HSC HSC HSC HSC ChemistryChemistryChemistryChemistry Revision Revision Revision Revision Module Module Module Module 3333 David Pham

# Chemical Monitoring and Management 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

Chemist: Luke (not his real name) Named Industry: Plastics (polymer) industry Luke is a chemist at a major Australian chemical manufacturing company that makes ethylene from ethane, and then polymerises it into polyethylene. Branch of Chemistry: Industrial/analytical chemistry Role of Chemist: Luke, being a chemist in the central lab, is not so much concerned as physically carrying tests out rather than overseeing them. He checks that equipment is operating properly, calibrating them from time to time. He trains shifts workers, who carry out the chemical tests. He occasionally carries out analyses to check reliability of these tests, solving problems that arise and looking for ways to improve the overall monitoring process. These tests monitor the quality of the product (polyethene and ethene), particularly before the next step in production, such as for impurities. Also, tests monitor the nature emissions and wastes from the plant, ensuring it meets environmental standards, such as pH, suspended solids, polluting chemicals and particulates in gaseous emissions. They also monitor the operating conditions of the cracking furnace, collaborating with these chemists, in order to optimise product yields. The efficient operation of plants as complex as this requires regular routine monitoring. ‘Luke’, as a skilled chemist, is available to oversee this routine work, check its reliability, solve problems which occur, and develop new procedures as circumstances or operating conditions change. Chemical Principle(s): As Luke works in analytical chemistry, he is concerned with determining which substances, and the amounts of each, are present in materials. Many of his analyses use gas chromatography. This is based upon the chemical principle of adsorption (gas-solid chromatography) and solubility (gas-liquid chromatography). This technique is used to separate components from a mixture out so that the amount of each can be measured. The adsorption and solubility (polarity of molecules) affect the extent to which the chemicals separate.

identify the need for collaboration between chemists as they collect and analyse data

Chemistry is a very broad discipline, with different chemists specialising in different fields. However, chemical problems of the world require expertise in more than one field of specialisation, especially in industry. For example, industry can require knowledge of physical (equilibria and reaction rates), organic (reaction mechanisms and optimisation of yield), and analytical, chemical engineering, and environmental specialisations. Solving problems from wide-ranging and complex problems required input form many chemists with different specialities, as they cannot solve these problems in isolation. Therefore it is essential for chemists to work collaboratively, regularly interact and exchange different viewpoints bout problems as they arise. This means that chemists need to have good communication skills – that they are able to communicate all aspects of their part particular disciplines skilfully and concisely (without excessive technical jargon), lest problems arise from misunderstandings and misapplications of principles. Similarly chemists need to work with scientists from other fields collaboratively too in some applications as all science has the potential to impact upon other areas.

describe an example of a chemical reaction such as combustion, where reactants form different products under different conditions and thus would need monitoring

Combustion is a chemical reaction which forms different products under different conditions. For a general hydrocarbon (alkane) a variety of products (CO2, CO and C(s)) can form under different conditions (varying amounts of available oxygen). For example, the combustion of octane in internal combustion engines is very common as it is the major component of petrol and as such its monitoring is crucial. By monitoring its reaction and discovering new technologies to assist the desired product creation, the negative impact of the combustion of octane can be minimised. The amount of toxic products such as impurity oxides and carbon soot can be minimised through monitoring of reaction and changing

reaction conditions as necessary. C8H18(l) + 25/2O2(g) 8CO2(g) + 9H2O(g) C8H18(l) + 11O2(g) 5CO2(g) +3CO(g) + 9H2O(g) C8H18(l) + 9O2(g) 3CO2(g) + 3CO(g) + 2C(s) + 9H2O(g) C8H18(l) + 7O2(g) 5CO(g) + 3C(s) + 9H2O(g)

In an environment of inadequate oxygen, CO2, CO, and C are all produced in varying quantities. Car emissions need to be monitored to ensure that these products are produced at acceptable levels to avoid excesses that may become an environmental hazard. A school application of the monitoring of combustion is that of Bunsen burners in the lab. Methane or propane gas’ combustion is observed and controlled, depending on the requirements, by increasing or reducing oxygen intake. Turning the air holes fully open results in cleaner combustion, as more air (oxygen) is allowed into the tube. The flame is bluish-transparent. If the air holes are partly open or closed, less air is available and incomplete combustion occurs. The flame is darker and more yellow, and deposits of soot can be noticed on nearby surfaces. C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g) C3H8(g) + 9/2O2(g) 2CO2(g) + CO(g) + 4H2O(g) C3H8(g) + 7/2O2(g) CO2(g) + CO(g) + C(s) + 4H2O(g) C3H8(g) + 3O2(g) 2CO(g) + C(s) + 4H2O(g) This reaction is monitored in order to control the desired reaction. When a visible, cooler flame is required the oxygen intake is lessened. When a hotter flame is required the oxygen intake is increased.

* gather, process and present information from secondary sources about the work of practising scientists identifying: • the variety of chemical

occupations • a specific chemical

occupation for a more detailed study

Some occupations requiring the application of chemical principles include: • environmental monitoring • research and development – e.g. surfactant/paint/drug • chemical engineer • metallurgical chemists • biochemist • plastics chemist • physical chemist • nuclear chemist • and much more… Chemical Industry chosen: Environmental Chemist Environmental chemistry is the scientific study of the chemical and biochemical phenomena that occur in natural places. It should not be confused with green chemistry, which seeks to reduce potential pollution at source. It can be defined as the study of the sources, reactions, transport, effects, and fates of chemical species in the air, soil, and water environments; and the effect of human activity on these. Environmental chemistry is an interdisciplinary science that includes atmospheric, aquatic and soil chemistry, as well as heavily relying on analytical chemistry and being related to environmental and other areas of science. In the twentieth century we became increasingly aware of the impact of humans upon the environment. The natural cycles that sustain our water supplies and atmosphere are being affected by the increasing use of resources resulting in pollution of air, land and water. Society now appreciates the importance of sustainable development, to ensure that the earth continues to support a rich diversity of life. The burning of fossil fuels in power stations and motor vehicles, mineral extraction processes, and the extensive use of various solvents and aerosol propellants all contribute to changing the composition of our atmosphere. Similarly, detergents, fertilisers, herbicides, fungicides and various industrial wastes are constantly being washed into our waterways. Chemical analysis using modern technologies can facilitate the collection of data about our environment to determine the influence of human activities on the changes in the composition of our atmosphere and waterways. Environmental chemists draw on a range of concepts from chemistry and various environmental sciences to assist in their study of what is happening to a chemical species in the environment. Important general concepts from chemistry include understanding chemical reactions and equations, solutions, units, sampling, and analytical techniques.

Environmental chemists are often employed by government agencies, the EPA, or mining companies as public servants. They monitor air, soil and water quality and interpret data to provide policy advice to statutory authorities. The chemist would ideally have a Bachelor of Science, followed up by postgraduate qualifications and development of expertise in analytical chemistry. They would have good understanding of chemical concepts, especially analysis – separation techniques and spectrometry. They would work in a team providing advice and concise reports on the formulation of government policies relating to air and water. One important role assigned to chemists is monitoring the chemical composition of our atmosphere and waterways and identifying changes that are occurring as a result of our modern lifestyle. Chemists have also played a key role in improving industrial productivity and developing processes that reduce the release of unwanted chemicals into the environment. Thus industrial processes are being increasingly monitored and refined in order to minimise their environmental impact, and alternative products and processes are continually sought in our efforts to maintain a sustainable lifestyle.

2. identify and describe the industrial uses of ammonia

Ammonia is used industrially as a feedstock (raw material from which a substance or industrial process is derived) mainly for: • fertilisers (derived from urea and ammonium and nitrates) to grow plants

where soils may be deficient in nitrogen compounds. To make solid fertilizer industrially, ammonia, which is a weak base, is reacted with sulfuric acid to form ammonium sulfate fertiliser and with nitric acid to form ammonium nitrate fertiliser.

• explosives (derived from nitric acid) such as TNT, nitroglycerine and nitrocellulose in order to destroy

• plastics (nylon and acrylic) for general everyday use such as clothing, containers and fibres

Other uses include cyanides (gold extraction), sulfonamides (antibiotics), aniline derivatives (dyes) and cationic detergents.

identify that ammonia can be synthesised from its component gases, nitrogen and hydrogen

describe that synthesis of ammonia occurs as a reversible reaction that will reach equilibrium

identify the reaction of hydrogen with nitrogen as exothermic

H2(g) + 3N2(g) 2NH3(g) ∆H = -92kJ/mol The industrial production of ammonium, known as the Haber Process, allows the production of ammonia from its constituent elements. The synthesis of ammonia is a reversible reaction. Drawing on from previous knowledge, all reversible reactions in a closed reaction system will reach equilibrium after a time, when the forward and backward reaction rates are equal. At standard conditions the equilibrium lies well to the left, and very little ammonia is present in the reaction mixture. The conditions in the Haber Process, however, make it viable commercially. The forward reaction is exothermic as ∆H is negative. This means that the substances involved lose energy as part of the reaction, which is given out as heat. For each mole of hydrogen and 3 moles of nitrogen used to produce 2 moles of ammonia, 92kJ of energy is released.

explain why the rate of reaction is increased by higher temperatures

explain why the yield of product in the Haber process is reduced at higher temperatures using Le Chatelier’s principle

Recall from previous studies how kinetic factors affect the rates of reaction, particularly temperature and pressure (for gaseous systems like the Haber Process). It is important in industry to have a high rate of production due to economic considerations. The kinetic theory of gases predicts that the rate of a reaction increases when more successful collisions occur in the shortest time. High temperatures favour an increase in reaction rate as the molecules have higher kinetic energy and can overcome the activation energy barrier. As such, the rate of reaction of the Haber Process is increased by higher temperatures. However the yield from the Haber Process is adversely affected by increased temperatures. The forward reaction is exothermic and as both reactions reach equilibrium after a time, Le Chatelier’s Principle comes into effect. The equilibrium shifts to oppose the change. Thus, if the temperature is increased the equilibrium position shifts to counteract the change, by reducing the latent heat by favouring the endothermic reaction. As such, the backwards reaction is preferred and yield is reduced.

explain that the use of a catalyst will lower the

Recall from previous studies that a catalyst suitable for a reaction will lower the activation energy required for a reaction, by providing an alternative pathway for

reaction temperature required and identify the catalyst(s) used in the Haber process

the reaction to proceed.

Note that, in a reversible reaction, the catalyst speeds both forward and backward reaction rates equally such that the equilibrium position is not changed, not affecting yields. However, the time taken to reach this equilibrium position is less as reaction rates are faster. As such, the temperature required to attain a high reaction rate is less, allowing the equilibrium to favour the products and hence increase profit, whereas using a temperature to attain an equivalent rate of reaction would reduce in a much lower yield. The catalyst used in the Haber Process is a mix of metals and oxides. Magnetite (Fe3O4) is fused with potassium, aluminium and calcium oxides (K2O, Al2O3, CaO) such that the magnetite is reduced to porous iron. It becomes finely ground, with large surface area, to increase the available surface of reaction. The gaseous nitrogen and hydrogen molecules are adsorbed on to the solid catalyst surface and rearrange forming the ammonia molecules.

analyse the impact of increased pressure on the system involved in the Haber process

Pressure is beneficial to both “wants” in the Haber Process. High gas pressure favours the frequency of successful molecular collisions. Essentially, the same number of molecules is in a smaller space, thus having a higher concentration.

Recall that kinetically the rate of reaction is given by the concentration. For example, for the Haber Process:

Thus, the forward rate of reaction is increased by increasing pressure. The backward reaction similarly increases, but to a lesser extent. Pressure is also important in shifting the equilibrium position of the mixture. The equilibrium shifts in order to counteract the change that caused it (Le Chatelier’s principle). By increasing the pressure we shift the equilibrium in favour of the reaction which produces less moles of gas. This is the forward reaction, favouring the production of ammonia. Thus, by increasing pressure we increase the amount of ammonia in the equilibrium mixture.

Pressure (atm) 100 300 600 1000 Yield (% v/v) 25 47 66 80

explain why the Haber process is based on a delicate balancing act involving reaction energy, reaction rate and equilibrium

In The Haber process we aim to maximise yield and reaction rate, and minimise cost in order to gain maximum profit. However, some of these concerns naturally conflict with one another. A delicate balance between all these conditions are required to achieve the most profitable yield for the least cost. Cost Reaction Rate Yield Pressure Low Pressure High Pressure High Pressure Temperature Low Temperature High Temperature Low Temperature

Thus compromise conditions are required, which balance energy, reaction rate and equilibrium (yield). The set of conditions which are commonly used vary, but there are typical ranges. However, the higher the reaction rate and the

higher the yield the cost is offset more. Reactants: N2 and H2 are kept in the ratio 1:3 in order to maximise yield per either reactant, irregardless of Le Chatelier’s principle as excess amounts of one reaction leads to more product but less efficiency. Pressure: 15-35 MPa (usually from 20 to 25MPa). Although equilibrium factors suggests that pressure should be as high as possible, economic and safety factors prevent this, to ensure the reaction vessel has a longer lifetime. Temperature: from 400o to 550o C. Equilibrium and kinetic factors are in conflict, as discussed above. This is the main compromise condition, and it is chosen to have a decent rate of reaction while retaining reasonable yield. Catalyst: Iron oxide (magnetite, Fe3O4), fused with other metal oxides (potassium, aluminium, calcium). The porous catalyst has a high surface area in order to provide a large surface for the reaction to occur upon. Obviously this increases the rate of reaction. The ammonia yield is around 15 to 20% each cycle. After each cycle ammonia is liquefied under pressure (while N2 and H2 remain gaseous) and is removed from the equilibrium. This shifts the reaction to the products further when the N2 and H2 are re-injected into the reaction chamber. After 5 to 6 cycles about 98% of the reactants are converted into ammonia.

explain why monitoring of the reaction vessel used in the Haber process is crucial and discuss the monitoring required

Industrial chemists and chemical engineers employed in the manufacturing of ammonia need to perform a range of monitoring activities to ensure quality control. These include: • Continuous monitoring of the high pressure reaction vessel, ensuring that the

production of ammonia occurs under safe conditions (i.e. pressure not too high) and yield is not compromised (i.e. pressure is too low). Pressure data from various sensors is monitored electronically.

• Monitoring of temperature, to ensure that it stays in the optimum range. If the temperature is too high then ammonia yield is reduced. Temperature data is similarly measured and monitored centrally from various temperature sensors.

• Monitoring the furnaces which produce the hydrogen and nitrogen feedstocks, which must be made in the correct ratios and kept free from contamination. Carbon oxide sensors send information about the gas stream to a central monitoring computer.

• Monitoring the catalyst, as the particle size needs to be monitored to ensure it has a high surface area. The catalyst lasts about 5-10 years.

• Monitoring the ammonia liquefaction process during each cycle to ensure optimal yield.

Research chemists in the ammonia industry continue to identify new catalyst and production line efficiencies. As most ammonia is used in the fertiliser industry and the manufacture of explosives, there is an ever-increasing demand for this product.

* 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

The Haber process was created at a crucial time. At the beginning of the twentieth century, there was a shortage of naturally occurring nitrogen sources, especially ammonia and nitrates. With world populations growing, the demand for food increased, putting pressure on natural nitrate sources such as manure. The demand for nitrogen compounds for making nitric acid in the chemical industry grew around the same time, as Germany was about to enter WWI. Nitric acid was used to make explosives such as TNT and dynamite, amongst others, to fuel the war. Natural reserves of nitrates such as Peruvian guano, obtained from sea-bird droppings, and Chilean sodium nitrate dwindled. Germany was highly dependant on overseas supplies of nitrate salts for agriculture and manufacture of explosives. The allied blockade of Chilean saltpetre did not even nearly meet the very high demand for ammonium nitrate, used for explosives. It was known that the atmosphere contains large quantities of diatomic nitrogen. It would be advantageous to convert this readily available gas to usable compounds for agriculture and industry, cheaply and on a large scale. Fritz Haber had studied under Robert Bunsen, in Germany, and was interested in the effect of heat on the chemistry of gases. In the early 1900s, Haber reacted nitrogen with hydrogen, using an iron catalyst, to form ammonia. Ammonia can be readily converted to a range of valuable products. In 1908 he had improved

the reaction and in 1911 he was rewarded with a directorship at a German institute. In 1914, Carl Bosch developed the chemical engineering necessary for the large-scale production of ammonia by the Haber-Bosch process. The industrial synthesis of ammonia facilitated the manufacture of fertilisers for continued food production, and nitric acid, an essential component in the manufacture of explosives and other ammunition. It has been suggested that without this process, Germany would almost certainly have run out of explosives and fertiliser for food by 1916, thereby ending the war. The Haber process now produces 100 million tons of nitrogen fertilizer per year, mostly in the form of anhydrous ammonia, ammonium nitrate, and urea. That fertilizer is responsible for sustaining one-third of the Earth's population, as well as various deleterious environmental consequences.

3. deduce the ions present in a sample from the results of tests

There are many ways to detect whether a certain ion is present or not in a sample. However, in order to distinguish between certain ions certain tests are required, as with some reagents, different ions react to give similar results. There is a sequence of steps known as the elimination process which we can use to determine the unknown species in a solution, and should be performed in order. However, we require solutions of at least 0.1M, with 1-2mL samples of each to achieve accurate results. If the unknown solution contains more than one anion or cation, the first one must be eliminated using the sequence (in order) and so on. For example, the ion is removed via precipitation and filtration, then subsequent tests are performed. Anions:

Carbonate, Chloride, Phosphate, Sulfate: CO3

2-, Cl-, PO43-, SO4

2- These can be distinguished from simple qualitative tests such as precipitation and gas evolution (first row). However, additional confirmation tests are required in a solution of these ions (second row). Anion Procedure Observation/Confirmation

Add 2M HNO3 dropwise into original solution

Effervescence of colourless CO2 gas, confirmed with lime water

CO32-

Test pH of original solution with universal indicator or otherwise

Solution has pH around 8 to 11 as carbonate is basic

Acidify with HNO3 to remove CO3

2- and add Ba2+ (Ba(NO3)2) White ppte of BaSO4 forms SO4

2-

Add Pb2+ (Pb(NO3)2) to acidified solution

White ppte of PbSO4 forms

Cl- Acidify with HNO3 to remove White ppte of AgCl forms, which

CO32- and add Ag+ (AgNO3) decolourises in sunlight

Add 1-2mL of 10% NH3 solution to the suspension and heat in water bath

AgCl ppte dissolves to form colourless Ag(NH3)2

+ complex

Make solution alkaline (pH=~10) with NH3 drops. Add Ba2+ (Ba(NO3)2)

White ppte of Ba3(PO4)2 forms in alkaline solution

Add ammonium molybdate to acidified unknown solution, then warm mixture gently

Yellow ppte of ammonium phosphomolybdate forms (NH4)3PO4.12MoO3.3H2O

PO43-

Acidify with 5M H2SO4 then add ammonium molybdate and ascorbic acid, heating to 90oC in water bath

Blue complex (molybdenum blue) forms. The more concentrated the solution, the more intense the blue

Cations:

Lead, Barium, Calcium, Copper, Iron: Pb2+, Ba2+, Ca2+, Cu2+, Fe2+, Fe3+ There are similar techniques of identifying ions via solution reactions as similar to anions above. Cations Procedure Observation/Confirmation

Add 5 drops of dil HCl to unknown solution

A faint white ppte of PbCl2 appears. It is soluble in hot water but slightly soluble in cold water

Pb2+

To original solution add dilute NaI dropwise

A yellow ppte confirms Pb2+ is present

To a fresh sample of solution, add 5-10mL of 1M H2SO4

A white ppte of either CaSO4 or BaSO4 can form – however, if too dilute CaSO4 may not form

To a fresh sample add NaF dropwise

A white ppte indicates CaF2 is present but not Ba2+

Ba2+ Ca2+

Use the original solution to conduct a flame test

Brick red: calcium Yellow-green: barium

Add 1M NaOH dropwise. Once ppte forms, add NH3(aq)

Blue ppte of Cu(OH)2 forms, which dissolves in excess ammonia to form a copper complex ion Cu(NH3)4

2+

Cu2+

Flame test with original Green flame indicates Cu2+ Fe2+ To a fresh sample add NaOH Brown ppte Fe(OH)3 indicates

Fe3+ Green/white ppte Fe(OH)2 indicates Fe2+

Acidify original solutions with 4M HCl, then remove two drops of each to a white tile

Add potassium hexacyanoferrate (III)

Dark blue colour indicates Fe2+, in Fe3(Fe(CN)6)2

Fe3+

Add potassium thiocyanate Blood red colour indicates Fe3+, in FeSCN2+

Flame tests are a simple way to identify some of these cations. Flame tests apply the principle of electron shell structure and electron excitations. When sufficient energy (here, heat from a Bunsen burner) is supplied to a metal ion, electron become excited and jump shells. When they fall back ‘down’, they release the potential energy they gained as light, causing distinctive colours. The procedure to qualitatively verify the presence of metal ions is covered in the practical section.

Cation Flame Colour Calcium Brick Red Barium Yellow-green (apple) Copper Green

* *

perform first-hand investigations to carry out a range of tests, including flame tests, to identify the following ions: • phosphate • calcium • sulfate • lead • carbonate • copper • chloride • iron • barium

• See Attachments • See Prac Book

gather, process and present information to describe and explain evidence for the need to monitor levels of one of the above ions (lead) in substances used in society

Lead is a toxic, heavy metal that must be continually monitored in society as it has severe impact upon human health, even at low concentrations. Its accumulation in air was caused by the practice of lead addition to petrol, causing it to accumulate in soils. The main sources of poisoning are from ingestion of lead contaminated soil (this is less of a problem in countries that no longer have leaded petrol) and from ingestion of lead dust or chips from deteriorating lead-based paints. This is particularly a problem in older houses where the sweet-tasting lead paint is likely to chip, but deteriorating lead-based paint can also powder and be inhaled. Lead has also been found in drinking water. It can come from plumbing and fixtures that are either made of lead or have trace amounts of lead in them. Lead can also be found in some imported cosmetics and toys. Lead poisoning occurs with the accumulation of large numbers of lead ions, and is difficult to extract. • The symptoms of chronic lead poisoning include neurological problems, such

as reduced cognitive abilities, or nausea, abdominal pain, irritability, insomnia, metal taste in oral cavity, excess lethargy or hyperactivity, headache and, in extreme cases, seizure and coma.

• It may cause damage to all areas of the body especially the brain, kidneys, and reproductive system by disrupting enzyme function. Constipation, diarrhea, vomiting, poor appetite, and weight loss are common in acute poisoning.

• Lead inhibits the formation of haemoglobin in blood, causing anaemia and reducing the ability of the blood to carry oxygen.

• It can cause neurological damage in the brain, especially in children as they absorb lead more easily than adults. This retards intellectual development, behaviour, size and hearing of children.

• Pregnant women are at risk of experiencing miscarriages and childbirth. The toxicity of lead comes from its ability to mimic other biologically important

metals, most notably calcium, iron and zinc which act in many enzymatic reactions. Lead is able to bind to and interact with many of the same enzymes as these metals but, due to its differing chemistry, does not properly function, thus interfering with the enzyme's ability to catalyze its normal reaction(s). The health and environmental destruction of lead thus makes it very necessary and important to monitor lead ion levels in our atmosphere, water, food and soil. The IATL utilizes AAS in measuring the lead concentrations of paint (mg/kg. mg/cm2, ppm), water (ug/L, ppb), and soils (mg/kg or ug/ft2 as dust), reported as noted. Surface lead is conducted with wipe samples and AAS, reported as µg/m2. Lead in air is conducted via NIOSH 7082 protocols with AAS in the lab, measured in µg/m3. K-fluorescent X-ray metering can measure bone-lead. Portable X-ray fluorescence (XRF) equipment can be used to measure lead concentrations and exposures in the field, from lead paint, children's toys, etc. Simple inexpensive test kits are available, which show color changes based on chemical reactions, but they are inexact.

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 is a technique used to accurately measure the concentration of metal ions in solution, especially if these ions are in such low concentrations that typical techniques such as gravimetric (precipitation) analysis fail. It applies the principle of atom absorbance spectra. This is the spectrum of wavelength left over once electrons in the ions absorb certain wavelengths, from white light transmitted through a sample. They correspond to the bright wavelengths in atomic emission spectra. In general, a white light passing through a gas will create absorption spectra.

The atomic absorption spectrometer was developed by Alan Walsh (CSIRO scientist) using this, applying this technique to metal ions, to measure their concentrations. The technique is very sensitive and can measure concentrations up to ppb.

A cathode lamp with carefully selected monochromatic light creates a ray, passing through an atomised sample, aspirated in a flame. It passes through a monochromator, and along the way some of the ray is absorbed in electron transitions. After passing through a monochromator, the intensity of the resultant ray is measured. Many standards are tested this way to make a calibration curve. As such, an unknown can be tested and interpolated on a curve to give very accurate results. AAS has had a great impact upon our understanding of trace elements, such as copper, zinc, cobalt and molybdenum. These trace elements are absorbed by human beings and animals through food, and a lack may cause deficiency diseases. The existence of these trace elements was not known until AAS was developed, due to their very low concentrations (undetectable by traditional volumetric or gravimetric analysis). There were also problems associated with interference from other ions in the sample. Using AAS, however, scientists can quickly and reliably establish which trace elements are present and which are required for specific biochemical pathways and functioning of the body. Prior to these developments, deficiency diseases could not be explained. However, some essential roles have been discovered: • Cobalt is an essential element of vitamin B12. It is vital for the production of

haemoglobin and for ruminants. It plays a role in resiting parasites and infection. Deficiencies cause pining in livestock and loss of appetite.

• Iron is required for the production and functioning of haemoglobin in blood. • Zinc is required for amino acid production metabolism and energy production.

It is also associated with insulin production, development of immune cells and regulation of bone calcification.

• Iodine is required for proper functioning of the thyroid gland. Deficiencies of these trace elements in soils or animal diets resulted in significant health problems. AAS analysis of blood or urine samples, or soil samples, can be used to determine whether trace elements are deficient. Trace elements can be added as necessary (dietary supplements or in fertilisers).

* gather, process and present information to interpret secondary data from AAS measurements and evaluate the effectiveness of this in pollution control

AAS is a technique that can be used to detect the presence of metal ions, including heavy metals such as lead, mercury and cadmium. Gravimetric or volumetric techniques are not suitable as they are insufficiently sensitive to detect low levels of metal pollutants. AAS is an automated procedure that is easy to use and provides rapid results. In order for an instrumental method to be useful in monitoring metals for pollution control, it must satisfy the following requirements: • Cost effective • Scientifically valid • High sensitivity • Easy to use and readily available AAS meets all these requirements. AAS allows for the detection of very small concentrations (ppm) form samples of air, water or food. A calibration graph can be drawn from the absorbance values obtained using solutions of known concentrations. AAS is widely used to monitor small concentrations of metals in the environment, particularly: Small concentration of toxic heavy metals such as lead, mercury and cadmium as they are highly toxic to animal life. As it is introduced into the food chain, it accumulates and becomes more concentrated at each stage. • Mercury levels in fish • Copper and aluminium in waterways • Zinc in oysters • Lead fallout beside highways Therefore, AAS is extremely effective in pollution control as it enables us to detect small concentrations of pollutants in our environment, which could not be previously detected, giving us a broadened understanding of the state of our environment and ensuring the health and safety of the public.

* identify data, plan, select • See Attachments

* equipment and perform firsthand investigations to measure the sulfate content of lawn fertiliser and explain the chemistry involved

• See Prac Book

* analyse information to evaluate the reliability of the results of the above investigation and to propose solutions to problems encountered in the procedure

In first-hand practical investigations the term ‘reliability’ has become synonymous with ‘reproducibility’. Reproducibility is the better term. The results of your experiment are reliable only if repeated measurements by you and other students give the same values (or a very narrow range of values) within the limits of the experimental design. Minimising experimental errors helps to ensure experimental reliability. It is quite common to repeat experiments five or more times to improve reliability. Keeping other variables under control and making accurate measurements are also essential to achieve reliability. The class was divided into groups of three to determine quantitatively the sulfate content of pure ammonium sulfate fertiliser. Even though each group of three performed the experiment only once, the splitting up of groups added inherent repetition. Results were similar enough within the limits of experimental design, even if they were inaccurate (compared to ‘real’ values). Thus, though the experiment is inaccurate (hence low validity) it is reliable enough. With improvements, however, it can become more valid and accurate. The possible problems, encountered in the procedure (and proposed solutions) were:

Problem Proposed Solution Weighing – some mass may be unaccounted for due to errors in collection and weighing (balance also measures up to 0.01g increments only)

Filter paper should be dried in an oven instead of by air, as moisture could still be present and contaminants added.

Incomplete Precipitation – BaSO4 forms in an equilibrium and thus production of precipitate may not reach equilibrium

Excess BaCl2 is added to shift equilibrium to the right, but not much else can be done

Presence of contaminant ions – phosphate and carbonates present may react with barium to form excess precipitate

Addition of HCl dissolves these precipitates

Small size of precipitate crystals – BaSO4 forms very fine crystals, which easily goes through normal filter paper, and even sintered glass crucibles.

Heating the solution (before adding BaCl2) caused crystals to become slightly larger. Addition of agar also causes crystals to coagulate.

Addition of Agar – may add excess mass

Not significant.

Contaminated Precipitate – unreacted ions (Ba2+, SO4

2-, NH4+)

which remain in the precipitate in the filter paper

Wash precipitate with demin water before drying and weighing

4. describe the composition

and layered structure of the atmosphere

The atmosphere is a thin gaseous layer that surrounds the Earth. There is no definite end, as it slowly becomes thinner and fades into space. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation and reducing temperature extremes between day and night. It is divided into layers, which are characterized by changes in the temperature gradient. Layer Range Description Troposphere 0-15 km The layer closest to the ground, it contains

75% of the air. Gases are well mixed. Stratosphere 15-50 km We find the ozone layer here. There is very

little mixing (pollutants last long). First two layers contain 99.9% of the Earth’s air.

Mesosphere 50-85 km Zone is very cold, due to sparse particles. Thermosphere 85+ km Very high frequency radiation is absorbed here,

(and above) leading to high temperatures. Higher sections are ionised and used for radio transmissions.

The atmosphere contains roughly (by molar volume)

• 78.08% nitrogen • 20.95% oxygen • 0.93% argon • 0.035% carbon dioxide • trace amounts of other gases • a variable amount (average around 1%) of water vapor For most gases the concentrations are best expressed as ppm, due to their low values.

identify the main pollutants found in the lower atmosphere and their sources

Pollutant Sources Description CO2 Fossil fuel burning Creates greenhouse effect (global

warming) CO Road traffic emission

(90%), bushfire (rest) Irritant to respiratory system (binds to haemoglobin and prevents oxygen absorption). It is removed naturally by soil organisms.

NOx Road traffic Nitrogen and oxygen reaction near spark to form NO, which reacts to form NO2. These produce photochemical smog and ozone, and nitric acid rain.

Ozone NOx by-product Oxidises very strongly, irritates eyes, poisonous above 20ppm.

SO2 Combustion of contaminated fuel,

It is an irritating, poisonous gas. Further discussed in Acid Rain topic.

volcanoes, bacteria Organics Exhaust of vehicles,

petroleum refining Benzene and 1,3-butadiene are carcinogenic and irritant to lungs.

describe the formation of a coordinate covalent bond

demonstrate the formation of coordinate covalent bonds using Lewis electron dot structures

• Skill A coordinate covalent bond is a bond in which the bonding pair of electrons is wholly donated by only one of the bonding atoms. It is formed when an electropositive atom nears an atom with a free electron pair. For example, a highly charged hydrogen ion can force a coordinate covalent bond when it nears the lone pair of NH3 to form NH4

+ or H2O to form H3O+.

Carbon monoxide and ozone also contain coordinate covalent bonds.

Once a coordinate covalent bond forms it is identical to a normal covalent bond.

compare the properties of the oxygen allotropes O2 and O3 and account for them on the basis of molecular structure and bonding

compare the properties of the gaseous forms of oxygen and the oxygen free radical

Dioxygen and Ozone are both allotropes of the same elements (oxygen), being different forms of the same element in the same state. The oxygen radical is a single, unbonded, neutral oxygen atom. They have differing properties, which can be explained by their molecular structures and bonding. Dioxygen: Dioxygen is the form of oxygen with which we are most familiar, O2. It consists of two oxygen atoms linked by a double covalent bond, which is very strong. Oxygen Radical: The oxygen radical is a single atom of oxygen, usually formed when oxygen is split (by UV radiation). There are two free radical electrons in a non-ground state, making these very reactive. Thus, they often react with other species (other radicals or molecules) very quickly, upon formation. It is often represented by O•. Ozone: Ozone consists of three oxygen atoms bonded together with a coordinate covalent bond, to form a resonance structure. It is a bent molecule and a very powerful oxidising agent due to its reactivity (each bond is weaker than oxygen’s, so oxygen radicals easily split off). Oxygen Radical Dioxygen Ozone Identity O O2 O3 Molecular Diagram

gas N/A Colourless Pale Blue liquid N/A Pale Blue Deep Blue

Colour

solid N/A Pale Blue Black-Violet Boiling Point N/A -183 oC -111 oC Melting Point N/A -219 oC -193 oC Density N/A ~Air ~1.5 Air Water Solubility N/A Sparingly Slight Bond Energy N/A 498kJ/mol 445kJ/mol Reactivity Very High Moderately High High Uses N/A Combustion,

rocket fuel, life support

Bleaching agent, disinfectant

We can explain some of these properties based upon the chemical structure and bonding: Melting/Boiling Points: Ozone has a higher molecular mass than oxygen, so it has more dispersion forces between them. It is also slightly polar, due to the bent structure and coordinate covalent bond. Thus, the strength of the intermolecular forces is greater, meaning its melting and boiling points are greater. Solubility: Ozone is slightly polar and hence dissolved more easily in water. Reactivity/Stability/Oxidation ability: As above, the oxygen radical is the most reactive due to unpaired electrons. Ozone has a less strong bond than oxygen, and is thus the next reactive. Oxygen, out of the three, is relatively least reactive.

describe ozone as a molecule able to act both as an upper atmosphere UV radiation shield and a lower atmosphere pollutant

Ozone is a lower atmosphere pollutant, as it is a toxic gas. It is a strong oxidant and attacks organic tissues easily, disrupting normal biochemical reactions in the body. It also readily attacks rubber and plastics, and is a respiratory irritant. It is formed as a by-product of sunlight on NOx and hydrocarbons. Ozone in the upper atmosphere, however, is beneficial to humans. In the stratosphere as it absorbs harmful UV-B and -C radiation. It exists in a very thin layer and is formed by the action of UV upon oxygen.

identify the origins of chlorofluorocarbons (CFCs) and halons in the atmosphere

* 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

discuss the problems associated with the use of CFCs and assess the effectiveness of steps taken to alleviate these problems

Halons and CFCs were used initially due to their beneficial properties. CFCs were developed to replace ammonia as refrigerant gas. They were unreactive and non-toxic and readily liquefied. They found used in refrigerant gases, propellants, blowing agents and solvents. They contain only carbon, fluorine and chlorine atoms only (at least one of each, and all single bonds) Halons were developed for fire extinguishing, especially for museums, aeroplanes and computer systems. They contain carbon, bromine and fluorine and many contain chlorine atoms (no hydrogen, all single bonds). In the lower atmosphere CFCs are very stable. This allows them to stay and, over time, diffuse into the stratosphere. Here, stronger UV radiation splits the molecule apart

CF3Cl(g) CF3(g) + Cl(g) This forms a chlorine radical, which is of major concern as it attacks the ozone in the stratosphere.

Cl(g) + O3(g) ClO(g) + O2(g) ClO(g) + O(g) O2(g) + Cl(g)

Thus, overall, we see that ozone is destroyed and the Cl radical regenerated, to destroy more ozone. One radical can destroy thousands of ozone before being removed by other means. Halons are even more deadly as they release bromine radicals, which are many times more deadly than chlorine. The use of CFCs and halons is thus harmful to the ozone layer. Scientists discovered in the 1970s the depletion of the ozone layer and its cause, prompting global concern. Thus, measures were taken to alleviate these problems. The Montreal Protocol was the result of worldwide determination to eradicate the threat to the ozone layer and allow its recovery. It required the phasing out of ozone-harming chemicals (CFCs, halons, CCl4) according to a timetable. Subsequent meetings and amendments tightened the schedule and provided support for less able nations to phase them out too. It prompted the

development of replacement compounds such as HCFCs and HFCs to replace CFCs, and has been effective overall. Indeed, we can quote “perhaps the sinle most successful agreement to date has been the Montreal Protocol,” signifying its effectiveness.

analyse the information available that indicates changes in atmospheric ozone concentrations, describe the changes observed and explain how this information was obtained

Ground-based instruments include UV spectrophotometers. They measure the intensity of light received from the sun at a wavelength at which ozone absorbs and then at wavelengths on either side of this range at which ozone does not absorb. A comparison of these intensities gives a measure of the total ozone in the atmosphere per unit area of Earth surface at that location. The Dobson ozone spectrophotometer is used to measure ozone layer thickness by measuring how much UV radiation reaches the ground. Ozone layer thickness is measured in Dobson Units (DU). Total Ozone mapping spectrophotometers (TOMS) have been used on NASA satellites for the past 20 years in order to observe changes in ozone concentration around the globe. These instruments used the same principle as ground-based spectrophotometers, but they are able to provide for much larger scale operations as they orbit the Earth. They can effectively scan through the atmosphere using spectrophotometers pointed down towards the Earth which receive information regarding the ozone concentration as a function of altitude and geographic position. This is because the concentration of ozone depends largely upon its altitude in the atmosphere. Its geographical position can determine when depletion is at its greatest, for example, depletion of ozone in the southern hemisphere, particularly in the Antarctic region, is greatest during spring where there is enough sun (UV) but not too much heat. Helium balloons can also carry spectrophotometers into the stratosphere to measure concentrations of various substances including ozone as a function of altitude. Ozone sondes are balloon-borne instruments that continuously estimate ozone concentration as they ascend into the atmosphere. A profile of ozone is obtained up to the burst point of the balloon - typically in excess of 30 km. In general, the concentration of ozone has decreased over the past thirty years.

In 1976, the British Antarctic Survey at Halley Bay noted a 10% drop in ozone levels in the stratosphere over Antarctica in the southern spring (August to October). This was unusual as levels had remained roughly constant since measurements had begun in 1957. These scientists made their measurements using ground-based Dobson UV spectrophotometers as well as on air samples collected by high-altitude balloons and aircraft. Even though they initially though their equipment was malfunctioning, in 1983 they became concerned due to observed record losses of ozone that spring. By 1985, atmospheric measurements over Antarctica showed a 50% reduction in ozone concentrations in the stratosphere over the previous decade. It was

discovered that starting from the 1970s, CFCs were slowly destroying the ozone layer in the stratosphere. Ozone depletion is localised and seasonal (over the Antarctic in spring) because winter in the Antarctic is a period of continuous darkness and the stratosphere at this location is extremely cold. Under these extremely cold conditions certain solid particles form that are able to catalyse a reaction between hydrogen chloride and chlorine nitrate.

HCl + ClONO2 Cl2 + HNO3 This conversion of hydrogen chloride and chlorine nitrate to molecular chlorine has no effect on ozone concentrations during winter. However, when the sun comes up early in spring, sunlight splits the chlorine molecules into two separate chlorine atoms and these atoms proceed to destroy ozone molecules.

Cl2 2Cl Thus, in spring, there is an extra source of chlorine atoms and so increased destruction of ozone. Springtime Artic ozone holes also occur, although they are less severe than their Antarctic counterparts as the Arctic stratosphere is generally warmer than their Antarctic counterparts.

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

As part of the process of phasing out ozone-destroying chemicals, chemists looked for short-term replacement compounds for CFCs and halons. HCFCs (hydrochloroflurocarbons) contain CH bonds which are susceptible to attack by reactive radicals and atoms in the troposphere. Hence only a small proportion of HCFCs reach the stratosphere. Consequently, their ODP is lower than that of CFCs, around 0.02 to 0.06 (around 10% of that of CFCs). As such, they are a temporary substitute and are expected to be phased out by 2030. An example is HCFC-123 (CF3CHCl3) which is used to produce plastic foam. HFCs (hydrofluorocarbons) decompose in the troposphere and contain no chlorine – hence, their ozone depletion capacity is zero. They thus can be used without fear for ozone depletion, and are a possible permanent substitute. HFCs are now widely used as replacements for CFCs. The most commonly used HFC is HFC-134a (CF3CFH2 or 1,1,1,2-tetrafluoroethane) and it is used in refrigeration and air conditioning. However, HFCs are more expensive and less efficient than CFCs. They are also highly damaging greenhouse gases, up to 12500 times more so than CO2. There is talk of banning HFC-134a and related substances for personal use, due to such climate change issues. As such, neither alternative class of chemicals for ozone replacement has been totally successful.

identify and name examples of isomers (excluding geometrical and optical) of haloalkanes up to eight carbon atoms

* gather, process and present information from secondary sources including simulations, molecular model kits or pictorial representations to model isomers of haloalkanes

• Skill Isomers are compounds with the same molecular formula but different structural formulae. Isomers do not necessarily share similar properties unless they also have the same functional groups. Some examples of haloalkane isomers are:

2-chloropropane 1-chloropropane

1,1-dibromo-1,2-dichloro-2,2difluoroethane

1,1-dibromo-2,2-dichloro-1,2difluoroethane 1,2-dibromo-1,2-dichloro-1,2difluoroethane

4-bromo-1,1,1-trichloro-2,4-diflurobutane 2-bromo-1,2,4-trichloro-3,4-diflurobutane

1-bromo-2,3,4-trichloro-1,4-diflurobutane

5. identify that water quality can be determined by considering: • concentrations of

common ions • total dissolved solids • hardness • turbidity • acidity • dissolved oxygen • biochemical oxygen

demand

The quality of water is determined by several factors, listed in the syllabus point on the left. Analytical and environmental chemists carry out a variety of qualitative and quantitative tests in order to determine the quality of water in our rivers and dams. Water quality can be determined via a combination of factors, in order to determine whether it is potable or not. Some typical values for fresh water are below. Note any value in the 2nd column would classify the water as polluted. Sea water differs from fresh water as TDS is much higher due to salts and pH is slightly greater than. Other properties remain similar.

Property Typical Clean Water Polluted Water Turbidity (NTU) <3 >20 TDS (mg/L) <100 >1000 (fresh water) pH 6.5 to 8.5 <6 or >9 DO (mg/L) 7-9 <4 BOD (mg/L) <5 >10 total Phosphate (mg/L)

<0.03 >0.05 for lakes/dams >0.1 for rivers/streams

Nitrate (mg/L) <0.1 >0.50 Faecal Coliforms (CFU/100mL)

<5 >200

Concentration of common ions: Potable water, in general, will have low ions concentration (otherwise it will taste salty). Sea water has, in general, very high concentrations.

Ion Concentration (Sydney Water Supply) (ppm)

Recommended Maximum (ppm)

Chloride 20 400 Sulfate 8 400 Nitrate 0.4 10 Fluoride 1 1.7 Sodium 10 300 Calcium 9 200 Aluminium 0.2 0.2

These are traditionally measured by “wet” methods, involving gravimetric or volumetric analysis and thus prone to errors. In modern times, instrumental techniques such as ion-selective electrodes, AAS and chromatography has superseded “wet” techniques due to superior accuracy. Total dissolved solids: TDS is the total mass of solids dissolved in unit volume of water, reported generally as mg/L or ppm. Potable water should have less than 500ppm. The amount of TDS can be found by evaporation (after filtration) thought it is liable to high inaccuracies due to experiment technique, such as ‘spitting.’ However, as TDS is composed almost entirely of ionic salts, measuring the electrical conductivity gives field scientists a quick method. Hardness: Water is hard if it has a high concentration of Ca or Mg ions, which forms a grey scum precipitate with soap. As such, limestone rocks are generally associated with hard water (as these ions leach out from their carbonate compounds).

Hardness Class soft moderate hard very saline Hardness (ppm) <60 61-120 121-180 181-500 >500

Hardness can be tested qualitatively (shaken in test tube) or quantitatively (analysis of [Ca2+] and [Mg2+] by EDTA titration or AAS). Turbidity: Turbidity in water means cloudiness or lack of transparency. It is caused by suspended solids. It not only gives water an undesirable appearance but also an undesirable taste. Turbidity gives a measure of the amount of suspended solids present. While filtering off suspended solids and determining their mass may work on fairly dirty water, it is not practical on drinking water due to minuscule particulates, with too little mass. It can be assessed via a turbidity tube (long measuring cylinder with marks on the bottom) or a secchi disk. Turbidity is caused by, heavy rains or floods, causing run-off across plant vegetation, picking up suspended matter such as soils and stirring up sediment. These processes are greatly accelerated by human intervention, such as land-clearing and ploughing, which loosen soils.

Acidity: The pH of a water sample is measured by indicator solutions, papers or a pH meter. A pH outside the range of 6.5-8.5 indicates a source of pollution, such as fertiliser run-off, industrial waste, or acid drainage from a mine site, or sulfide contamination (forming sulfuric acid). Dissolved Oxygen: High levels of DO are required for high water quality, as aquatic life required it for respiration.

Quality Healthy Moderately Polluted

Severely Polluted

Dead

DO (ppm), 25oC 6-8 4-6 2-4 <1 To increase the DO, we can increase surface area, or agitate the water. Aquatic plants also increase DO by photosynthesis. DO can be measured in several ways. A potentiometric or polarographic oxygen probe is quickest and simples. Winkler titration is a volumetric technique involving a series of steps. • The first step involves the quantitative reaction between dissolved oxygen

and Mn2+ ions in solution • In the second step, acidified KI and molecular iodine is generated • The amount of iodine generated us determined in the final step by iodometric

titration with standard sodium thiosulfate with starch indicator. Note the analysis requires water free of sediment and air bubble (sample taken underwater). The temperature is also important. Biochemical Oxygen Demand: The BOD is the amount of DO required by organic matter (particularly decomposers of dead waste) in a water sample. Bodies with large amounts of organic matter usually become quickly deficient in DO due to action of aerobic bacteria. This drop in DO seriously affects aquatic life. Chemists measure the BOD by the 5-day BOD test; a sample’s DO is measured at the beginning and end of a 5-day test period. 5 days is usually sufficient for natural organic waste to be decomposed in non-polluted waterways.

BOD5 = DO0 – DO5 Water System BOD (ppm) unpolluted water 1-3 polluted water >5 domestic, untreated sewerage 350 abattoir effluent 2600 effluent from paper pulp factory 25000

In more polluted waterways we need to dilute the solution before measuring, or re-aeration every few days as appropriate, as they quickly run out of the required DO.

identify factors that affect the concentrations of a range of ions in solution in natural bodies of water such as rivers and oceans

The natural concentration of ions in water bodies is easily disturbed by a large number of factors, natural and artificial. This is of concern due to the salinity adversely affecting the outback. It is linked to poor land and water management, as contamination occurs. Some factors which affect the concentration are: Factor Effect agriculture Farmers usually fertilise their soils to grow crops.

Rainwater carries some of this fertiliser from the soil into water bodies, increasing the concentration of NO3

-, NH4

+, and PO43-. Leeching of animal faeces from

grazing properties similarly leads to increased nitrogen and phosphorus concentration in waterways.

industrial effluent Various industries discharge diluted waste into rivers, which may contain ions, leading to possible heavy metal contamination.

pH of rain water The more acidic the rain or ground water, the more minerals that will be dissolved. These find their way to rivers and lakes and eventually raise the concentration of certain ions (e.g. NH4

+). heavy rain/flooding The concentrations of ions in the water will temporarily

decrease due to the large input of fresh water from sustained heavy rain. The frequency of heavy rain and

flooding influences the ion levels in waterways. leaching of rocks and soils

Ground water may remain in contact with minerals in the ground for a long time, causing them to dissolve. This ground water may find their way to water bodies.

differing solubilities of rock and soil minerals

Some minerals dissolve in water more readily, such as SO4

2- and Cl- compounds versus silicates or O2- compounds. Limestone is readily leached, increasing Ca2+ and HCO3

- ions. water temperature Minerals dissolve faster at higher temperatures. rate of evaporation In hot climates the water evaporates faster and

increases the concentration of ions. aquatic organisms Marine organism activity changes the balance of ions in

water, especially calcium and carbonate ions used in shelled invertebrate exoskeletons.

describe the design and composition of microscopic membrane filters and explain how they purify contaminated water

Microscopic membrane filters are a thin film of synthetic polymer through which pores filter out unwanted particles. The smaller the pores, the more particles and impurities it is able to remove and the more expensive it is. They are an alternative to large scale chemical treatments of water to remove harmful micro-organisms with the added advantages of being able to remove molecules of carbon compounds. They use gravity, vacuum or pressure pumps or centrifugal force to force the liquid through the membrane and the clean water is collected from inside the tube. The porous polymer sheets (commonly made of polypropylene, polytetrafluoroethene and polysulphone) are folded or wound around a central rigid core to form a catridge and held in place by surrounding mesh.

Microscopic membrane filters have microscopic pore and the use of appropriately sized filters can avoid the need to chemically treat the water. The filters can be classified as microfiltration, ultrafiltration, nanofiltration or reverse osmosis membranes depending on the size of the pore. Water is made to flow across the membrane, not through it. This reduces the blockage factor. Microfiltration removes protozoans, bacteria, colloids, some colouration and some viruses.

Note that there is no purification system which removes all contaminants; each technology removes a specific type of contaminant and has its own advantages and limitations. Whilst microscopic filters are used in some water treatment plants to purify the water for industrial and domestic use, these are not used in Sydney’s water supply due to economic considerations. Filtration cannot be used to remove particles smaller than about 10-9, so it cannot remove dissolved substances such as phosphates and nitrates and heavy metal ions. In this case, reverse osmosis is used, which involves applying pressure to a solution to push water molecules through a membrane, leaving impurities behind. Depth membranes The filter consists of a sheet of fibrous materials

compressed together to form a maze of flow channels to form a thick mat that traps particles. They are mostly used a pre-filters as they can remove a large load of suspended substances economically. Usually, a synthetic polymer is dissolved into a suitable solvent, with the addition of water-soluble powders of a particular size, and this solution is sprayed onto a conveyor belt. It then evaporates, forming a polymer membrane containing particles of water-soluble powder, which is then placed in water. The remaining solvent and powder particles dissolve, leaving a microscopic layer of polymer that forms pores and channels where the water-soluble particles were located.

Surface Filters They are made from lots of layers which prevent large particles from going through the spaces between the fibres of the filter. These particles accumulate mainly on the surface of the filter. Surface filters remove 99.9% of suspended solids, and they can be used as pre-filters or as a later filtration process.

Screen Filters They are thin membranes that act like a sieve, with pores of uniform size. This filter delivers more control over pore size. It is produced by firing a source of ions through a polymer sheet of precise depth. These ions create damaged pores within the polymer which are etched using a strong alkali and washed. Screen filters are usually made from polyesters and polycarbonate.

Composite and layered filters

A variety of different filters is used to combine the properties of the membranes, such as the added strength of one material to the filtering properties of another.

Microfiltration (MF) membranes 100 to 1000nm

Can remove fine silt, colloids (200 to 500nm in size) and a range of microbes such as bacteria and protozoa but few viruses. Used in small rural treatment plants. The filters are composed of bundles of hollow polymer threads.

The most widely used in water treatment in Australia, because it is simpler to operate and requires less constant operational control

Ultrafiltration (UF) membranes 5 to 50nm

Remove all microbes including viruses and some large organic molecules (mm>10,000). A vacuum pump usually draws water through the filtering surface. Water colour is improved. Paint molecules and particulates of 100-200nm are also filtered out. To remove viruses, ultrafiltration is needed. This method id very efficient but

Not widely used in Australia because of the lower levels of synthetic chemicals (such as pesticides) which would require the smaller pore size and the high cost of these membrane processes.

it is expensive to install and operate.

Nanofiltration membranes 0.5 to 5nm

Removes all organic molecules with molecular masses down to 300amu as well as many divalent and trivalent cations. They are usually made of cellulose acetate or polyamide polymers, and can remove hard ions and heavy metal ions if appropriate surface coating is used. Uses higher operating pressures and is more expensive than ultrafiltration.

Reverse Osmosis 0.1 to 1nm

Removes all solutes including ions. This process is much more expensive than nanofiltration, and is used to desalinate sea water

Capillary membrane filter

Another type of membrane filter has the porous material made into hollow capillaries with an outside diameter of about 200µm and an inside diameter of 100µm. For each capillary, dirty water flows from the outside through the wall of the capillary and clean water comes out of the inside. Large numbers of hollow capillaries are bundled together to make a filtering unit with a very large surface area enabling the filtration of smaller particles and due to the large surface area, the filtration process is faster. Capillary membrane filters can be easily cleaned by blowing air from the clean inside to dislodge trapped particles which are then washed away by dirty water on the outside.

describe and assess the effectiveness of methods used to purify and sanitise mass water supplies

Screening: Large objects including fish and plant debris are removed with screens (305 to 140 µm) that acts as sieves. Aeration: The water is sprayed into the air to: • Increase concentration of dissolved oxygen • oxidise iron and manganese salts to remove colour and odour (forms insoluble

oxides which are removed in subsequent stages) Flocculation: Fine suspended particles in the water are made to precipitate. Coagulants such as Al2(SO4)3 (alum) and iron (III) chloride are added to cause the particles to form a larger gelatinous precipitate of Al(OH)2 which attracts suspended solids (by a process called adsorption), precipitated iron and some bacteria. The finely divided particles of aluminium hydroxide clump together or coagulate into heavier particles in a process called flocculation. Flocs are easier to filter due to their greater size and weight. Sedimentation (settling/clarification): The water is passed through into large tanks and allowed to stand so the flocs settle to the bottom to form a sludge which can be periodically removed and reused as compost. About 95% of the suspended impurities are removed by sedimentation. Flocculation and sedimentation are effective as they remove up to 99.9% of the bacteria and 99% of the viruses from water supplies. Filtration: The water from the settling tanks is transferred to filtration tanks where layers of sand, gravel and anthracite coal are used to filter the water of any remaining suspended material. Charcoal filters may also be used to remove coloured ions and coloured inorganic solutes. By the end of this stage, the turbidity of the water is less than 0.5NTU. The residual of the treatment chemicals added to the water is usually very low or undetectable. Non-active components of chemicals such as chlorine form ferric chloride remain in the water but they are effectively inert or neutral in water at the quantities added and hence have no health impact. Chlorination and microbiological tests: The filtered water is then disinfected with chlorine gas and various hypochlorites

(OCl-). These chemicals prevent the growth of algae and kill bacteria and micro-organisms such as E. Coli. Chlorination sanitises the water but monitoring is required to ensure chlorinated alkanes are not produced.

Cl2 + H2O HOCl + H+ + Cl- Cl2 + H2O 2H+ + Cl- + OCl-

Biochemists test the water for presence of bacteria called coliform which are associated with pollution from animal excretion. Fluoridation: Fluorine (in compounds such as NaF, CaF2 and Na2SiF6) is added to the water in very small amounts (about 1ppm) before it is pumped to storage reservoirs, to reduce tooth decay by hardening tooth enamel. pH of water: This can be adjusted with buffers. Hydrated lime or Na2CO3 or HCl for alkaline water can be added to achieve the required pH of 7 to 8.5. This is important as acidic water is corrosive.

Assessment: These methods are very effective in that the process is fast and reliable. 95% of suspended particles are removed through sedimentation and 99.9% of bacteria and 99% of viruses are removed through flocculation. Whilst chlorination is a cost-effective way of removing pathogens and most disease-causing agents, it doesn’t remove all organisms. In addition, this process can remove large amounts of contaminated matter but not extremely fine particles. This can have a significant effect on society as seen through the death of ~100 people and 204,300 infected during the Giardia and Cryptosporidium scare in Warragamba Dam, Sydney in 1998, in which sand filtration and chlorination failed to remove the undesirable organisms from the water. These organisms threatened human halt and prompted the improvement of current purification methods. Sydney Water is now required to test for those organisms in a sample of at least 100L of water before the water can be transferred to homes. Water supplies are monitored daily (by microbiological testing of water samples) at water treatment plants and throughout each catchment during storms and other events which may affect water quality to ensure there is no contamination. Careful monitoring prior to, during and post treatment makes this process effective in removing most coloured substances, odours, suspended solids and bacteria from the water. Each of the six main steps serves a different purpose and should be combined to create clean and potable water.

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

Heavy Metals: Heavy metals are metals with high atomic mass. They are toxic to living organisms and accumulate in living tissue. Tests to identify heavy metal pollution include: • Precipitation – Heavy metals tend to precipitate with sodium sulfide solution.

However, this test does not distinguish which heavy metals are present. Cation Test Hg2+ With NaO it forms a yellow or red precipitate of HgO.

waterways with KI forms a red precipitate, Hg2 that dissolves in excess KI Acidify and add Na2S: a black precipitate of HgS forms.

Cd2+ With NaOH forms a white precipitate of Cd(OH)2 which does not dissolved in excess NaOH but does dissolve in excess ammonia. Acidify and add Na2S: a yellow precipitate of CdS forms.

Zn2+ With NaOH forms a white precipitate of Zn(OH)2 which dissolves in excess NaOH and excess ammonia, forming colourless solutions. Acidify and add Na2S: no precipitate forms. However, if solution is made alkaline, white precipitate of ZnS forms.

Cr3+ With NaOH forms a white precipitate of Cr(OH)3 which dissolves in excess NaOH (to form a colourless solution) but does dissolve in excess ammonia. Acidify and add Na2S: no precipitate forms. However, if solution is made alkaline, grey-blue precipitate Cr(OH)3 forms.

Al3+ With NaOH forms a white precipitate of Al(OH)3 which dissolves in excess NaOH (to form a colourless solution) but does dissolve in excess ammonia. Acidify and add Na2S: no precipitate forms. However, if solution is made alkaline, white precipitate Al(OH)3 forms.

• Flame Tests – The presence of heavy metals in the sample of water can be determined by placing it in methanol, igniting it and observing the colour of the flame

• AAS – The sample of water is vaporised in a flame or graphite furnace. A light of known wavelength is passed through and absorbed by the sample. The amount of absorption determines the concentration of the heavy metal.

• Chromatography Eutrophication: Algal blooms are excessive growths of algae and other aquatic organisms in a water body. They result from water that is polluted with excessive amounts of nitrogen and phosphorus nutrients from sources such as farm water runoff containing fertilisers and effluent water from sewerage treatment plants. Detrimental effects of algal blooms: • the water becomes unsuitable for normal uses • cyanobacteria produce certain poisons which can kill livestock and cause

serious illness in humans • while the surface layer of algae generates oxygen during daylight, at night it

consumes dissolved oxygen from the water, causing fish to suffocate and die, making the water body very unpleasant

• the surface layer of algae blocks sunlight from getting to aquatic plants and hence impedes their ability to photosynthesise

Eutrophication is the enrichment of waterways with excessive nutrients that leads to abundant algal growth. To avoid algal blooms and eutrophication, the EPA recommends the following N:P ratio and nutrient levels in waterways: • N:P ratio > 10:1 • Nitrogen level = 0.1 to 1 ppm • Phosphorus level = 0.01 to 0.1 ppm Nitrate levels can be monitored using: • The brown ring test, where a test tube is filled with the sample of water. A few

drops of FeSO4 and concentrated H2SO4 are added. The formation of a brown ring at the junction indicates the presence of nitrate ions.

• Organic nitrogen can de determined volumetrically by converting the nitrogen compounds to ammonia, which is estimated by acid-base titration.

Phosphate levels can be measured by: • Adding dilute HNO3 to remove any CO3

2- (CO2 gas is released). Ba(NO3)2 is then added to precipitate out any SO4

2- through filtration. Ammonia, then Ba(NO3)2 is added to the sample. The formation of a white precipitate confirms the presence of phosphate

2PO43-

(aq) + 3Ba2+(aq) Ba3(PO4)2(s)

• Colorimetry: the intensity of light transmitted through the coloured solution is

measure and compared to the intensity of light passing through standardised solutions. Phosphates form a blue complex with molybdate ions. The intensity of this blue complex is proportional to the concentration of phosphate.

* *

perform first-hand investigations to use qualitative and quantitative tests to analyse and compare the quality of water samples

• See Attachments • See Prac Book

gather, process and present information on the features of the local town water supply in terms of: • catchment area • possible sources of

contamination in this catchment

• chemical tests available to determine 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

Warragamba Catchment Area A catchment is the area which is drained by a river. Water from rain (or otherwise) flows downhill into the body of water. Warragamba Dam is the primary source of Sydney town water supply, located to the south-west of Sydney, and is more than 900,000km2 in area and is supplied primarily by the Wollondilly, Coxs, Nattai and Kowmung Rivers. Warragamba Dam is the largest dam in the catchment and supplies over 80% of Sydney’s water needs (3 billion litres of water a day). Land uses of the area include: residential, rural-residential, agriculture, mining and water protection. Sources of possible contamination include: Turbidity Surface water run-off into rivers from bushland and

grazing land in the catchment after heavy rains leads to temporary increases in turbidity and nutrient levels of the water

Treated/untreated sewage effluent

Sewage treatment plants along some of the catchment rivers discharge sewage into the river. These treatment plants are usually far enough upstream that little phosphorus and nitrogen contamination is detected from dam walls.

Microbes Catchment water contains variable levels of microbes including cyanobacteria, coliform bacteria as well as cryptosporidium and Giardia. Water run-off from agricultural land contributes to this problem.

Pesticides Low levels of organochlorine and organophosphate pesticides have been detected in the catchment

Mining Zinc, copper and lead have been detected in areas near abandoned mines.

Grazing Cattle graze extensively along the creeks and rivers in the catchment area. Cattle faeces are carried into creeks and rivers during storms.

Native and feral animals

These are carriers of parasites which can enter the surface water.

Factors for testing include: True colour, taste, odour, pH, conductivity, turbidity, hardness, dissolved oxygen, concentration of ions (F-, Cl-, Fe2+, Mn2+, Al3+) Chemical Tests Tests for water quality are carried out on a daily basis for the Warragamba Catchment. Contaminants may affect water quality, so there are tests both for water quality and for contaminants themselves. These tests are performed at a range of different sites as contaminations may be localised. • Heavy metal ions – Precipitation, AAS, Chromatography • Nitrate and phosphate levels – Precipitation, colorimetry, kjeldahl method,

brown ring test • Turbidity (caused by suspended solids) – Turbidity tube, secchi disk • Microbe levels –A sample is placed on a nutrient bed and incubated 12-24

hours. The number of colonies is counted and expressed as CFU/100mL. • Colour, taste, odour (physical) – Physical testing, colorimetry • Hardness - Titration • pH - probe • Dissolved solids – Evaporation followed by weighing, comparing conductivity

of distilled water sample and water sample from catchment. • Dissolved oxygen – Titration, Electrolysis Method (oxygen probe)

Physical treatments: • Screening out large debris • Flocculation to increase particle size • Sedimentation to remove larger suspended particles • Filtration to remove finer suspended particles Chemical additives and processes • Aeration to oxidise soluble iron and manganese salts to insoluble compounds • Oxidation of iron and manganese salts by e.g. KMnO4

3Mn2+(aq) + 2MnO4

-(aq) + 2H2O(l) 5MnO2(s) + 4H+

(aq) • Lime softening to precipitate out high levels of calcium and magnesium ions

Ca2+(aq) + CO3

2-(aq) CaCO3(s)

• Addition of FeCl3 to precipitate out phosphate ions in the coagulation tank Fe3+

(aq) + PO43-

(aq) FePO4(s)

• pH adjustment post-treatment • Addition of chlorine and ammonia to kill microbes • Addition of fluorine ions to assist in tooth decay prevention Chlorine Chlorine is added to sanitise and disinfect the water by killing pathogens and coliforms and preventing their regrowth in the pipelines. It can be added in low concentrations through chlorine gas, liquid sodium hypochlorite and calcium hypochlorite tablets after the filtration process to kill off any bacteria to make it consumable.

Cl2(g) + H2O(l) HOCl(aq) + HCl(aq) The OCl- (hypochlorite ion) from HOCl destroys bacteria. Sydney Water tests for the residual chlorine that needs to be present to make sure that the water quality is protected. Chlorine is the most commonly used disinfectant in Australia as it is cheap, easy to use, effective at low doses against a wide range of infectious micro-organisms, can protect water within the pipe system, and has a long history of safe use around the world. Chlorine dissipates over a short period of time, and so in drinking water systems where the water travels through very long pipes, ammonia is added to form chloramine, which lasts longer in the pipe network as it is less reactive. Fluorine In accordance with the Fluoridation of Public Water Supplies Act 1957, Sydney Water adds fluorine in small amounts (1mg/L) in the form of sodium fluoride, sodium fluorosilicate or hydrofluosilicic acid to strengthen tooth enamel (decreasing likelihood of tooth decay) and to further stabilise the water before distribution. Limewater Ca(OH)2 Limewater or sodium hydroxide or sodium carbonate is added to improve the quality of salty water by raising the pH of the incoming water to 7.5 to 8. It also increases the water’s buffering capacity, resisting changes in pH. Carbon dioxide can also be added to react with the lime to form Ca(HCO3)2 which buffers the water, increases hardness, and reduces the overall corrosive nature of the water. The addition of lime and carbon dioxide has no adverse health effects. Pre-oxidant In a few cases, a pre-oxidant such as KMnO4 or chlorine may be added in small amounts in manganese ion concentration is high. They oxidise dissolved metals, such as iron, manganese and aluminium and/or dissolved organics to an insoluble form which will allow them to be removed by the filtration process. Other • Sulfuric acid is added to break down any colour caused by organic matter

and to lower the pH to aid coagulation • Chlorine dioxide may be used to decompose suspended organic matter • Calcium chloride removes excess fluorides • Hydrogen peroxide oxygenates surface waters and treats serious pollution