University of Canterbury
End of Year Examinations 2003
Prescription Number(s): CHEM 323
Paper Title: Applied Physical Chemistry
Time Allowed: THREE HOURS
Number of pages: NINE
This paper is divided in to TWO sections.
Answer BOTH questions in Section A.
Answer THREE questions out of FIVE in
Section B.
All questions are of equal value
TURN OVER
2 CHEM 323
3 CHEM 323
SECTION A
(Answer BOTH questions from this section)
1. (a) The radiative heating model predicts that the warmest atmospheric
temperatures occur nearest to the ground and that they decrease continuously
with increasing altitude. However, the stratosphere and thermosphere actually
get warmer with increasing altitude. Describe briefly the processes that lead
to such heating with increasing altitude.
(b) (i) Write down the mechanism for ozone formation and destruction
proposed by Chapman in the 1930s.
(ii) Describe why the number of O3 molecules is the same just before
sunrise as it was just after sunset when other ozone-depleting species
are absent.
(iii) Explain why the number of oxygen atoms (O) increases with altitude.
(c) The steady-state concentration of ozone is actually three times lower than the
level predicted by the Chapman mechanism. Describe how holding and null
cycles reduce the level of ozone destruction when all three catalytic ozone-
depleting families (HOx, ClOx and NOx) are present. That is, explain why all
three cycles do not simply add together to give the greatest ozone depletion.
TURN OVER
4 CHEM 323
2. (a) So-called SBR, which stands for ‘styrene butadiene rubber’, is poly(1,3-
butadiene-ran-styrene). Its major use is in making tyres. On the other hand,
poly(styrene-b-1,3-butadiene-b-styrene) finds use as a so-called ‘thermoplastic
elastomer’.
(i) What type of copolymer is each of these two polymers?
(ii) How do these two copolymers differ in structure?
(iii) Outline how each of these copolymers is made.
(iv) Discuss the material properties of these two copolymers.
(b) The scheme below shows three different ways of synthesizing polyethylene:
Br CH2 Br + 2 Na
10
– NaBr
190oC, 2000 bar heptane, 60oC
n CH2 CH2 CH2 CH2 n CH2 CH2
benzoyl peroxide n Al(CH2-CH3)3/TiCl4
catalyst
For each of these three syntheses:
(i) Outline the chemistry involved. As part of your answer you should
state whether it is step-growth or chain-growth polymerisation and, if
the latter, which type of chain-growth polymerisation it is.
(ii) Give the molecular architecture of the polyethylene that is produced,
explaining the reasoning behind your answer in each case.
Question 2 continued on following page
5 CHEM 323
Question 2 continued
(c) The scheme below shows two different syntheses of poly(methyl
methacrylate):
CH3 CH3
CH3
azoisobutyronitrile K2S2O8, water
CH2 C CH2 C CH2 C
sodium dodecyl sulfate,
CO stirring
CO2CH3 CO2CH3
OCH 3
In each case above, the fundamental chemistry is the same but the preparation
process is different.
(i) Give the name of each type of preparation process involved above.
(ii) Describe each of these preparation processes.
(iii) Indicate how the two final products are similar and how they are
different.
TURN OVER
6 CHEM 323
SECTION B
(Answer THREE questions from this section)
3. (a) A diagram of a chlor-alkali electrolysis cell is shown below. In the chlor-
alkali process, the desired anode reaction results in the product chlorine.
Explain, in detail, why RuO2-coated titanium is preferred over graphite as the
anode material. Your answer should include discussion of the
thermodynamics and kinetics of the anodic reaction(s), the problems of O2
contamination of Cl2, the overpotential required for the electrode reaction, and
consumption of the anode.
Useful data:
2Cl– Cl2 + 2e– Ee = 1.31 V vs SHE for 25% NaCl
2H2O O2 + 4H+ + 4e– Ee = 1 V vs SHE at pH 4
(b) The operating potential of the chlor-alkali cell is given by the expression
cell
below. Carefully explain why each of the terms |c|, |a|, Ee , |iRsoln| and
|iRmem| appear in the expression
cell cell
Eapplied = Ee – |c| – |a| – |iRsoln| – |iRmem|
Include in your answer an explanation of why a membrane is required in the
electrolysis cell.
7 CHEM 323
4. Write notes on the use of any TWO of the following experimental systems, (a) to
(d), in the determination of the kinetics and mechanism for fast chemical reactions.
You should include a brief discussion of how the method operates (diagrams may
be helpful) and any unique information that is obtained.
(a) Flash photolysis or pulsed-laser photolysis.
(b) Fast-flow reactors (e.g. a selected-ion flow tube as used for studying
ion-molecule processes).
(c) Stopped-flow spectrometers.
(d) Any other modern experimental technique that you have read about but which
is not included in (a) to (c) above.
5. (a) (5 marks)
Explain why rainfall is naturally acidic, using chemical equations where
appropriate. Describe how different soil types neutralise this acidity.
(b) (3 marks)
Describe how human activity has worsened the problem of acid rain through
increased emissions of NOx and sulfur compounds.
(c) (2 marks)
Explain why increasingly acidic rainfall is not a global problem.
(d) (4 marks)
Describe the intrinsic spectroscopic properties of molecules that act as
greenhouse gases. Illustrate your answer with appropriate examples.
(e) (6 marks)
Explain what is meant by the ‘relative warming potential’ of a molecule. In
your discussion explain why chlorofluorocarbons (CFCs) have a much larger
relative warming potential than H2O and CO2.
TURN OVER
8 CHEM 323
6. The chemical structure of a polymer plays a key role in determining its material
properties, and therefore its usage. For example, plastic bank notes are coated with a
polyurethane,
O H H O
O R1 O C N R2 N C
n
because the polar link groups of this polymer enable fast binding of ink.
In a similar way, explain the link between chemical structure and properties in each
of the following examples (note: only brief answers are required and, in each case,
a chemical structure or structures should be given, as exemplified above):
(a) Polystyrene is used as pipes for caustic materials.
OH
(b) In contrast to most polymers, poly(vinyl alcohol), CH 2 CH , is water
n
soluble and so finds use as laundry bags, which can be placed directly into
washing machines.
(c) It is important for toothbrush bristles to be water resistant and so nylon-6,10 is
preferred over nylon-6,6 for this usage.
(d) For uses in which electrical insulation is important, poly(butylene terephthalate)
is preferred over poly(ethylene terephthalate).
(e) Poly(vinyl chloride) is tougher than polystyrene.
(Useful information: The stronger the intermolecular forces between polymer
molecules, the tougher the polymer.)
(f) Electric kettles are made from polypropylene rather than polyethylene.
(Useful information: As a thermoplastic is heated, a temperature is reached at
which it goes from being a hard to a soft material. This ‘softening point’ is
related to the ease with which free rotation of backbone bonds can occur.)
CN
(g) Copolymerization of styrene with a little acrylonitrile, CH 2 CH , produces
‘styrene-acrylonitrile’, a copolymer with better oil and grease resistance than
polystyrene homopolymer.
9 CHEM 323
7. (a) Use a Jablonski diagram to explain how a four-level laser works and comment
on the inherent advantages that a four-level system offers over a three-level
system.
(b) REMPI-TOFMS is a powerful tool used for the chemical analysis of oil
components, aerosols and general headspace analysis (commercial sniffer).
(i) What is REMPI?
(ii) How does TOFMS work?
(iii) How is REMPI-TOFMS used to differentiate between chemical
isomers?
END OF PAPER
TURN OVER