2/2/2011
HSC
CHEMISTRY
PROBLEM SOLVING AND PROCESSING
INFORMATION
Year 12 Miss Hanna | Anthony Bekhit
Part A
Use available evidence to gather and present data from
secondary sources and analyse progress in the recent
development and use of a named biopolymer. This analysis
should name the specific enzyme(s) used or organism used to
synthesis the material and an evaluation on the use or the
potential use of the polymer produced related to its
properties.
Introduction
As the century advances, so does the human race. In the past fossil
fuels has been very depended on for many things, such as the creation
of polymers. Although, there is a finite amount of fossil fuel in the
world and it is known that the supply will not last very long. As a
result, scientists are developing alternative options for the use of fossil
fuels.
Crude oil was very depended on for the production of plastics. These
plastics, which are produced by petrochemicals, are non-biodegradable.
Therefore making this kind of plastics is very harmful to the
environment, as the amount of these unwanted plastics builds up and
loiters rubbish tips without any decay or decomposition. Consequently,
research has begun into the production of synthetic biopolymers and
using
them
to
create
plastics,
as
its
properties
will
make
it
biodegradable and will reduce the necessity for non-biodegradable
plastics.
A polymer is a long chemical chain formed from the repetition of
numerous monomer units. For these monomer units to form the
polymer a small molecule must be eliminated, generally this molecule
is water (H2O). The units may be of the same chemical or different.
This is illustrated in figure 1.1, as it shows the monomer units of
Terephthalic acid and Ethylene Glycol form and water molecules are
removed, forming Poly(Ethylene Terephthalate) or more commonly
known as PET.
Figure 1.1
How the Biopolymer is Produced
A biopolymer is also long chemical chain formed by the repetition
of monomer cells. Although, these monomer cells are formed from
renewable sources, such as plants and micro-organisms, which cause
the biopolymer to be biodegradable and even biocompatible. An
example of a biopolymer is Biopol, formed from two other biopolymers
Polyhydroxybutyrate (PHB) and Polyhydroxyvalerate (PHV).
Polyhydroxybutyrate (PHB) is the most commonly used and
created biopolymer, and is also used to form copolymers with other
biopolymers. Although it has a low tensile strength unlike the desired
polypropylene formed using petrochemicals and having high tensile
strength. Thus PHB was combined with Polyhydroxyvalerate (PHV)
to
create
a
biopolymer
with
high
tensile
strength,
just
like
polypropylene yet this has a benefit of being biodegradable. Figure 1.2
shows PHB PHV and the copolymer of Biopol.
The bacteria that causes the natural creation of the monomer units
of PHB is Azobacter and the bacteria used to create the monomer
units of PHV is known as Pseudomonas.
Figure 1.2
Biopol is now synthetically produced industrially through the use
of bacteria, in particular Alcaligenes Eutrophus, growing in tanks
and feeding on a carbon based food source. The polymer is followed by
a purification step. This is done by first isolating the polymer then
dissolving it in Trichloromethane or a chlorinated hydrocarbon, then
precipitating and drying the Biopol once the waste solid has been
removed.
Recently, industries have created more economical and efficient
ways of producing Biopol, of using biotechnology. Genes from the
micro-organisms
that
produce
Biopol,
such
as
the
Alcaligenes
Eutrophus, are taken and then inserted into bacteria such as E. coli.
Therefore allowing E. coli. to produce Biopol. The use of the bacteria E.
coli. allows cheaper food sources to be used to feed the bacteria;
examples of food sources that is used to grow the bacteria include
whey, molasses and agricultural waste. Figure 1.3 shows the structure
of E. coli.
The advantages of using E. coli. as the bacteria to make Biopol also
include; faster growth,
easier
formation of waste biomass.
Figure 1.3
recovery,
better
yields and
less
Properties if the Biopolymer
Polypropylene is a polymer produced via the use of petrochemicals
and its properties mean it is very useful. Although, polypropylene is
not biodegradable, therefore there is a large build up of waste plastic.
Consequently, Biopol is a very desired and sort after biopolymer as its
properties are similar to that of polypropylene yet it is biodegradable
and is beneficial as it is also biocompatible. These desirable properties
include;

Insoluble in water

Permeable to oxygen ( allows oxygen to pass through)

Impervious to UV light

Unresponsive to acids and bases

Soluble in chlorinated hydrocarbons (Trichloromethane)

Biocompatible

Biodegradable

High melting point ( 170 degrees)

High tensile strength

Non-toxic

Higher density then water (unlike polypropylene which has a
lower density then water)
Uses of the Biopolymer
The uses for Biopol are a very extensive range, ranging from
medical applications to kitchen utensils, and uses for it are still being
discovered. These uses include;

Medical applications – such as surgical pins and sutures. Often
there is no polymer produced through petrochemicals that can
replace this as they are not biocompatible, meaning the body
will not be reject or will react to the Biopol. It is also
biodegradable, indicating no surgery will be needed for the
removal of the pins or sutures. Other helpful properties for this
use are high tensile strength (it will not break easily), non-toxic
(will not poison the body) and insoluble in water.

Disposable containers – for instance shampoo and cosmetic
containers. Properties allowing Biopol to be useful for this are
non-toxic,
insoluble
in
water,
permeable
to
oxygen,
biodegradable, high melting point and high tensile strength.
Figure 1.4 shows two shampoo bottles, one being Polyethyleneterephthalate (PET) and the other Biopol.

Disposable items such as razors, rubbish bags, nappies and
plastic utensils. The useful properties that make it this useful are
non-toxic,
biodegradable
(will
take
about
two
years
to
decompose), impervious to UV light, permeable to oxygen and
insoluble in water.
Figure 1.5 shows some of the uses of Biopol such as the shampoo
bottles, surgical applications and plastic utensils.
Figure 1.4
Figure 1.5
Conclusion
Biopolymers are very beneficial to the environment, as they are
biodegradable resulting in an improvement of waste management and
also by using renewable sources to create the biopolymers. Although,
it is more expensive to produce the biopolymers than the plastics that
are made by the use of petrochemicals. However scientists are
developing ways to create biopolymers using transgenic plants and
subsequently lowering the costs and making the biopolymers price
competitive with the petrochemical plastics.
Part B
Gather and present information on the structure and
chemistry of a dry cell or a lead-acid cell and evaluate it in
comparison to:





Button cell
Fuel cell
Vanadium redox cell
Lithium cell
Device (e.g. the Gratzel cell)
In terms of:




Chemistry
Cost and practicality
Impact on society
Environmental impact
Introduction
Battery’s contain cell(s) in which electricity is produced via a
serious of chemical reactions. These chemical reactions that are taking
place are called redox reactions.
At the anode (negatively charged electrode), the oxidation reaction
occurs, while at the cathode (positively charged electrode), the
reduction
reaction
occurs.
Although,
for
the
electricity
to
be
generated the half reactions must be separated and the electrons are
to be transported from the anode to the cathode through a wire. A
current is therefore produced.
These electrodes are submerged into solutions in different locations
allowing a current to be produced. Although, a salt bridge between
the two solutions is required as it allows the migration of ions to occur
and create a neutral balance of ions. This solution must be able to
conduct electricity. This substance is known as the electrolytes. Figure
2.1 is an example of a battery that shows the anode, the cathode, the
path of the electrons through the wire and also the salt bridge.
Figure 2.1
Dry Cell (Leclanche Cell)
The dry cell is also known as the Leclanche cell. It is most widely
and commonly used battery, as it is the most affordable. Its uses
include torches and radios. The anode of the dry cell is zinc, while the
cathode is graphite (carbon rod). Figure 2.2 shows the half reactions
occurring at the anode and the cathode. The electrolyte solution used
is a mix of ammonium chloride, zinc chloride and manganese dioxide.
Figure 2.3 shows a cross-section of the structure of a dry cell.
Figure 2.2
The energy density of the dry cell is 0.09 kWh/kg. This is also the
most affordable battery available for commercial use.
The dry cell also had a very large affect on society as it was one of
the first portable batteries to be produced which allowed it to make
torches, radios, toys and clocks to be portable. However, the
disadvantages for dry cells are it does not produce high currents for
its size and it may develop leaks as the zinc casing corrodes. As a
result, the dry cell batteries are harmful to the environment only in
the sense that it releasing hazardous material and is creating waste
material.
Figure 2.3
Button Cell
Another battery is the silver oxide battery or other wisely known
as the button as it is small just like a button of a shirt. Figure 2.5
displays how small the silver oxide cell is compared to a button. The
button is also a commonly used battery as it is very compact and can
consequently be used for petite appliances such as watches and
calculators. The negative terminal of the button is zinc, whereas the
positive terminal is silver oxide. Figure 2.4 shows the half reactions
occurring at the anode and the cathode.
ANODE:- Zn(s) + 2OH-(aq) -----> ZnO(s) + H2O(l) + 2eCATHODE:- Ag2O(s) + H2O(l) + 2e- -----> 2Ag(s) + 2OH-(aq)
Figure 2.4
The electrolyte used for the button depends on the use and required
needs. The most
commonly used
electrolyte used is potassium
hydroxide as this provides higher bursts of currents but it lasts for a
shorter time. The use of sodium hydroxide as the electrolyte will result
in the battery to last for a longer amount of time but will provide
lower currents. Figure 2.6 illustrates the structure of the button cell.
The current produced by the button is 0.125 kWh/kg compared to
the dry cell producing 0.09 kWh/kg. The button has a much higher
output of current compared to the dry cell, therefore making it much
more desired although the button is generally too small to be used for
any other applications.
The Button Cell is more expensive than the dry cell. The battery
has had a big impact on society especially as it is non-toxic and can be
used inside the body. Therefore, the button is much better than the dry
cell as it does not produce any hazardous materials that will harm the
environment.
Shirt Button
Silver Oxide Cell (Button)
Figure 2.5
Figure 2.6
Fuel Cell
The fuel cell is one type of galvanic cell that can be recharged
simply by adding more fuel. These batteries work by adding hydrogen
and oxygen together to create water and heat, and produce
electricity. This is done by inserting hydrogen gas into the anode
which splits the hydrogen gas into electrons and hydrogen ions, while
on the other hand oxygen gas is inserted into the cathode and is
separated into oxygen ions. The hydrogen ions and the oxygen ions
are then combined to form water, while the electrons are passed
through a circuit which generates electricity. Figure 2.7 shows the half
reactions occurring at the anode and the cathode, and figure 2.8
displays the structure and the process of the fuel cell.
Figure 2.7
Although the fuel cell is reasonably cheaper than the dry cell, it does
not give a high enough output of electricity, as a result more than one
fuel cell are stacked to produce the current as the dry cell. Also the
hydrogen that is used to supply the battery is difficult to store and is
not easily accessible so alternative fuels are being considered.
Even though fuel cells are not being used widely throughout society
they are predestined for use in motors and appliances, especially as it
has an extremely high efficiency rate. Also the fuel cell is very
environmentally friendly as it has only water and heat as its
emissions, as a pose to dry cells with contain hazardous materials.
Figure 2.8
Vanadium Redox Cell
The Vanadium Redox battery consists of two compartments in
which are two different electrolyte solutions, one consisting of
vanadium sulfate and the other consisting of vanadium dioxide
sulphate. These two solutions are separated by a porous membrane. At
the anode v2+ oxidises to v3+, therefore allowing electrons to flow to
the cathode and create electricity. Whilst the electrons travel to the
cathode are taken by VO2+ and reduce it to VO2+, and water is
produced. For the battery to sustain its electrical neutrality sulfate
ions are transferred through the porous membrane. Figure 2.9 shows
the half reactions occurring at the anode and the cathode.
Figure 2.9
The Vanadium Redox battery can easily be recharged by passing
an electric current in the reverse direction and therefore reversing
the solution flow. The battery may also be recharged by simply
replacing the electrolyte solutions as the electrodes did not undergo
any reaction. Figure 2.10 shows a schematic drawing of the Vanadium
Redox battery.
The Vanadium Redox battery has a very high efficiency and is
very cheap to purchase and to recharge. Also existing Vanadium
Redox batteries can be readily upgraded by changing the electrolyte
or the container. Also when it is recharged it will not affect the
battery in any way. Therefore, the Vanadium Redox battery is
cheaper than the dry cell and can be recharged unlike the dry cell.
The fact that both electrolytes are the same element will mean that
waste disposal will be very minimal unlike the dry cell where leakages
will ruin the battery. Also the life cycle of the Vanadium Redox
battery is very long in relation to the dry cell therefore meaning the
Vanadium Redox is a better battery.
Figure 2.10
Lithium Cell
There is a diversity of Lithium batteries but the most common and
used one is the Lithium-manganese dioxide cell. The anode of this
battery is Lithium and the cathode is the Carbon. Although, for this
battery, a non-aqueous electrolyte must be used as the Lithium reacts
with water, therefore the electrolyte solution used is Lithium Iodide.
Figure 2.11 shows the half reactions occurring at the anode and the
cathode, and figure 2.12 illustrates the structure of a Lithium battery.
Figure 2.11
Lithium
Anode
Li —> Li+ + e
Cathode MnIVO2 + Li+ + e —> MnIIIO2(Li+)
batteries
are
much more preferred then dry cell as it is longer lasting, rechargeable
and provides twice the electricity a dry cell of the same size would.
Although, the Lithium battery is much more expensive.
The improvement of the Lithium battery over the dry cell has had
a
large
affect
on
society
as
it
provided
longer
lasting
and
rechargeable batteries which is very useful, specifically in the medical
appliances. However, lithium is harmful to the environment and must
be carefully disposed of to prevent any environmental damage.
Figure 2.12
The Gratzel Cell
The Gratzel cell is a photovoltaic cell that can produce electricity
from solar light, very similar to solar panels. Yet instead the Gratzel
battery allows some of the light to enter and uses it to remove an
electron from the anode, Titanium Dioxide. The electron then passes
through the circuit and oxidises the iodine from the electrolyte
solution. Figure 2.9 is a diagram of the Gratzel battery.
The Titanium Dioxide is a very cheap and general material that
can be found easily. This therefore makes it easier to create then the
dry cell. However, the Gratzel has a low efficiency rate, low current
rate and is not able to absorb the full light spectrum.
The Gratzel uses the environment to generate the electricity
although it still has hazardous waste material that is harmful to the
environment, similar to that of the dry cell.
Figure 2.9
Bibliography
A

srar, J and Gruys, K, Biodegradable Polymer (Biopol),
http://www.wileyvch.de/books/biopoly/pdf_v04/bpol4003_53_68.pdf, viewed 27th
January 2011.
 Smith, R 2005, Conquering Chemistry, McGraw Hill, North Ryde
NSW
 17
August
http://www.powerstream.com/BatteryFAQ.html,
2003,
PowerStream
Technologies, viewed 1st February 2011.
 July 2010, http://www.ceic.unsw.edu.au/centers/vrb/Adv.htm,
UNSW, viewed 24th January 2011.
 AUS-e-TUTE
n.d.,
http://www.ausetute.com.au/battery.html
Chemistry Tutorial : Electrochemical Cells & Batteries, viewed
24th January 2011.
 Matthew
Schiller,
2010,
http://www.easychem.com.au/production-ofmaterials/electrochemical-methods/comparison-of-battery-cells,
viewed 1st February 2010.
 ‘Electrochemistry’, search.com, 2006,
viewed 27th January 2011,
http://www.search.com/reference/El
ectrochemistry
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