IB DP Chemistry A.6 Nanotechnology SL Paper 3

 

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Question 

There has been significant growth in the use of carbon nanotubes, CNT.
a. Explain these properties of carbon nanotubes.

b(i)Alloying metals changes their properties. Suggest one property of magnesium that could be improved by making a magnesium-CNT alloy.
b(ii)Pure magnesium needed for making alloys can be obtained by electrolysis of molten magnesium chloride.

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

$\mathrm{b}$ (iii)Calculate the theoretical mass of magnesium obtained if a current of $3.00 \mathrm{~A}$ is used for 10.0 hours. Use charge $(Q)=\operatorname{current}(I) \times \operatorname{time}(t)$ and section 2 of the data booklet
$\mathrm{b}$ (iv)Suggest a gas which should be continuously passed over the molten magnesium in the electrolytic cell.
c. Zeolites can be used as catalysts in the manufacture of CNT. Explain, with reference to their structure, the high selectivity of zeolites.
d. Experiments have been done to explore the nematic liquid crystal behaviour of CNT. Justify how CNT molecules could be classified as nematic.

▶️Answer/Explanation

Markscheme

a. Excellent strength: defect-free $A N D$ rigid/regular 2D/3D
Excellent conductivity: delocalized electrons
Accept “carbons/atoms are all covalently bonded to each other” for M1.
b(i)Any of:
ductility
strength/resistance to deformation
malleability
hardness
resistance to corrosion/chemical resistance
range of working temperatures
density
Do not accept “conductivity”.

b(ii)Anode: $2 \mathrm{Cl}^{-} \rightarrow \mathrm{Cl}_2(\mathrm{~g})+2 \mathrm{e}^{-}$
Cathode: $\mathrm{Mg}^{2+}+2 \mathrm{e}^{-} \rightarrow \mathrm{Mg}(1)$
Accept $\mathrm{Cl}^{-} \rightarrow \mathrm{Cl}_2(\mathrm{~g})+e^{-}$.
Award [1 max] for correct equations at incorrect electrodes.
$$
\begin{aligned}
& \mathrm{b}(\mathrm{iii}) Q=I \times t=3.00 \times 10.0 \times 3600=» 108000 \mathrm{C} \\
& 《 \frac{Q}{F}=\frac{108000 \mathrm{C}}{96500 \mathrm{C} \mathrm{mol}^{-1}}=» 1.12\left(\mathrm{~mol} \mathrm{e}^{-} »\right. \\
& \text { « } \frac{1.12 \mathrm{~mol}}{2}=0.560 \mathrm{~mol} \mathrm{Mg} » \\
& \left.\ll m=0.560 \mathrm{~mol} \times 24.31 \mathrm{~g} \mathrm{~mol}^{-1}=» 13.6 \varkappa \mathrm{g}\right\rangle \\
&
\end{aligned}
$$
Award [3] for correct final answer.
b(iv)Argon/Ar/helium/He
Accept any identified noble/inert gas.
Accept name OR formula.
Do not accept “nitrogen $/ \mathrm{N}_2$ “.

c. pores/cavities/channels/holes/cage-like structures
«only» reactants with appropriate/specific size/geometry/structure fit inside/go through/are activated/can react
Accept “molecules/ions” for “reactants” in M2.
d. rod-shaped molecules
OR
«randomly distributed but» generally align
OR
no positional order $A N D$ have «some» directional order/pattern
Accept “linear” for “rod-shaped”.

 

 
 

Question 

Nanotechnology has allowed the manipulation of materials on the atomic level.
a. Describe the structure and bonding of a carbon nanotube.
Structure:
Bonding:
b. Suggest one application for carbon nanotubes.

▶️Answer/Explanation

Markscheme
a. Structure:
giant covalent/network covalent $[\boldsymbol{V}]$
Note: Accept “cylindrical/tube shaped”.
Bonding:
each carbon covalently bonded to 3 other carbons
OR
each bond has order of 1.5
Note: Accept “has delocalized electrons” OR “has sp2 hybridization”.

b. Any one of:
3D electrodes [ $\checkmark]$
catalysts $[\boldsymbol{\sim}]$
biosensors [ $\boldsymbol{\swarrow}]$
molecular stents $[\boldsymbol{\sim}]$
body armour $[\boldsymbol{\nu}]$
synthetic muscles $[\boldsymbol{\sim}]$
micro transistors/circuitry/capacitors/electrodes [ $\boldsymbol{\sim}]$
reinforcing phase in a matrix/composite material «such as concrete» [ $\boldsymbol{V}]$
micro antenna $[\boldsymbol{V}]$
stealth technology $[\boldsymbol{\sim}]$
water/air filtration $[\boldsymbol{} \boldsymbol{]}$
solar cells $[\boldsymbol{\sim}]$
tennis racquets [ $\boldsymbol{c}$ ]
microelectronic circuits [ $\boldsymbol{V}]$

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

 
 

Question 

Catalysts are commonly used in industry.
a. Describe how a heterogeneous catalyst provides an alternative pathway for a reaction.
b. Distinguish between heterogeneous and homogeneous catalysts, giving one difference.
c. Nanotubes are used to support the active material in nanocatalysts.
Explain why oxygen cannot be used for the chemical vapour deposition (CVD) preparation of carbon nanotubes.

▶️Answer/Explanation

Markscheme
a. reactant(s) adsorb onto active sites/surface
NOTE: Do not accept “absorb” for “adsorb” for M1.
Accept “bonds to” for “adsorb” for M1.
«reactant» bonds weakens «and products are desorbed»
NOTE: Accept “bonds break/stretch “and products are desorbed»” for M2.
Award [1 max] for “lowers activation energy”.
b. Any one of the following:

NOTE: Accept “heterogeneous adsorb reactants and homogeneous” but do not accept “absorb” for “adsorb”. Accept “heterogeneous have active sites and homogeneous do not”.
c. high temperature used oxygen $/ \mathrm{O}_2$ reacts with carbon/ $\mathrm{C}$ OR carbon dioxide $/ \mathrm{CO}_2$ can form

 
 

Question 

Metals are extracted from their ores by several methods, including electrolysis and reduction with carbon.
a. Determine the mass of aluminium, in g, that could be extracted from an appropriate solution by a charge of $48250 \mathrm{C}$. Use sections 2 and 6 of the data booklet.
b. Once extracted, the purity of the metal can be assessed using ICP-MS. Suggest two advantages of using plasma technology rather than regular mass spectrometry.
c. Explain the action of metals as heterogeneous catalysts.
d. Outline how alloys conduct electricity and why they are often harder than pure metals.
Conduct electricity:
Harder than pure metals:
e. Carbon nanotubes are added to metals to increase tensile strength.
Write an equation for the formation of carbon nanotubes from carbon monoxide.

▶️Answer/Explanation

Markscheme

a. moles of electrons «= $\frac{48250 \mathrm{C}}{96500 \mathrm{C} \mathrm{mol}^{-1}} »=0.5000$ «mol» [ $\left.\triangle\right]$ moles of aluminium «= $\frac{0.5000 \mathrm{~mol}}{3} »=0.1667 « \mathrm{~mol} »[\boldsymbol{C}]$ mass of aluminium $«=26.98 \mathrm{~g} \mathrm{~mol}^{-1} \times 0.1667 \mathrm{~mol} »=4.50 « \mathrm{~g} »[/]$
Note: Award [3] for correct final answer.
b. Any two of: larger linear calibration [ $\boldsymbol{U}]$ «accurate» detection of multiple elements/metals $[\boldsymbol{\sim}$ ] «accurate» detection of elements in low concentration $[\boldsymbol{V}]$ temperature around $10000 \mathrm{~K}$ atomises/ionises every material [ $\boldsymbol{\sim}$ ]
c. Any two of:
reactant(s) adsorb onto active sites/surface [ $\boldsymbol{U}]$
bonds weakened/broken/stretched «in adsorbed reactants» OR
activation energy lowered [ $\checkmark$ ]
products desorbed $[\boldsymbol{}]$
Note: Accept “products released” for M3.

d. Conduct electricity:
«delocalized/valence» electrons free to move «under potential difference» $[\boldsymbol{\sim}]$
Harder than pure metals:
atoms/ions of different sizes prevent layers «of atoms/ions» from sliding over one another $[\boldsymbol{V}]$
e. $2 \mathrm{CO}(\mathrm{g}) \rightarrow \mathrm{C}(\mathrm{s})+\mathrm{CO}_2(\mathrm{~g})[\boldsymbol{V}]$

 
 

Question 

While heating solid cholesteryl benzoate, Reinitzer discovered the liquid crystal phase.
a. Outline two observations that he could have made.
b. The structure of biphenyl nitrile is shown.

,Describe, giving a reason, a feature of the molecular structure, other than its polarity, that allows biphenyl nitrile to show liquid crystal behaviour.
c. Arc discharge, consisting of two inert metal electrodes in a liquid solvent, is one method of producing carbon nanotubes (CNTs).
Predict, giving a reason, the electrode at which the solvent cyclohexane, $\mathrm{C}_6 \mathrm{H}_{12}$, will decompose to form CNTs.

▶️Answer/Explanation

Markscheme
a. Any two of:
cloudy/foggy/hazy phase «at first melting point»
clear liquid phase «at second melting point/higher temperature»
two «different» melting points
OR
new phase observed over a wide temperature range
Accept “exhibit both liquid and solid properties at the same time” for M3.

b. ALTERNATIVE 1:
«bulky/long» $\mathrm{C}_5 \mathrm{H}_{11} / \mathrm{R} /$ alkyl «group/chain» $A N D$ prevents molecules from packing closer together «to form solid state»
ALTERNATIVE 2:
biphenyl «fragment»/two benzene rings/two aromatic rings $A N D$ «makes molecule» rigid/rod-shaped
Accept “rigid/rod-shaped molecule, so aligns with other molecules” for ALTERNATIVE 2.
c. «average» oxidation state of $\mathrm{C}$ in $\mathrm{C}_6 \mathrm{H}_{12} /$ cyclohexane $=-2$ AND in CNTs $=0$
OR
oxidation state of $\mathrm{C}$ in $\mathrm{CNTs}$ is higher than in $\mathrm{C}_6 \mathrm{H}_{12} /$ cyclohexane
OR
loss of H’s/hydrogens
«oxidation at» anode/positive/+ «electrode»
Accept “oxidation number” for “oxidation state”.

 
 

Question

In the last 15 years several Nobel prizes have been awarded in the area of nanotechnology, from the development of the scanning probe microscope, to the discovery of fullerenes. By 2015 nanotechnology could employ two million workers worldwide.

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

[4]
b.

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.

[4]
c.
▶️Answer/Explanation

Markscheme

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;

b.

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;

c.

Examiners report

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.

b.

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.

c.

Question

Nano-sized ‘test-tubes’ with one open end, can be formed from carbon structures.

Carbon nanotubes can be used as catalysts.

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

[2]
a.

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

[1]
b.

Suggest two reasons why they are effective heterogeneous catalysts.

[2]
c.i.

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

[1]
c.ii.
▶️Answer/Explanation

Markscheme

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

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

a.

covalent bonds are very strong;

b.

large surface area;

Do not accept “reactive surface”.

high selectivity related to dimensions of tube;

c.i.

unknown health effects;

Accept potentially harmful as easily ingested/inhaled.

Accept difficulty of preparing nanotubes in required amounts.

c.ii.

Examiners report

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

a.

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

b.

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

c.i.

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

c.ii.

Question

Nanotechnology creates and uses structures that have novel properties because of their size.

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

[1]
a.

Discuss two implications of nanotechnology.

[2]
c.
▶️Answer/Explanation

Markscheme

1 nm to 100 nm;

a.

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;

c.

Examiners report

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.

a.

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.

c.

Question

Exciting developments have taken place in recent years in the area of nanotechnology.

Carbon nanotubes can be used to make designer catalysts.

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

[2]
a.

(i)     Describe the structure of carbon nanotubes.

(ii)     State one physical property of carbon nanotubes.

[3]
b.

Suggest two concerns about the use of nanotechnology.

[2]
c.
▶️Answer/Explanation

Markscheme

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.

a.

(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;

b.

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.

c.

Examiners report

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

a.

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

b.

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

c.

Question

Many recent developments in chemistry have involved making use of devices that operate on a nanoscale.

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

[2]
a.i.

State one public concern regarding the development of nanotechnology.

[1]
a.ii.

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.

[2]
b.
▶️Answer/Explanation

Markscheme

a scale of 1–100nm;

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

a.i.

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

a.ii.

in the walls carbon atoms only form hexagons;

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

b.

Examiners report

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.

a.i.

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.

a.ii.

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.

b.

Question

Polyacrylonitrile is an important polymer used in the manufacture of carbon fibres. The monomer has the structure below.

N13/4/CHEMI/SP3/ENG/TZ0/09

The rate of the polymerization reaction from the gaseous monomer is increased in the presence of a zeolite with the cage structure shown.

N13/4/CHEMI/SP3/ENG/TZ0/09

A new range of light batteries has been developed that uses open carbon nanotubes, covered with silicon, as electrodes.

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

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

[2]
a.i.

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.

[2]
a.ii.

Identify the role of the zeolite in the reaction.

[1]
b.i.

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

[1]
b.ii.

Outline the structure of the open carbon nanotubes.

[1]
c.i.

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

[1]
c.ii.
▶️Answer/Explanation

Markscheme

N13/4/CHEMI/SP3/ENG/TZ0/09.a.i_01/M /

N13/4/CHEMI/SP3/ENG/TZ0/09.a.i_02/M ;

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.

a.i.

chains pack together better;

strong intermolecular/attractive forces between chains;

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

a.ii.

catalyst;

b.i.

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

Accept “large surface area”.

b.ii.

cylinder with hexagons of carbon (atoms);

Accept suitable diagram.

Do not award mark if pentagons are also mentioned.

c.i.

(electrical) conductor;

Accept low density.

Do not accept light.

c.ii.

Examiners report

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.

a.i.

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.

a.ii.

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.

b.i.

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.

b.ii.

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.

c.i.

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.

c.ii.

Question

There is much debate about the need for laws to regulate research and development into nanotechnology.

Define the term nanotechnology.

[2]
a.

Discuss two concerns about its development and use.

[2]
b.
▶️Answer/Explanation

Markscheme

(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;

a.

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.

b.

Examiners report

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.

a.

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.

b.

Question

In 1989 Don Eigler and his team carried out one of the first experiments in nanotechnology.

They spelled out the IBM logo with 35 xenon atoms.

M15/4/CHEMI/SP3/ENG/TZ1/09

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

[2]
a.

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.

[1]
b.
▶️Answer/Explanation

Markscheme

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”.

a.

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

b.

Examiners report

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

a.

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.

b.

Question

Nanotechnology has expanded in the past 30 years.

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

Sides:

Ends:

[1]
b.

Outline why bundles of carbon nanotubes have high tensile strength.

[1]
c.

Discuss two concerns regarding the development of nanotechnology.

[2]
d.
▶️Answer/Explanation

Markscheme

Sides:

(atoms arranged in) hexagons

and

Ends:

(atoms arranged in) pentagons (and hexagons);

b.

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

c.

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.

d.

Examiners report

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.

b.

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.

c.

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.

d.

Question

Nanocatalysts have large surface areas per unit mass.

Identify one concern of using nanoscale catalysts.

[1]
a.

Explain how zeolites act as selective catalysts.

[2]
b.

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

[2]
c.
▶️Answer/Explanation

Markscheme

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).

a.

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

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

b.

Catalyst:
iron/Fe
OR
iron«0» «penta» carbonyl/Fe (CO)5

Conditions:
high temperature/any value or range within the range 900–1600 °C
AND
high pressure/any value or range within the range 10–100 atm 

Accept “cobalt-molybdenum/Co-Mo/CoMo”.
Accept high pressures expressed in kPa/Pa.

c.

Question

Research has led to the discovery of new catalysts that are in high demand and used in many chemical industries.

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

[2]
a.

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.

[3]
b.
▶️Answer/Explanation

Markscheme

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.

a.

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”.

b.

Question

Lanthanum nanoparticles are incorporated into certain catalysts and the electrodes of some fuel cells.

State the major advantage that nanoparticles have in these applications.

[1]
a.

Suggest why nanoparticles need to be handled with care.

[1]
b.
▶️Answer/Explanation

Markscheme

large surface area

[1 mark]

a.

«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]

b.

Question

Nanotechnology has many applications.

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

[2]
a.

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

[1]
b.

Discuss one possible risk associated with the use of nanotechnology.

[1]
c.
▶️Answer/Explanation

Markscheme

Fe(CO)5 (g) → Fe (s) + 5CO (g)

2CO (g) → C (s) + CO2 (g)

a.

large surface area «on which carbon nanotubes form»

b.

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.

c.

Question

Aluminium and high density polyethene (HDPE) are both materials readily found in the kitchen, for example as saucepans and mixing bowls respectively. In these applications it is important that they are impermeable to water.

Both materials are also used in other applications that are more demanding of their physical properties. Carbon nanotubes are often incorporated into their structures to improve certain properties.

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

[2]
a.

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

[1]
b.i.

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

[1]
b.ii.

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

[3]
b.iii.

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

[1]
b.iv.
▶️Answer/Explanation

Markscheme

«close packed» lattice of metal atoms/ions

no spaces for water molecules to pass though the structure

[2 marks]

a.

composite

[1 mark]

b.i.

melting point

OR

permeability

OR

density

OR

conductivity

OR

elasticity/stiffness

OR

brittleness/flexibility

OR

«tensile» strength

Accept “colour/transparency”.

[1 mark]

b.ii.

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]

b.iii.

rod shaped molecules

[1 mark]

b.iv.

Question

Chemical vapour deposition (CVD) produces multi-walled carbon nanotubes (MWCNT) of a more appropriate size for use in liquid crystals than production by arc discharge.

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

[2]
a.

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

[3]
b.
▶️Answer/Explanation

Markscheme

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]

a.

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]

b.
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