SCHOOL OF CHEMISTRY & PHYSICS
UNIVERSITY OF KWAZULU-NATAL, PIETERMARITZBURG CAMPUS
CTEC323: MATERIALS
JUNE 2013 MAIN EXAMINATIONS
DURATION: 3 HOURS
TOTAL MARKS: 100
External Examiner
Internal Examiners:
Prof. Neil Coville
Dr. Stephen Ojwach (Course coordinator)
University of Witwatersrand
University of KwaZulu-Natal
Dr. Irvin Booysen
University of KwaZulu-Natal
Instructions:
• This paper contains two sections, A and B.
• Answer ALL questions in both sections.
• There are10 pages (including a Periodic Table and Data sheet).
• Students are requested to write legibly to ensure accurate marking.
SECTION A: CATALYSIS (50 MARKS)
Question 1
(a) Define the following phrases as used in catalysis. Give one example in each
case.
(i)
(ii)
Catalyst inhibitor
Rate determining step
(4)
(b) State four areas where catalysis is applied in modern society and technology.
(2)
University of KwaZulu-Natal, School of Chemistry and Physics, Pietermaritzburg Campus
June 2013 Main Examination Session, CTEC323 PB Materials
(c) Consider the following proposed mechanism for the decomposition of ozone, O 3.
O3
K1
O2 (g) + O
Step 1 (fast)
K-1
K2
O3 ( g ) + O( g ) →
2O2 ( g )
Step 2 (slow reaction)
(i)
Identify the reactants, intermediates and products of the reaction.
(ii)
Applying the Steady State Approximation, show that the above mechanism
leads to the rate law R = K
(iii)
[O3 ] 2
.
[O2 ]
Provide a physical interpretation of the above reaction mechanism.
(6)
(d) In a given hydroformylation of styrene, the following data was obtained using
0.01 mmol of catalysts 1, 2 and 3 (Scheme 1).
O
O
catalyst
+
+
CO/H2
catalyst = 1, 2, 3
B
A
Scheme 1
Catalyst
1
2
3
Time (h)
1.5
0.5
1
Total
Yield
(g)
50.5
40.5
55.2
A
65
95
80
Product (%)
B
35
5
20
As a catalyst development scientist, which catalyst would you recommend in this
particular process? Justify your choice.
(4)
[16]
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University of KwaZulu-Natal, School of Chemistry and Physics, Pietermaritzburg Campus
June 2013 Main Examination Session, CTEC323 PB Materials
Question 2
(a)
By using illustrations/examples, distinguish between ligand substitution and
migratory insertion reactions in organometallic complexes.
(4)
(b)
Carefully examine the hydroformylation reaction below catalysed by Co(CO) 4 H
and answer the questions that follow.
R
H
III
OC
O
Co
CO
OC
H
+ H2
CO
-CO
B
I
+CO
H
OC
Co
CO
CO
OC
OC
Co
CO
OC
H
R
+ CO
A
II
R
(i)
Identify the type of reactions labelled I, II and III.
(ii)
Give the identity of A and B.
(iii)
Give two commercial applications of the above process other than the
production of aldehydes.
(7)
(c) State and briefly explain any three principal stages in the Shell Higher Olefin
process (SHOP).
(6)
[17]
Page 3 of 10
University of KwaZulu-Natal, School of Chemistry and Physics, Pietermaritzburg Campus
June 2013 Main Examination Session, CTEC323 PB Materials
Question 3
(a)
Compare and contrast homogeneous and heterogeneous catalysis.
(4)
(b)
Explain the role of particle size and presence of inhibitors on the rate of
adsorption in heterogeneous catalysts.
(c)
(4)
State and explain any three strategies that can be employed to achieve
effective separation of homogeneous catalysts from the reaction mixture.
(6)
(d)
Fischer-Tropsch process is a technology adopted by SASOL (South Africa)
to produce fuel.
(i) Give four possible raw materials that can be used in the process.
(ii) What is the significance of the water gas shift reaction in this process.
(3)
[17]
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University of KwaZulu-Natal, School of Chemistry and Physics, Pietermaritzburg Campus
June 2013 Main Examination Session, CTEC323 PB Materials
SECTION B: NANOTECHNOLOGY (50 MARKS)
Question 1:
1.1
a.
Define Nanotechnology.
(1)
b.
Provide three advantages of nanomaterials in comparison to their corresponding
bulk material.
c.
(3)
Explain the two design approaches of nanofabrication and state an example of
each.
1.2
(4)
Examine the overlay cyclic voltammograms (CVs) of ferrocene and a
ruthenium(II) complex shown in Fig. 1 and the peak potentials and currents
tabulated.
a.
Calculate the halfwave potential (E ½ ) of ferrocene?
(2)
b.
Determine whether the CV of the complex is reversible or quasi-reversible.
(3)
c.
Establish whether the electrochemical process illustrated on the complex’s CV
is ascribed to the Ru(II/III) or Ru(II/IV) redox couple.
Ferrocene
Complex
E pa (V)
0.35
0.74
E pc (V)
0.27
0.66
I pa (μA)
2.82
2.56
(2)
I pc (μA)
2.82
2.56
Page 5 of 10
University of KwaZulu-Natal, School of Chemistry and Physics, Pietermaritzburg Campus
June 2013 Main Examination Session, CTEC323 PB Materials
1.3
The development of microscopic techniques has been pivotal in the discovery of
nanomaterials.
a.
Distinguish between Transmission Electron Microscopy and Scanning Electron
Microscopy in terms of sample preparation, interaction of the incident beam
with the sample and nature of the generated image.
b.
(6)
A force of 4 x 10-9 N is required to hold the cantilever that has stretched from 10
nm to a length of 15 nm. How much force is required to stretch the cantilever to
a further 3 nm.
(2)
[23]
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University of KwaZulu-Natal, School of Chemistry and Physics, Pietermaritzburg Campus
June 2013 Main Examination Session, CTEC323 PB Materials
Question 2:
2.1
Carbon nanotubes were discovered in 1991 from the arc evaporation synthesis
of graphite and fullerenes.
a.
Using the given Raman spectrum of a single walled carbon nanotube (SWCNT),
explain the shown vibrational modes. In addition, list the vibrational band
which occurs in the range of 2400 to 2700 cm-1.
b.
(4)
If the G-band has a wavelength of 6.5 μm, calculate the wavenumber of the
infrared radiation for this band.
c.
(2)
Calculate the energy in Joules of one photon of the radiation described in (b)
(2)
2.2
The synthesis of CdSe quantum dots is achieved via arrested nucleation using
trioctylphosphine oxide (TOPO ≡ Oct 3 PO) as a capping agent. The reaction is
described by the equation:
Me 2 Cd + nnBu 3 PSe + mnOct 3 PO → (nOct 3 PO) m (CdSe)n + n/2C 2 H 6 + nnBu 3 P
Page 7 of 10
University of KwaZulu-Natal, School of Chemistry and Physics, Pietermaritzburg Campus
June 2013 Main Examination Session, CTEC323 PB Materials
a.
What advantages do capping agents afford in the above mentioned synthetic
procedure?
b.
What benefits do Quantum Dot Photovoltaic cells (QDPVCs) have over
conventional silicon based PVCs?
2.3
(3)
(3)
Self Assembled Monolayers (SAMs) are self-organized and ordered molecules
that form on a solid substrate.
a.
Describe the synthetic procedure for organosilicon SAMs and the role of the byproduct in forming defects.
b.
(5)
Determine the ion barrier factor of an alkyl thiol adsorbed on an Au electrode
to afford a SAM from the following information. Using 0.1 M KOH as a redox
probe to characterize the SAM, analysis of the gold oxidation peak for the
SAM-modified electrode indicated a total charge of 6.73 x 10-7 C. The total
charge obtained for the unmodified electrode, in contrast, was 2.6 x 10-6 C.
Briefly explain what the ion barrier factor means with respect to the SAM
2.4
surface coverage.
(3)
Briefly explain the electrospinning process with the aid of a diagram.
(5)
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