Module 3 Chemical Monitoring and Management

HSC Chemistry Module 3: Chemical Monitoring and management Summary

Chemical Monitoring and Management: 1. Chemical Scientists 

Gather, process and present information from secondary sources about the work of practicing scientists identifying: -the variety of chemical occupations -a specific chemical occupation for a more detailed study

Range of Chemical occupations The Royal Australian Chemical Institute (RACI) has thirteen national divisions for membership: -Analytical -Biomolecular -Cereal -Chemical education -Colloid and surface science -Environment -Industrial -Inorganic -Electrochemistry -Organic -Physical -Polymer -Solid state 

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

Laboratory Toxicologist Branch of chemistry Company What is a toxicologist?

Analytical Chemistry UK based Altrix A scientist who specialises in identifying, controlling and preventing the effects of chemicals on human health. They may work in natural environments, industry or laboratories. They can be employed in a hospital lab, university, government agency, private research organisation or corporate employers.

Role of Altrix lab toxicologists

Generally, they conduct tests on toxic or radioactive chemicals, take careful notes and write detailed reports on their findings in order to set new industry standards or environmental protection laws Altrix lab toxicologists provide drug-testing services to government and corporate employers who need to screen job applicants for evidence of drug abuse or infectious diseases e.g. hepatitis. Lab toxicologists must be able to: Page | 1

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HSC Chemistry Module 3: Chemical Monitoring and management Summary -work as part of a multi-disciplinary team -participate in special research projects and activities -comply with Good laboratory Practice and OH&S procedures. The company uses a non-evasive mouth swab of hair sample and a high-tech method of gas chromatography and mass spectrometry. The toxicologist also needs to report the results back to the client and be prepared to appear as ‘expert witness’ in a legal challenge. Lab toxicologists need to collaborate by: -comparing analysis results with results obtained by team members to confirm the validity of the results -discuss results and conclusions with other professionals. -managing the usage of equipment, scheduling of tests and deadlines -keep up to date with new developments by communicating with other scientists, attending seminars and conferences Chemical Principle: Samples are first dissolved in a suitable solvent. The samples are Gas Chromatography injected into a chromatography column which vaporises the sample. A stream of inert ‘carrier gas’ (e.g. helium) carries it through the column. Different molecules ‘adsorb’ at different rates and are picked up by a sensitive electronic detector and sent to a computer for analysis.



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

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HSC Chemistry Module 3: Chemical Monitoring and management Summary Real chemists rarely work alone. Most chemists have expertise in only a specialised field and must therefore cooperate, communicate and collaborate with both their colleagues and clients. 

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

Many chemical reactions are sensitive to any change in conditions i.e. temperature, pressure, concentration, catalysts. As a specific example, consider the effect of oxygen availability on the combustion of natural gas , which is mostly methane: Complete combustion If there is a good supply of oxygen, methane will undergo complete combustion, forming carbon dioxide gas and water:

Incomplete Combustion If there is a shortage of oxygen, incomplete combustion will occur, forming carbon monoxide or carbon (soot):

Incomplete combustion is undesirable (esp. in industry and in internal combustion engines) because: -Less energy is released per unit of fuel used -carbon monoxide is toxic -soot clogs up equipment Management A chemical engineer could monitor combustion by: -measuring the flow, and mixing of air and fuel -measuring combustion temperature -measuring exhaust gas composition

2. Maximise Production 

Identify and describe the industrial uses of ammonia

Ammonia ranks second to sulfuric acid in terms of quantity produced worldwide per year. It is one of the world’s most important industrial chemicals. In particular, it is used in the manufacture of: Page | 3 Robert Lee Chin

HSC Chemistry Module 3: Chemical Monitoring and management Summary -explosives -dyes and pigments -fibres and plastics (e.g. rayon, nylon) -household cleaners and detergents -pharmaceuticals -fertilisers (ammonium nitrate, urea, sulfate of ammonia) The common fertiliser “sulfate of ammonia” is produced industrially by reacting sulfuric acid with ammonia in an acid-base reaction: Ammonia gas is also used as a refrigerant. 

Gather and process information from secondary sources to describe the conditions under which Haber developed the industrial synthesis of ammonia and evaluate its success at that time in world history

History: Development of Ammonia Synthesis (aka “The Haber Process”) Prior to WW1, Nitrogen compounds were essential to manufacture fertilisers and explosives (e.g. TNT, dynamite, ammonium nitrate). This was largely dependent on the supply of natural “saltpetre” deposits (sodium nitrate) from Chile (and to a lesser extent, guano and ammoniacal liquor). It was known that the atmosphere contained large quantities of diatomic nitrogen. Thus, a cheap, large-scale process would be advantageous to convert this into useful compounds for agriculture and industry. In 1908, German chemist Fritz Haber developed a laboratory method to synthesise ammonia from hydrogen gas and atmospheric nitrogen gas in the lab, using an iron catalyst. Carl Bosch later developed the high pressure technology required for this process on an industrial scale. Nitrogen is readily available from air and hydrogen gas could be obtained from hydrocarbons. This removed Germany’s dependence on mining and shipping from Chile. A process called the Ostwald process was then used to convert the ammonia into nitric acid and nitrates. This was hugely important at the time because Europe was on the brink of WW1- explosives and food supplies were to become critical. During WW1, the British cut off Germany’s supply of saltpetre from Chile, however, the Haber process allowed Germany to be self-sufficient in producing ammonia for fertilisers and explosives. This was successful in allowing Germany to lengthen the war, thereby leading to more human suffering and destruction. However, the Haber process also led to the development of many useful products, including fertilisers (food for ↑ world population), explosives and textiles, which we take for granted yet depend on every day. 

Identify that ammonia can be synthesised from its component gases, nitrogen and hydrogen The Haber process is still used for the industrial synthesis of ammonia. Under pressure and heat, nitrogen and ammonia gas react in the molar volume ratio 1:3 to produce 2 molar volumes of ammonia gas: Page | 4 Robert Lee Chin

HSC Chemistry Module 3: Chemical Monitoring and management Summary

 

Describe that synthesis of ammonia occurs as a reversible reaction that will reach equilibrium Identify the reaction of hydrogen with nitrogen as exothermic

The synthesis of ammonia is a reversible reaction. This means once some ammonia is produced (forward reaction), some nitrogen and hydrogen are also produced (reverse reaction). Under normal pressure and heat, the rate of reaction is slow and the equilibrium yields little ammonia. It is also exothermic, producing 46kJ of heat for every mole of ammonia produced: N2(g)+3H2(g) 2NH3(g) + heat ΔH=-92kJ 

Explain why the rate of reaction is increased by higher temperatures

Increasing temperature increases the speed and kinetic energy of the particles. This increases the frequency of collisions and also the amount of energy available for the reaction. Most of the increased rate of reaction comes from the colliding particles exceeding the activation energy. The rate of both the forward and reverse reaction is increased. 

Explain that the use of a catalyst will lower the reaction temperature required and identify the catalyst(s) used

Using a catalyst reduces the activation energy required. At a given temperature a catalyst increases the likelihood that particle collisions will exceed the activation energy. The catalyst used in the Haber process is the iron mineral “magnetite” (Fe3O4), with the surface reduced to elemental iron. The catalyst is finely ground to increase surface area. Gaseous nitrogen and hydrogen molecules adsorb to the iron catalyst, forming ammonia. 

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

The forward reaction is exothermic. According to Le Chatelier’s principle, if a system at equilibrium is disturbed, the system will shift to minimise the change. Thus increasing the temperature shifts the equilibrium to the left and the yield of ammonia is reduced. 

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

Increased pressure causes the equilibrium to shift to the right, increasing the yield of ammonia. By Le Chatelier’s principle, the system will favour the right side because the product (2 moles of ammonia gas) takes up less volume than the reactants (1 mole of nitrogen and 3 moles of hydrogen gas). N2(g) + 3H2(g) 2NH3(g) 4 moles 2 moles Page | 5 Robert Lee Chin

HSC Chemistry Module 3: Chemical Monitoring and management Summary Increasing pressure also increases the rate of reaction because the gas molecules are forced closer together. To reach an economic yield, H2 and N2 gases are pumped in at the ideal mole ratio of 3:1 under pressure of 15-25MPa. 

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

Today, the Haber process is performed using atmospheric nitrogen and hydrogen obtained by reacting steam and methane, using a nickel catalyst:

Increasing reaction temperature increases the energy available to overcome the activation energy and hence the rate of reaction increases. However, increasing temperature also favours the decomposition of ammonia gas (Le Chatelier’s principle). A compromise is 400°C. To achieve an economic yield of 30%, the following conditions are used: -1:3 ratio of nitrogen to hydrogen -pressures of 15-25MPa -Temperature of 400°C-500°C -Iron oxide (Fe3O4) catalyst -Unreacted gases are returned to the reaction vessel -ammonia is constantly removed as a liquid 

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

The raw materials must be monitored to ensure they are clean. Any CO2 detected must be removed (it is often diverted to a nearby fertile plant for urea manufacture). Any O2 present could result in an explosion with the hydrogen. The catalyst surface has to be monitored to ensure maximum adsorption of the reactant gases. Contaminants i.e. carbon monoxide and sulfur compounds can damage the catalyst, as can too high temperatures. A chemical engineer monitors the reaction vessel to ensure the temperature and pressure conditions, levels of contaminating gases and ratio of reactant gases are maintained within an acceptable range.

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HSC Chemistry Module 3: Chemical Monitoring and management Summary

3. Manufactured products are analysed 

Deduce the ions present in a sample from the results of tests

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HSC Chemistry Module 3: Chemical Monitoring and management Summary

Solubility Rules The following are soluble:  All salts of group I metals  All salts formed by the ammonium ion  All nitrates and acetates Page | 8 Robert Lee Chin

HSC Chemistry Module 3: Chemical Monitoring and management Summary  All chlorides, bromides and iodides EXCEPT those of silver, lead and mercury  All sulfates EXCEPT lead, barium, mercury and strontium (calcium and silver sulfates are only slightly soluble) The following are insoluble:  All carbonates, hydroxides and phosphates EXCEPT those of Group 1 and ammonium

Cations Barium Calcium

phosphate White White

Lead Copper

white Blue-green Green

Iron (II) Iron (III) silver



sulfate White White (slightly soluble) White

Yellow

White (slightly soluble)

Solubility Table Anions carbonate White White

White Bright blue to green Yellow/gold ? yellow

chloride

hydroxide White

white

White Pale blue

White, darkens in light

White Yellow White

Perform first hand investigations to carry out a range of tests, including flame tests, to identify the following ions: -phosphate -carbonate -chloride -barium -Calcium -Lead -Copper -Iron

Experiment: Test for cations Aim: to carry out flame tests and a series of chemical reactions in order to devise tests for identifying the following cations in solution when these are the only ions that could be present. Cations: Ba2+ Cu2+ Fe2+

Pb2+ Ca2+ Fe3+ Page | 9

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nitrate

HSC Chemistry Module 3: Chemical Monitoring and management Summary Equipment: A Flame Tests 5 mL concentrated (6 M) HCl Platinum or nichrome wire Small beaker Bunsen burner Tongs Small samples of: -Nitrates of barium, calcium, copper, iron(II), -Chlorides of barium, calcium, copper, iron(II), iron(III) B

Precipitation reactions

Dropper bottles, each containing one of the following 0.1molL-1 solutions: Cation Solutions

Test solutions

Pb(NO3)2 Ba(NO3)2 FeSO4 CuSO4 CuSO4 CaCl2 FeCl3

Na2SO4 HCl NaOH Ammonia solution Acidified KMnO4 NaF

6 test tubes 5 mL HCl (6 M) Test tube rack Distilled water

Safety: -Wear safety glasses and protective aprons -Concentrated NaOH and HNO3 are corrosive. Do not allow direct contact with skin or clothes. If contact occurs, wash with large amounts of water for 10-15 min -Do not touch heated wire -metal salts are poisonous. Avoid direct contact with skin or eyes -Dispose of chemicals as directed by teacher Method: A Flame Tests Note: Not all metal ions produce distinctive colours 1/ Clean wire thoroughly using a small amount of concentrated HCl, then heating strongly. Repeat until no further colouration of flame. 2/ Dip wire into clean, concentrated HCl, then into one of the solids. Place in flame and observe flame colour 3/

Repeat steps 1-2 for each solid, cleaning wire thoroughly in between each compound.

B

Precipitation Reactions Page | 10

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HSC Chemistry Module 3: Chemical Monitoring and management Summary 1/

Add 10 drops of each cation to each of the 6 test tubes

2/

Add 10 drops of the Cl- solution to each test tube. If no precipitate forms, add a few more drops. Record results Lead Barium nitrate nitrate

Copper Iron (II) Calcium Iron (III) sulfate sulfate chloride chloride

3/

Thoroughly clean all test tubes with distilled water

4/

Repeat steps 1-3 for SO42-

5/

Repeat steps 1-3 for OH-, if precipitate forms add excess OH-

6/

Repeat steps 1-3 for OH-, if precipitate forms add excess NH3

7/

Add 10 drops of Fe2+ and Fe3+ solutions to separate test tubes. Add 10 drops of SCN- to each test tube. Record the results.

8/

Add 10 drops of Fe2+ and Fe3+ solutions to separate test tubes. Add 10 drops of MNO4- to each test tube. Record the results.

8/

Add 10 drops of Ca2+ solution to a test tube and add 10 drops of F- solution. Record the results.

8/

Add 10 drops of Pb2+ solution to a test tube and add 10 drops of I- solution. Record the results.

Results: A Flame Test Compound Barium Nitrate [Ba(NO3)2]

Ions present in compound Ba2+

Flame Colour Red-orange Page | 11

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HSC Chemistry Module 3: Chemical Monitoring and management Summary Calcium nitrate [Na(NO3)2] Copper nitrate [Cu(NO3)2] Iron (II) nitrate [Fe(NO3)2] Barium chloride [Ba(Cl)2]

Apple green

Fe2+ Ba2+

-

blue green Blue green

Ca2+ Cu2+

Calcium chloride [Ca(Cl)2] Copper chloride [CuCl2]

Red orange Apple green

Fe2+ Fe3+

Iron (II) Chloride [FeCl2] Iron (III) chloride [FeCl3]

B

Ca2+ Cu2+

-

Precipitate Reactions

Test cations

Cl-

SO42-

OH-

Excess OH-

Pb2+

White ppt

White ppt

White ppt

Ppt dissolves

Excess NH3 White ppt

Pale blue ppt

Clear blue gel

Ppt dissolves

Cu2+ Ba2+ Ca2+

Additional tests Yellow ppt with I-

White ppt White ppt

Fe2+

Green ppt, turns brown

Fe3+

Brown gel

White ppt with FDecolourises acidified MnO4Red complex with SCN-

Cation Lead

Test and result Gives white ppt with Cl- and with SO42-; with OH- gives white ppt which dissolves in excess OH-. Forms yellow ppt with addition of I-.

Copper

No ppt with Cl- or SO42- but with OH- gives pale blue ppt which dissolves in excess NH3

Barium

Gives white ppt with SO42- but not with Cl- or OH-

Calcium

Gives white ppt with F- but no ppt with Cl-, OH- or SO42-

Iron (II)

No ppt with Cl- or SO42- but ppt with OH-; decolourises acidified MnO4

Iron (III)

No ppt with Cl- or SO42- but ppt with OH-; forms red colour with SCN-

Experiment: Tests for anions Page | 12 Robert Lee Chin

HSC Chemistry Module 3: Chemical Monitoring and management Summary Aim: To carry out a series of chemical reactions in order to devise tests for identifying the following cations in solution when these are the only ions that could be present. Anions: PO43SO42CO32ClEquipment: Dropper bottles containing one of the following 0.1molL-1 solutions: Anion Solutions Na2SO4 Na2CO3 Na3PO4 NaCl

Test Solutions -Pb(NO3)2 -Ba(NO3)2 -HNO3 -AgNO3 -NaOH 4 test tubes

Test tube rack

Safety: -Wear safety glasses and protective aprons -Concentrated NaOH and HNO3 are corrosive. Metal salts are poisonous- do not allow either to directly contact skin or eyes -Silver nitrate stains clothes and skins brown -Dispose of chemicals as directed by teacher Method: 1/

Add 10 drops of each of the anion solutions to each of 4 test tubes Sodium sulfate

Sodium carbonate

Sodium phosphate

Sodium Chloride

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HSC Chemistry Module 3: Chemical Monitoring and management Summary 2/

Add 10 drops of HNO3 to each of the test tubes and warm gently.

3/

Record results and use to describe a test for a particular anion.

4/

Thoroughly clean all test tubes with distilled water between tests

5/

For the remaining three anions, put 10 drops in each of 3 test tubes, add 5 drops HNO3 and then 5 drops of Ag+. Record results

6/

Repeat steps 4-5 with Pb2+ and Ba2+

7/

After the Ba2+ test add 10 drops of NaOH to each of the test tubes and record any changes.

Results: Test anion/solutio n CO32-

H+

Ag+

Gas bubbles

Ba2+ and H+

Ba2+ & OH-

n/A White ppt

Cl-

Pb2+

n/A White ppt

SO42PO43-

White ppt Anion

Chloride Sulfate Phosphate Carbonate

Test and result Precipitate with acidified Ag+, but not with Ba2+ Precipitate with acidified Ba2+ Precipitate with Ba2+ in alkaline solution, but not in acid solution Produces bubbles of gas with addition of HNO3

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HSC Chemistry Module 3: Chemical Monitoring and management Summary



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

Certain human activities release harmful ions into the environment. It is therefore essential to monitor the levels of these ions in the air, soil, water and food to protect people and the environment Phosphate Ions At normal concentrations, phosphate ions (PO43-) form an essential part of the natural environment. Human activities such as fertiliser run-off from agriculture and sewage discharge into waterways have increased phosphate concentrations in water environments. Also, water used in irrigation reduces the water flow, making the problem more likely. Increased phosphate concentrations result in eutrophication, a process in where aquatic plants and algae are “over-fertilised” and grow excessively. This clogs waterways and when the plant life dies and rots, it takes the oxygen out of the water, putrefying it and killing the ecosystem. Lead Ions Lead is a toxic metal, not normally found in the natural environment in significant amounts. Even low concentrations are dangerous because it accumulates in the body until it reaches toxic levels. Lead poisoning results in neurological diseases in humans. Lead compounds used to be present in paints and petrol. Lead based petrol is a particular concern as it releases lead fumes into the air. To reduce the environmental impact, lead-based paints were banned and unleaded petrol introduced. Lead emissions from industry are also monitored now. Previous lead emissions still require monitoring as the lead persists in the environment for long periods. 

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

The reliability of any analysis can be assessed by how close the results are when the method is repeated. Results can be considered reliable when various group results are in close agreement. The major difficulty in separating solid barium sulfate (BaSO4) is the very small crystal size. Ordinary filtration using filter paper is ineffective. One solution is to use a sintered glass crucible and vacuum filter. 

Gather, process and present information to interpret secondary data from AAS measurements and evaluate the effectiveness of this in pollution control Page | 15

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HSC Chemistry Module 3: Chemical Monitoring and management Summary Case Study: Arsenic concentrations in Bangladesh Arsenic in groundwater poses a health hazard to over 20 million people in Bangladesh. Solar oxidation and removal of arsenic (SORAS) is a technique that uses irradiation of water with sunlight in UV transparent bottles to reduce arsenic in drinking water. Groundwater in Bangladesh contains both Fe2+ and Fe3+ ions. Fe3+ forms a precipitate [Iron (III) hydroxide)] with OH-. Arsenic (III) is only weakly adsorbed to this precipitate but arsenic (V) is strongly adsorbed. SORAS involves adding lemon juice to a litre of water in a PET bottle. Adding acid speeds up the photo-oxidation process. The bottle is placed into sunlight for 4-5 hours where UV light, oxygen and water in the bottle oxidises As (III) into As (V) and Fe2+ into Fe3+:

The precipitate is allowed to settle and the clear liquid is decanted off.

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HSC Chemistry Module 3: Chemical Monitoring and management Summary



Groundwater Sample

Absorbance

Concentration (μgL-1)

Before SORAS After SORAS

0.28 0.13

121.74 56.52

Daily adult intake (safe daily intake: 150 μg and 2L water/day) 243.48 113.04

Describe the use of atomic absorption spectrometry (AAS), in detecting concentrations of metal ions in solutions and assess its impact on scientific understanding of trace elements

When particular samples of atoms are energised, they emit light of a characteristic frequency, producing a characteristic absorption spectrum. The amount of light emitted is usually too small for measuring minute concentrations. The exact frequencies of light emitted by an atom are also the same frequencies that atom will absorb and this is more easily measured. AAS is a technique for determining the concentration of a particular element, usually a metal in a sample. It involves beaming light (of the frequency the target atom will absorb) through a vaporised sample, which reemits it in all directions. A detector absorbs the light and measures the intensity. The amount of light absorbed is directly proportional to the number of ‘target’ atoms present, so it measures it quantitatively.

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HSC Chemistry Module 3: Chemical Monitoring and management Summary Flame vaporises sample. Target atoms Lamp containing absorb specific element to be analysed frequency light beam Optical system to select and intensify specific frequency light Fuel and air

Electronic detector

Sample

The electronic detector interprets the data as a pattern of narrow bright bands called an absorption spectrum. Each different element has its own unique absorption frequencies and therefore, absorption spectrum. The light emitted by a sample shows very narrow bright lines on a dark background, because only specific frequencies are emitted. Because the target element will also absorb these same frequencies, the light absorption spectrum shows dark lines on a bright background. The relative intensity and pattern of the absorption spectrum indicates the concentration of the element.

Emission

Absorption

Impact on scientific understanding of trace elements The study of pollutant concentrations in the environment is more accurate and reliable since the development of AAS by CSIRO scientist, Alan Walsh, in the 1950s. It is used areas, such as medicine, agriculture, mineral exploration, metallurgy, food analysis, biochemistry and environmental monitoring. It has been described as the most significant advance in chemical analysis of the 20th Century and can be used for over 65 elements. Trace elements are elements essential in trace amounts to living organisms. AAS enabled the measurement of the concentrations of many metals in the bodies of plants and animals and in their surrounding environments.

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HSC Chemistry Module 3: Chemical Monitoring and management Summary In WA, farmers found their sheep were chronically sick, despite good pastures and disease control. AAS showed cobalt deficiencies in the soil and the pasture. Further studies showed that all animals require cobalt for enzyme production. The sheep were given a slow release cobalt ‘pill’ and the multi-million dollar industry was saved. Arid areas of Victoria could not support legumes until molybdenum deficiencies were detected by AAS. 

Identify data, plan, select equipment and perform first-hand investigations to measure the sulfate content of lawn fertiliser and explain the chemistry involved

Investigation: Determination of sulfate in lawn fertiliser Aim: To gravimetrically determine the m/m % of sulfate in a typical lawn fertiliser Equipment: -Burette and pipette -retort stand and clamp -electronic scale -Ammonium sulfate [(NH3)2SO4] fertiliser -dilute HCl -0.2 M BaCl2 solution -2 x 250mL beakers -sintered glass filter -250 mL vacuum flask Method: 1/ Accurately weigh ≈2 g fertiliser sample 2/

Dissolve in excess (about 100mL) HCl

3/

Filter to remove any insoluble material

4/

Slowly add excess BaCl2 (about 100ml), stirring well.

Mixture Suction Filtrate

4/

Filter using sintered glass filter and vacuum flask to remove solid BaSO4. Rinse residue with pure water Page | 19

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HSC Chemistry Module 3: Chemical Monitoring and management Summary 5/

Dry residue in an oven and weigh

Results

4. Human Activity and the Atmosphere 

Describe the composition and layered structure of the atmosphere

Structure The atmosphere consists of two main layers: the troposphere and the stratosphere. The troposphere extends up to an altitude of 15km. In the troposphere are over 90% of Earth’s gases and the temperature drops with altitude. The top of the troposphere is known as the tropopause and the temperature is stable. Above the troposphere is the stratosphere, where temperature rises with altitude.

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HSC Chemistry Module 3: Chemical Monitoring and management Summary

100 Thermosphere

Ionosphere

90

80

70 Mesosphere

Altitude (km) 60

0.001 atmospheres

50

40 Stratosphere

Ozone layer

30 Highest concentration of ozone 20

0.1 atmospheres Mr. Everest

10

Troposphere 1.0 atmosphere

0 -100

-80

-60

-40

-20

0

20

Temperature (°C)

Composition Water vapour varies from 0.5-1.0%, but other gases remain in constant. In dry air: Nitrogen ≈78.1% Oxygen ≈20.9% Argon ≈00.9% This represents 99.9%. The remaining 0.1% consists of carbon dioxide, inert gases, methane and ozone. Despite the small concentrations, these gases are of most concern.

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HSC Chemistry Module 3: Chemical Monitoring and management Summary 

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

Pollution Nitrogen oxides, NOx

Artificial Sources Motor vehicles Electricity production

Natural sources Action of sunlight Soil bacteria lightning

Volatile organic compounds Carbon monoxide, CO

Unburnt fuel, solvents, thinners, alcohols, paints, hydrocarbons

Emitted by vegetation e.g. eucalyptus oil

Incomplete fuel combustion (vehicles, smelters, power stations)

Carbon dioxide, CO2

Combustion of fuels for transport and electricity production Smelting of metals

Sulfur Dioxide, SO2

Smelting of metals Industrial production of sulfuric acid Incineration of waste products Petroleum refineries Combustion of fossil fuels Mining (underground and open cut)

Incomplete biomass combustion (volcanic eruptions, decomposing organic matter) Respiration of plants and animals Volcanoes Bushfires Decomposition of organic matter Soil bacteria Volcanoes

(NO, NO2)

Particles

Lead

Ozone



Lead smelting Leaded motor vehicles from the 80’s Old batteries Photochemical smog Electric discharge in DC motor commutators

Burning biomass Soil from erosion Pollen and spores Agricultural and industrial practices Erosion of lead ores

Action of UV light on atmosphere

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

In the upper atmosphere (stratosphere), where concentrations of ozone are up to 8 ppm, it protects us against dangerous UV radiation. Up to 90% of all UV is absorbed by the ozone layer. In the lower atmosphere (troposphere), ozone is a toxic pollutant. Ozone is highly reactive, capable of oxidising many substances. Concentrations as low as 0.2 ppm cause lung damage, life-threatening for asthma suffers. Page | 22 Robert Lee Chin

HSC Chemistry Module 3: Chemical Monitoring and management Summary Ironically, human activities destroy ozone in the stratosphere and produce ozone in the troposphere.  Describe the formation of a coordinate covalent bond Non-metallic compounds contain covalent bonds. A covalent bond is formed by a shared pair of electrons. A coordinate covalent bond forms when one atom provides both the electrons for the covalent bond. Otherwise, the bond is indistinguishable from a normal covalent bond. 

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

Ozone, O3 To form ozone, another oxygen atom must bond to the O2 molecule. The middle oxygen atom provides both the electrons for the single covalent bond with the third oxygen atom. O

O

O

O

O

O

Sulfur dioxide, SO2 The sulfur atoms supplies both pairs of electrons to form the coordinate covalent bonds O

S

O

O

S O

Sulfur Trioxide, SO3 In SO2, the sulfur has a pair of free electrons. It is possible for an oxygen atom to form a coordinate covalent bond here. Note that the sulfur only needs 6 electrons to have a ‘complete’ shell. O O

S

O

O

O

S O Sulfate ion, SO42-

As shown in SO3, the sulfur only needs 6 electrons for a complete shell. If two electrons are added (maybe from a metal), they can form another coordinate covalent bond. O

O O

S

O

O

O

S O

O

Hydronium Ion, H3O+ A proton forms a coordinate covalent bond with the oxygen from the water molecule

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HSC Chemistry Module 3: Chemical Monitoring and management Summary H

O

H+

H

O

H

H

H

Ammonium Ion, NH4 H

H

N

H

H+

H

H

 Compare the properties of the gaseous forms of oxygen and the oxygen free radical Compare the properties of the oxygen allotropes O2 and O3 and account for them on the basis of molecular structure and bonding H



N H

O2 (oxygen gas)

O3 (ozone)

Colourless odourless gas

Pale blue, toxic gas with sharp, pungent odour

Moderately reactive. Decomposed by high-energy UV light

Highly reactive Decomposed by medium energy UV light Formed by UV and electric discharge on oxygen

Formed by photosynthesis

Essential for life

M.P. B.P. Density (liquid at 20°C)

218.75°C -182.96°C 1.331gL-1

Causes coughing chest pain and rapid heartbeat Concentration greater then 1ppm is toxic -192.5°C -110.5°C 1.998 gL-1

O(oxygen free radical) Oxygen atom with unpaired electrons and energy levels higher than ground state Extremely reactive

Formed by UV light on oxygen and also on ozone

Highly reactive with chemicals in living cells

\ Diatomic molecule i.e. 2 oxygen atoms held together by a covalent double bond

Three oxygen atoms held together with 1 double covalent bond and 1 single covalent bond

Each radical contains two unpaired valence shell electrons

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HSC Chemistry Module 3: Chemical Monitoring and management Summary Linear molecule

Bent molecule, due to electron pairs getting as far away from each other as possible

Single atom in molecule

O O

O

Explanation of differences between O2 and O3 The differences are due to bonding and structure. Differences in physical properties are due to the larger size of the O3 molecule, which increases dispersion forces between molecules The differences in reactivity are due to bonding. The double covalent bond in O2 is strong, requiring 500 kJmol-1 to exceed the activation energy. In contrast, it only takes 100 kJmol-1 to break any of the bonds in O3, so it readily enters oxidation reactions. This is because the two covalent bonds consist of a single and a partial bond. Oxygen Free radicals and ozone formation In the stratosphere, UV radiation causes O2 molecules to split into separate oxygen atoms called “oxygen free radicals”. The energy absorbed in splitting and the unpaired electrons make them extremely reactive. Although oxygen free-radicals are highly reactive, most gases in the atmosphere are unreactive. Nitrogen molecules are stable, argon is completely inert and O2 is relatively reactive. So oxygen free radicals react with O2 molecules to form ozone. Because ozone has nothing to react with, it can reach concentrations of up to 8 ppm. Paradoxically, the UV radiation which creates oxygen free-radicals and thus, ozone, are strongly absorbed (over 90%) by ozone. 

Identify the origins of chlorofluorocarbons (CFC) and halons in the atmosphere

Alkanes of alkenes with a halogen replacing a hydrogen are named haloalkanes or haloalkenes. Halogens often involved are Br, I, Cl & F. Chlorofluorocarbons (CFCs) are a group of haloalkanes containing fluorine & chlorine and are responsible for destroying the ozone. Halons are fluorocarbon compounds containing bromine which are even more destructive to the ozone than CFCs.

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HSC Chemistry Module 3: Chemical Monitoring and management Summary CFCs were first used as refrigerants in the 1930’s as a ‘safer’ alternative to ammonia. Their properties of inertness and low boiling point led to many uses including, dry cleaning fluids, solvents, insecticides (e.g. DDT), propellants, fire extinguishers and foam blowing agent Halons were used in fire extinguishers to protect against electrical fires. Fortunately, they were never used as extensively as CFCs. They were found to be so inert they did not react with the troposphere. They gradually diffuse into the stratosphere where they react with UV light to form chlorine and, fluorine free radicals. Substance CFCs Chloroform dichloromethane

Formula

Previous Use

CHCl3 CH2Cl2

anaesthetic

CCl4

Cleaning fluid

dichlorodifluoromethane

CCl2F2

propellant

Chlorofluoromethane Chlorotrifluoromethane Trichlorofluromethane dichlorodifluoromethane

CH2ClF CClF3 CCl3F CC2F2

refrigerant

C14H9Cl5

insecticide

Tetrachloromethane

Dichlorodiphenyltrichloroethane



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

Naming Simple halogens Use prefixes for the halogen group (i.e. Bromo, Chloro, Fluoro, Iodo) Use prefixes for more than one of the same halogen (e.g. di, tri, tetra) If more than one halogen atom is present, list them alphabetically by halogen name. E.g. C4H5BrCl2I2 is called “Bromodichlorodiiodobutane”. Number the carbon atom with the halogen attached, giving preference to any double bond. Otherwise, give lowest number to the halogen group Examples: a) 3,4-dibromo-1,2,5-trichloro-4-fluroheptane

b) 1,1,2,3-tetrachloropropane Page | 26 Robert Lee Chin

HSC Chemistry Module 3: Chemical Monitoring and management Summary

c) 2,3-difluoro-4-iodopentane

d) Tetra chloromethane



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

Example Isomer: BromoDichlorofluoropropane- C3H4BrCl2F (23 Isomers) H

F

Br

1-bromo-1, 1-dichloro-2-fluoropropane

H

F C

H C

Br C

Cl 1-bromo-1, 1-dichloro-3-fluoropropane

H

Cl H C

F H C

Br C Cl

Cl 1-bromo-1, 3-dichloro-2-fluoropropane

H

H C Cl H C Cl F H C

H C H H C H H Cl C

C Cl Br Cl C Br Cl Br C

H

H C Cl H Cl C

C Cl Br Cl Br C

F

H

C H C F C

H

H C

Cl F C

Br C Cl

H 1-bromo-2, 2-dichloro-1-fluoropropane

H

F C

Cl H C

Br C Cl

H 1-bromo-2, 2-dichloro-3-fluoropropane

H

Cl H C

H Cl C

Br C F

H 1-bromo-2, 3-dichloro-1-fluoropropane

H

H C

Cl C

C H

H

H

Cl

F

H H H

H

1-bromo-1, 3-dichloro-3-fluoropropane 1-bromo-1, 3-dichloro-1-fluoropropane

F 1-bromo-1, 2-dichloro-1-fluoropropane 1-bromo-1, 2-dichloro-2-fluoropropane

H 1-bromo-1, 2-dichloro-3-fluoropropane

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HSC Chemistry Module 3: Chemical Monitoring and management Summary 1-bromo-2, 3-dichloro-2-fluoropropane

Cl

F

Br

C Cl Cl C H H C F H H C

C Br H C Br H C Br F Br C

H

H

C Cl H C Cl F C Cl Cl Cl C

F

Cl C

H C

C H

H

H Cl

Br H

Cl H

2-bromo-1, 1-dichloro-1-fluoropropane

H

H C

Br C

Cl C

F 2-bromo-1, 1-dichloro-2-fluoropropane

H

H C F H C

H C Br F C

C Cl Cl Cl C

H

Cl H

Br H

H Cl

C Cl H C Cl H C Cl F C

C Br H C Br F C Br Cl C

C Cl H C F H C F H C

H

Cl

H

H H H

H

F H H H

H H

1-bromo-2, 3-dichloro-3-fluoropropane 1-bromo-3, 3-dichloro-1-fluoropropane 1-bromo-3, 3-dichloro-2-fluoropropane

H 1-bromo-3, 3-dichloro-3-fluoropropane

2-bromo-1, 1-dichloro-3-fluoropropane

H 2-bromo-1, 3-dichloro-1-fluoropropane Cl H H

2-bromo-1, 3-dichloro-2-fluoropropane 2-bromo-1, 2-dichloro-1-fluoropropane 2-bromo-1, 2-dichloro-3-fluoropropane

H



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 photodisassociation when exposed to UV radiation to form reactive chlorine free radicals. For example:

Page | 28 Robert Lee Chin

HSC Chemistry Module 3: Chemical Monitoring and management Summary The chlorine radicals then react with ozone to form the chlorine monoxide radical. Further reaction by oxygen radicals regenerates the chlorine radical. It is acting as a catalyst for ozone decomposition.

By adding the two above reactions, we get the net equation:

Ozone has been converted into oxygen and oxygen radicals, which could have formed more ozone, have been ‘mopped up’. This process is more frequent in Winter and Spring due to more ice particles which provide a surface catalyst.  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 Hydrochlorofluorocarbons (HCFCs) and hydrochlorocarbons (HFCs) are the two main alternatives for CFCs. HCFCs substitute some of the chlorine atoms with hydrogen. They are decomposed by OH free radicals in the troposphere, however, this process is slow and they can still reach the stratosphere and form chlorine radicals. HFCs contain no chlorine and are under being trialled. They react with OH more readily than CFCs. Because they contain no chlorine, they produce no undesirable radicals in the stratosphere. However, both HCFCs and HFCs are greenhouse gases with long atmospheric lives (due to their stability). Hydrocarbons have replaced CFCs as aerosol propellants and refrigerants in air conditioners. They do not affect the ozone, but they are flammable. The main HCF used in Australia is 1,1,1,2-tetrafluoroethane: 

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

Problems include: -Depletion of the ozone layer, leading to more UV reaching Earth, which increases risk of sunburn, cancers, crop failure Page | 29 Robert Lee Chin

HSC Chemistry Module 3: Chemical Monitoring and management Summary -an enhanced greenhouse effect, contributing to global warming Steps to alleviate problems The Montreal Protocol, a 1987 International agreement between many countries to eliminate CFC emissions. Further assistance has been given to developing countries to phases out CFCs. The effectiveness is dependant on government regulation of use and production of CFCs. CFCs were gradually replaced by similar chemicals such as HCFCs and HFCs. However, they have their own problems, namely that they are greenhouse gases with long atmospheric lives. The use of air pump mechanisms in aerosol cans has been more effective. Although CFCs cannot be removed, the effects of high UV levels can be alleviated by using new sunscreens, as advised by organisation such as the Cancer council and use of UV stabilisers in polymers to reduce photodisassociation by UV. 

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

CFCs were first developed to replace ammonia in refrigerators, as many poisoning fatalities had occurred. CFCs were found to be very inert and non-toxic in the troposphere and they soon became widely used. Measurements of ozone concentrations in the 1970’s indicated CFCs were depleting the ozone in the stratosphere. In the 70’s, Scientist in Holland investigated the effect of nitrous oxide on the atmosphere and found the sources were from artificial fertiliser and aircraft exhausts. This led to increased concern over the stability of the ozone layer. Further investigations showed CFCs to be ozone depleting and later tests showed that halons were even more readily broken down by UV than CFCs, releasing bromine free radicals. Regular measurements have been made since the 1920’s and more intensive measurements since the 1970’s. A worldwide decline in stratospheric ozone layers of about 10% has been recorded. It has been found that a ‘hole’ develops over Antarctica each spring and the decline exceeds 50% The concentration of ozone is measured using analysis devices sent up by balloons or using a Dobson spectrophotometer which measures the intensity of different frequencies of UV radiation and compares it to a frequency which is not strongly absorbed by ozone. Similar instruments can be sent up by satellites in orbit, which measure the amount of UV scattered by the atmosphere to give ozone concentrations at different altitudes. Even partial destruction can result in harmful UV exposure, leading to skin cancers, sunburn and disrupted plant growth, even leading to a worldwide food crisis.

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HSC Chemistry Module 3: Chemical Monitoring and management Summary

5. Monitoring and Management in water  Identify that water quality can be determined by considering: -Concentrations of common ions -Total dissolved solids -Hardness -Turbidity -Acidity -Dissolved oxygen and biochemical oxygen demand Concentrations of common ions The concentration of common ions e.g. Chloride and sulfate, can be determined by gravimetric analysis using precipitation reactions (e.g. adding silver ions to chloride and weighting the precipitate). AAS is used to determine concentrations of metal ions e.g. Sodium, aluminium, magnesium Total dissolved solids (TDS) TDS are determined by evaporating a filtered sample of a known volume. Most dissolved solids are ions, so their presence can be determined using a data logger set to record electrical conductivity. The amount of TDS is converted to ppm and expressed as Hardness Hardness is due to the presence of Ca2+ and Mg2+. These react with soap molecules to form an insoluble precipitate resulting in poor lathering ability and blockage of water pipes. Hardness is tested by precipitating the Mg2+ or Ca2+ ions with sodium carbonate (Na2CO3) of a known concentration, followed by gravimetric analysis of the weighed solids. Turbidity Turbidity is a measure of the ability of water to support life. It results from suspended solids in the water, causing ‘cloudiness’ which prevents light penetration and therefore, photosynthesis which in turn reduces the oxygen concentration. It is tested by pouring a sample into a turbidity tube until the cross at the base becomes invisible. However, the turbidity cannot be accurately measured, only compared.

High turbidity

Low turbidity

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HSC Chemistry Module 3: Chemical Monitoring and management Summary

Acidity Safe drinking water has a pH of ≈6.5 due to dissolved CO2. pH values ±2 units from neutral indicate polluted water. Water pH is tested using either universal indicator with colour comparison chart or a pH probe. Dissolved oxygen (DO) This measurement is important for safety of drinking water. Low O2 concentrations indicate stagnant water. DO is measured using the Winkler test, which fixes the oxygen concentration for later determination by titration. The amount of manganese dioxide produced by adding manganese (II) ions and hydroxide ions is a measure of the DO. Acidified Iodide ions are the added to produce a yellow iodine solution. This is then titrated against a standard sodium thiosulphate solution using a starch indicator. The indicator turns the solution blue, which disappears at the endpoint. The overall reaction is: Therefore, 1 mole of dissolved oxygen produces 4 moles of thiosulphate (S2O32-) Biochemical oxygen demand (BOD) BOD5 measures the amount of oxygen used by bacteria and microorganisms in a sealed container. One sample is kept in the dark for 5 days, so no photosynthesis (and therefore no oxygen is produced) occurs while the other is tested immediately. The BOD is the difference between the initial and the final DO values and is given in mg/L. Although BOD gives precise quantitative measurements, it is commonly used as an indicator of water quality. 

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

Factors include: -rainfall frequency (e.g. floods and droughts) -water temperature -evaporation rates -soil/rock type -water pH -pathway of water (if it flows through ground aquifers the water will be ‘harder’) -presence of animal faeces Human activities Farming practise such as removal of vegetation and irrigation increases salt concentration in rivers. Water flowing through fertilized land becomes contaminated with nitrate and phosphate ions. Mining exposes sulphides which are oxidised by the air, forming sulfuric Page | 32 Robert Lee Chin

HSC Chemistry Module 3: Chemical Monitoring and management Summary acid. Other human activities include sewage treatment run-off, heavy metals from factories, mines and storage dumps.



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

There are several methods to purify water. Most are variations on the following process:

Flocculation Water is collected in dams and pumped to a treatment site where larger debris is removed via screens. Fine particles normally have electric charges which prevents them from joining. Separation of fine particles involves adding coagulating agents such as Iron (III) chloride (FeCl3). This neutralises the surface charges so the particles join and also forms iron (III) hydroxide Fe(OH)3 precipitate. The particles ‘flocculate’ into a large mass which is easily filtered. Filtration The water is passed through beds of sand and carbon. The sand traps the floc and the carbon absorbs organic molecules which have unpleasant odours and tastes. Chlorination The water is clear of any particles at this stage, but may contain dangerous microbes. There are several chemicals which may be added to sanitise the water: -Chlorine gas (Cl2) at 2 ppm -sodium hypochlorite (NaClO(l)) at 1L/4000L -calcium hypochlorite Ca(OCl(s))2 -Monochloramine (NH2Cl), less powerful but longer-lasting, is made by reacting ammonia (NH3) with chlorine (Cl2) pH adjustment Water is normally slightly acidic (pH≈6.5) due to dissolved CO2. The easiest way to neutralise water is by using forced draft degasifiers. Lime is commonly used at the start of water treatment, as it increases water hardness, facilitating flocculating and minimising the risk of heavy metals from pipe fittings dissolving into the water. Page | 33 Robert Lee Chin

HSC Chemistry Module 3: Chemical Monitoring and management Summary Assessment of effectiveness This involves testing water samples for microbes throughout the entire purification and sanitisation process esp. during sanitisation. Also required are public health surveys and medical reports of incidences of water-borne illnesses In Australia, the incidence of health problems arsing from sub-standard water is nil in most years. However, in 1998 there was an outbreak of cryptosporidium and giardinia in NSW. Nowadays, water supplies are monitored daily at water treatment plants and catchment areas. This is considered highly effective and less costly than installing microscopic filters. 

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

Microscopic Membrane Filters These filters are able to filter out even microbes, avoiding the need to chemically treat the water i.e. they filter out all small particles, including microbes. They can be classified as micro-, ultra-, nano-filtration (as small as 1μm) or reverse osmosis. The membrane is generally made into a film or a ‘capillary tube’. It is composed of polymers (e.g. polypropylene), which are dissolved in a mixture of solvents. Water-soluble powders are added to form the pores. The mixture is spread on a plate or moulded into a tube for the solvent to evaporate. Once the membrane solidifies, it is placed in water to produce the microscopic pores. Semi-permameable membranes for reverse osmosis are made of cellulose acetate, polyamide or composite films. Under pressure, these have high water permeability but block most other ions, molecules and atoms. Fine particles Although each pore is microscopic, the large trapped on outside number of pores creates a large surface area of capillary tube Dirty water is forced through the pores in the pipe under high pressure to speed up the process. For sheet filters, water is passed across the membrane as this reduces blockage. For capillary tubes, water is passed through the pores into the tube under high pressure. Clean water passes through

Compared to sand filters, membrane filters are very expensive but also effective. Other countries such as Singapore use membrane filters to recycle sewage water for re-use. In Australia, they are mainly used for filtering high-quality bottled drinking water. 

Perform a first-hand investigation to use qualitative and quantitative tests to analyse and compare the quality of water supplies Page | 34

Robert Lee Chin

HSC Chemistry Module 3: Chemical Monitoring and management Summary



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 Heavy metal pollution Heavy metal pollution of water is caused by unacceptably high levels of ions of arsenic, cadmium, copper, lead, mercury, nickel and zinc. The most likely and dangerous of these are lead and mercury. Gravimetric analysis using precipitation reactions will not work, because dangerous concentrations are too small to be detected. Instead, AAS or mass spectroscopy are used Eutrophication Eutrophication involves excessive nutrient content due to fertilisers in waterways. Fertilises containing nitrate and phosphorus ions cause excessive algae growth and oxygen depletion when they die and decay. When this occurs, the biochemical oxygen demand (BOD) is said to be extreme. This oxygen depletion kills all other organisms in the waterway. Eutrophication usually occurs when water flows through farmland or when sewage water is discharged into waterways. Spectrophotometry is one method to determine phosphate concentrations. It involves reacting the water sample with the reagent ammonium molybdite [(NH4)2MoO4], then adding ascorbic acid which turns the sample blue. The blueness of the solution is proportional to the amount of phosphate. A photometer is used to measure the amount of light passing through the solution to a detector.

Light passes through

Photometer measures intensity of light

Other quantitat ive methods include AAS and BOD tests.



Gather, process and present information on the features of local town water supply in terms of : -catchment area -possible sources of contamination in this catchment -chemical tests available to determine levels and Page | 35 Robert Lee Chin

HSC Chemistry Module 3: Chemical Monitoring and management Summary -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 Local water supply: Hunter Water Supply Catchment Area Water comes from three main catchments: Grahamstown Dam supplies 30-45% of water to is the lower Hunter and has an area of 100km2. It is used for many other activities including agriculture, recreation, tourism, residential & urban developments. Water is routinely monitored for pathogens before it reaches the catchment area. Chichester Dam supplies 40% of water and has an area of 197km2. It is bound from the North and East by the Great Dividing Range. It is located near Barrington Tops National Park and is therefore pristine and largely unaffected by human activities. Environmental flow releases into the connecting Williams river sustain natural ecosystems along Chichester River. Tomago and Anna Bat sandbeds contribute to surface supplies and provide backup in times of drought. Tomago sandbeds supplies the Tilligerry peninsular while Anna bay supplies the Tomaree peninsula. Together, they cover an area of 275km2 along a 10-15km coastal strip. Porous sand means there is little surface run-off. Sources of contamination Land in these catchments used for a variety of other purposes: -residential -Industry -Transport and construction -Agriculture -Mining -Recreation -Defence for activities The groundwater supply can be contaminated due to residential septic tanks and past history of sand mining in the area. Types of contaminants and Tests Contaminant suspended fine particles (clay and silts) Suspended organic matter manganese Acidic or basic compounds Microorganisms (pathogens)

Test Turbidity test using turbidity tube AAS, mass spectroscopy pH probe, universal indicator BOD5, microscopic filters

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HSC Chemistry Module 3: Chemical Monitoring and management Summary

Physical & Chemical Processes used to purify water and chemical additives Screening: sieves remove larger solids e.g. twigs, fish, leaves

↓ Coagulation/flocculation: Alum (hydrated potassium aluminium sulfate, KAl[SO4]2·H2O) or a polymer is added to the water to make small particles clump together, forming an easy-to-remove ‘floc’.

↓ Sedimentation: The floc and water flow into sedimentation basins, the ‘floc’ settles as sludge at the bottom.

↓ Filtration: Water flows through sandbeds to remove suspended matter. Sandbed filters are routinely cleaned by backwashing.

↓ Disinfection: Chlorine (Cl2) is added to kill any pathogens

↓ Sludge drying: ‘Floc’ sludge is piped to drying lagoons

↓ Fluoridation: Fluoride is added to reduce dental caries

↓ pH adjustment: lime [Ca(OH)2] is added to stabilise pH (esp. ‘soft’ water) and prevent corrosion of pipelines

Page | 37 Robert Lee Chin