9.4 C
M
M
1.2.1 – Outline the role of a chemist employed in a named industry or enterprise, identifying the branch of chemistry undertaken by the chemist and explaining a chemical principle that the chemist uses.
1.2.2 – Identify the need for collaboration between chemists as they collect and analyse data.
1.3.1 – Gather, process and present information from secondary sources about the work of practising scientists identifying: – the variety of chemical occupations, – a specific occupation for a more detailed study.
Environmental chemists use special techniques to monitor pollution in air, chemical spills, surveying land and water pollution. They usually work for the Government or private companies to ensure they comply with environmental guidelines.
Metallurgical chemists study metals, alloys and their properties. They also research in the development of new alloys and optimise their production. These chemists work for companies such as BHP.
Inorganic chemists research the synthesis of inorganic chemicals such as ammonia, acids and nitrates. Organic chemists research the synthesis of organic chemicals such as solvents, soaps and hydrocarbons. Both types of chemists are widely employed in the chemical industry.
Biochemists study the chemical interactions within living things. They research the effects of certain chemicals on living things to evaluate their potential toxicity. They may work for
Government departments, pharmaceutical or agricultural industries.
Polymer chemists investigate the properties of polymers and their development. They aim to improve the structures and alter the properties of polymers to create new products. They can work for industrial companies, government agencies and universities.
An organic chemist, working in a linear low-density polyethylene (LLDPE) factory, for example, may have to:
 use computers to predict the properties of the polymer based on different monomers, temperature and catalyst.
 constantly monitor the equipment to ensure the required conditions and the purity of the reagents are maintained. An impurity may contaminate the catalyst, slow the reaction or stop it altogether. A change in the purity of the reagents may lower the quality of and/or change the properties of the polymer.
 carry out quality control processes to ensure the product satisfies. A test of viscosity would indicate if the polyethylene is suitable to be used as a thin-layer film. A test of density would indicate the level of branching in the molecule.
 evaluate the processes by the research and development of the product including problems of contamination, bagging of product, the flow rate through the extruder and the economy of production. This is why collaboration of data is necessary between chemists, chemical engineers and technicians.
- I -

1.2.3 – Describe an example of a chemical reaction such as combustion, where reactants form different products under different conditions and thus would need monitoring.
The combustion of petrol in an internal combustion engine produces different products depending on the abundance of oxygen. In a plentiful supply, the octane burns completely to produce carbon dioxide and water:
2C
8
H
18(l)
+ 50O
2(g)
→ 16CO
2(g)
+ 18H
2
O
(l)
If the supply of oxygen is less abundant, the reaction undergoes incomplete combustion. This will produce, depending on the oxygen supply, carbon monoxide and carbon (soot):
2C
8
H
18(l)
+ 17O
2(g)
→ 16CO
(g)
+ 9H
2
O
(l)
2C
8
H
18(l)
+ 9O
2(g)
→ 16C
(s)
+ 9H
2
O
(l)
Different driving conditions, such as stop-starting, idling and speeding, produce different conditions for combustion. Since carbon dioxide is a greenhouse gas, carbon monoxide is a toxic gas and soot is a carcinogenic substance, and to minimise environmental pollution, chemical engineers that work in the automotive industry have to monitor the levels of these gases.
- II -

2.2.1 – Identify and describe the industrial uses of ammonia.
Ammonia (NH
3
) is a very important industrial chemical. Most of the ammonia manufactured is used to make fertilisers such as ammonium nitrate and urea. Ammonia can be oxidised to produce nitric acid for the manufacture of explosives such as nitroglycerine. It is also used in the production of plastics such as PAN and nylon as well as being used as a refrigerant gas.
Domestically it is used as a cleaning agent and disinfectant.
2.2.2 – Identify that ammonia can be synthesised from its component gases, nitrogen and hydrogen.
2.2.3 – Describe that the synthesis of ammonia occurs as a reversible reaction that will reach equilibrium.
2.2.4 – Identify the reaction of hydrogen with nitrogen as exothermic.
Ammonia is manufactured by the Haber process, where nitrogen gas and hydrogen gas are reacted using an iron catalyst to form ammonia gas. This reaction is a reversible exothermic equilibrium:
N
2(g)
+ 3H
2(g)

2NH
3(g)
ΔH = –92kJ
2.2.5 – Explain why the rate of reaction is increased by higher temperatures.
2.2.6 – Explain why the yield of product in the Haber process is reduced at higher temperatures using Le
Chatelier’s Principle.
Using collision theory, we can deduce that as the temperatures increase, the kinetic energy between the molecules of gas increases, thus creating more successful collisions. This in turn increases the rate of reaction.
Under Le Chatelier’s Principle, if the temperature of an equilibrium system is increased, the endothermic reaction is favoured. Since the production of ammonia is the exothermic reaction, thus its yield will be reduced.
2.2.7 – Explain why the Haber process is based on a delicate balancing act involving reaction energy, reaction rate and equilibrium.
The ‘balancing act’ is a balance of temperature against reaction rate and against the yield of the product. A high temperature would reduce the yield but a low temperature would not provide enough activation energy for the reaction to occur. A moderate temperature is thus used with a catalyst so a lowered activation energy is reached. This combination allows a greater yield than a high temperature alone.
2.2.8 – Explain that the use of a catalyst will lower the reaction temperature required and identify the catalyst(s) used in the Haber process.
The reaction between hydrogen and nitrogen is very slow at room temperature since nitrogen is an unreactive molecule with a strong triple covalent bond. A catalyst will lower the reaction temperature required (since too high a temperature is economically impractical and will reduce yield of ammonia). The catalyst used in the Haber process is an iron catalyst, Fe
3
O
4
, allows the reaction to run at a moderate temperature of about 450 – 550°C.
2.2.9 – Analyse the impact of increased pressure on the system involved in the Haber process.
High pressure drives the molecules together, increasing the rates of reaction. Since the system is in equilibrium, with both reagents and products being gases, the Le Chatelie r’s Principle predicts
- III -

that increased pressure on the system will favour the reaction with the lower number of moles.
Thus the ammonia-forming reaction is favoured, and the yield is increased. Increased pressure is used in the Haber process, about 15 – 25MPa (150 – 250 atmospheres).
2.2.10 – Explain why monitoring of the reaction vessel used in the Haber process is crucial and discuss the monitoring required.
The continual monitoring of the reaction vessel of the Haber process is crucial. Automatic monitors measure a variety of conditions, mainly temperature and pressure of the reaction vessel and the stoichiometric ratio of the gases.
The ratio of the gases is necessary to ensure maximum yield from the reagents. The temperature is recorded to maintain maximum efficiency of the yield and so that the heat generated by the exothermic reaction can be fed back to maintain the temperature. Pressure of the vessel is monitored for safety reasons and to maintain a high yield. The catalyst is also monitored to ensure that it is not poisoned by gases such as CO which are by-products of the hydrogen production process.
2.3.1 – Gather and process information from secondary sources to describe the conditions under which
Haber developed the industrial synthesis of ammonia and evaluate its significance at that time in world history.
Fritz Haber was born in 1868 in Prussia, the son of a prosperous German chemical merchant.
After his education, Haber left his father’s business to study organic chemistry at the University of
Jena. At the age of 25, Haber began teaching and researching physical chemistry and quickly gained recognition for his research into electrochemistry and thermodynamics.
During the first decade of the twentieth century, world-wide demand for nitrogen-based fertilisers was exceeding supply. The largest source for fertiliser production was the huge guano (sea bird droppings) deposits on the coast of Chile. Many scientists desired to solve the problem on this fast disappearing supply of ammonia and nitrogenous compounds.
Haber invented his process for the large-scale production of ammonia from nitrogen and hydrogen gas, both of which are abundant and inexpensive. By using a moderate temperature
(~500°C), high pressure (~30MPa), an iron catalyst, he, together with Carl Bosch, a chemical engineer, was able to force the relatively unreactive gases to combine into ammonia. By this breakthrough many further products, such as fertilisers and explosives could be made.
During the outbreak of World War I in 1914, Haber was placed in charge of a research centre for chemistry and physics, and placed his services before the German government. For the duration of the war, Haber, a loyalist to his country, produced many breakthroughs that helped sustain
Germany.
The significance of the Haber process is enormous, because gave Germany, though it was landlocked, the essential raw materials for the production of fertilisers, for the growing of crops, and of nitric acid, the basis of explosives. In this way, Haber allowed Germany to be independent of Chile and other countries, and shouldered the German military machine with his achievements for four years. Without him, Germany would have never had a chance to win the war.
- IV -

3.2.1 – Deduce the ions present in a sample from the results of tests.
3.3.1 – Perform first-hand investigations to carry out a range of tests, including flame tests, to identify the following ions: – phosphate, – sulfate, – carbonate, – chloride, – barium, – calcium, – lead, – copper, – iron.
C
ATION
Barium Ion (Ba 2+ )
P
RECIPITATE
T
ESTS forms white ppt with CO
3
SO
4
2 –
and PO
4
3 – forms no ppt with OH –
2 –
,
F
LAME
T
EST
Lime-green flame when barium nitrate soln. was sprayed into bunsen flame
Calcium Ion (Ca 2+ )
Brick-red flame when calcium nitrate soln. was sprayed into bunsen flame
Lead Ion (Pb 2+ )
Copper Ion (Cu 2+ )
Iron(II) Ion (Fe 2+ )
Iron(III) Ion (Fe 3+ ) forms white ppt with SO
4
2
OH
–
and PO
4
3 –
– , forms white ppt with Cl
–
, OH
–
CO
3
2 – , SO
4
2 – and PO
4
3 – tested with NH
3
(aq) to form a deep blue solution forms pale-blue ppt with OH
– forms a white ppt with OH – which quickly turns brown forms with thiocyanate ions
(SCN
–
) to form a blood red soln. (FeSCN 2+ )
Blue-green flame when copper nitrate soln. was sprayed into bunsen flame
A
NION
P
RECIPITATE
T
ESTS
Phosphate Ion (PO
Carbonate Ion (CO
4
3
3 –
Sulfate Ion (SO
4
2 –
)
2 –
)
) forms a yellow precipitate when
HNO
3
and ammonium molybate
is added and the solution warmed. white precipitate with barium nitrate, calcium nitrate or lead nitrate addition of acid produces CO
2
gas. all metal ions produce white precipitate.
Chloride Ion (Cl
–
) forms a white precipitate with AgNO
3(aq)
3.3.2 – Gather, process and present information to describe and explain evidence for the need to monitor levels of one of the above ions in substances used in society.
One metal that must be monitored carefully is lead. Lead is a toxic, heavy metal. It can damage all the organs of the body, especially the brain, kidneys and reproductive system, by disrupting enzyme function. Lead inhibits the formation of haemoglobin in blood, causing anaemia and reducing the ability of blood to carry oxygen. It can cause neurological damage in the brain, especially in children.
- V -

Lead accumulates in the body and is difficult to excrete, and increases in concentration in the higher end of the food chain (a process called biomagnification). Its accumulation in air has been caused by the (now-ceased practice of) addition of lead into petrol, the mining and refining of lead and deterioration of lead-based paints.
The health and environmental destruction of lead makes it very necessary and important to monitor lead ion levels in our atmosphere, water, food and soil.
3.2.2 – Describe the use of atomic absorption spectroscopy (AAS) in detecting concentrations of metal ions in solutions and assess its impact on scientific understanding of the effects of trace elements.
Atomic absorption spectroscopy (AAS) is an important technique in measuring the concentrations of metal ions in very minute quantities. In atomic spectroscopy a liquid sample containing the metal ion to be tested is aspirated through a plastic tube into a flame hot enough to vaporise the molecules into atoms. A cathode lamp of the specific metal passes through the vaporised sample.
A detector measures the amount passing through the flame and gives out the absorbance
(amount absorbed) reading.
The basis of AAS is the result of the electron structure of the atom. Under quantum theory, electrons move to higher or lower energy levels by absorbing or releasing electromagnetic radiation of a particular frequency. Since each element has a different set of electron energy levels, each has its own set of absorption lines. The greater the concentration of the metal ion, the more radiation is absorbed and the less reaches the detector. According to the Beel-Lambert
Law, the amount of light absorbed is proportional to the amount of a substance present. A calibration graph using solutions of known concentrations allows the concentration of the unknown to be determined.
The development of the AAS has allowed chemists to measure accurately and rapidly concentrations of metal ions in water systems and in animals and plants. Such has lead to our understanding of trace elements, those elements which are required by living things in very minute quantities. Prior to this understanding, there were instances where animals had health problems in seemingly good pastureland due to deficiencies in cobalt and human illnesses, due to lack of trace elements in their diet, could not be diagnosed. Now, with atomic absorption spectroscopy, these problems are easily and effectively rectified.
3.3.3 – Identify data, plan, select equipment and perform a first-hand investigation to measure the sulfate content of lawn fertiliser and explain the chemistry involved.
3.3.4 – Analyse information to evaluate the reliability 1 of the results of the above investigation and to propose solutions to problems encountered in the procedure.
A sample of fertiliser containing (NH
4
)
2
SO
4
was crushed by a mortar and pestle and weighed to a mass of 10 grams. It was then dissolved in a beaker of warm water. Ba(NO
3
)
2
was added dropby-drop in excess until no more white precipitate of BaSO
4
will form. The precipitate was then filtered with extra-fine filter paper or a suction-filter, dried and weighed. The sulfate content was then calculated.
The chemistry of this experiment is totally valid 2 ; we attempt to precipitate the sulfate ions in the fertiliser with an excess of barium ions. The solubility of BaSO
4
is very low so the remaining SO
4
2 – in solution is negligible. So we assume, without loss of any significant precision, that all the SO
4
2 – precipitates as BaSO
4
. Upon weighing the amount of BaSO
4
formed, we can calculate how much
SO
4
2 –
in original sample.
1 My tutor suggests this dot-point would be better expressed as “evaluate the validity”.
2 Kudos to phen0l: the validity and reliability evaluation is adapted from his notes.
- VI -

Like all other gravimetric experiments, extreme care is needed to be able to repeat similar results.
To ensure no loss of the original fertiliser, or BaSO
4
when weighing, the experiment must be conducted in a room free of fans or draught. Another problem encountered is the minute size of the BaSO
4
crystals, making it very difficult to filter. To counter this, we add concentrated HCl acid which is somewhat adsorbed onto the BaSO
4
surface during precipitation. This makes the surface of microcrystals slightly charged and hence attracts other charged microcrystals. This helps the microcrystals to coagulate into larger crystals which would not pass right through the sintered glass funnel. However, there are surely crystals that pass through and this is the main source of error. Of course, the repetitions conducted, more reliable the results become.
3.3.5 – Gather, process and present information to interpret secondary data from AAS measurements and evaluate the effectiveness of this in pollution control.
In the University of Sydney’s High School Chemistry Workshop, an AAS machine was demonstrated to us and used to test the concentration of Fe 2+ ions in various samples of water.
The results were as follows:
S OURCE OF W ATER A BSORBANCE R EADING C ONCENTRATION ( PPM )
Tap
Creek
0.003
0.0012
0.0
0.2
A rusted rainwater tank 0.252 4.0
As can be seen, the ability of the AAS technique to measure in parts per million (ppm) allows chemists to measure metal ions of a very low concentration. However, the AAS must be daily calibrated with the ion to be measured for the machine to measure accurately. By monitoring the ions that are known pollutants, atomic absorption spectroscopy is a very effective and inexpensive method to control pollution.
4.2.1 – Describe the composition and layered structure of the atmosphere.
The atmosphere has a layered structure, based on the temperature increases/decreases relative to the height. The troposphere is the layer closest to the earth, up to ~15 km above sea level, where the temperature decreases as the altitude increases. The troposphere is the layer with the most mass of gas (~80%), and all weather occurs in this layer. The next closest layer, the stratosphere, extends from ~15km to ~50km altitude, where the temperature increases as the altitude increases. The ozone ‘layer’ is found in the bottom of the stratosphere. The next layer up is the mesosphere, up to ~75km, where the temperatures fall with altitude increases. No water vapour or ozone is present in this layer. The thermosphere is the next layer, extending to ~200km, where temperature increases with altitude, until ~1200°C. The exosphere, the furthermost layer of the atmosphere verges into space and its limits are not defined.
4.2.2 – Identify the main pollutants found in the lower atmosphere and their sources.
Tropospheric pollutants are derived mainly from the combustion of fossil fuels in power stations, motor vehicles and industry and emissions from the smelting and purification of minerals. Carbon monoxide and carbon (in the form of soot) are formed from the incomplete combustion of fossil fuels and from natural sources such as bushfires. Oxides of nitrogen are formed by lightning, bacterial decay, emissions from combustion engines and coal-fired power-stations. Hydrocarbons vapours are emitted from exhausts gases and landfills and natural sources, such as ruminant animals such as cows and sheep. Sulfur dioxide is produced naturally by volcanoes and geysers
- VII -

and artificially by coal-fired power-stations, combustion of fossil fuels and smelting of sulphide metal ores.
4.2.3 – Describe the ozone as a molecule able to act both as an upper atmosphere UV radiation shield and a lower atmosphere pollutant.
Ozone serves as an important molecule in the upper atmosphere (the stratosphere) because, being reactive, it absorbs UV radiation to form diatomic oxygen, and similarly, diatomic oxygen absorbs UV radiation to form ozone:
O
3(g)
→ UV radiation → O
2(g)
+ O•
(g) activation energy diatomic oxygen oxygen radical ozone
O
2(g)
+ O•
(g)
→ UV radiation → O
3(g) diatomic oxygen oxygen radical activation energy ozone
This absorption of UV radiation minimises the amount of radiation that reaches the earth. UV radiation causes damage to the DNA of living cells (in humans the depletion of protein-53 in the
DNA strand). The damage caused interrupts the genes controlling the lifespan of cells, and in turn produces cancerous tumours. Therefore ozone is a molecule that acts as an UV radiation shield in the upper atmosphere.
However, in the lower atmosphere (the troposphere), ozone is seen as a pollutant because it is a poisonous gas. Ozone causes eye irritation and in high concentrations (>0.12ppm), breathing problems in asthmatics. Furthermore, ozone, because of its high reactivity, attacks double bonds in molecules, especially polymers, causing their deterioration. Ozone is also a component of photochemical smog.
4.2.4 – Describe the formation of a coordinate covalent bond.
The coordinate covalent bond is a bond formed by one atom donating the electron pair only. It can be formed by a molecule reacting with its radical (i.e. an atom of the same element with unpaired electrons). An example of this is the formation of ozone, where UV radiation, or some other form of activation energy, causes diatomic oxygen to react with the oxygen radical to form ozone:
O
2(g)
+ O •
(g)
→ UV radiation → O
3(g) diatomic oxygen oxygen radical activation energy ozone
The oxygen radical bonds to a pair of electrons in one of the oxygen atoms in diatomic oxygen molecule without ‘sharing’ any of its own. This is the coordinate covalent bond of ozone.
4.2.5 – Demonstrate the formation of coordinate covalent bonds using Lewis electron dot structures.
3
A coordinate covalent bond forms when one atom in a species (a molecule or ion containing nonmetallic atoms) provides both electrons in the covalent bond. Some ions, such as hydronium and ammonium, contain a coordinate covalent bond. In the formation of the hydronium ion, one of the
3 Diagrams sourced from http://hsc.csu.edu.au
- VIII -

non-bonding electron pairs on the oxygen atom is used to form a covalent bond between the hydrogen ion (H + ) and the oxygen atom.
4.2.6 – Compare the properties of the oxygen allotropes of O molecular structure and bonding.
2
and O
3
and account for them on the basis of
P ROPERTY D IATOMIC O XYGEN O ZONE
Symbol
M P (°C)
BP (°C)
Density
Reactivity
O
2
–219
–193
Slightly denser than air
Highly reactive
O
3
–183
–111
~1.5 times denser than air
Very highly reactive
Stability Stable Dissociates readily to form O
2
4.2.7 – Compare the properties of the gaseous forms of oxygen and the oxygen free radical.
When a diatomic oxygen molecule is split by high energy UV the atoms produced are represented on the Lewis diagram 4 by:
These energetic oxygen atoms have unpaired electrons called free radicals. The unpaired electrons make the radical very reactive, more so than diatomic oxygen and ozone.
4.2.8 – Identify the origins of chlorofluorocarbons (CFCs) and halons in the atmosphere.
Chlorofluorocarbons (CFCs) and halons (bromofluorocarbons) were used as refrigerants in pre-
1980 ’s air conditioners and refrigerators, used as propellants in spray-cans and used in the manufacture of plastics. When molecules of these compounds were used or leaked out, they escaped into the atmosphere.
4.2.9 – Identify and name examples of isomers (excluding geometrical and optical) of haloalkanes up to eight carbon atoms.
4.3.2 – Gather, process and present information from secondary sources including simulations, molecular model kits or pictorial representations to model isomers of haloalkanes.
Haloalkanes are molecules that contain only carbon, hydrogen and at least one halogen (Group
VII of the Periodic Table), and single bonds. Examples of haloalkanes include:
4 Diagrams sourced from http://hsc.csu.edu.au
- IX -

tetrachloromethane
CCl
4 trichloromethane
(chloroform)
1,2-dibromoethane
2-chloropropane
CHCl
3
C
2
H
4
Br
2
C
3
H
7
Cl
C
5
H
9
Br
2
F 1,5-dibromo-3fluoropentane
1-chlorobutane
1,1-dibromobutane
1-iodobutane
C
4
H
9
Cl
C
4
H
8
Br
2
C
4
H
9
I
- X -

4.2.10 – Discuss the problems associated with the use of CFCs and assess the effectiveness of steps taken to alleviate these problems.
4.3.1 – Present information from secondary sources to write the equations to show the reactions involving
CFCs and ozone to demonstrate the removal of ozone from the atmosphere.
CFCs undergo photodissociation (reactions using the energy of light to break bonds); thereupon they release chlorine atom radicals. It is these radicals which destroy ozone molecules:
1) CClF
3(g)
→ example of a CFC
UV radiation → photodissociation
CF
3(g)
+ Cl•
(g) fluorocarbon radical chlorine radical
2) Cl•
(g) chlorine radical
+ O
3(g) ozone molecule
→ ClO
(g) radical
+ O
2(g) oxygen molecule
3) ClO
(g) radical
+ O
(g) oxygen radical
→ O
2(g)
+ oxygen molecule
Cl •
(g) chlorine radical
Therefore, the direct effect of CFC use is the long-term depletion of the ozone layer ; the chlorine radical is regenerated in the process and can thus deplete more ozone molecules. Since the ozone layer is important in the lower stratosphere as a UV absorption shield, its depletion will result in more UV rays reaching the earth ; further, UV radiation can damage the skin and eyes of animals and promote cancerous tumours .
In 1987, the Montreal Protocol was signed to alleviate the problems cause by CFC use. The member countries of the protocol promised to immediately replace all CFCs with HCFCs
(hydrochlorofluorocarbons), which are less reactive and destructive than CFCs. It was planned that HCFCs will then be phased and out replaced by other hydrocarbons by the year 2000. The protocol also offered assistance to developing countries to help them minimise their use of CFCs.
The protocol has been effective in that CFCs have been removed from all developed countries, but in developing countries CFCs are still in use. However the protocol has been very effective in that CFC use has been dramatically minimised and 2003 was the first year that the rate of ozone depletion has levelled off.
4.2.11 – Analyse information available that indicates changes in atmospheric ozone concentrations, describe the changes observed and explain how this information was obtained.
In the late 1980s, the TOMS (Total Ozone Mapping Spectrometer) aboard the Nimbus-7 satellite recorded significant thinning of the ozone layer over Antarctica, evidence led to the acceptance of the theory that CFCs and the chlorine radicals they produce led to the decline of the ozone layer.
Since then, very large decreases (known as ‘holes’) have been observed by TOMS.
There is an increase in ozone thinning during spring in Antarctica after a long winter, because ice crystal surfaces help generate molecular chlorine by the reaction of HCl and ClONO2. The Cl2 photodissociates with the extra UV radiation in spring to produce more chlorine free radicals that increases ozone depletion. By summer the Cl2 levels have depleted and ozone concentrations return to normal levels.
The information about ozone concentrations are collected by TOMS on satellites, spectrometers on scientific balloons and ground-based spectrometers.
- XI -

4.3.3 – Present information from secondary sources to identify alternative chemicals used to replace CFCs and evaluate the effectiveness of their use as a replacement for CFCs.
CFCs have been replaced by other compounds with significantly lower ozone depletion potential
(ODP). HCFCs (hydrochlorofluorocarbons) were the first CFC-replacement chemicals, since they react in the troposphere with OH free radicals; however because this was a slow reaction, some
HCFCs still reached the stratosphere where they released chlorine atoms.
HFCs (hydrofluorocarbons) are now more readily used as replacements of CFCs in refrigeration and air conditioning units as they contain no chlorine atoms and thus have zero ODP.
Hydrocarbons (such as butane) have replaced CFCs as aerosol propellants.
HFCs and hydrocarbons are effective replacements of CFCs and help restore the ozone depletion that CFC use has caused. With them, CFCs have been removed from all developed countries and the rate of ozone depletion, in this year, has levelled off for the first time.
5.2.1 – Identify that water quality can be determined by considering: – concentration of common ions, – total dissolved solids, – hardness, – turbidity, – acidity, – dissolved oxygen and biochemical oxygen demand.
Water quality can be monitored by considering the following:
Concentration of
Common Ions
Total Dissolved Solids
Hardness
In testing water quality, the following cations are usually determined: Na + , Mg 2+ , Ca determined: Cl – , SO
4
2 –
2+ , K + . The following anions are also
, HCO 3 – , Fl – . AAS is used to determine the concentration of specific metal ions in the water. ISE (Ion selective electrodes) can be used for both anions and cations.
Gravimetric analysis can also be used by precipitating specific ions out of solution.
The measure of TDS is done either by evaporation of a water sample, or conductivity (in milliSiemens per metre) and multiplying the conductivity by 0.68 (for a result in mg/L). TDS indicates the levels of mineral salts in the water.
Hardness is a measure of the water’s ability to ‘lather’ (to form soap bubbles). Calcium and magnesium ions present, however, will precipitate and form insoluble scum. Hardness can be determined quantitatively by titrating water with EDTA or relatively by seeing how many drops of soap solution needs to be added to lather the water.
- XII -

Turbidity
Acidity
Water is described as turbid if it contains suspended particles. It is measured in mg/L or NTU. It is measured by pouring a sample of water down a calibrated device called a turbidity tube (with a black cross on the bottom), and added until the cross can no longer be seen.
Some living things can only survive in water with a specific pH level. Acidity (or basicity) of the water sample is usually measured with a pH meter or narrow range pH paper.
Dissolved Oxygen (DO)
Dissolved oxygen levels indicate the water’s ability to support aquatic life. Oxygen levels increase where there is increased contact between water and air (such as tumbling of water and wave formation). DO can be measured by a thallium oxygensensitive probe, or by a Winkler titration.
Biochemical oxygen demand is a measure of the rate of oxygen
Biochemical Oxygen
Demand (BOD) use of microscopic organisms. It is also an indirect measure of organic waste present in the water. A DO test is done a sample of water; it is sealed and left in the dark for a period of (5) days and the DO test repeated. The difference between DO levels is the
BOD level (high BOD levels indicate pollution).
5.2.2 – Identify factors that affect the concentrations of a range of ions in solution in natural bodies of water such as rivers and oceans.
Factors which affect the concentration of ions in natural water systems include:

Climatic factors, such as rain and floods: these will initially dilute the concentration of ions in the water, but over the longer term, will cause mineral ions to be leeched from the soil and water. The type of rock over which the water moves will determine the types of ions present (eg. limestone rocks produce Ca 2+ and CO
3
2 –
ions).

Industrial wastes and runoff: these will increase the concentration of specific ions (used in industry) into local waterways. Waste water can also be acidic or alkaline and contain heavy metals.

Agriculture and farming: fertilisers contain various salts of nitrogen and phosphorous.
During rain the concentration of NH
4
+ , NO
3
– and PO
4
3 – increase in local waterways.

Sewage discharge: nitrates and phosphates are likely to be present in sewage discharge into water systems such as ocean outfalls.
5.2.3 – Describe and assess the effectiveness of methods used to purify and sanitise mass water supplies.
Water is purified and sanitised in four steps: screening, flocculation, filtration and chlorination.
Screening is used to remove large particles from the catchment such as tree branches and animal carcasses. Flocculation is the addition of a flocculant such as iron (III) chloride (FeCl
3
) or aluminium hydroxide to coagulate suspended particulates and settle in settling tanks. Filtration is then performed through sand and anthracite (a type of coal) filters to remove all undissolved particulates. Chlorination is then performed with the addition of sodium hypochlorite (NaOCl) and chloramine to kill bacteria because hypochlorite (OCl
–
) ions destroy their cell walls.
- XIII -

Our screening and flocculation methods are very effective compared to world standards, but does not work well in high turbidity. Our chlorination method is very effective, but is more expensive than other methods. An example of failure, however, was shown three years ago when
Cryptosporidium and Giardia entered our drinking water. Overall, an assessment of the purification and sanitation of our mass water supplies has shown that these methods are very effective in delivering us clean and drinkable water.
5.2.4 – Describe the design and composition of microscopic membrane filters and explain how they purify contaminated water.
A membrane filter can further purify water. It is usually made from two tubes, the inner one being a filter with many fine pores. Water is run across the outer tube and is filtered as it falls through the inner tube. Ultrafilters are those which have filter pores as small as 2 nanometres to remove particles including large molecules, protozoans, spores and bacteria. Nanofilters are those which have a pore size of 1 nanometre to filter out smaller organic molecules and those with special coatings can also remove multivalent cations. Many of these filters are made from polymers, such as cellulose acetate, which are arranged in various configurations (spirals, flat sheets, hollow tubes etc). They are very useful for filtering drinking water and can be reused after cleaning.
5.3.1 – Perform first-hand investigations to use qualitative and quantitative tests to analyse and compare the quality of water samples.
5.3.2 – Gather, process and present information on the range and chemistry of the tests used to: – identify heavy metal pollution of water, – monitor possible eutrophication of waterways.
To identify heavy metal pollution:

A water sample can be tested with atomic absorption spectroscopy with the correct light source for the specific ion to be tested.

Na
2
S is added to the water sample. If a precipitate forms, the heavy metal present could be: Pb 2+ , Ag + , Hg 2+ , Cu 2+ , Cd 2+ , Au 2+

A base is added to the water sample. If a precipitate forms, the heavy metal present could be: Cu + , Zn 2+ , Fe 3+ , Co 2+ , Mn 2+ , Ni 2+ , Al 3+
To monitor eutrophication of waterways, the concentrations of nitrogen, phosphorous and their ratio (N:P) must be considered.
To monitor nitrate:

FeSO
4
was added into the sample, followed by concentrated H
2
SO
4
. If a brown ring forms halfway down the solution, NO
3
–
is present.
To monitor phosphorous:

5 drops of NH
3(aq)
is added to a 10mL sample of water. 5 drops of Ba(NO
3
)
2(aq)
is added; a white precipitate will form. Add Mg 2+ ions in an ammonia/ammonium buffer; if white precipitate remains, PO
4
3 –
ions are present.
To prevent algae blooms caused by eutrophication, N:P ratio should be 10:1, but the concentration of the ions should be taken into consideration since all cyanobacteria grow well in high levels of nitrates.
- XIV -

5.3.3 – Gather, process and present information on the features of the local town water supply in terms of:
– catchment, – possible sources of contamination in this catchment, – chemical tests available to determine the levels and types of contaminants, – physical and chemical processes used to purify water, – chemical additives in the water and the reasons for the presence of these additives.
Sydney’s water supply is collected from four main catchment areas totalling 1600 hectares: the
Upper Nepean, Woronora, Warragamba and Shoalhaven, and includes a complex network of dams and reservoirs. The largest dam, Warragamba, was completed in 1960 and holds about 2 million megalitres of water. The catchment is protected from contamination by security parameter fencing and prohibition of farming in the vicinity. Possible sources of contamination, however, are falling branches and silt from rainwater.
Most of the water travels to Prospect Water Filtration Plant, where 3000ML of water are treated per day. Screening is used to remove large particles from the catchment such as tree branches and animal carcasses. The addition of a flocculant such as iron (III) chloride (FeCl
3
) or aluminium hydroxide (Al(OH)
3
) forces suspended particulates to coagulate and settle in settling tanks.
Filtration is then performed through sand and anthracite (a type of coal) filters to remove all undissolved particulates.
Water entering the plant is tested for manganese concentration, pH, algae levels, true colour, hardness, temperature, turbidity and conductivity.
Chemical additives are added to the water as needed:

Chlorination is performed with the addition of sodium hypochlorite (NaOCl) and chloramine to kill bacteria because hypochlorite (OCl
–
) ions destroy their cell walls.

Fluoride ions is added to protect against cavities and increase tooth enamel hardness.

Sulfuric acid to break down any discolouration caused by the presence of organic matter.


Lime water (Ca(OH)
2
), sodium carbonate or sodium hydroxide to lower acidity.
Chlorine dioxide to decompose any suspended organic matter.
Water leaving the plant are retested to ensure the treatments are effective, including testing the concentrations of fluoride, chloride, iron, manganese and aluminium ions.
- XV -