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»

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 one concern of using nanoscale catalysts.

Explain how zeolites act as selective catalysts.

Carbon nanotubes, which can be produced by the HIPCO process, show great potential as nanocatalysts. Identify the catalyst and conditions used in the HIPCO process.

Catalyst:

Conditions:
 

possible toxicity «of small airborne particles»
OR
unknown health effects
OR
small particle size «and large surface area» may increase reaction rate to dangerous levels
OR
immune system/allergy concerns
OR
uncertain impact on environment

Accept specific health effect (eg. may cause cancer/effect on respiratory system, etc).

Titanium compounds are used as catalysts in the manufacture of high-density polyethene (HDPE). Discuss two factors scientists would have considered in choosing these catalysts.

Describe a structural feature of low-density polyethene (LDPE) that explains why LDPE has a different melting point from that of HDPE.

State one environmental impact of the disposal of these polyethenes by using incineration.

no other product formed (except HDPE);

expensive but effective;

little or no environmental/health impact;

not easily poisoned by impurities;

cause (considerable) increase in rate;

ability to work under mild/severe conditions;

side-chains / branching present (in LDPE);

limits closer packing / chains further apart / OWTTE;

less van der Waals’/dispersion/London forces / OWTTE;

Award mark for less intermolecular forces. Do not accept weaker.

low(er) melting point (than HDPE);

No mark for different melting point.

Accept reverse argument for HDPE.

\({\text{C}}{{\text{O}}_2}\) is a greenhouse gas / causes climate change / global warming / formation of soot/particulates / melting of polar ice caps / rising sea levels / OWTTE;

Accept CO produced is toxic/poisonous.

(a) was surprisingly poorly answered, with very few candidates understanding how to discuss two factors in choosing catalysts, although they should have studied several factors.

(b) was answered well.

(c) was answered well.

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]

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]

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]

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]

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]

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.

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]

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]

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]

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]

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]

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”.

Explain why iron is obtained from its ores using chemical reducing agents but aluminium is obtained from its ores using electrolysis.

Both carbon monoxide and hydrogen can be used to reduce iron ores. State the equations for the reduction of magnetite, Fe₃O₄, with

(i)     carbon monoxide.

(ii)     hydrogen.

Explain why much of the iron produced in a blast furnace is converted into steel.

State the materials used for the positive and negative electrodes in the production of aluminium by electrolysis.

Positive electrode:

Negative electrode:

Al is more reactive than Fe / Al is higher than Fe in the reactivity series;

it is harder to reduce aluminium ores compared to iron ores / \({\text{F}}{{\text{e}}^{3 + }}\) is a better oxidizing agent than \({\text{A}}{{\text{l}}^{3 + }}\) / OWTTE;

(i)     \({\text{F}}{{\text{e}}_{\text{3}}}{{\text{O}}_{\text{4}}} + {\text{4CO}} \to {\text{3Fe}} + {\text{4C}}{{\text{O}}_{\text{2}}}\);

(ii)     \({\text{F}}{{\text{e}}_3}{{\text{O}}_4} + {\text{4}}{{\text{H}}_2} \to {\text{3Fe}} + {\text{4}}{{\text{H}}_2}{\text{O}}\);

steel has more desirable (physical) characteristics than iron / steel is stronger than iron / OWTTE;

by adjusting the composition of steel it can be given specific properties / OWTTE;

Positive electrode

graphite/carbon;

Negative electrode

graphite/carbon (on a steel liner);

Part (a), which required candidates to explain the relative reactivity of iron and aluminium, proved challenging for most candidates.

Many candidates could correctly state the products of reduction of magnetite but several failed to balance the equations and thus lost marks.

Most candidates could explain the advantages of steel over iron in part (c).

Very few candidates could identify the electrodes used in the production of aluminium, but most could explain the importance of recycling aluminium in part (d).

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]

Describe how the structures of ceramics differ from those of metals.

Name two fuels that are obtained from petroleum.

Describe one environmental problem that can result from the combustion of these fuels in the internal combustion engine and identify the specific combustion product responsible.

Plastic litter is an environmental problem that results from the use of petroleum as a chemical feedstock. Identify the property of plastics that is responsible for this.

One product that is made from crude oil is the chemical feedstock that can be used to synthesize commercial liquid-crystal displays. Discuss the properties that a substance must have to make it suitable for use as a liquid-crystal display.

Any two for [1]

petrol/gasoline

kerosene/paraffin/aviation fuel

diesel

fuel oil/gas oil

petroleum gas/refinery gas

global warming;

carbon dioxide;

OR

air pollution;

carbon monoxide / particulates / oxides of nitrogen/NO/\({\text{N}}{{\text{O}}_{\text{2}}}\) / \({\text{VO}}{{\text{C}}_{\text{s}}}\);

Accept oxides of sulphur/SO₂.

OR

acid rain;

oxides of nitrogen/NO/\({\text{N}}{{\text{O}}_{\text{2}}}\);

Accept oxides of sulphur/SO₂.

slow decomposition / not biodegradeable;

chemically stable;

liquid crystal phase over a suitable range of temperatures;

rapid switching speed;

In part (a) a significant number of candidates named two fuels obtained from petroleum.

A significant number of candidates described the environmental problem.

The non-biodegradable property of plastics was stated correctly by many candidates.

The properties of a material that made it suitable for use as a liquid crystal display demonstrated poor understanding by many candidates.

Describe the meaning of the term liquid crystals. State and explain which diagram, I or II, represents molecules that are in a liquid crystalline phase.

Distinguish between thermotropic and lyotropic liquid crystals and state one example of each type.

Discuss the properties needed for a substance to be used in liquid crystal displays.

liquid crystals are fluids that exhibit orientation of the molecules/an orderly arrangement of molecules;

II, since there is one-dimensional order (characteristic of a liquid crystalline phase);

thermotropic liquid crystals are pure substances that show liquid crystal behaviour over a temperature range (between the solid and liquid states);

example (of thermotropic liquid crystals) is biphenyl nitriles;

lyotropic liquid crystals are solutions that show the liquid crystal state at certain concentrations;

example (of lyotropic liquid crystals) is soap in water;

Award marks for examples, only if they are associated with the correct class of liquid crystals.

chemically stable;

a liquid crystal phase stable over a suitable range of temperatures;

polar in order to change orientation when an electric field is applied;

rapid switching speed;

Candidates were able to define liquid crystals but often confused the two diagrams.

Candidates also had difficulty distinguishing between thermotropic and lyotropic crystals and providing suitable examples for each. This emphasised again that candidates had not learnt definitions accurately with correct chemical terminology.

Describe the liquid-crystal state, in terms of molecular arrangement, and explain what happens as temperature increases.

Discuss three properties a substance should have if it is to be used in liquid-crystal displays.

(rod-shaped) molecules aligned in the same direction;

increasing temperature causes arrangement to lose its directional order/molecules to become more randomly arranged;

until normal liquid state occurs;

chemically stable so that it does not undergo reactions;

liquid-crystal phase stable over a range of temperatures so that frequent malfunctions do not occur;

molecules should be polar so the electronic current can influence direction;

there should be a rapid change in direction / fast switching speed;

Award [2 max] if no reasons are given.

Liquid-crystals were known well by many candidates. Some were ill-prepared to answer these questions.

Liquid-crystals were known well by many candidates. Some were ill-prepared to answer these questions.

Describe how the two forms differ in their chemical structure.

Explain in terms of their structures how the flexibility of the two forms of poly(ethene) differ.

Describe why pentane is sometimes added during the formation ofpoly(phenylethene), also known as polystyrene.

State one use for the product formed from this process.

HDPE/high density polyethene has little/no branching/side chains and low density has (many) branches/side chains;

branching in LDPE/ low density polyethene prevents chains fitting closely together;

weaker intermolecular/van der Waals’/London/dispersion forces so more flexible;

Accept opposite statements for HDPE/high density polyethene.

vaporizes causing it to expand/form expanded polystyrene / OWTTE;

(thermal) insulator / packaging material / absorb shock;

Do not accept just cups.

The answers to this often betrayed a confusion between isotactic and atactic polypropene. That being said the link between packing and the strength of the dispersion forces was relatively well understood at least to the extent of gaining one of the marks. Most candidates were aware of the role of pentane and even the weakest were scoring the mark for a use of expanded polystyrene.

The answers to this often betrayed a confusion between isotactic and atactic polypropene. That being said the link between packing and the strength of the dispersion forces was relatively well understood at least to the extent of gaining one of the marks. Most candidates were aware of the role of pentane and even the weakest were scoring the mark for a use of expanded polystyrene.

The answers to this often betrayed a confusion between isotactic and atactic polypropene. That being said the link between packing and the strength of the dispersion forces was relatively well understood at least to the extent of gaining one of the marks. Most candidates were aware of the role of pentane and even the weakest were scoring the mark for a use of expanded polystyrene.

The answers to this often betrayed a confusion between isotactic and atactic polypropene. That being said the link between packing and the strength of the dispersion forces was relatively well understood at least to the extent of gaining one of the marks. Most candidates were aware of the role of pentane and even the weakest were scoring the mark for a use of expanded polystyrene.

Define the term nanotechnology, and state why it is of interest to chemists.

(i)     Describe the structure of carbon nanotubes.

(ii)     State one physical property of carbon nanotubes.

Suggest two concerns about the use of nanotechnology.

nanotechnology involves research and technology developments at the 1 nm to 100 nm range;

structures with novel properties (because of their small size);

ability to manipulate on the atomic scale;

Overlap here between definition and matters of interest, so accept any two.

(i)     (main) cylinder consists of carbon hexagons / OWTTE;

pentagons close structures/tubes at ends / OWTTE;

Marks may also be scored by means of a suitable diagram showing above.

(ii)     high tensile strength / low density / high thermal conductivity / (electrical) conductors / (electrical) semi-conductors / high melting points;

health concerns / concern that the human immune system will be defenceless against particles on the nanoscale;

potential toxicity of materials / toxicity regulations are difficult (to apply);

possible explosive nature of large scale manufacture of nanoparticles;

political issues;

Apply OWTTE throughout.

Many candidates were able to define the term nanotechnology and scored M1 but only about half managed to score M2.

In (b)(i), although most mentioned hexagons and pentagons, many failed to mention cylinders and ends of tubes.

In (c) many candidates were able to score at least one mark, some scored both marks but, again, some vague answers were seen.

Deduce an equation for the discharge of the ions at each electrode.

Positive electrode (anode):

Negative electrode (cathode):

(i)     Outline why aluminium is alloyed with copper and magnesium when used to construct aircraft bodies.

(ii)     State two properties of aluminium that make it suitable for use in overhead power cables.

Positive electrode (anode):

\({\text{2}}{{\text{O}}^{2 - }} \to {{\text{O}}_2}{\text{(g)}} + {\text{4}}{{\text{e}}^ - }/{{\text{O}}^{2 - }} \to \frac{1}{2}{{\text{O}}_2}{\text{(g)}} + {\text{2}}{{\text{e}}^ - }/{\text{2}}{{\text{O}}^{2 - }} - {\text{4}}{{\text{e}}^ - } \to {{\text{O}}_2}{\text{(g)}}/\)

\({{\text{O}}^{2 - }} - {\text{2}}{{\text{e}}^ - } \to \frac{1}{2}{{\text{O}}_2}{\text{(g)}}\);

Allow C(s) + 2O^2– \( \to \) CO₂(g) + 4e^–.

Negative electrode (cathode):

\({\text{A}}{{\text{l}}^{3 + }} + {\text{3}}{{\text{e}}^ - } \to {\text{Al(l)}}\);

Accept e instead of e^–.

Ignore state symbols.

If correct equations shown at wrong electrodes, award [1 max].

(i)     harder/stronger (than pure aluminium);

(ii)     Award [1] for any two of:

good conductor of electricity;

resists corrosion;

Do not allow rusting.

low density;

Do not allow lighter/light mass/light weight.

ductile;

Do not allow malleable.

In (a), most were able to write the correct half-equation for the cathode though incorrect states were commonly seen, e.g. (aq). The anode half-equation was not well known.

Both parts of (b) were well done. In (ii), incorrect answers included malleability and light mass.

Polyacrylonitrile is similar to polypropene and can exist in two forms.

Draw the structure of the isotactic form of polyacrylonitrile showing three repeating units.

Polyacrylonitrile is similar to polypropene and can exist in two forms.

Explain why the isotactic form is more suitable for the manufacture of strong fibres.

Identify the role of the zeolite in the reaction.

Suggest an explanation for its efficiency in favouring the production of the crystalline polymer.

Outline the structure of the open carbon nanotubes.

State a property of these nanotubes that makes them suitable for this use.

 /

 ;

Continuation bonds at end of structure needed.

Hydrogen atoms must be included.

Award [1] for chain with CN groups on alternate carbons.

Award [2] for correct chain with CN on alternate carbons with same orientation.

chains pack together better;

strong intermolecular/attractive forces between chains;

chains do not move past each other easily (so fibre strong/rigid);

catalyst;

(selective) because of dimensions/shape/size (of cage);

Accept “large surface area”.

cylinder with hexagons of carbon (atoms);

Accept suitable diagram.

Do not award mark if pentagons are also mentioned.

(electrical) conductor;

Accept low density.

Do not accept light.

Some very strange polymers were suggested in (a) (i) with the –CN group becoming integrated into the carbon backbone. Candidates were, however, able to explain why the isotactic form is more suitable for fibres. The role of the zeolite in (b) was usually correctly identified but it was not known that the dimensions, size or shape of the cage were an explanation for its efficiency. Most were able to give a good account of carbon nanotubes although some introduced pentagons at the end. This was specifically ruled out in the question – open carbon nano-tubes.

Some very strange polymers were suggested in (a) (i) with the –CN group becoming integrated into the carbon backbone. Candidates were, however, able to explain why the isotactic form is more suitable for fibres. The role of the zeolite in (b) was usually correctly identified but it was not known that the dimensions, size or shape of the cage were an explanation for its efficiency. Most were able to give a good account of carbon nanotubes although some introduced pentagons at the end. This was specifically ruled out in the question – open carbon nano-tubes.

Some very strange polymers were suggested in (a) (i) with the –CN group becoming integrated into the carbon backbone. Candidates were, however, able to explain why the isotactic form is more suitable for fibres. The role of the zeolite in (b) was usually correctly identified but it was not known that the dimensions, size or shape of the cage were an explanation for its efficiency. Most were able to give a good account of carbon nanotubes although some introduced pentagons at the end. This was specifically ruled out in the question – open carbon nano-tubes.

Some very strange polymers were suggested in (a) (i) with the –CN group becoming integrated into the carbon backbone. Candidates were, however, able to explain why the isotactic form is more suitable for fibres. The role of the zeolite in (b) was usually correctly identified but it was not known that the dimensions, size or shape of the cage were an explanation for its efficiency. Most were able to give a good account of carbon nanotubes although some introduced pentagons at the end. This was specifically ruled out in the question – open carbon nano-tubes.

Some very strange polymers were suggested in (a) (i) with the –CN group becoming integrated into the carbon backbone. Candidates were, however, able to explain why the isotactic form is more suitable for fibres. The role of the zeolite in (b) was usually correctly identified but it was not known that the dimensions, size or shape of the cage were an explanation for its efficiency. Most were able to give a good account of carbon nanotubes although some introduced pentagons at the end. This was specifically ruled out in the question – open carbon nano-tubes.

Some very strange polymers were suggested in (a) (i) with the –CN group becoming integrated into the carbon backbone. Candidates were, however, able to explain why the isotactic form is more suitable for fibres. The role of the zeolite in (b) was usually correctly identified but it was not known that the dimensions, size or shape of the cage were an explanation for its efficiency. Most were able to give a good account of carbon nanotubes although some introduced pentagons at the end. This was specifically ruled out in the question – open carbon nano-tubes.

Nitrogen dioxide is formed in a two-stage process. Describe one anthropogenic (man-made) source of nitrogen dioxide and state the two chemical equations for its formation.

Both of these air pollutants also contribute to acid deposition. State one chemical equation for each gas to describe how each forms an acidic solution.

combustion of fuels (at high temperature);

Accept internal combustion/aircraft/jet engines.

\({{\text{N}}_2} + {{\text{O}}_2} \to {\text{2NO}}\) and \(2{\text{NO}} + {{\text{O}}_2} \to {\text{2N}}{{\text{O}}_2}\);

\({\text{2N}}{{\text{O}}_2} + {{\text{H}}_2}{\text{O}} \to {\text{HN}}{{\text{O}}_2} + {\text{HN}}{{\text{O}}_3}/{\text{4N}}{{\text{O}}_2} + {\text{2}}{{\text{H}}_2}{\text{O}} + {{\text{O}}_2} \to {\text{4HN}}{{\text{O}}_3}\);

\({\text{S}}{{\text{O}}_2} + {{\text{H}}_2}{\text{O}} \to {{\text{H}}_2}{\text{S}}{{\text{O}}_3}/{\text{2S}}{{\text{O}}_2} + {\text{2}}{{\text{H}}_2}{\text{O}} + {{\text{O}}_2} \to {\text{2}}{{\text{H}}_2}{\text{S}}{{\text{O}}_4}\);

The man-made source of nitrogen oxide was generally very well answered, although the equations for its formation proved demanding.

The chemical equation for the formation of sulfuric acid was given correctly by many candidates, but it was surprising to see that a significant number of candidates did not know the chemical formula for nitric acid.

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⁻ = \(\frac{{2700\,{\text{C}}}}{{96\,500\,{\text{C}}\,{\text{mo}}{{\text{l}}^{ - 1}}}}\) =» 2.80 × 10⁻² «mol»

«\(\frac{{1.07{\rm{g}}}}{{0.0280{\rm{mol}}}}\)=» 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”

Describe the nematic liquid-crystal phase in terms of the arrangement of the molecules.

Explain the effect of increasing the temperature on the nematic liquid crystal.

no layered arrangement / molecules distributed randomly;

(on average) molecules point in same direction/orientation/directional order;

Accept suitable diagram.

directional order decreases/is lost / starts to behave like a liquid;

extra energy causes greater movement/overcomes intermolecular forces;

Very few of the candidates scored full marks on the description of the nematic liquid-crystal phase.

Probably because of the difficulty of selecting the correct words, and surprisingly only a few scored the mark in terms of the effect of the extra energy, namely causing greater movement or overcoming intermolecular forces.

(a)     For two different addition polymers, describe and explain one way in which the properties of addition polymers may be modified.

Polymer one:

Polymer two:

(b)     Describe and explain how the extent of branching affects the properties of poly(ethene).

(c)     Discuss two advantages and two disadvantages of using poly(ethene).

(a)     Accept two of the following four pairs of answers.

plasticizers in polyvinyl chloride;

the more plasticizer the more flexible the plastic;

OR

volatile hydrocarbons in the formation of (expanded) polystyrene;

volatile hydrocarbons vaporize during the formation of the polystyrene and reduce the density of (expanded) polystyrene / improving insulating properties;

OR

sulfur added to diene/2-methyl-1,3-butadiene/rubber (produces cross-link polymer);

maintains its spring/softness (for longer periods of time);

OR

blowing air/steam during the polymerisation to form polyurethane;

reduces density/increases springiness

(b)     high degree of branching produces low density polyethene;

small degree of branching produces high density polyethenes;

HDPE/low branching is stiffer/stronger/more resistant to heat and corrosion/less permeable to gases / LDPE/high branching is more flexible/weaker/less resistant to heat and corrosion/more permeable to gases;

(c)     Advantages:

polymer’s properties can be customized / OWTTE

can be recycled/reused

cheap

chemically inert

transparent

non-toxic

Any two correct answers scores [1].

Disadvantages:

rely on non-renewable energy sources

volume occupied by plastics in landfill

non-biodegradability

burning produces toxic gases

burning produces carbon dioxide (greenhouse gas)

burning printed polyethene can release toxic (heavy) metals/substances

may cause suffocation/death of animals

Any two correct answers scores [1].

The way in which the properties of addition polymers depend on their structure and methods for modifying this appeared to be very poorly understood, with only a handful of candidates scoring well on any parts of this question. In Part (b) many candidates discussed the difference between isotactic and atactic polymers rather than the effects of branching.

Explain why the molten electrolyte also contains cryolite.

State a half-equation for the reaction at the negative electrode (cathode).

Oxygen is produced at the positive electrode (anode). State the name of another gas produced at this electrode.

State two properties of aluminium that make it suitable for use as an overhead electric cable.

Alloys of aluminium with nickel are used to make engine parts. Explain, by referring to the structure of these alloys, why they are less malleable than pure aluminium.

it lowers the operating temperature/melting point (of alumina) / it saves heat/energy / improves conductivity / acts as a solvent;

Do not accept lowers melting point of aluminium.

Do not accept “lowers boiling point”.

\({\text{Al(l}}{{\text{)}}^{3 + }} + {\text{3}}{{\text{e}}^ - } \to {\text{Al (l)}}\);

Ignore state symbols.

Accept e instead of e^–.

carbon dioxide / carbon monoxide / fluorine / tetrafluoromethane;

Do not accept formulas since the name is asked for specifically.

high/good (electrical) conductivity and low density;

Do not accept lighter.

Accept malleable/ductile/resistant to (further) corrosion as one property.

Reference to high/good conductivity or low density needed.

in alloy different sized/Ni atoms/ions/particles disrupt regular structure;

stops layers from slipping/sliding / OWTTE;

Do not accept “stop layers moving”.

Accept diagrams if explanation clear.

This was reasonably well answered. However a surprising number of candidates were unable to write the half equation for reaction at the negative electrode in (a) (ii), and few candidates were able to give an explanation of the reduced malleability of the alloys in terms of their structure in b (ii).

This was reasonably well answered. However a surprising number of candidates were unable to write the half equation for reaction at the negative electrode in (a) (ii), and few candidates were able to give an explanation of the reduced malleability of the alloys in terms of their structure in b (ii).

This was reasonably well answered. However a surprising number of candidates were unable to write the half equation for reaction at the negative electrode in (a) (ii), and few candidates were able to give an explanation of the reduced malleability of the alloys in terms of their structure in b (ii).

This was reasonably well answered. However a surprising number of candidates were unable to write the half equation for reaction at the negative electrode in (a) (ii), and few candidates were able to give an explanation of the reduced malleability of the alloys in terms of their structure in b (ii).

This was reasonably well answered. However a surprising number of candidates were unable to write the half equation for reaction at the negative electrode in (a) (ii), and few candidates were able to give an explanation of the reduced malleability of the alloys in terms of their structure in b (ii).

State the equation for the reaction of coke with air in the blast furnace.

The product formed in part (i) reacts with coke to produce carbon monoxide. Explain, giving an equation, why this reaction is important in the extraction of iron.

\({\text{C(s)}} + {{\text{O}}_2}{\text{(g)}} \to {\text{C}}{{\text{O}}_2}{\text{(g)}}\);

Ignore state symbols.

CO acts as a reducing agent / reaction is endothermic/cools (this part of) furnace;

\({\text{C}}{{\text{O}}_2}{\text{(g)}} + {\text{C(s)}} \to {\text{2CO(g)}}/{\text{F}}{{\text{e}}_2}{{\text{O}}_3}{\text{(s)}} + {\text{3CO(g)}} \to {\text{2Fe(l)}} + {\text{3C}}{{\text{O}}_2}{\text{(g)}}\);

Ignore state symbols.

Generally the equation for the reaction of coke with air was given correctly.

The correct equation for the reaction of \({\text{C}}{{\text{O}}_2}\) with coke was sometimes missing

The initial products of the fractional distillation of oil often undergo cracking. This can be carried out in a number of ways. State the major reason for choosing each of the following techniques.

Catalytic cracking:

Thermal cracking:

Steam cracking:

Explain how these differ from homogeneous catalysts.

Identify one disadvantage of using heterogeneous catalysts.

Many of the compounds produced by cracking are used in the manufacture of addition polymers. State the essential structural feature of these compounds and explain its importance.

The polymers often have other substances added to modify their properties. One group of additives are plasticizers. State how plasticizers modify the physical properties of polyvinyl chloride and explain at the molecular level how this is achieved.

Catalytic cracking:

used to produce moderate length alkanes (for fuels) / lower temperature / lower energy consumption / more control of product;

Thermal cracking:

used to crack very long chain starting material;

Steam cracking:

used to produce low molar mass alkenes (for petrochemicals);

heterogeneous catalysts in a different phase to the reactants / homogeneous catalysts in the same phase as reactants;

easily poisoned / efficiency decreases over time / forms clumps / only effective on surface / require high surface area;

carbon-carbon double bond;

breaks allowing addition reaction / allows monomers/molecules to join together/polymerize;

make the polymer more flexible;

fits between/increases separation between polymer chains / allow polymer chains to slide past each other more easily / weaken intermolecular attraction;

Few candidates appear to have any knowledge of the different cracking techniques, though more appeared familiar with issues relating to catalysts. Quite a number of candidates were aware carbon-carbon double bonds were needed for addition polymerization, though the nature and effect of plasticizers was less well known

Few candidates appear to have any knowledge of the different cracking techniques, though more appeared familiar with issues relating to catalysts. Quite a number of candidates were aware carbon-carbon double bonds were needed for addition polymerization, though the nature and effect of plasticizers was less well known

Few candidates appear to have any knowledge of the different cracking techniques, though more appeared familiar with issues relating to catalysts. Quite a number of candidates were aware carbon-carbon double bonds were needed for addition polymerization, though the nature and effect of plasticizers was less well known

Few candidates appear to have any knowledge of the different cracking techniques, though more appeared familiar with issues relating to catalysts. Quite a number of candidates were aware carbon-carbon double bonds were needed for addition polymerization, though the nature and effect of plasticizers was less well known

Few candidates appear to have any knowledge of the different cracking techniques, though more appeared familiar with issues relating to catalysts. Quite a number of candidates were aware carbon-carbon double bonds were needed for addition polymerization, though the nature and effect of plasticizers was less well known

State the size range of structures which are involved in nanotechnology.

Discuss two implications of nanotechnology.

1 nm to 100 nm;

reference to effect on human health (e.g. unknown, immune system may not cope, unsatisfactory toxicity regulations);

reference to effect on employment (e.g. increased job opportunities, adverse effect on traditional industries);

reference to effect on quality of life (e.g. medical advances, faster computers, improved performance of electronic equipment);

reference to public opinion (e.g. need to improve information, encourage discussion, seek approval);

reference to nanotechnology being developed in wealthier nations hence increasing the divide between different nations;

As a relatively new topic, nanotechnology still seems to present a significant challenge to the small proportion of candidates studying Option C and whilst many knew the scale upon which it operated and a few could gain credit for implications, usually related to health concerns, hardly any could distinguish between physical and chemical techniques.

As a relatively new topic, nanotechnology still seems to present a significant challenge to the small proportion of candidates studying Option C and whilst many knew the scale upon which it operated and a few could gain credit for implications, usually related to health concerns, hardly any could distinguish between physical and chemical techniques.

State the difference between homogeneous and heterogeneous catalysts.

State one advantage and one disadvantage that homogeneous catalysts have over heterogeneous catalysts.

Advantage:

Disadvantage:

Apart from their selectivity to form the required product and their cost, discuss two other factors which should be considered when choosing a suitable catalyst for an industrial process.

homogeneous catalysts are in the same phase/state as the reactants and heterogeneous catalysts are in a different phase/state to the reactants;

Advantage

often works faster / all the catalyst is exposed to the reactants / OWTTE;

Disadvantage

difficult to remove the catalyst from the products / more limited range of acceptable catalysts;

efficiency;

ability to work under a variety of conditions;

environmental impact;

problems with the catalyst becoming poisoned (by impurities);

Most candidates correctly stated the difference between homogeneous and heterogeneous catalysts.

Most candidates could state one advantage and one disadvantage of homogeneous catalysts.

Candidates were less successful in part (c) in discussing the choice of a suitable catalyst.

Ethene can be polymerized to form high-density poly(ethene), HDPE, or low-density poly(ethene), LDPE, depending on the reaction conditions. Describe the main structural difference between HDPE and LDPE and explain how this accounts for their different properties.

(i)     The repeating unit of poly(propene) has the formula:

–[–\({\text{C}}{{\text{H}}_{\text{2}}}{\text{–CH(C}}{{\text{H}}_{\text{3}}}{\text{)}}\)–]–

Draw a section of the polymer containing five repeating units to illustrate atactic

poly(propene).

(ii)     Explain why isotactic poly(propene) is tough and can be used to make car bumpers (fenders), whereas atactic poly(propene) is soft and flexible making it suitable for sealants.

HDPE has little branching whereas LDPE has branching/side chains / OWTTE;

HDPE is stronger/more rigid / LDPE is weaker/more flexible/resilient;

HDPE chains pack more closely together / LDPE chains pack less closely together; HDPE has stronger van der Waals’ forces / LDPE has weaker van der Waals’ forces;

(i)      ;

There must be five –CH₃ groups and they must be shown in random orientation.

Allow the following structure:

(ii)     isotactic has all methyl groups oriented/pointing in the same direction/has a more regular structure / atactic has the methyl groups oriented/pointing in different directions/arranged randomly/has an irregular structure;

in isotactic the chains can pack more closely together (making it more crystalline/tough) / in atactic the chains pack less closely together (making it soft/flexible);

isotactic has stronger van der Waals’ forces / atactic has weaker van der Waals’ forces;

In (a) most candidates were aware of the differences between HDPE and LDPE, but often failed to fully score as they referred to intermolecular forces in a rather vague, instead of specific, manner.

Most candidates found it difficult to draw the structure of atactic poly(propene) in part (b)(i). Most candidates were very familiar with the difference in structure of isotactic and atactic poly(propene), but many failed to fully score as their responses lacked the required specificity for the intermolecular forces.

State a balanced equation for the thermal cracking of \({{\text{C}}_{{\text{20}}}}{{\text{H}}_{{\text{42}}}}\) in which octane and ethene are products.

(i)     Other than density, state two differences in the physical properties of HDPE and LDPE.

(ii)     Outline how the differences in (b)(i) relate to differences in their chemical structure.

It has been said that bitumen and heavy fuel oils are too valuable a resource to use for road surfacing and electricity generation. Comment on this statement.

\({{\text{C}}_{20}}{{\text{H}}_{42}} \to {{\text{C}}_8}{{\text{H}}_{18}} + {{\text{C}}_2}{{\text{H}}_4} + {{\text{C}}_{10}}{{\text{H}}_{20}}/{{\text{C}}_{20}}{{\text{H}}_{42}} \to {{\text{C}}_{\text{8}}}{{\text{H}}_{{\text{18}}}} + {\text{6}}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{4}}}\)

Accept any correctly balanced equation that includes octane and at least one ethene molecule as products.

correct reactants and products;

balanced equation;

M2 can only be scored if M1 is correct.

(i)     Award [1] for any two.

HDPE has higher mp;

HDPE is more rigid / less flexible;

HDPE is stronger;

Accept opposite statements for LDPE.

(ii)     HDPE has straight chain and LDPE has branched chain / LDPE has more branched chains;

more valuable for (cracking to provide) chemical precursors/petrochemicals / may be cracked to produce same substances now obtained from lighter fractions / OWTTE;

Only about a third of the candidates were able to score both marks by giving a balanced equation producing octane and ethene. Others scored one mark as they failed to balance the equation.

(i)     Less than half the candidates gave two physical properties that differed between LDPE and HDPE.

(ii)     A small number of candidates attributed the difference to the branching in the chains.

The answers were mostly unsatisfactory as they failed to recognize the value of cracking products for the petrochemical industry.

Detergents are one example of lyotropic liquid crystals.

State one other example of a lyotropic liquid crystal and describe the difference between lyotropic and thermotropic liquid crystals.

soap / kevlar / fatty acids / lipid bilayer / cellulose / silk proteins / DNA;

lyotropic liquid crystals

solutions that show the liquid-crystal state at certain concentrations;

thermotropic liquid crystals

(pure substances that) show liquid-crystal behaviour over temperature ranges (between the solid and liquid states);

This was probably the best answered question in this option with many candidates being able to state the difference between the two types of liquid crystals, as well as give an example of a substance that can have a lytropic liquid crystal state.

Describe an alloy.

Explain how alloying can modify the structure and properties of metals.

homogeneous mixture of metals/a metal and non-metal;

alloying element(s) disrupts regular/repeating (metal) lattice;

difficult for one layer to slide over another / atoms smaller than the metal cations can fit into the (holes of) metal lattice disrupting bonding;

can make metal harder/stronger/more corrosion resistant/brittle;

Many candidates did not gain the mark as they omitted the required word homogeneous.

Many candidates did not gain the mark as they omitted the required word homogeneous (a), but they could explain how alloying can modify the structure (b).

Describe these ‘test-tubes’ with reference to the structures of carbon allotropes.

These tubes are believed to be stronger than steel. Explain the strength of these ‘test-tubes’ on a molecular level.

Suggest two reasons why they are effective heterogeneous catalysts.

State one potential concern associated with the use of carbon nanotubes.

walls have rolled/single sheets of graphite/carbons bonded in hexagons;

ends have half a buckyball (fullerene)/carbons in pentagons (and hexagons);

covalent bonds are very strong;

large surface area;

Do not accept “reactive surface”.

high selectivity related to dimensions of tube;

unknown health effects;

Accept potentially harmful as easily ingested/inhaled.

Accept difficulty of preparing nanotubes in required amounts.

Responses to this question were generally poor perhaps reflecting the unfamiliarity of candidates with the new syllabus content.

Responses to this question were generally poor perhaps reflecting the unfamiliarity of candidates with the new syllabus content.

Responses to this question were generally poor perhaps reflecting the unfamiliarity of candidates with the new syllabus content.

Responses to this question were generally poor perhaps reflecting the unfamiliarity of candidates with the new syllabus content.

After the discovery of \({{\text{C}}_{60}}\), chemists discovered carbon nanotubes. Describe the structure and properties of carbon nanotubes.

Nanotechnology could provide new solutions for developing countries where basic services such as good health care, education, safe drinking water and reliable energy are often lacking. Discuss some of the potential risks associated with developing nanotechnology.

main cylinder is made only from carbon hexagons, with pentagons required to close the structure at the ends;

single or multiple walled tubes made from concentric nanotubes can be formed;

bundles of the tubes have high tensile strength;

other substances (elements, metal oxides etc.) can be inserted inside the tubes;

strong covalent bonding / no weak bonds;

behaviour of electrons depends on the length of a tube and hence some forms are conductors and some are semiconductors;

hazards associated with small airborne particles are not known / long term effects unknown / OWTTE;

may not be covered by current toxicology regulations (as properties depend on the size of the particle) / may be toxic / OWWTE;

human immune system may be defenceless against new nanoscale products / OWTTE;

(there may be social problems) as poorer societies may suffer as established technologies become redundant and demands for commodities change / OWTTE;

Candidates had considerable difficulty describing the structure and properties of carbon nanotubes and often speculated very vaguely on the impact of nanotechnology. Responses were often superficial.

Candidates had considerable difficulty describing the structure and properties of carbon nanotubes and often speculated very vaguely on the impact of nanotechnology. Responses were often superficial.

State the scale at which nanotechnology takes place and outline the importance of working at this scale.

State one public concern regarding the development of nanotechnology.

One development has been the production of nanotubes. Describe the way in which the arrangement of carbon atoms in the wall and sealed end of a nanotube differ.

a scale of 1–100nm;

careful positioning of individual atoms / ability to control/manipulate at atomic scale / production of material with novel properties;

health concerns / toxicity / effects on the human immune system / the lack of public involvement in policy discussions;

in the walls carbon atoms only form hexagons;

in the ends the carbon atoms form both hexagons and pentagons;

Though many candidates could quote the scale that nanotechnology deals with, few could state specific concerns about its implementation, and hardly any could distinguish between the bonding in the walls and the ends of nanotubes.

Though many candidates could quote the scale that nanotechnology deals with, few could state specific concerns about its implementation, and hardly any could distinguish between the bonding in the walls and the ends of nanotubes.

Though many candidates could quote the scale that nanotechnology deals with, few could state specific concerns about its implementation, and hardly any could distinguish between the bonding in the walls and the ends of nanotubes.

Distinguish between homogeneous and heterogeneous catalysts.

Discuss two factors which need to be considered when selecting a catalyst for a particular chemical process.

Identify the catalyst used in the catalytic cracking of long chain hydrocarbons and state one other condition needed.

State an equation for the catalytic cracking of the straight chain hydrocarbon pentadecane, \({{\text{C}}_{{\text{15}}}}{{\text{H}}_{{\text{32}}}}\), to produce two products with similar masses.

homogeneous catalysts are in the same phase/state as reactants and heterogeneous catalysts are in a different phase/state to reactants;

should produce only the desired product / selectivity;

efficiency;

should be able to work under both mild and severe conditions / should be able to work at high temperatures;

should not produce an (unwanted) environmental impact;

cost / economic viability / OWTTE;

ease of poisoning/contamination;

(catalyst a mixture of) silica/silicon dioxide/ \({\text{Si}}{{\text{O}}_2}\) and alumina/aluminium oxide/\({\text{A}}{{\text{l}}_{\text{2}}}{{\text{O}}_{\text{3}}}\) / zeolites/aluminosilicates;

high temperature / 500 °C;

\({{\text{C}}_{15}}{{\text{H}}_{32}} \to {{\text{C}}_8}{{\text{H}}_{18}} + {{\text{C}}_7}{{\text{H}}_{14}}/{{\text{C}}_{15}}{{\text{H}}_{32}} \to {{\text{C}}_8}{{\text{H}}_{16}} + {{\text{C}}_7}{{\text{H}}_{16}}\);

Most candidates were aware of the differences between homogeneous and heterogeneous catalysts.

Few candidates could name the catalyst but knew one other condition needed for catalytic cracking.

Most correctly stated an equation for the catalytic cracking of pentadecane, but some added oxygen or water, and some had too many hydrogen atoms in the products.

State the overall redox equation when carbon monoxide reduces Fe₂O₃ to Fe.

Predict the magnetic properties of Fe₂O₃ and Al₂O₃ in terms of the electron structure of the metal ion, giving your reasons.

Fe₂O₃:

Al₂O₃:
 

Molten alumina, Al₂O₃(l), was electrolysed by passing 2.00×10⁶ C through the cell. Calculate the mass of aluminium produced, using sections 2 and 6 of the data booklet.

Fe₂O₃ (s) + 3CO (g) → 2Fe (l) + 3CO₂ (g)

Fe₂O₃:
paramagnetic
AND
unpaired electrons present «so magnetic moments do not cancel out»

Al₂O₃:
diamagnetic
AND
no unpaired electrons/all electrons are paired «so magnetic moments cancel out»

Award [1 max] for “Fe₂O₃ paramagnetic AND Al₂O₃ diamagnetic”.

Award [1 max] for “Fe₂O₃ unpaired electrons present AND Al₂O₃ no unpaired electrons/all electrons are paired”.

Award [1 max] for “Magnetic moments do not cancel out in Fe₂O₃ but do in Al₂O₃”.

Unpaired and paired electrons may also be conveyed by orbital diagrams for the respective ions.

\(n\left( {\rm{e}} \right) = \frac{{2.00 \times {{10}^6}}}{{96500}}/20.7 \ll {\rm{mol}} \gg \)

OR
n(Al)=\(\frac{1}{3}\)n(e)/6.91«mol»

m(Al)=«6.91×26.98=»186«g»

Award [2] for correct final answer for any value within the range 186–189 «g».

(i)     Strongest intermolecular forces:

(ii)     Highest density:

(iii)     Greatest flexibility:

The polymer polyvinyl chloride (PVC), also known as poly(chloroethene), is hard and brittle when pure. Explain, in terms of intermolecular forces, how adding a plasticizer to PVC modifies the properties of the polymer.

(i)     A;

(ii)     A;

(iii)     B;

closely packed molecules with crystalline structure;

(plasticizers) separate the PVC molecules/polymer chains / disrupt crystalline structure;

decrease/weaken intermolecular forces/intermolecular dipole-dipole interactions/van der Waals’/London Dispersion;

Do not accept mention of H-bonding

makes it (PVC) softer/more flexible/more easily moulded;

Many candidates were able to score three marks in (a) and most gave a good account of (b). Many, however, neglected to mention intermolecular forces, specifically requested in the question.

Many candidates were able to score three marks in (a) and most gave a good account of (b). Many, however, neglected to mention intermolecular forces, specifically requested in the question.

Use high-density poly(ethene) and low-density poly(ethene) as examples to explain the difference that branching can make to the properties of a polymer.

During the formation of poly(styrene), a volatile hydrocarbon such as pentane is often added. Describe how this affects the properties of the polymer and give one use for this product.

in HDPE there is little branching / in LDPE there is branching/side chains;

long chains can pack closely together/have greater forces of attraction so (HDPE) is more dense/more rigid/stronger;

side chains make (LDPE) more flexible/ideal for film products (such as food wrapping);

Accept opposite statements for marking points 2 and 3.

makes the polymer low density/good thermal insulator/expanded/softer/better shock absorber;

packaging/insulation;

Award [1 max] if thermal insulation given for both answers.

Most candidates had difficulty explaining the difference between HDPE and LDPE in terms of branching. Many mixed up the branching and properties, for example stating that increased branching led to a higher density.

Part (b), which required candidates to explain why pentane is added to poly(styrene) to improve its thermal insulation properties, was also difficult for most candidates.

Explain how pure aluminium oxide is obtained from bauxite.

Explain why sodium hexafluoroaluminate, \({\text{N}}{{\text{a}}_{\text{3}}}{\text{Al}}{{\text{F}}_{\text{6}}}\), (cryolite) is added to the aluminium oxide before electrolysis takes place to produce aluminium.

State the half-equations for the reactions taking place at the positive and negative electrodes during the production of aluminium by electrolysis.

Positive electrode (anode):

Negative electrode (cathode):

Before the introduction of the electrolytic method by Hall and Héroult in the 1880s it was very difficult to obtain aluminium metal from its ores. Suggest one way in which it was achieved.

The worldwide production of aluminium by electrolysis makes a significant impact on global warming. Suggest two different ways in which the process increases the amount of carbon dioxide in the atmosphere.

(bauxite) is reacted with (concentrated) sodium hydroxide/NaOH (solution at high temperature);

forms sodium aluminate / \({\text{Al(OH}}{{\text{)}}_3} + {\text{O}}{{\text{H}}^ - } \to {\text{Al(OH)}}_4^ - \);

Accept both ionic and non-ionic equations and different, correct representations of the aluminate ion (Al(OH )₄^–, AlO₂^–).

solution is filtered / insoluble impurities removed (by filtration);

reaction reversed by cooling / diluting solution / adding water;

Accept passing CO₂ through the solution.

mixture seeded with alumina crystals;

pure hydroxide precipitated / \({\text{Al(OH)}}_4^ -  \to {\text{Al (OH}}{{\text{)}}_3} + {\text{O}}{{\text{H}}^ - }\);

Accept both ionic and non-ionic equations and different, correct representations of the aluminate ion (Al(OH)₄^–, AlO₂^–).

(pure) \({\text{Al(OH}}{{\text{)}}_3}\) heated / \({\text{2Al(OH}}{{\text{)}}_3} \to {\text{A}}{{\text{l}}_2}{{\text{O}}_3} + {\text{3}}{{\text{H}}_2}{\text{O}}\);

Award [1 max] for “Alumina is soluble in alkali, but impurities are not” / OWTTE.

Ignore state symbols.

melting point of the cryolite solution is much lower than the melting point of alumina/Al₂O₃ / it lowers the melting point (of the mixture);

Do not allow lowers melting point of aluminium.

Do not allow lowers required/operating temperature.

Accept improves conductivity of the electrolyte/aluminium oxide.

Positive electrode (anode):

\({\text{2}}{{\text{O}}^{2 - }} \to {{\text{O}}_2} + {\text{4}}{{\text{e}}^ - }/{{\text{O}}^{2 - }} \to \frac{1}{2}{{\text{O}}_2} + {\text{2}}{{\text{e}}^ - }/{\text{C}} + {\text{2}}{{\text{O}}^{2 - }} \to {\text{C}}{{\text{O}}_2} + {\text{4}}{{\text{e}}^ - }\);

Negative electrode (cathode):

\({\text{A}}{{\text{l}}^{3 + }} + {\text{3}}{{\text{e}}^ - } \to {\text{Al}}\);

Allow e instead of e^–.

Accept multiples of the correct equations, such as 2Al³⁺ + 6e^– \( \to \) 2Al .

Award [1 max] if correct equations but at wrong electrodes.

Ignore state symbols.

by reduction with a more reactive metal/metal above Al in electrochemical

series/ECS/reactivity series / OWTTE;

Accept equations for displacement reactions of Al₂O₃ with more reactive metals.

graphite/carbon electrodes converted/oxidized (into CO₂);

the fossil fuels used to provide energy/transport (produce CO₂);

This question was probably the worst answered question on the whole paper. In the first section many candidates confused the purification process with the electrolytic extraction and answers that scored any marks were rare. Many candidates knew the reasons for the addition of cryolite, but it was unusual to find both electrode equations correct and balanced. Hardly any had the lateral thinking skills to suggest displacement by a more reactive metal as a possible way of obtaining aluminium, but most students knew of at least one way in which aluminium production resulted in the emission of carbon dioxide.

This question was probably the worst answered question on the whole paper. In the first section many candidates confused the purification process with the electrolytic extraction and answers that scored any marks were rare. Many candidates knew the reasons for the addition of cryolite, but it was unusual to find both electrode equations correct and balanced. Hardly any had the lateral thinking skills to suggest displacement by a more reactive metal as a possible way of obtaining aluminium, but most students knew of at least one way in which aluminium production resulted in the emission of carbon dioxide.

This question was probably the worst answered question on the whole paper. In the first section many candidates confused the purification process with the electrolytic extraction and answers that scored any marks were rare. Many candidates knew the reasons for the addition of cryolite, but it was unusual to find both electrode equations correct and balanced. Hardly any had the lateral thinking skills to suggest displacement by a more reactive metal as a possible way of obtaining aluminium, but most students knew of at least one way in which aluminium production resulted in the emission of carbon dioxide.

This question was probably the worst answered question on the whole paper. In the first section many candidates confused the purification process with the electrolytic extraction and answers that scored any marks were rare. Many candidates knew the reasons for the addition of cryolite, but it was unusual to find both electrode equations correct and balanced. Hardly any had the lateral thinking skills to suggest displacement by a more reactive metal as a possible way of obtaining aluminium, but most students knew of at least one way in which aluminium production resulted in the emission of carbon dioxide.

This question was probably the worst answered question on the whole paper. In the first section many candidates confused the purification process with the electrolytic extraction and answers that scored any marks were rare. Many candidates knew the reasons for the addition of cryolite, but it was unusual to find both electrode equations correct and balanced. Hardly any had the lateral thinking skills to suggest displacement by a more reactive metal as a possible way of obtaining aluminium, but most students knew of at least one way in which aluminium production resulted in the emission of carbon dioxide.

Distinguish between the arrangement of carbon atoms at the sides and at the ends of carbon nanotubes.

Sides:

Ends:

Outline why bundles of carbon nanotubes have high tensile strength.

Discuss two concerns regarding the development of nanotechnology.

Sides:

(atoms arranged in) hexagons

and

Ends:

(atoms arranged in) pentagons (and hexagons);

strong covalent/C–C bonding (in the walls of the nanotubes) / OWTTE;

possible toxicity of small (airborne) particles;

explosive / small size/large surface area means dangerously fast reactions;

unknown health effects / immune system/allergy concerns;

uncertain impact on environment;

lack of public awareness about dangers;

increasing economic disparity between developed and developing nations;

Accept other valid concerns.

A correct definition of nanotechnology was often seen and many candidates knew the difference between the arrangement of carbon atoms at the sides and at the ends of carbon nanotubes. Reference to the presence of strong covalent bonding between the carbon atoms to explain the high tensile strength of the bundles of nanotubes was not seen in most scripts.

A correct definition of nanotechnology was often seen and many candidates knew the difference between the arrangement of carbon atoms at the sides and at the ends of carbon nanotubes. Reference to the presence of strong covalent bonding between the carbon atoms to explain the high tensile strength of the bundles of nanotubes was not seen in most scripts.

A correct definition of nanotechnology was often seen and many candidates knew the difference between the arrangement of carbon atoms at the sides and at the ends of carbon nanotubes. Reference to the presence of strong covalent bonding between the carbon atoms to explain the high tensile strength of the bundles of nanotubes was not seen in most scripts.

State the difference in the structure of the two polymers.

Isotactic:

Atactic:

Explain how the difference in structure results in the different properties of isotactic and atactic poly(propene).

Isotactic: methyl groups all oriented on same side of polymer chain and

Atactic: methyl groups oriented randomly;

Diagram alone is not sufficient – unless difference stated in words.

closer packing of isotactic chains;

isotactic has stronger van der Waals’/London/dispersion/intermolecular forces (than atactic);

Accept opposite statements for atactic.

Allow vdW as abbreviation for van der Waals’ or FDL for London/dispersion.

The orientations of methyl groups in isotactic and atactic poly(propene) were known by more than half of the candidates, but the explanations of the properties did not involve intermolecular forces for the majority of candidates.

The orientations of methyl groups in isotactic and atactic poly(propene) were known by more than half of the candidates, but the explanations of the properties did not involve intermolecular forces for the majority of candidates.

State the type of catalysis occurring in reaction I.

Outline the mechanism by which each catalyst lowers the activation energy in the reactions above, and state a particular disadvantage of each type of catalysis.

homogeneous;

Allow “prone to poisoning” as a disadvantage for either but not both.

Homogeneous catalysis was usually identified in part (a). In (b), few got the correct mechanism for \({\text{F}}{{\text{e}}^{2 + }}{\text{(aq)}}\), namely the fact that there is a change in the oxidation state. The command term outline needs to be differentiated from state. Correct disadvantages were usually identified and for Fe(s) most knew that the mechanism involved reactants being adsorbed onto the surface. Outline is an objective 2 command term, as given on P.11 of the guide and equates to giving a brief account or summary. Hence simply stating heterogeneous for the mechanism was incorrect for Fe(s) for example. Candidates need to pay close attention to the command terms as part of their examination preparation.

Homogeneous catalysis was usually identified in part (a). In (b), few got the correct mechanism for \({\text{F}}{{\text{e}}^{2 + }}{\text{(aq)}}\), namely the fact that there is a change in the oxidation state. The command term outline needs to be differentiated from state. Correct disadvantages were usually identified and for Fe(s) most knew that the mechanism involved reactants being adsorbed onto the surface. Outline is an objective 2 command term, as given on P.11 of the guide and equates to giving a brief account or summary. Hence simply stating heterogeneous for the mechanism was incorrect for Fe(s) for example. Candidates need to pay close attention to the command terms as part of their examination preparation.

Liquid-crystal displays are used in many electronic appliances. The molecule below has liquid-crystal display properties.

Suggest three reasons why the molecule is suitable for use in liquid-crystal display devices.

rod shape / rigid;

chemically stable (due to hydrocarbon rings and chain);

polar (due to the presence of F) / OWTTE;

can change orientation / rapid switching in electric field/when voltage is applied;

Examiners reported an average understanding of liquid crystal properties.

Distinguish between a homogeneous and a heterogeneous catalyst.

Other than cost, state one advantage and one disadvantage of using a homogeneous catalyst rather than a heterogeneous catalyst.

Advantage:

Disadvantage:

Other than selectivity and cost, list three factors which should be considered when choosing a catalyst for a particular industrial process.

homogeneous catalyst is in the same phase/state as the reactants and heterogeneous is in a different phase/state to the reactants;

Advantage:

all catalyst exposed to reactants / does not depend on surface area / react more rapidly / OWTTE;

Disadvantage:

difficult to remove from products;

Accept “Cannot always be used at high temperature”.

Apply ECF if C2. (a) the wrong way round.

amount of reactant converted to product per amount of catalyst;

Accept efficiency / conversion rate.

ability to work under different/a range of conditions;

toxicity / environmental/health impact;

catalytic poisoning / active sites become blocked;

lifetime of catalyst;

ease of removal;

This question was relatively well tackled. Almost all knew the difference between the two types of catalysts, though many referred to “state” than the more correct “phase” and could not identify an advantage and a disadvantage and knew of at least some of the factors that need to be considered in decisions relating to the choice of a catalyst.

This question was relatively well tackled. Almost all knew the difference between the two types of catalysts, though many referred to “state” than the more correct “phase” and could not identify an advantage and a disadvantage and knew of at least some of the factors that need to be considered in decisions relating to the choice of a catalyst.

This question was relatively well tackled. Almost all knew the difference between the two types of catalysts, though many referred to “state” than the more correct “phase” and could not identify an advantage and a disadvantage and knew of at least some of the factors that need to be considered in decisions relating to the choice of a catalyst.

State the property of the liquid-crystal molecules that allows them to align when a voltage is applied.

List two substances that can behave as liquid crystals.

Distinguish between thermotropic and lyotropic liquid crystals.

Thermotropic liquid crystals:

Lyotropic liquid crystals:

polarity / presence of dipole (moment);

Any two for [1]

graphite

cellulose

(spider) silk

DNA

biphenyl nitriles

soap

Kevlar

Thermotropic liquid crystals:

pure substances and exhibit liquid-crystal properties in a certain temperature range;

Lyotropic liquid crystals:

solutions and exhibit liquid-crystal properties in a certain concentration range;

Award [1 max] for thermotropic pure substances and lyotropic solutions.

Award [1 max] for thermotropic in a certain temperature range and lyotropic solutions in a certain concentration range.

The majority of candidates recognized polarity as the property of liquid crystals in part (a) and were able to give two substances that could act as liquid crystals in part (b).

The majority of candidates recognized polarity as the property of liquid crystals in part (a) and were able to give two substances that could act as liquid crystals in part (b).

Many candidates knew that thermotropic liquid crystals worked within a temperature range and lyotropic liquid crystals work within a concentration range in part (c), but only few candidates distinguished between the two types fully.

State an ionic equation, including the state symbols, to show how hydrogen sulfide gas, \({{\text{H}}_{\text{2}}}{\text{S(g)}}\), is able to remove mercury(II) ions, \({\text{H}}{{\text{g}}^{2 + }}{\text{(aq)}}\), when it is bubbled through a water sample.

\({\text{H}}{{\text{g}}^{2 + }}{\text{(aq)}} + {{\text{S}}^{2 - }}{\text{(aq)}} \to {\text{HgS(s)}}/{{\text{H}}_2}{\text{S(g)}} + {\text{H}}{{\text{g}}^{2 + }}{\text{(aq)}} \to {\text{HgS(s)}} + {\text{2}}{{\text{H}}^ + }{\text{(aq)}}/\)

\({{\text{H}}_2}{\text{S(aq)}} + {\text{H}}{{\text{g}}^{2 + }}{\text{(aq)}} \to {\text{HgS(s)}} + {\text{2}}{{\text{H}}^ + }{\text{(aq)}}\);

correctly balanced equation;

correct state symbols;

Neither mark can be awarded for an incorrect equation.

Part a), relating to the reaction precipitating mercury sulfide, was very challenging and arguably marginal to the syllabus and as a result hardly any students gained any marks; unbalanced equations, especially yielding hydrogen as a product, proliferated. The process of eutrophication was better known, but many students incorrectly attributed the depletion of oxygen to the excessive growth of plants and algae rather than their subsequent death and decay.

Explain the function of the molten cryolite.

State the half-equations for the reactions that take place at each electrode.

Positive electrode (anode):

Negative electrode (cathode):

Outline two different ways that carbon dioxide may be produced during the production of aluminium.

melting point of the cryolite solution is much lower than the melting point of alumina/Al2O3 / it lowers the melting point of the mixture / cell operates at lower temperature;

Allow lowers melting point or lowers melting point of aluminium oxide.

Do not allow lowers melting point of aluminium.

Positive electrode:

\({\text{2}}{{\text{O}}^{2 - }} \to {{\text{O}}_2} + {\text{4}}{{\text{e}}^ - }/{{\text{O}}^{2 - }} \to \frac{1}{2}{{\text{O}}_2} + {\text{2}}{{\text{e}}^ - }\);

Negative electrode:

\({\text{A}}{{\text{l}}^{3 + }} + {\text{3}}{{\text{e}}^ - } \to {\text{Al}}\);

Award [1] for correct equations but wrong electrodes.

Allow e instead of \({e^ - }\).

use of fossil fuels (to provide energy);

oxidation of the (graphite) positive electrode/anode;

This was either answered very well or very poorly.

Only the best candidates could state half-equations for the electrolysis of aluminium.

Many candidates scored one mark out of two for outlining how carbon dioxide may be produced during aluminium production in (b). C.1.10 states that candidates should know the environmental impacts of aluminium production.

The following reaction occurs during the cracking of tetradecane, \({{\text{C}}_{{\text{14}}}}{{\text{H}}_{{\text{30}}}}\).

\[{{\text{C}}_{14}}{{\text{H}}_{30}}{\text{(g)}} \to {{\text{C}}_{10}}{{\text{H}}_{22}}{\text{(g)}} + {\text{2}}{{\text{C}}_2}{{\text{H}}_4}{\text{(g)}}\]

Suggest a use for each of the products formed in the reaction.

\({{\text{C}}_{{\text{10}}}}{{\text{H}}_{{\text{22}}}}\):

\({{\text{C}}_{\text{2}}}{{\text{H}}_{\text{4}}}\):

State the main type of product obtained from steam cracking.

Catalytic cracking uses silica as a heterogeneous catalyst. Explain the mode of action of a heterogeneous catalyst.

State one advantage of using a heterogeneous catalyst rather than a homogeneous catalyst.

Discuss two factors that need to be considered when choosing a catalyst for a process.

C₁₀H₂₂: gasoline/petrol / fuel / kerosene;

Do not allow just combustion or cars.

Allow gas for cars/automobiles instead of gasoline but not gas alone.

C₂H₄: chemical feedstock / OWTTE;

Accept suitable example such as manufacturing plastics/polymers but not just plastics.

alkenes;

solid surface has active sites / reactants adsorb on solid surface;

Do not accept absorb instead of adsorb.

brings reactants close together in correct orientation;

weakens reactant bonds / reactants bonds are easier to break;

can be easily removed/filtered from reaction mixture / large amount of reactant molecules pass over catalyst that is in a fixed position / can be used at high temperatures;

selectivity to produce (a high yield of) the desired product / OWTTE;

extent to which rate of reaction is increased/Ea is lowered;

amount of reactant converted to product per amount of catalyst;

Accept efficiency / conversion rate.

ability to work under different/a range of conditions;

environmental/health impact;

catalytic poisoning / active sites become blocked;

cost in relation to life expectancy / OWTTE;

ease of removal from reaction mixture;

Less than half of the candidates knew the uses of the products of cracking in (a) and very few candidates knew the product of steam cracking in (b).

Less than half of the candidates knew the uses of the products of cracking in (a) and very few candidates knew the product of steam cracking in (b).

The mode of action of heterogeneous catalysts was also not well answered. The majority of candidates wrote about catalysts in general gaining no marks on part (c).

Parts (d) and (e) about the advantage of heterogeneous catalysts over homogeneous catalysts, and factors to be considered when selecting a catalyst were well answered by the majority of candidates.

Parts (d) and (e) about the advantage of heterogeneous catalysts over homogeneous catalysts, and factors to be considered when selecting a catalyst were well answered by the majority of candidates.

Identify the structural feature of cholesteryl benzoate which makes it suitable for use as a liquid crystal.

Suggest the essential feature a liquid-crystal molecule must have so that the display can be turned “on” and “off”.

rigid / rod-shaped;

polar (group/molecule);

Many candidates knew the essential feature that a liquid-crystal molecule must have for the display being turned off and on but the description of the principles of a liquid-crystal display device was often poorly presented and not clearly understood.

Many candidates knew the essential feature that a liquid-crystal molecule must have for the display being turned off and on but the description of the principles of a liquid-crystal display device was often poorly presented and not clearly understood.

Define the term nanotechnology.

Discuss two concerns about its development and use.

(research/technology development at) 1–100 nm (range);

Award [1 max] for any one of:

creates/uses structures with novel properties (because of their small size) / OWTTE;

builds on ability to control/manipulate at atomic scale / OWTTE;

explosive / small size/large surface area means very fast reactions at possibly dangerous levels;

unknown health effects / immune system/allergy concerns;

industry not concerned about impact of product;

lack of public awareness about dangers;

nanoparticle waste products may require new methods of disposal;

nanoweapons more difficult to detect than conventional weapons (resulting in weapons of mass destruction);

possible toxicity (of small airborne particles);

Do not allow just “may cause environmental destruction”.

Accept other valid concerns.

Accept OWTTE throughout.

Both parts of question 12 were reasonably well answered, though a small minority of candidates either did not give the 1-100 nm range or failed to give correct units here. In (b) some vague answers such as “may cause environmental destruction” were cited, which did not score.

Both parts of question 12 were reasonably well answered, though a small minority of candidates either did not give the 1-100 nm range or failed to give correct units here. In (b) some vague answers such as “may cause environmental destruction” were cited, which did not score.

Outline the technique used to manipulate the atoms in this way.

The atomic radius of xenon is \(1.36 \times {10^{ - 10}}{\text{ m}}\). Estimate the approximate length, in m, of the “I” in the original IBM image.

physical;

atoms placed in specific positions;

using a scanning tunnelling microscope/STM / atomic/scanning force microscope/AFM/SFM;

Accept “using a scanning probe/device/instrument”.

any value in the range \({10^{ - 9}}-{10^{ - 8}}{\text{ (m)}}\);

Manipulating the atoms using an atomic force microscope was not well known.

With the help of the given diagram some candidates were able to estimate a reasonable length. The range of length accepted in the markscheme was generous.

Suggest why some biodegradable plastics do not decompose in landfill sites.

High-level and low-level wastes are two types of radioactive waste. Compare the half-lives and the methods of disposal of the two types of waste.

limited supply of oxygen (prevents the bacteria from acting);

Do not accept air.

high-level waste has longer half-life / low-level waste has shorter half-life;

high-level waste is vitrified/made into glass/buried underground/in granite/in deep mines/under water/in steel containers/in cooling ponds / OWTTE;

low-level waste is stored under water/in steel containers/in cooling ponds/filtered/discharged directly into sea / OWTTE;

Accept cooling ponds/steel containers/under water/concrete containers only once.

This was generally well done although few realised that oxygen was needed for the decomposition of the plastics in landfill sites.

This was generally well done although few realised that oxygen was needed for the decomposition of the plastics in landfill sites.

Suggest two reasons for this shift.

A lot of feedstock is used in the production of plastics. Discuss two advantages and one disadvantage of using plastic for packaging instead of cardboard.

Two advantages:

One disadvantage:

increasing cost of oil (relative to other energy sources);

limited supply (of petroleum);

other sources of energy available / alternative energy sources;

(use as a raw material) reduces/delays greenhouse gas/global warming/climate change problems;

concerns about greenhouse gases/climate change causing changes in behaviour / OWTTE;

Do not accept just “greenhouse gases/climate change”;

products from raw materials can be recycled / fuels cannot be recycled;

increasing demand as raw material from continued economic growth/demand for wider variety of products;

more profit to be made (by using as raw material);

reduced availability of other sources of hydrocarbons;

Accept political factors, such as “conflicts disrupting production”.

Advantages:

Any two for [2 max] of:

waterproof so strong when wet;

can be transparent so contents can be seen;

better insulates the item it is packing if expanded plastic/bubble wrap used;

can be vacuum sealed to exclude air/keep food fresh;

better protection against knocks as it can be moulded to fit the item;

Disadvantages:

Any one of:

uses valuable petroleum resources which are non-renewable;

(may) not be burned safely because toxic gases are produced;

(may) not be bio-degradable/recyclable so will linger in landfill;

Accept other valid answers for both advantages and disadvantages.

Each answer must be qualified.

Many candidates did achieve at least one mark, usually referring to the increasing demand of crude oil as a raw material linked to demand for wider variety of products. Any other reasons were often inadequately communicated. There were many responses referring to the ‘production of greenhouse gases’ with no further qualification with respect to the shift in behaviour. The second part of this question produced answers which often failed to precisely address the advantages and disadvantages of the use of plastics versus cardboard specifically for packaging.

Many candidates did achieve at least one mark, usually referring to the increasing demand of crude oil as a raw material linked to demand for wider variety of products. Any other reasons were often inadequately communicated. There were many responses referring to the ‘production of greenhouse gases’ with no further qualification with respect to the shift in behaviour. The second part of this question produced answers which often failed to precisely address the advantages and disadvantages of the use of plastics versus cardboard specifically for packaging.

State one negative impact that the production of iron and steel has on the environment.

waste rock from mining / airborne ash from blast furnace / the mine destroys the (natural) environment / uses energy resources / acid rain / carbon dioxide / greenhouse gas emissions;

Many students confused the conversion of iron to steel with the smelting of iron ore. A significant number seemed to have memorised a method of heat treatment of steel and many could indentify ways in which the iron and steel industry has an environmental impact.

State three factors which need to be considered when an industrial catalyst is chosen. In each case explain why they are important.

This was related to assessment statement C.4.3. It proved to be challenging; candidates did not show a good understanding and answers were not well organized.

selectivity – does the catalyst give a good yield of the desired compound / OWTTE;

efficiency – how much faster does the reaction occur/reach equilibrium / OWTTE;

economic – cost / how long the catalyst will last / how easily is it poisoned / OWTTE;

environmental impact – toxicity / regeneration / recyclability/ease of separation of catalyst from reaction mixture / OWTTE;

versatility – ability to work under a range of conditions / ability to work with a range of substances / OWTTE;

Award [1 max] for any three correct factors without explanation.

(i)     Describe the meaning of the term liquid crystals and state which of the representations below (A, B or C) best describes molecules present in the liquid-crystalline phase.

(ii)     Deduce, with reasoning, which of the following substance(s) is/are most likely to show liquid-crystalline behaviour.

Substance I:

Liquid-crystalline behaviour (yes/no):

Reasoning:

Substance II:

Liquid-crystalline behaviour (yes/no):

Reasoning:

Substance III:

Liquid-crystalline behaviour (yes/no):

Reasoning:

(iii)     Suggest why octane does not show liquid-crystalline behaviour.

(i)     State one difference between thermotropic and lyotropic liquid crystals.

(ii)     Identify, by stating yes or no, the substance(s) which show(s) thermotropic liquid crystalline behaviour.

(i)     (LCs are) fluids that exhibit molecular orientation/orderly molecular arrangement and A;

Accept LCs show properties of liquids and crystals simultaneously and A.

(ii)     I: no, since ionic (so high mp) / lacks long axis;

Allow no since it is not a molecule/not rod-shaped.

II: yes, since has long axis present (so limits ability of molecules to pack lowering mp);

Allow yes since rod-shaped.

has polar functional group / is polar (increasing intermolecular interactions) / (planar/flat) benzene ring present (assists stacking);

III: no, since lacks long axis;

Allow no since non-polar.

Allow no since not rod-shaped.

Award [1 max] for stating II only will show LC behaviour OR I: No, II: Yes and III: No.

Award [2 max] if one correct reason is given for each substance but LC behaviour is either incorrect or not given.

Award [3 max] if correct reasons are given for all three substances, but LC behaviour is either incorrect or not given.

(iii)     (free) rotation about carbon-carbon single bonds (hence greater flexibility) so octane molecules not rod-shaped / OWTTE;

Do not allow mark for non-polar (molecule) only.

(i)     Thermotropic: pure substances and lyotropic: solutions / thermotropic: show LC behaviour over limited temperature range (between solid and liquid states) and lyotropic: shows LC behaviour at certain concentrations;

(ii)     X: yes and Y: no and Z: yes;

Award mark if no is stated only for Y or yes is only stated for X and Z.

This proved to be the most challenging question in option C. Candidates were able to identify A as the molecules present in the liquid-crystalline phase but were unable to describe the state for part (a)(i). Majority of the candidates were not able to score more than two marks for part (ii). Most were unable to identify substance I as ionic and substance II was often identified as ‘yes’ but without sound support. For (a)(iii), again students struggled with explicit sound reasoning. Response for (a)(iii) was poor with most stating non-polar as the reason for inability of octane to show liquid-crystalline behavior. Very few candidates were able to identify and explain if molecules will behave as a liquid crystal. Majority of the candidates were unable to score the point. Candidates were able to state the difference between the two liquid crystals in (b)(i) correctly but were not able to apply the information correctly in (b)(ii) to identify which substances shoe thermotropic liquid-crystalline behaviour.

This proved to be the most challenging question in option C. Candidates were able to identify A as the molecules present in the liquid-crystalline phase but were unable to describe the state for part (a)(i). Majority of the candidates were not able to score more than two marks for part (ii). Most were unable to identify substance I as ionic and substance II was often identified as ‘yes’ but without sound support. For (a)(iii), again students struggled with explicit sound reasoning. Response for (a)(iii) was poor with most stating non-polar as the reason for inability of octane to show liquid-crystalline behavior. Very few candidates were able to identify and explain if molecules will behave as a liquid crystal. Majority of the candidates were unable to score the point. Candidates were able to state the difference between the two liquid crystals in (b)(i) correctly but were not able to apply the information correctly in (b)(ii) to identify which substances shoe thermotropic liquid-crystalline behaviour.

Describe what is meant by the term alloy.

State the main improvement made to the properties of aluminium when it is alloyed.

homogeneous mixture of metals/metal(s) and non-metal(s);

increase in aluminium’s strength;

Most candidates did not gain the mark for alloys in part (b) because they did not state that the mixture was homogeneous which was needed for the mark.

The majority of candidates knew that alloying aluminium increased its strength in part (c).

Explain why PVC is less flexible than polyethene.

State how PVC can be made more flexible during its manufacture and explain the increase in flexibility on a molecular level.

PVC can exist in isotactic and atactic forms. Draw the structure of the isotactic form showing a chain of at least six carbon atoms.

C–Cl bond / molecule is polar;

stronger intermolecular/van der Waals’/London/dispersion forces/dipole-dipole attraction;

addition of plasticizers;

Allow misspelling within reason.

get between polymer chains / keeps chains further apart and reduces attraction (between the chains);

 ;

Accept any structure with all the Cl atoms shown on the same side.

Continuation bonds at end of structure not needed.

Hydrogen atoms must be included.

Most answers in (a) did not mention the polarity of the C–Cl bond.

The explanation of PVC's flexibility in (b) did not usually refer to the polymer chains being pushed apart.

A significant number of candidates drew the isotactic form of polypropene instead of PVC in response to (c).

The diagram below shows eight molecules in the liquid state. Suggest, with a diagram, a possible arrangement that these rod-shaped molecules could adopt in the nematic liquid-crystal phase.

Suggest, with reference to the structure, why the molecule is able to change orientation in an electric field.

Suggest how the C₅H₁₁ chain contributes to the liquid-crystal properties of the compound.

Explain why a liquid-crystal device may be unreliable at low temperatures.

diagram should have molecules with a parallel alignment in any direction (not just upwards);

diagram should have molecules in an irregular arrangement in space;

Ignore relative separation between molecules.

Award [1 max] if number of molecules < 7.

Award [1 max] if stated “molecules align parallel to each other but with an irregular arrangement in space / OWTTE” but with no diagram drawn.

Allow the representation of molecules by lines.

polar/dipole moment due to the presence of C\( \equiv \)N (bond) / difference in electronegativity between C and N;

prevents close packing of molecules / OWTTE;

makes the molecule (longer and) more rod-like;

molecules become more ordered / molecules unable to change orientation (as they approach fixed arrangement of solid state) / molecules move slower / viscosity (of medium) increases (so LCD response time increases);

Well answered by many, although some candidates left the question blank. Candidates were more likely to align molecules in the same direction, but only some of them kept the arrangement of the molecules random and hence received the second mark.

The majority recognized that the alignment is due to the polarity, but only a few candidates attributed that to the CN bond.

Quite well answered about the role of the pentyl group in the liquid-crystal properties of the compound.

The better students were able to explain why a liquid-crystal device is unreliable at low temperature.

(i)     Describe the production of aluminium from its purified ore. Explain the role of cryolite and deduce the equations for the reactions occurring at the two electrodes.

Production of aluminium:

Role of cryolite:

Negative electrode (cathode):

Positive electrode (anode):

(ii)     Outline why aluminium was not available in large quantities before 1900.

(i)     State one advantage of using an alloy rather than the pure metal.

(ii)     Outline why the range of metals alloyed with aluminium for this use is very limited.

Suggest one possible environmental impact that can result from the large-scale production of aluminium.

(i)     Production of aluminium:

electrolysis of molten alumina/aluminium oxide/\({\text{A}}{{\text{l}}_{\text{2}}}{{\text{O}}_{\text{3}}}\);

Role of cryolite:

(molten) cryolite (saves money due to) lower operating temperature / solvent with a lower melting point (than aluminium oxide);

Accept lowers the melting point of aluminium oxide.

Negative electrode (cathode):

\({\text{A}}{{\text{l}}^{3 + }}{\text{(l)}} + {\text{3}}{{\text{e}}^ - } \to {\text{Al(l)}}\);

Positive electrode (anode):

\({\text{2}}{{\text{O}}^{2 - }}{\text{(l)}} \to {{\text{O}}_2}{\text{(g)}} + {\text{4}}{{\text{e}}^ - }\);

Allow e for e^–.

Ignore state symbols.

Penalize use of equilibrium sign once only.

Award [1 max] for M3 and M4 if correct equations are given but at the wrong electrodes.

(ii)     no electricity / electricity not widely available before 1900;

(i)     to control/improve properties / alloys are stronger/more durable/less reactive/less malleable/less ductile than pure metals;

(ii)     only a small number of metals have low densities / many low density metals are too reactive / alloys need presence of other metallic atoms of slightly different size (few metals like this);

(purification of ore produces) waste \({\text{F}}{{\text{e}}_2}{{\text{O}}_3}\)/iron(III) oxide/red mud;

carbon dioxide/ \({\text{C}}{{\text{O}}_2}\) from burning electrodes;

environmental impacts of power generation;

aluminium production a significant contributor to global warming;

mining the ore damages the landscape/local ecology;

generation of fluorides/polyfluorinated carbons/fluorine containing waste products;

(i)     Many candidates understood the principles behind the production of aluminium and the role of the cryolite, although not always managing to state the principles accurately to be able to score the first two marks, but many candidates showed weakness in writing the correct half-equations at the correct electrodes. 

(ii)     About half of the candidates stated the there was no electricity available at that time.

(i)     More than half of the candidates were able to give an advantage of using an alloy over using the pure metal. A few candidates stated the misconception that alloys were less brittle than pure metals.

(ii)     Some candidates offered sensible suggestions mainly focusing on the importance of finding a low density metal.

Quite well answered. Not many candidates discussed the impact of the purification of the bauxite or its mining. Candidates focused on the impact of the generation of large amounts of electricity and global warming.

Magnetite, Fe₃O₄, is a common ore of iron. Calculate the average oxidation state of iron in the compound and comment on your answer.

State the equation for the reduction of this ore to iron with carbon monoxide.

Outline why iron is obtained from its ores using chemical reducing agents but aluminium is obtained using electrolysis.

\( + \frac{8}{3}/ + 2\frac{2}{3}\) ;

Accept +2.7 but not +3.

+2 and +3 / contains two (or more) iron ions with different oxidation states / contains \({\text{F}}{{\text{e}}^{{\text{2}} + }}\) and \({\text{F}}{{\text{e}}^{{\text{3}} + }}\);

Accept II and III oxidation number notation for oxidation states but not 2+ and 3+ unless ions are referred to explicitly.

Accept “contains different iron compounds/FeO and Fe₂O₃”.

\({\text{F}}{{\text{e}}_3}{{\text{O}}_4}{\text{(s)}} + {\text{4CO(g)}} \to {\text{3Fe(l)}} + {\text{4C}}{{\text{O}}_2}{\text{(g)}}\);

Accept “Fe₃O₄(s) + CO(g) \( \to \) 3FeO(s) + CO₂(g) and

FeO(s) + CO(g) \( \to \) Fe(l ) + CO₂(g)”.

Ignore state symbols.

Al is more reactive than Fe / Al is higher than Fe in the reactivity series / Al is a stronger reducing agent / it is harder to reduce aluminium ores compared to iron ores / \({\text{F}}{{\text{e}}^{3 + }}/{\text{F}}{{\text{e}}^{2 + }}\) is a stronger oxidizing agent / \({\text{A}}{{\text{l}}^{3 + }}\) has a very negative E° value;

This was a challenging question but some candidates managed to calculate the average oxidation state of iron as +8/3, and very few were able to deduce that both +2 and +3 oxidation states were present in the ore.

It was disappointing that most candidates could not give a correct equation for the reduction, considering that both reactants and one product are already given in the question.

Some candidates gave the higher reactivity of aluminium as the reason why it could not be extracted by the use of reducing agents.

Compare the positional and directional order in a crystalline solid, nematic phase liquid crystal and a pure liquid. Show your answer by stating yes or no in the table below.

Need all three across table for each mark.

The positional and directional order were generally compared correctly.

Identify the two functional groups in the monomer from which this polymer is manufactured.

An expanded form of the plastic is often used in packaging. Describe how this is manufactured.

Discuss two advantages and one disadvantage of using the expanded form as a packaging material.

Two advantages:

One disadvantage:

alkenyl/C=C and phenyl/–\({{\text{C}}_{\text{6}}}{{\text{H}}_5}\);

Accept alkene and benzene ring/aromatic ring/arene but not benzene.

pentane/volatile hydrocarbon added (during polymerization process);

heating causes pentane/volatile hydrocarbon to evaporate/vaporize/produce bubbles of gas (expanding the polystyrene);

Accept other suitable identified blowing agents such as carbon dioxide.

Advantages:

Any two for [2 max]:

low/reduced density;

Accept “small mass”.

Do not accept “light”.

can be shaped (around object);

good shock absorber;

insulator;

Disadvantage:

Award [1] for disadvantage:

disposal takes up a lot of space (in landfill);

Accept “non-biodegradable/polluting/hazardous to wildlife”.

Some candidates identified two functional groups in the monomer. 

About half of the candidates described how the expanded form of the plastic could be manufactured.

Most candidates were able to score one or two marks. “Good shock absorber” was a popular answer. Candidates should be encouraged to use precise terminology such as “has low density” instead of “light”.

(i)     State equations for the reactions that occur at each electrode in a lead-acid battery when it delivers a current.

Positive electrode (cathode):

Negative electrode (anode):

(ii)     State equations for the reactions that occur at each electrode in a nickel-cadmium (NiCad) battery when it delivers a current.

Positive electrode (cathode):

Negative electrode (anode):

Another source of power for portable devices is the fuel cell. Compare fuel cells with lead-acid rechargeable batteries, stating one similarity and two differences.

Similarity:

Differences:

(i)     Lead-acid:

Positive electrode (cathode):

\({\text{Pb}}{{\text{O}}_2}{\text{(s)}} + {\text{SO}}_4^{2 - }{\text{(aq)}} + {\text{4}}{{\text{H}}^ + }{\text{(aq)}} + {\text{2}}{{\text{e}}^ - } \to {\text{PbS}}{{\text{O}}_4}{\text{(s)}} + {\text{2}}{{\text{H}}_2}{\text{O(l)}}\) /

\({\text{Pb}}{{\text{O}}_2}{\text{(s)}} + {\text{HSO}}_4^ - {\text{(aq)}} + {\text{3}}{{\text{H}}^ + }{\text{(aq)}} + {\text{2}}{{\text{e}}^ - } \to {\text{PbS}}{{\text{O}}_4}{\text{(s)}} + {\text{2}}{{\text{H}}_2}{\text{O(l)}}\);

Negative electrode (anode):

\({\text{Pb(s)}} + {\text{SO}}_4^{2 - }{\text{(aq)}} \to {\text{PbS}}{{\text{O}}_4}{\text{(s)}} + {\text{2}}{{\text{e}}^ - }\) /

\({\text{Pb(s)}} + {\text{HSO}}_4^ - {\text{(aq)}} \to {\text{PbS}}{{\text{O}}_4}{\text{(s)}} + {\text{2}}{{\text{e}}^ - } + {{\text{H}}^ + }{\text{(aq)}}\);

Allow e for e^– throughout.

Ignore state symbols.

Award [1 max] if correct equations are given but at the wrong electrodes.

(ii)     NiCad:

Positive electrode (cathode):

\({\text{NiO(OH)(s)}} + {{\text{H}}_2}{\text{O(l)}} + {{\text{e}}^ - } \to {\text{Ni(OH}}{{\text{)}}_2}{\text{(s)}} + {\text{O}}{{\text{H}}^ - }{\text{(aq)}}\);

Negative electrode (anode):

\({\text{Cd(s)}} + {\text{2O}}{{\text{H}}^ - }{\text{(aq)}} \to {\text{Cd(OH}}{{\text{)}}_2}{\text{(s)}} + {\text{2}}{{\text{e}}^ - }\);

Allow e for e^– throughout.

Ignore state symbols.

Award [1 max] if correct equations are given but at the wrong electrodes.

Similarity:

(both) convert chemical energy to electrical energy / (both are) voltaic cells;

Differences:

Award [2 max] for any two.

rechargeable batteries employ reversible reactions while fuel cells have irreversible reactions;

fuel cells work non-stop while rechargeable batteries take time to recharge;

fuel cells need a constant supply of reactants/fuel while rechargeable batteries do not need any other substances;

fuel cells convert energy and rechargeable batteries store energy;

fuel cell products must be constantly removed but not for rechargeable batteries;

fuel cells are less polluting/more expensive/weigh less/last longer (than lead-acid rechargeable batteries);

fuel cells have inert/Pt electrodes/components while lead-acid rechargeable batteries have active/non-inert/Pb and \({\text{Pb}}{{\text{O}}_{\text{2}}}\) electrodes;

fuel cells run at higher temperatures than rechargeable batteries;

fuel cells are less portable than rechargeable batteries / fuel cells require pumps/cooling systems while rechargeable batteries do not;

Award [2 max] if three valid points (one similarity and two differences) are given without comparison and [1 max] if two valid points are given without comparison.

(i)     Poorly answered even by strong candidates. Very few candidates gave the correct equations for the reactions occurring at the electrodes of a lead-acid battery.

(ii) This part-question was also poorly answered with very few candidates scoring one out of the two possible marks.

Many candidates scored at least one mark, but many answers only reflected a shallow understanding of fuel cells and lead-acid batteries. Quite a few candidates are still neglecting to satisfy the demands of the “compare” command term that requires reference to both items in every point of comparison.

Explain why alloying can modify the structure and properties of a metal.

(alloying element(s)) atoms/ions have different size;

Allow suitable diagram.

disrupts regular/repeating (metal) lattice;

difficult for one layer to slide over another / added atoms/ions smaller than metal atoms/ions can fit into the (holes of) metal lattice disrupting bonding;

If “particles” is penalised in M1, allow “particles” in M3.

Do not award mark for different or unique properties of alloys.

The common errors in (a) were to give a formula rather than the name of an ore and to add it at R. Whilst part (ii) was generally answered correctly it was slightly alarming to see oxygen given from time to time. Few seemed to know the equation of the reaction primarily responsible for the temperature of 1900 °C. Slag was usually correctly identified in (c) but the equations given seldom started from the raw material, \({\text{CaC}}{{\text{O}}_{\text{3}}}\). Part (d) was often answered successfully whilst candidates were generally unable to earn both marks in (e) (i). Most understood the effect of tempering on steel.

State an equation for the reaction by which iron (III) oxide, Fe₂O₃, is reduced to iron in the blast furnace.

\({\text{F}}{{\text{e}}_2}{{\text{O}}_3}{\text{(s)}} + {\text{3CO(g)}} \to {\text{2Fe(l)}} + {\text{3C}}{{\text{O}}_2}{\text{(g)}}/{\text{F}}{{\text{e}}_2}{{\text{O}}_3}{\text{(s)}} + {\text{3}}{{\text{H}}_2}{\text{(g)}} \to {\text{2Fe(l)}} + {\text{3}}{{\text{H}}_2}{\text{O(g)}}\) /

\({\text{2F}}{{\text{e}}_2}{{\text{O}}_3}{\text{(s)}} + {\text{3C(s)}} \to {\text{4Fe(l)}} + {\text{3C}}{{\text{O}}_2}{\text{(g)}}/{\text{F}}{{\text{e}}_2}{{\text{O}}_3}{\text{(s)}} + {\text{3C(s)}} \to {\text{2Fe(l)}} + {\text{3CO(g)}}\);

Ignore state symbols.

It was pleasing to see a good number of correctly balanced equations here. The precise explanation of how alloying of steel affects physical properties was rarely seen. The correct description of how quenched steel is tempered was rarely seen with the most common answer being heated and rapidly cooled.

Describe the meaning of the term liquid crystals.

When a liquid-crystal display is warmed with a hairdryer, the display loses its clarity and may no longer be visible. Explain why this happens on a molecular level.

fluids that have physical properties dependent on molecular orientation/orderly molecular arrangement;

Allow “fluids that exhibit molecular orientation/orderly molecular arrangement”.

Allow “(LCs) show properties of liquids and crystals simultaneously”.

thermal agitation disrupts directional order of liquid crystal / OWTTE;

rotation of plane polarized light disrupted / crystals no longer have ability to affect light in same way / OWTTE;

An understanding of liquid crystals was generally conveyed. Some candidates stated that liquid crystals show properties of liquids and solids simultaneously which did not score as they did not mention the crystalline state explicitly for solids. In (b) only the really top-tier candidates were able to explain the question asked on a molecular level, i.e. the fact that thermal agitation disrupts the directional order of the liquid crystal and as a result the rotation of plane polarized light is disrupted. This question proved to be possibly one of the hardest questions on the paper overall for candidates.

An understanding of liquid crystals was generally conveyed. Some candidates stated that liquid crystals show properties of liquids and solids simultaneously which did not score as they did not mention the crystalline state explicitly for solids. In (b) only the really top-tier candidates were able to explain the question asked on a molecular level, i.e. the fact that thermal agitation disrupts the directional order of the liquid crystal and as a result the rotation of plane polarized light is disrupted. This question proved to be possibly one of the hardest questions on the paper overall for candidates.

State an equation that shows why rain water is naturally acidic.

Outline the process responsible for the production of each acid and state an equation to show its formation.

Acid rain has caused damage to limestone buildings and marble statues. State an equation to represent the reaction of acid rain with limestone or marble.

\({\text{C}}{{\text{O}}_2} + {{\text{H}}_{\text{2}}}{\text{O}} \rightleftharpoons {{\text{H}}_{\text{2}}}{\text{C}}{{\text{O}}_{\text{3}}}/{\text{C}}{{\text{O}}_{\text{2}}} + {{\text{H}}_{\text{2}}}{\text{O}} \rightleftharpoons {{\text{H}}^ + } + {\text{HCO}}_3^ - \);

Do not penalize absence of reversible sign.

Do not accept CO₂ + H₂O \( \to \) 2H⁺ + CO₃^2–.

Acid 1:

\({\text{(HN}}{{\text{O}}_{\text{2}}}{\text{/HN}}{{\text{O}}_{\text{3}}}{\text{)}}\) high temperature in internal combustion/jet engine;

reaction between \({{\text{N}}_{\text{2}}}\) and \({{\text{O}}_{\text{2}}}\) at high temperature/lightning;

Accept either of the above for first mark.

\({\text{2N}}{{\text{O}}_2} + {{\text{H}}_2}{\text{O}} \to {\text{HN}}{{\text{O}}_3} + {\text{HN}}{{\text{O}}_2}/{\text{4N}}{{\text{O}}_2} + {{\text{O}}_2} + {\text{2}}{{\text{H}}_2}{\text{O}} \to {\text{4HN}}{{\text{O}}_3}\);

Acid 2:

\({\text{(}}{{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{3}}}{\text{/}}{{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}{\text{)}}\) from burning of coal / smelting plants / sulfuric acid plants / volcanic activity;

Do not accept combustion of fossil fuels.

\({\text{S}}{{\text{O}}_2} + {{\text{H}}_2}{\text{O}} \to {{\text{H}}_2}{\text{S}}{{\text{O}}_3}/{\text{S}}{{\text{O}}_3} + {{\text{H}}_2}{\text{O}} \to {{\text{H}}_2}{\text{S}}{{\text{O}}_4}\);

Allow H₂SO₃/H₂SO₄ to be Acid 1 and HNO₂/HNO₃ to be Acid 2.

\({\text{CaC}}{{\text{O}}_{\text{3}}} + {\text{2HN}}{{\text{O}}_{\text{3}}} \to {\text{Ca(N}}{{\text{O}}_{\text{3}}}{{\text{)}}_{\text{2}}} + {\text{C}}{{\text{O}}_{\text{2}}} + {{\text{H}}_{\text{2}}}{\text{O}}\);

Accept equation with H₂SO₃ or H₂SO₄ or ionic equations.

Do not accept equations with H₂CO₃.

Most candidates correctly identified carbon dioxide as the source of natural water acidity and wrote an acceptable equation. Many also identified sources of nitric and sulphuric acid, though these equations often proved trickier, with many candidates writing equations for the formation of the oxide from which the acid is derived. Balanced equations for the reaction with limestone also proved to be a challenge, with carbonic acid often appearing as a product.

Most candidates correctly identified carbon dioxide as the source of natural water acidity and wrote an acceptable equation. Many also identified sources of nitric and sulphuric acid, though these equations often proved trickier, with many candidates writing equations for the formation of the oxide from which the acid is derived. Balanced equations for the reaction with limestone also proved to be a challenge, with carbonic acid often appearing as a product.

Most candidates correctly identified carbon dioxide as the source of natural water acidity and wrote an acceptable equation. Many also identified sources of nitric and sulphuric acid, though these equations often proved trickier, with many candidates writing equations for the formation of the oxide from which the acid is derived. Balanced equations for the reaction with limestone also proved to be a challenge, with carbonic acid often appearing as a product.

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]

Sketch the atactic form of polychloroethene showing four units.

(i) Explain, in molecular terms, why PVC becomes more flexible and softer when a plasticizer is added.

(ii) State one type of compound which can be used as a plasticizer.

Suggest an environmental issue associated with the use of PVC.

(i)
«plasticizer molecules» fit between chains
OR
«plasticizer molecules» prevent chains from forming crystalline regions
OR
«plasticizer molecules» keeps strands/chains/molecules separated
OR
«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”.

(ii)
ester/phthalate/citrate

Accept other general or specific names of plasticizers.

Suggest how changing the size or shape of the hydrocarbon chain would affect the molecule’s liquid crystal behaviour.

Explain why the nitrile group enables these molecules to be used in liquid-crystal displays (LCDs).

(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

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»

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 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.

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]

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]