131293-question-paper-unit-f332-chemistry-of-natural-resources-advance-notice

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for Unit F332 ( Chemistry of Natural Resources ). The examination paper will contain 
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of the work covered in Unit F332 to answer these questions. There are 20 marks available 
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For issue on or after:
13 March 2012
AS GCE CHEMISTRY B (SALTERS)
F332   Chemistry of Natural Resources
ADVANCE NOTICE
OCR is an exempt Charity
Turn over
© OCR 2012 [T/500/7966]
DC (SHW (CGW) 00660 1/11) 43795/4
Duration: 1 hour 45 minutes
*F314890612*

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F332 Jun12© OCR 2012
Plastic Fantastic
From RSC’s Education in Chemistry ‘Infochem’ supplement, Jan 2005.
Y ou can’t miss the addition polymer poly(ethene) (PE, polythene). It’s in your house, in the streets and 
roads, in supermarkets, in your garden and maybe even in you. The list of PE products is endless – 
shampoo and detergent bottles, gas and plumbing supply pipes, electrical insulation, car wheel arches 
and petrol tanks, food packaging and crates, and milk, ketchup and healthcare bottles. Poly(ethene) is 
also used in bullet proof vests, in hip and bone replacements, and as a waterproof coating on skis, sail 
boards, and canoes. So ubiquitous is this plastic – PE is the most widely used plastic, commanding 
ca. 36 per cent of the total European market – that it’s hard to imagine life without it. And yet, like 
many other products we have come to rely on for our current lifestyles, poly(ethene) was discovered by 
accident.
A serendipitous discovery
In 1933, Reginald Gibson and Eric Fawcett, two research chemists at ICI’s Winnington Laboratory in 
Cheshire, were working on high pressure and high temperature reactions. They were trying to develop 
new products for ICI’s rapidly growing dyestuffs industry. They tried to react ethene and benzaldehyde 
(benzenecarbaldehyde) at 2000 atm (1 atm = 101325 Pa) and 170 °C in the hope of producing potential 
intermediates in the manufacture of dyes.
H HH
O
HH
C+C
O
Figure 1: The equation for the reaction expected to occur between benzaldehyde and ethene
The high pressure apparatus had a mercury gas compressor. Benzaldehyde was contained in an 
inverted glass tube, sealed with mercury and placed in a steel tube in a reaction vessel. The vessel 
was sealed and put in an oil thermostat, regulated to 170 °C. Ethene was bubbled through the mercury 
into the benzaldehyde – mercury separated the gas from benzaldehyde rather like a piston.
Gibson and Fawcett started the experiment on Friday afternoon, and left it to run over the weekend. On 
the Monday morning, they found that the pressure in the system had fallen to ca. 500 atm because of a 
small leak in the oil system. Ethene had expanded and forced the benzaldehyde through the mercury 
into the oil system. They couldn’t replace the benzaldehyde so, having fixed the leak, they restored the 
pressure by adding more ethene. After a few hours they stopped the reaction and allowed it to cool. 
No liquid product had formed, but instead a trace amount – 0.2 g – of a waxy solid had formed on the 
inside wall of the glass tube. Spectroscopic analysis revealed that this contained only hydrogen and 
carbon in the same ratio as ethene. They had discovered poly(ethene).

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F332 Jun12 Turn over© OCR 2012
Unfortunately, when they tried to repeat the experiment, decomposition of ethene to carbon occurred, 
which being exothermic caused an explosion, bursting a pressure joint near the oil thermostat and 
setting it on fire. ICI management immediately stopped high pressure work on ethene until safer 
premises could be found. That might have been the end of the story but …
Poly(ethene) – rediscovered
Two years later, and in an isolated building with walls one-foot thick, Michael Perrin, another research 
chemist, decided to do some more experiments with ethene.
Frank Bebbington, now 94 years old and one of Perrin’s research assistants at the time, told Education 
in Chemistry , ‘On 20 December 1935 I assembled equipment in a deliberate attempt to polymerise 
ethylene [ethene] under the same conditions that Gibson and Fawcett had used, but on a smaller 
scale. Immediately we put the pressure up to 2000 atm the pressure in the reaction vessel started to 
fall away very slowly, and again we thought there was a small leak in the system. I felt embarrassed 
because I had assembled the equipment. I compressed more ethylene to take the pressure back up to 
2000 atm. At 1.00 pm everybody, except me, went to lunch; I was left to keep the pressure at 2000 atm. 
When they came back we stopped the experiment, and cooled the vessel. We opened it up, and to 
our amazement, it contained white powder – 8.5 g of the stuff to be precise. We had rediscovered 
poly(ethene). We immediately called the research director, Dr J. Swallow, who took the powder in his 
fingers and said “I wonder if it’s a plastic?”’.
The next couple of attempts to repeat the experiment, however, gave only 0.5 g, 1 g and an explosive 
decomposition reaction. ‘But’, says Bebbington, ‘once you’ve made 8.5 g of something, you know you 
can do it and we were determined to find out how’.
Bebbington remembers, ‘after about 200 experiments, we discovered that the key to the successful 
polymerisation of ethylene [ethene] was an impurity in the ethylene – ie oxygen. Too much O 2 – 
ca. 500–1000 ppm (parts per million) – led to decomposition of the ethylene, 20–200 ppm of O 2 gave 
polyethylene, and no oxygen – no polyethylene’. ‘Oxygen’, explained Bebbington, ‘was acting not as a 
catalyst but as an initiator because it was being used up during the polymerisation reaction’.
The role of oxygen in the polymerisation process
It has since been shown that oxygen reacts with some of the ethene to give an organic peroxide. 
Organic peroxides are very reactive molecules containing oxygen–oxygen single bonds that are quite 
weak and that break easily to give free radicals, represented here as Ra .
The free radical, Ra , uses one of the electrons in one of the C=C bonds to form a new bond between 
itself and the left hand carbon atom. The other electron returns to the right hand carbon.
This can be shown using ‘half curly arrow’ notation:
Ra Ra CH2 CH2 CH2 CH2+

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F332 Jun12© OCR 2012
This produces a bigger free radical – lengthened by CH 2CH2 – that can react with another ethene 
molecule in the same way:
RaCH2CH2 CH2 = CH2 RaCH2CH2CH2CH2+
So now the radical is even bigger. It can react with another ethene – and so on and so on. The polymer 
chain gets longer and longer.
The chain doesn’t grow indefinitely. Sooner or later two free radicals will collide together.
Ra(CH2)m Ra(CH2)m(CH2)nRa(CH2)nRa+
That immediately stops the growth of two chains and produces one of the final molecules in the 
poly(ethene). It is important to realise that the poly(ethene) is going to be a mixture of molecules of 
different sizes, made in this sort of random way.
Moving on
By April 1936 the first pound of poly(ethene) had been made. It was sent to the Nobel Division of ICI 
in Ardeer, Scotland, where the only injection moulding machines existed, and a few small pill boxes 
were made. Back at Winnington, Perrin and his team made more poly(ethene) and started testing 
their new material. The PE that they had made was low density polyethene (see Figure 2). Its excellent 
insulating properties at high frequencies soon attracted the telephone industry, which was quick to spot 
it as a replacement for gutta-percha to insulate telephone cables. (Gutta-percha – latex from rubber 
trees in the Far East – was becoming increasingly difficult to obtain because of the imminent war.) On 
1 September 1939 poly(ethene) became an official product of ICI.
During World War II all PE was made for the Government, specifically for high frequency experimental 
radar cable. The successful development of radar is said to have shortened the war by years. A 
poly(ethene) tube, called Pluto, was also laid across the Channel for transferring petrol from the UK to 
France.
Since its discovery over 70 years ago, there have been many improvements to the synthesis of 
poly(ethene). These have centred on the development of several types of catalyst – notably Ziegler–
Natta catalysts in the 1950s and metallocene catalysts in the 1970s – so that the polymerisation can 
be done at lower pressures and temperatures, thus using less energy and making the process more 
environmentally acceptable.

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Poly(ethene) – it’s so useful
In its simplest form poly(ethene) consists of a long backbone of carbon atoms with two hydrogen atoms 
attached to each. This is called linear poly(ethene) or high density poly(ethene) (HDPE). Sometimes the 
hydrogen atoms are replaced by other PE molecules, which gives branched or low density poly(ethene) 
(LDPE) – the molecules don’t pack together so well.
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
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H
H
C
H
H
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H
H
C
H
H
C
H
H
H
H
H
H
C
C
C
H
H
H
H
C
C
Figure 2: Part of the structure of the polymer chain in LDPE (left) and HDPE (right)
Approximately two thirds of all injection moulded PE items are made from HDPE – industrial containers, 
such as crates and pallets, gas and water pipes, canoes, car parts, and food containers, carbonated 
bottle bases and caps; LDPE is used mainly for food packaging films, waterproof films, and electrical 
cable insulation.
As well as poly(ethene), many other polymers can be made from alkene monomers. These include 
poly(propene), which is used to make drain pipes and crates and poly(chloroethene), or PVC, which is 
used to make the coating for electrical wires.
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