysis of molten lithium chloride. Calculate the time, in seconds, taken to deposit 0.694 g Li using a current of 2.00 A.

Q (charge) = I (current) × t (time)

ionic  [✔]

lithium has an unpaired electron  [✔]

all electrons in lithium hydride are paired  [✔]

Note: Award [1 max] for correct electron configurations of Li AND Li⁺ AND H^- without discussion of pairing.

emission spectra of both «⁶Li and natural Li» give same colour/produce same «range of» wavelengths
OR
they have same electron transitions/same nuclear charge  [✔]

Note: Accept “the spectra are almost identical”.

ICP-MS  [✔]

Note: Accept “MS/mass spectrometry”.

n«= $\frac{\text{m}}{{\text{M}}_{\text{r}}}=\frac{0.694}{6.94}$ » = 0.100 «mol»  [✔]

«t = $\frac{\text{0}\text{.100 mol}\times 96500\text{ C mo}{\text{l}}^{-1}}{\text{2}\text{.00 C }{\text{s}}^{-1}}$ =»
4830 «s»  [✔]

Note: Accept “4820” OR “4825 «s»”.

Award [2] for correct final answer.

Many students correctly used the data tables and chart to deduce the bonding is ionic.

Only a few students were aware of the connection between electron pairing and magnetic properties.

Surprisingly few candidates referred to the fact that the two spectra shown are almost identical.

Again relatively few students were able to suggest ICP-MS as a more appropriate alternative.

About half the candidates who attempted this were able to calculate the amount of lithium being formed and hence the time required.

Determine the mass of aluminium, in g, that could be extracted from an appropriate solution by a charge of 48250 C. Use sections 2 and 6 of the data booklet.

Once extracted, the purity of the metal can be assessed using ICP-MS. Suggest two advantages of using plasma technology rather than regular mass spectrometry.

Explain the action of metals as heterogeneous catalysts.

Outline how alloys conduct electricity and why they are often harder than pure metals.

Conduct electricity:

Harder than pure metals:

Carbon nanotubes are added to metals to increase tensile strength.

Write an equation for the formation of carbon nanotubes from carbon monoxide.

moles of electrons «= $\frac{48250\text{ C}}{96500\text{ C mo}{\text{l}}^{-1}}$ » = 0.5000 «mol»  [✔]

moles of aluminium «= $\frac{0.5000\text{ mol}}{3}$ » = 0.1667 «mol»  [✔]

mass of aluminium «= 26.98 g mol^–1 × 0.1667mol» = 4.50 «g»  [✔]

Note: Award [3] for correct final answer.

Any two of:
larger linear calibration  [✔]

«accurate» detection of multiple elements/metals [✔]

«accurate» detection of elements in low concentration [✔]

temperature around 10000 K atomises/ionises every material [✔]

Any two of:
reactant(s) adsorb onto active sites/surface  [✔]

bonds weakened/broken/stretched «in adsorbed reactants»
OR
activation energy lowered  [✔]

products desorbed [✔]

Note: Accept “products released” for M3.

Conduct electricity:
«delocalized/valence» electrons free to move «under potential difference»  [✔]

Harder than pure metals:
atoms/ions of different sizes prevent layers «of atoms/ions» from sliding over one another  [✔]

2CO(g) → C(s) + CO₂ (g)  [✔]

Many students scored at least one point typically the 1st mark with many obtaining the 2nd and 3rd marks as well. If students struggled it was typically with the second mark where the number of electrons was required.

This was question was not answered well. Most candidates did not seem to understand any advantages of ICP-MS or how to describe them.

This question was reasonably answered with many candidates receiving a mark for the action of a catalyst. Teachers should remind students to use the terms adsorb/desorb with this type of process, not absorb.

Most candidates were awarded M1 for how alloys conduct electricity. Some struggled with describing why they are harder than pure metals. Teachers should remind student to use proper terminology such as atoms or ions not nuclei for this type of answer.

This was a very poorly answered question. Very few candidates knew the correct balanced equation or gave an equation that was not balanced.

Describe the characteristics of the nematic liquid crystal phase and the effect that an electric field has on it.

Shape of molecules:

Distribution:

Effect of electric field:

Shape of molecules:
linear
OR
rod «shaped»  [✔]

Distribution:
no positional order AND «some» directional order  [✔]

Note: Accept “partly ordered”.

Effect of electric field:
«directional» order increases
OR
molecules align in same direction  [✔]

Most students were able to obtain at least one mark on this question. The distribution was the most challenging part.

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.

Describe the arrangement of soap molecules in the nematic liquid crystal phase.

State how liquid crystals are affected by an electric field.

molecules point/align in same direction/orientation
OR
molecules have directional order ✔

molecules randomly distributed
OR
molecules not in a layered arrangement
OR
molecules do not have positional order ✔

NOTE: Accept suitable diagram for M1 and M2.

molecules align with field ✔

Discuss why different methods of reduction are needed to extract metals.

Determine the percentage of ionic bonding in alumina using sections 8 and 29 of the data booklet.

Write half-equations for the electrolysis of molten alumina using graphite electrodes, deducing the state symbols of the products.

Anode (positive electrode):

Cathode (negative electrode):

ions of more reactive metals are harder to reduce
OR
more reactive metals have more negative electrode potentials ✔

electrolysis is needed/used for most reactive metals
OR
carbon is used to reduce metal oxides of intermediate reactivity/less reactive than carbon
OR
heating ore is sufficient for less reactive metals ✔

NOTE: Award [1 max] for “«ease of reduction/extraction» depends on reactivity”.

electronegativity difference = 1.8 «and average electronegativity = 2.5» ✔
57 «%» ✔

NOTE: Accept any value in the range 52−65 %.
Award [2] for correct final answer.

Anode (positive electrode):
2O²⁻ → 4e⁻ + O₂(g)
OR
2O²⁻ + C → 4e⁻ + CO₂ (g) ✔

NOTE: Award [1 max] for M1 and M2 if correct half-equations are given at the wrong electrodes OR if incorrect reversed half-equations are given at the correct electrodes.

Cathode (negative electrode):
Al³⁺ + 3e⁻ → Al (l) ✔
O₂ gas AND Al liquid ✔

NOTE: Only state symbols of products required, which might be written as (g) and (l) in half-equations. Ignore any incorrect or missing state symbols for reactants.

Draw a section of an isotactic polypropene polymer chain containing four repeating units.

Predict, with a reason, whether isotactic or atactic polypropene has the higher melting point.

Polypropene is a thermoplastic. Outline what is meant by thermoplastic.

Discuss why the recycling of plastics is an energy intensive process.

NOTE: Continuation bonds must be shown.
Ignore square brackets and “n”.
Do not accept one repeating unit in square brackets with a subscript of 4.
Accept condensed structure provided all C to C bonds are shown and CH₃ groups on same side.
Accept

Do not accept syndiotactic (alternating orientation of the CH₃ groups).

isotactic «has higher melting point» AND ordered chains pack more closely
OR
isotactic «has higher melting point» AND stronger intermolecular/London/dispersion forces ✔

NOTE: Accept “van der Waals’ forces”/”vdW”.

softens when heated «and hardens when cooled» ✔

Any two of:
collection/transportation of plastic waste ✔
separation of different types «of plastic»
OR
separation of plastic from other materials ✔
melting plastic ✔
processing/washing/cleaning/drying/manufacture of recycled plastic ✔

Outline how a lyotropic liquid crystal differs from a thermotropic liquid crystal.

Explain the effect of increasing the temperature of a nematic liquid crystal on its directional order.

Do not award any credit if one type only is described as the question asks how they differ.

decreases AND as energy «added» overcomes interparticle forces
OR
decreases AND as energy «added» causes faster movement «of particles»

Describe how a heterogeneous catalyst provides an alternative pathway for a reaction.

Distinguish between heterogeneous and homogeneous catalysts, giving one difference.

Nanotubes are used to support the active material in nanocatalysts.

Explain why oxygen cannot be used for the chemical vapour deposition (CVD) preparation of carbon nanotubes.

reactant(s) adsorb onto active sites/surface ✔

NOTE: Do not accept “absorb” for “adsorb” for M1.
Accept “bonds to” for “adsorb” for M1.

«reactant» bonds weakens «and products are desorbed» ✔

NOTE: Accept “bonds break/stretch «and products are desorbed»” for M2.
Award [1 max] for “lowers activation energy”.

Any one of the following:

NOTE: Accept “heterogeneous adsorb reactants and homogeneous” but do not accept “absorb” for “adsorb”.
Accept “heterogeneous have active sites and homogeneous do not”.

high temperature used ✔

oxygen/O₂ reacts with carbon/C
OR
carbon dioxide/CO₂ can form ✔