Chemical Monitoring and ManagementPart 1: Monitoring and Managing Reactions

A Chemist in Industry A chemist employed by the government in the Department of Mines and Energy would be working in the branch of analytical chemistry in inorganic chemistry in environmental monitoring. Their duties include:

Fieldwork collection of water and soil samples from mining sites and mine rehabilitation areas

Co-ordinating the duties of technicians within the laboratory Maintaining analytical standards of the laboratory to Australian standards, so results

can be compared between laboratories Preparing reports on samples for private groups and other government agencies

(e.g. EPA, Department of Land and Water Conservation) and making recommendations

Liaising with community groups, local councils and mine managers on managing contamination of soil by runoff and groundwater near mine sites.

The analytical methods used include flame atomic absorption spectroscopy for heavy metal analysis. The chemical principle behind this field is that many ores contain metal sulfides, which are insoluble and do not pose a problem in this form.

When exposed to air and water, the metal sulfides oxidise to sulfates, which are more soluble. Thus, heavy metals enter ground water as metal sulfate salts. Maintaining the acidity of mullock and slag helps to prevent the mobilisation of heavy metals into ground water.

4 H 2O+S2−¿⇌SO42−¿+8H+¿+8 e−¿¿¿ ¿¿

4 H2O+2O2+8 e−¿⇌8OH−¿¿ ¿

S2−¿+2O2⇌SO 42−¿¿¿

Collaboration between ChemistsChemistry is a very broad discipline and chemist specialise in particular areas, beginning during university and continuing during their career. In industry, expertise in a number of areas may be required to complete a task. Chemists tend to work in co-operative teams as wide-ranging and complex chemical issues require input from many chemists with different fields of specialisation.

They cannot perform their role in isolation as their aspect of the issue may have ramifications on other aspects handled by other chemists. It is important for chemists to work collaboratively, communicating regularly with each other and exchanging different viewpoints about problems without excessive technical jargon to ensure they work together effectively.

Chemical Reactions Requiring MonitoringCombustion forms different products under different conditions and it is important for the reaction to be monitored to ensure maximum energy output and minimal emission of harmful waste products. Thus, if an undesirable product starts to form, conditions can be changed to stop its formation. The combustion of a gas (e.g. propane from liquefied petroleum gas (LPG)) in a Bunsen burner needs monitoring.

For a high temperature flame, the air hole is opened completely so enough oxygen reaches the gas for complete combustion:

C3H8 (g) + 5O2 (g) 3CO2 (g) + 4H2O (g)

If the air hole is partly open, incomplete combustion occurs producing some carbon monoxide, and when the air hole is not open at all, carbon is produced, giving the low temperature flame its yellow colour:

2C3H8 (g) + 7O2 (g) 6CO (g) + 8H2O (g)

C3H8 (g) + 2O2 (g) 3C (s) + 4H2O (g)

In internal combustion engines, it is important to adjust the fuel-to-air ratio in the combustion of fuels as more complete combustion realises more energy, and incomplete combustion also produces poisonous carbon monoxide.

Part 2: Maximising Production

Industrial Uses of AmmoniaAmmonia is a very important industrial chemical and is used widely in both its pure form and as a feedstock for a variety of other chemicals. It is used to make fertilisers, fibres and plastics (e.g. nylon), household cleaners, detergent, effluent treatment and nitric acid, which can be used to make explosives. Ammonia is reacted with sulfuric acid or nitric acid to form solid fertiliser industrially (e.g. ammonium sulfate, ammonium nitrate). It is also used in metal extraction (e.g. nickel and gold), refrigeration and some pharmaceuticals.

The Synthesis of AmmoniaThe Haber process is the industrial process of ammonia synthesis from its component gases, nitrogen and oxygen. The synthesis of ammonia occurs as a reversible reaction that will reach equilibrium. The forward reaction of nitrogen and hydrogen to produce ammonia is exothermic.

N2(g) + 3H2(g) ⇌ 2NH3(g) ∆H = -92kJ/mol

N2 can be collected by the distillation of liquid air, while H2 can come from the electrolysis of water or when natural gas is brought in contact with steam:

CH4 (g) + H2O (g) CO (g) + 3H2 (g)

Temperature and Yield of the Haber Process Higher temperatures increase the kinetic energy of the reactant molecules, giving more of the molecules enough energy to overcome the activation energy, thus attaining the equilibrium faster and increasing the rate of reaction.

However, as the synthesis of ammonia is exothermic, a high yield is favoured by low temperatures, but then the reaction rate is too slow to form ammonia at a reasonable rate. According to Le Chatelier’s principle, high temperatures would favour the decomposition of ammonia into nitrogen and hydrogen as the Haber process is exothermic. Consequently, the yield of ammonia is reduced at higher temperatures.

Compromise and Pressure in the Haber ProcessHigh temperatures are favoured for a fast rate of reaction, but since the reaction is exothermic, this would reduce the yield. High gas pressures increase the reaction rate as more effective collisions occur and the equilibrium is shifted to the right.

Thus, a compromise is struck between a high yield and a rapid reaction rate. Ammonia production if favoured by high pressures of 2.5x104 kPa (250 atm.) and temperatures of about 400°C. The reaction is prevented from reaching equilibrium by continually removing ammonia by liquefying it under pressure. The unreacted nitrogen and hydrogen recirculate in the reaction chamber for reuse and the reaction is effectively driven to completion.

Heat released is removed to maintain the temperature and used to heat reactant entering the chamber. As a stoichiometric mixture of nitrogen and hydrogen is used, leftover reactants will recycle without the accumulation of any one reactant.

Also, pressures are not made as high as possible due to economic and safety considerations, including lower running costs, longer lifetime of the reaction vessel and to improve the safety of workers.

Catalysts in the Haber ProcessA catalyst is a substance that increases the rate of reaction by lowering the activation energy for the reaction. This results in a lower temperature at which the reaction is carried out, as the reactants require less energy for successful collisions. A catalyst of magnetite, Fe3O4 (FeO.Fe2O3) which has a surface layer that reduces to free iron, is used.

Monitoring the Reaction Vessel Used in the Haber ProcessMany conditions need to be maintained for safety and efficiency, so monitoring is essential:

Temperature and pressure need to be kept in the range for optimum conversion of the reactants to the products. Excessive temperatures can damage the catalyst

Mixture of the reactants needs to be kept at stoichiometric ratios to avoid the build-up of one reactant

The exclusion of oxygen as it is explosive. Sulfur compounds and carbon monoxide can poison the catalyst and reduce the adsorption of the reactants

The purity of the product needs to be maintained Avoid the accumulation of unreactive gases (e.g. argon and methane) which can

lower the efficiency of the conversion The ammonia liquefaction process is monitored to ensure optimal yield

Significance of Haber Process in World HistoryIn 1904, some Austrian industrialists asked Haber to study the formation of ammonia from nitrogen and hydrogen, and in 1905, he published his work, recording the production of small amounts of ammonia from nitrogen and hydrogen at 1000°C using an iron catalyst.

In this period, Germany was importing large amounts of nitrate salts from guano deposits in Chile and the islands off the coast of Peru, which were rich in phosphates and nitrogen compounds. This demand arose from that discovery that adding nitrates, phosphates and potassium were effective at increasing agricultural crop yields.

By 1913, Germany was importing one third of the nitrate salts exported from South America. With the outbreak of WWI in 1914, the British navy prevented the import of nitrogen compounds into Germany and without the Haber process Germany would have run out of explosives and food. Consequently, Haber’s contribution effectively prolonged the war by overcoming Germany’s supply constraints.

The Haber process enabled the relatively cheap production of ammonia on a large scale. Carl Bosch overcame the high pressure engineering problems and supervised the building of ammonia industrial plants during the war. This process allowed Germany to become independent of imported nitrogen compounds, which also prolonged the length of the war.

However, over the long run, the Haber process has benefited humans as with increasing populations, traditional farming techniques were insufficient (e.g. crop rotation) as greater quantities of food were required, leading to the depletion of natural deposits of nitrogenous

fertilisers, but the Haber process was able to overcome these shortages. The industrial synthesis of ammonia has facilitated the manufacture of fertilisers for food production, which has helped to sustain the world’s population.

Part 3: Manufactured Products are Analysed

Ion TestingQualitative analysis of unknown chemicals such as precipitation tests and flame tests can identify many soluble ions.

Ion Colour in Solution Confirmatory Test Spot TestCationBariumBa2+

Colourless H2SO4 solution forms white ppt. BaSO4

Sodium sulfate solution forms white BaSO4 ppt.

CalciumCa2+

Colourless Forms white ppt. with NaF

LeadPb2+

Colourless Forms bright yellow ppt. with KI

Sodium hydroxide solution forms Pb(OH)2 ppt, which dissolves with excess NaOH

Copper(II)Cu2+

Blue Sodium hydroxide solution forms blue ppt. of Cu(OH)2

Iron(II)Fe2+

Pale Green If left for a day, it changes to an orange brown solution. Decolourises KMnO4. K3Fe(CN)6 forms blue ppt.

Sodium hydroxide solution forms green ppt., which does not dissolve with excess NaOH

Iron(III)Fe3+

Orange-Brown Solution of K4[Fe(CN)6] forms blue ppt. of KFe[Fe(CN)]6

Sodium hydroxide solution forms reddish-brown Fe(OH)3 ppt., which does not dissolve with excess NaOH

AnionChlorideCl-

Silver nitrate solution forms white AgCl ppt., which slowly darkens when exposed to light

SulfateSO4

2-Forms white precipitate with Ba2+ ions

CarbonateCO3

2-Forms bubbles of CO2 when acid is added

Evolve carbon dioxide gas when reacted with an acid

PhosphatePO4

3-HNO3 and (NH4)2MoO4 form yellow ppt. of (NH4)2PO4.12MoO3

Ammonium molybdate solution acidified with HNO3 forms canary yellow ppt. of ammonium phosphomolybdate

Atomic Absorption Spectroscopy (AAS)Atomic absorption spectroscopy (AAS) is a technique used to identify the presence and concentration of metal ions in solution and is very sensitive being able to detect very small concentrations of elements. It works using the principle of the absorption spectra of elements where atoms absorb radiation of specific wavelengths characteristic of the element.

To determine the concentration of a certain metal ion in a sample, the following steps occur within an atomic absorption spectrometer:

Using a cathode of the element being measured, a cathode lamp generates light of specific wavelengths characteristic of the element being analysed

A series of diluted standard solutions of the metal being analysed are vaporised in the flame. As the light passes through the atomised sample, certain wavelengths are absorbed by electrons as they become excited

After passing through a monochromators, the intensity of the resultant beam is measured, usually by photomultiplier tubes. The diluted standard solutions tested produces a calibration curve to which the unknown sample can be compared with

The relative intensity within each of the bands in the absorption spectrum indicates the concentration of the element in the test sample

A trace element is an element required in minute amounts for the normal growth of organisms and work by helping enzymes to function. Before the development of AAS, analytical methods were not sensitive enough to detect these elements’ concentrations.

Through AAS, scientists have become aware that very small amounts of certain elements can have a large impact on a biological system, especially in agriculture where trace elements in soil can affect plant growth.

Also, elements required for specific biochemical pathways and body functions have been identified, such as:

Iron for properly functioning haemoglobin Iodine for a properly functioning thyroid Zinc for amino acid production, metabolism and energy production.

Other applications of AAS include: Monitoring pollutants in the air, water, soil and food (esp. heavy metals) Testing blood and urine samples for excess or deficiency of certain element for the

diagnosis of certain medical conditions Detecting metal content in mineral samples to determine economic viability of

mining and metal extraction processes

Part 4: Human Activity and the Atmosphere

Composition and Structure of the AtmosphereThe atmosphere is a layer of gas about 200-300km thick that surrounds the Earth. Nitrogen, oxygen and argon account for 78.08%, 20.95% and 0.93% of the atmosphere respectively. Carbon dioxide concentrations are at 350ppm.

The troposphere is the atmospheric layer closest to the Earth’s surface, with an altitude of 0-15km, where temperature decreases with altitude, reaching a minimum of -50°C, so convection ensures that gases are well mixed. The stratosphere is at an altitude of 15-50km. It is the region where temperature increases with altitude from -50°C to 0°C, so there is little vertical mixing. The temperature minimum at the tropopause means that substances do not easily transfer between these two regions.

The mesosphere extends from 50-80km above the Earth’s surface, with temperature dropping with increasing altitude to about -100°C and is the coldest layer of the atmosphere. The thermosphere is located from 85km above the Earth’s surface with temperatures increasing with altitude. Gas species include ions, atoms and free electrons, which would be unstable at lower altitudes.

Pressure steadily decreases as altitude increases and there are no maxima or minima. At the tropopause, pressure is about 10kPa and 0.1kPa at the stratopause.

Pollutants in the Lower AtmospherePollutant Source EffectsCarbon monoxide Incomplete combustion in cars, bush, forest and farm

fires, cigarettes, slow combustion stovesDirect poison

Methane Decomposition of organic matter, natural gas seepage Greenhouse effectSulfur dioxide Combustion with impurities in the fuel, metal

extraction, chemical manufacturingSmog, acid rain

Radioactivity Combustion, uranium mining, nuclear power plants, medical and scientific use of radioisotopes

Harmful to humans and other living matter

Chlorofluorocarbons (CFCs)

Fridges, air conditioning, foam plastics, electronics cleaning, halon fire extinguishers

Ozone depletion in the stratosphere

Oxides of nitrogen High temperature combustion in vehicles and power stations

Acid rain, photochemical smog

Particulates Combustion, agricultural and industrial processes (e.g. mining) bush fires, dust storms, asbestos and fibrous cement boards

Respiratory problems

OzoneOzone is an allotrope of oxygen. Near the surface, the concentration of ozone is only 0.02ppm, while in the stratosphere it ranges from 2-8ppm. Ozone is toxic to humans and other life forms if inhaled or they come into contact with it. Ozone can cause respiratory issues, headaches and fatigue. As a strong oxidant, it attacks essential biological compounds, disrupting biochemical processes in the body.

In the stratosphere, ozone protects all life forms by filtering out short wavelength UV radiation that damages living tissue. Without it, strong UV rays would be able to break bonds in important biomolecules, such as proteins and DNA. Greater exposure to UV can cause sunburn, skin cancer, cataracts and increased mutations.

However, ozone is a pollutant in the lower atmosphere when there are high concentrations of NO2 in the presence of sunlight. The sunlight splits an O atom of the NO2 molecule, which combines with O2 to form O3, contributing to photochemical smog.

Coordinate Covalent BondsA coordinate covalent bond is where the both of the shared electrons came from only one of the atoms. An ozone molecule consists of 3 oxygen atoms joined together. This occurs when one of the O atoms of the O2 molecule use a lone pair of electrons to form a new covalent bond with the third O molecule.

Allotropes of OxygenProperty O2 O3

Description Colourless gas condensing to a pale blue liquid, odourless,essential for all living matter

Colourless gas condensing to a distinct blue liquid, strong and distinctive odour, poisonous

Boiling point -183°C -111°CMelting point -219°C -193°CDensity Slightly denser than air 1.5 times that of airSolubility in water Sparingly soluble More soluble than O2

Stability Very stable Easily decomposed to O2

Reactivity Reacts with most elements to form oxides, moderately strong oxidising agent

More reactive than oxygen, very strong oxidising agent

Uses Medically for breathing problems, steel-making, used in space shuttles and rockets

Sterilisers in kitchens, purification of water, bleaching agent

Allotropes are different forms of the same element that exist in the same state and have different properties. Differences in physical properties are due to ozone being larger and heavier than the oxygen, increasing dispersion forces between molecules. When molecular oxygen reacts, the double bond needs to be broken which requires more energy to break than a bond in ozone which is about 1.5 bonds, thus ozone is more reactive than oxygen.

A free radical is a neutral species that has an unpaired electron and can be formed by splitting a molecule into two neutral fragments. O2 and O3 molecules are more stable than the O atom as they have a full valence shell, while the radical only has 6 valence electrons. O2 is moderately reactive, O3 is more reactive and O atoms are even more reactive.

O atoms readily react with most organic compounds at room temperature, while oxygen only reacts with organic compounds at elevated temperatures.

Chlorofluorocarbons and Halons in the AtmosphereChlorofluorocarbons (CFCs) are compounds that contain chlorine, fluorine and carbon. CFCs were introduced as ‘freons’ to replace ammonia in refrigerants. Their dependence on pressure made them ideal working fluids. Its properties of low melting points, being odourless, non-flammable and very inert made them attractive to use as solvents, propellants and blowing agents in foams.

After WWII, CFCs became widely used in aerosol spray cans and later in the production of foam plastics, such as polystyrene, as a foaming agent and the cleaning of circuit boards. The use of CFC products resulted in the direct release of CFCs into the atmosphere. As they were inert and non-toxic, their release was not considered an issue.

Halons are compounds of carbon, bromine and other halogens. Halons were used extensively in fire extinguishers because of their fire retardant properties, such as bromochlorodifluoromethane that were used in BCF fire extinguishers.

Naming HaloalkanesHaloalkanes are compounds where one or more of the H atoms have been replaced by an atom of a halogen, such as chloroethene (C2H5Cl). Isomers are compounds with the same molecular formula, but different structural formula.

1) Chloro-, fluoro-, bromo- and iodo-, are used as prefixes for the haloalkane2) The halogen’s position is denoted by the number of the corresponding carbon. If

more than one of each halogen atom is present, di-, tri-, tetra- are used and a location number is given for each such atom

3) The carbons are numbered so that it leads to the smaller sum of the substituent numbers

4) If more than one halogen atom is present, they are listed alphabetically according to the halogen

5) If this leads to 2 possible names, the correct name is the one that gives the lowest numbers to the most electronegative halogen with F > Cl > Br > I

Problems with the Use of CFCs In the stratosphere, short wavelength UV radiation acts upon oxygen gas to form oxygen atoms, which combine with O2 molecules to form ozone. The ozone then absorbs longer wavelength UV radiation, which decomposes the ozone back to oxygen.

Production: O2 (g) + UV light 2O· (g) O2 (g) + O· (g) O3 (g)

Decomposition: O3 (g) + UV light O2 (g) + O· (g) O· (g) + O· (g) O2 (g)

Due to the inertness of CFCs, they are not decomposed by oxygen or sunlight at low altitudes and are not washed out of the atmosphere by rain as they are insoluble. As such, they accumulate in the troposphere and slowly diffuse into the stratosphere, where they can come into contact with short wavelength UV radiation, breaking off a chlorine atom of the CFC molecule.

This reacts with ozone to form a ClO free radical that is very reactive and will react with free oxygen atoms to form an oxygen molecule as well as a separate Cl atom.

Cl·(g) + O3(g) ClO·(g) + O2(g)

ClO·(g) + O·(g) Cl·(g) + O2(g)

Overall: O·(g) + O3(g) 2O2(g)

The net result is that an ozone molecule and an oxygen atom have been converted into two oxygen molecules and the Cl atom is free to continue the process. This results in a chain reaction where one Cl atom may destroy thousands of ozone molecules.

An issue is the localised and seasonal nature of ozone depletion over the Antarctic in spring as in the Antarctic winter, the polar vortex traps air above the South Pole. During this time, the extremely cold conditions and no sunlight mean that ice particles catalyse this reaction in polar stratospheric clouds:

HCl(g) + ClONO2(g) Cl2(g) + HNO3(g)

However in spring, the sunlight is able to split Cl2 molecules, meaning there is an extra source of chlorine atoms and greater rates of ozone depletion.

Ozone depletion allows higher levels of UV radiation to reach the Earth’s surface and results in:

Increased incidence of skin cancer and sun burn Increased risk of eye cataracts Increased risk of illness and disease as it reduces immune response Reduced plant growth due to interference with photosynthesis

Since 1987, there have been several international agreements that nations have undertaken to phase out the use of CFCs and ozone depleting compounds. The original agreement was the Montreal Protocol, with the most recent agreement in 1992 that aimed to stop halon usage and the manufacture and use of CFCs. Developed nations were required to phase out the use of CFCs by the end of 1995 and halons by 1993, while developing nations had until the end of 2010. Alternatives to CFCs have been developed (e.g. HFCs), which has helped most countries to achieve targets to phase out the use of CFCs.

Although there has been extensive depletion of ozone, the damage is reversible and stratospheric ozone will eventually recover. However, even if nations stop using ozone depleting substances now, it will still take 50 to 100 years for complete recovery to occur as CFCs are still present and take time to disappear. However, as emissions are reduced, concentrations of CFCs will fall and so diffusion into the stratosphere and ozone depletion will decrease. The World Meteorological Organisation suggests that the hole in the ozone layer over the Antarctic has shrunk by 15% in recent years and that the ozone layer will recover to its 1980s levels in 2068. Some sources suggest that the concentration of CFCs remains largely the same and the ozone hole hasn't becoming smaller. Scientists can monitor progress

through using ground-based instruments, instruments in satellites and from instruments in balloons.

Measuring Ozone ConcentrationsGround Based MeasurementsUV Spectrophotometers can be used to make measure ozone levels, including the Dobson Spectrophotometer and Light Detection and Ranging (LIDAR). It makes total ozone measurements by comparing a frequency of the UV spectrum that is strongly absorbed by ozone (308nm) with one that is not (351nm), either from the Sun or using ultraviolet lasers beams that are detected using spectrophotometers.

Airborne MeasurementsThis can involve balloons, rockets and aircraft. Ozone sondes (balloon borne) usually measure the ozone concentration using electrochemical concentration cells that measures the current produced when a solution of KI (aq) reacts with O3 in the air pumped into the cell, which is proportional to the concentration of O3.

Rockets measure ozone using photospectroscopy which uses film or electronic sensors sensitive to UV to measure wavelengths affected by ozone. Aircraft are used to make detailed measurements of ozone, carrying multiple instruments to achieve this.

Satellite MeasurementsThese provide comprehensive data regarding ozone concentrations globally. The Total Ozone Mapping Spectrometer (TOMS) provides global measurements of total column ozone on a daily basis and as measured using Dobson Units. Global ozone maps are being provided by the Ozone Monitoring Instrument (OMI) aboard the Aura satellite.

Part 5: Water Monitoring and ManagementDetermining Water QualityDefinition Impacts Possible SourcesCations, heavy metal cationsPositively charged ions

Unhealthy balance of cations can impair cell functioning. Most heavy metals are toxic to living things, with organisms higher in food chain being more vulnerable.

-Industrial discharge-Mine drainage-Road runoff-Atmospheric pollution

AnionsNegatively charged ions

Nitrates and phosphates can cause eutrophication. If DO is low, sulfates can form H2S. If acidic, H2SO4 can form.

-NO3- and PO4

3- come from ag. and urban runoff-SO4

2- and CO32- comes from

surrounding geologyTotal Dissolved SolidsThe total mass of dissolved solids per unit volume of water

High levels of dissolved salts can:-Impair cell function in aquatic organisms-Impact on crops-Be unsatisfactory for stock-Cause corrosion of irrigation equipment

-Wastewater plant effluent-Urban runoff-Agricultural runoff (esp. in heavy fertilised areas)

HardnessMeasure of ability of water sample to lather soap (levels of Mg2+

and Ca2+)

Difficult to use as it can:-Prevent effective washing-Cause blockages of pipes as Ca2+ precipitates in presence of CO3

2-

-Geology (esp. in limestone areas)-Industrial influences (e.g. cement dust)

TurbidityMeasures of the suspended solids in water. Ability of the sample of scatter light

High amounts of suspended solids can:-Smother gills (suffocation)-Block entry of light into water and limit photosynthesis-Impair recreational waters-Damage irrigation equipment (e.g. blockage)

-Urban runoff (esp. in construction areas)-Roads-Agricultural areas (esp. cleared or turned ground)

AcidityMeasure of the pH (acidity/alkalinity) of water sample

Excessive changes to pH can:-Damage cell function-Damage egg hatching and spawning-Increase levels of toxic metals and ammonia being released into environment

-Agricultural runoff (esp. manures and composts)-Acidic mine drainage-Acid rain

Dissolved OxygenMeasures of amount of oxygen dissolved in the water

Low levels of DO can:-Result in suffocation of organisms-Change water pH (toxicity effects)High levels or varying DO levels can:-Cause pH changes outside the organisms level of tolerance

-Aquatic plants and algae supply DO, but too much leads to swings-Agitation of water aerates it (e.g. rocks)-Lack of flow decreases DO

Biochemical Oxygen DemandMeasure of DO needed to completely breakdown organic matter in the water by aerobic bacteria.

High BOD can cause oxygen levels to fall-suffocation of aquatic life-changes in toxicity of metals(Measure of organic pollution)

-Urban and agricultural runoffs-Discharge from industry and sewage treatment plants.

Name Type of Analysis Description of Analysis

Cations, heavy metal cations

AAS -Tested on the Atomic Absorption Spectrophotometer and concentration of heavy metals obtained

Anions Colourimetric (NO3

-, PO43-)

turbidimerric (SO4

2-)

-Nitrate passed through Cd reduction column to convert nitrate to nitrite. Reagents added to produce pink reaction product. Compared with standards to give concentrations-Sample digested with acid to convert phosphorous to phosphates. Reagents added to produce blue reaction product. Compared with standards to give concentrations-Turbidity determined before and after addition of BaCl2

Total Dissolved Solids

Gravimetric and electrode

-A crucible is weighed and a shaken sample of a known volume of water is passed through filter paper-Dissolved material passes through filter paper-Crucible is heated to allow water to evaporate until a constant weight is attained-Conductivity assuming all dissolved solids are ionic

Hardness Titration or AAS -Tested on Atomic Absorption Spectrophotometer and concentrations of Ca2+ and Mg2+ obtained-Alternatively titrated against EDTA and concentration determined by volumes of EDTA used

Turbidity Gravimetric -Filter paper is weighed and shaken sample of known volume of water is passed through filter paper-Suspended material is retained on filter paper-Filter paper is placed in oven until a constant weight is attained-Turbidity tube

Acidity pH probe, indicator

-Measured using pH electrode-Indicators change colour

Dissolved Oxygen

Probe or titration

-DO meter (measure concentration of oxygen in solution)-Titration using the Winkler method

Biochemical Oxygen Demand

Probe or titration

-A sample is collected and split into two-One same is tested immediately for DO, while the other is kept in the dark at 20°C for 5 days-Bacteria present will multiply and use organic material as food source, also consuming oxygen-After 5 days, a DO test is done on the second sample-The BOD is calculated from the different between the initial and final dissolve oxygen levels

Analysing Water QualityWinkler Method of Determining Dissolved Oxygen1) Add 2mL manganese sulfate solution to a 100mL sample of water, then add 2mL of the

alkaline iodide solution – stopper and mix2) Add 2mL of conc. H2SO4 – stopper and mix to dissolve the precipitate (solution should be

yellow-brown)3) Pipette 100mL of this into a conical flask and using starch as an indicator, titrate with

sodium thiosulfate solution until the colour changes from blue-black to colourless

Concentration of Ions in Natural Water BodiesFactor EffectSewerage Treatment Plant Effluent

Increase in the TDS of the water, especially with phosphate and nitrate ions

Agriculture Fertiliser runoff and manure increase the level of phosphates and nitrates in the water, so BOD and turbidity increase. Ammonia is commonly used in poultry farming, which oxidises to form nitrates. Copper and arsenic previously used in fungicides.

Land clearing Removal of vegetation results in an increase in suspended and dissolved solids, due to the lack of plant roots. Exposes soil to more leaching. Bark, twigs and leaves washed into waterways

Industrial Effluent Contributes to an increase in ion concentration in waterways, particularly heavy metals

Landfill Sites Older tips are not lined with PVC and clay, so leachate water flowed into waterways and contained lead, mercury and other heavy metals

Stormwater Can increase concentration of nitrates and phosphates from sewerage, fertilisers and pet droppings. High in heavy metals from road runoff.

Geology Most natural minerals are leached from the soils already, so ion concentrations in water are low. Water flowing through limestone areas can increase the level of calcium ions

Water Temperature Many minerals are more soluble at higher temperaturesRate of Evaporation Greater evaporation rates increase the concentration ionsFrequency of Rainfall

More frequent rainfall increases the runoff into waterways. Flooding/heavy rain can reduce the ion concentration but lead to increased turbidity from agitation

Methods to Purify and Sanitise Water SuppliesStep 1: AerationWater is sprayed into the air to increase the concentration of dissolved oxygen. Dissolved hydrogen sulfide gas is oxidised to sulfate ions and iron salts are oxidised to insoluble iron oxides to be removed later

Step 2: FlocculationWater contains small suspended particles, which are prevented from settling due to the repulsion between their negative surfaces, but can be made to precipitate by flocculation. Alum (aluminium sulfate) is added to the water to produce a gelatinous precipitate of aluminium hydroxide, which traps suspended particles, including some microbes.

Al3+(aq) + 3H2O(l) Al(OH)3(s) + 3H+

(aq)

The hydrogen ions are attracted to the surface of the aluminium flocs, with the negative surfaces of the clay colloids attracted to the positive surfaces of the flocs. Iron oxides and other soluble coloured compounds also adhere to flocs.

Step 3: SedimentationThe treated water is allowed to stand so that the flocs settle at the bottom of the tank and form a sludge, which can be removed periodically (removes ~95% of suspended impurities)

Step 4: FiltrationWater from settling tanks is passed through a filter of sand and gravel to remove remaining suspended particles, and other minerals, bacteria and coloured matter. The water should now be clear (<3 NTU), but if there is still colour from dissolved organic matter, it is passed through layers of activated carbon which adsorbs the coloured matter onto its surface.

Step 5: Chlorination and Microbiological TestsThe filtrated water is chlorinated to kill bacteria and other microbes through the production of hypochlorite ions. Biochemists test for coliforms that are associated with manure. The level of chlorine is monitored to prevent the formation of carcinogenic chlorinated alkanes.

Cl2(g) + H2O(l) 2H+(aq) + Cl-

(aq) + OCl-(aq)

Step 6: FluoridationCompounds such as sodium fluoride, calcium fluoride and sodium fluorsilicate (Na2SiF6) are added to the water to achieve a fluoride concentration of about 1ppm. This is because this small amount of fluoride is enough to strengthen tooth enamel and prevent tooth decay. The water should now have a pH between 7 and 8.5, though lime may be added to achieve the desired pH. The pH adjustment is important as it reduces the corrosion of water pipes.

Assessment:Current methods are not perfect at removing pathogens as such by the Giardia and Cryptosporidium incident in Sydney in 1998. Further techniques could be introduced (e.g. membrane filters and ozone sterilisation), but this would be more expensive. Thus, water is monitored daily at treatment plants.

Microscopic Membrane FiltersMicroscopic membrane filters have microscopic pores and the use of appropriate sized filters can avoid the need to chemically treat the water and are classified according to the pore size. The membrane is made from synthetic polymers (e.g. polypropylene, polytetrafluororethylene and polysulphone) dissolved in a mixture of solvents. Water soluble powders of a particular size are added and the mixture is spread over a plate and left for the solvent to dry.

The membrane formed is then placed in water, so the powder particles dissolve, leaving a very thin polymer sheet with definite sized microscopic pores. Semi-permeable membranes for reverse osmosis are either made of cellulose acetate or a layer of polyamide attached to another polymer. Water is made to flow across the membrane, not through it, to reduce the blockage factor.

Microfiltration is useful for removing solid particles such as suspended solids but it is not able to remove dissolved natural organic matter. Of the membrane filters, it has the largest pores and the actual filter material is bundles of hollow fibre polymer threads.

Ultrafiltration is not as fine as nanofiltration, but does not require the same energy to perform the separation. It can remove bacteria, many viruses, some proteins and other natural organic substances, some dyes and constituents greater than 10 000 amu. However, it is not very effective at separating large organic molecules from each other.

Nanofiltration is able to remove organic molecules ranging from 300 – 1000 amu as well as many divalent and trivalent cations. They are commonly composed of cellulose acetate or polyamide polymers. It is capable of removing sugars, divalent salts, bacteria, all viruses, proteins, particles, pesticides, herbicides and dyes.

It is not effective on small molecular weight organic materials, such as methanol, and particles with large charges are more likely to be rejected. However, a significant amount of the water produced is needed in the backwashing of the membrane, making it unfeasible.

Reverse osmosis is usually used in desalination plants. Sea water is forced into a cylinder (with tiny hollow fibres of semi-permeable membrane) under high pressure and water moves into the fibres, leaving behind a more concentrated salt solution as the tiny pores allow small water molecules through, but not larger particles.

Purification Technique Pore Size Usually Removes…Sand filtration 100 microns Most silt, sand and adhering microbesMicrofiltration 0.1-1 microns More and silt and sand and various microbes,

but not virusesUltrafiltration 0.005-0.05

micronsSilts, sands, clays, many viruses and some coloured organic molecules

Nanofiltration 0.5-5 nanometres

All organic molecules down to 300 amu, and some salts with di/trivalent cations

Heavy Metal DetectionHeavy metals are a range of metals with relatively high atomic mass that are toxic at very low concentrations (e.g. Pb, Cd, Cu, Hg). These metals can build up in tissues of aquatic organisms and these levels increase along the food chain as they bioaccumulate.

The concentration of heavy metals can be determined quantitatively using flame AAS or qualitatively using precipitation reactions. Heavy metal pollution can generally be identified using a precipitation test with Na2S solution.

Monitoring the Eutrophication of WaterwaysEutrophication is the enrichment of bodies of water by excess nutrients. As Australian soils are nutrient deficient, farmers have added large volumes of fertiliser for agricultural purposes, but when it rains, some of this can be washed into water. Other sources are animal manure and treated sewerage.

This results in an increase in nutrients, especially phosphorus, which stimulates the growth of aquatic plants and algae. This also happens to blue-green algae, which releases toxins into the surrounding water killing small organisms and causing liver damage to livestock.

Excess plant growth strips the water of CO2 due to photosynthesis, which alters the pH as carbonic acid is effectively removed. The pH becomes alkaline, affecting the health of other aquatic organisms and may increase the toxicity of some metals as they are more likely to dissolve. However, at night when the plants respire, they may strip the water of O2, causing large fluctuations in dissolved oxygen, which can stress organisms and make them more vulnerable to diseases and reproduction issues. Filtration can be used to take out the algal

cells, but the toxins remain, which can then be removed by running the water over activated carbon.

Nitrate Analysis1) Filter the sample and divide it into 2 subsamples2) Test the first subsample for nitrite by adding a few drops of sulphanilamide solution and

NED reagent and swirling, which should result in a pink colour.3) Determine its absorbance using a UV-Vis spectrophotometer4) Reduce any nitrate in second subsample to nitrite by passing it through a cadmium

reduction column5) Using the second subsample, repeat steps 3 and 4 and determine the level of nitrate by

subtracting the nitrite from the first subsample from the second subsample

Phosphate Analysis1) a) To determine the level of total phosphorous, pour a 25mL sample of the water into a

small beaker and add 2-3mL of concentrated H2SO4. Heat the solution gently on a hotplate to release all the bound and biological phosphates. Allow to cool then neutralise with a few drops of NaOH

b) To determine the level of dissolved phosphorous, filter a 25mL sample of the water, which should remove any clays, particulates and algae

2) Transfer the samples from either Step 1a or 1b (depending on what is being measured) into a test tube

3) Add a few drops of mixed reagent (H2SO4, potassium antimonyl tartrate, ammonium molybdite, citric acid) to the test tube, which should develop a blue colour

4) Determine its absorbance using a UV-Vis spectrophotometer

The Sydney CatchmentA catchment is an area where water is collected by the natural landscape. Sydney’s catchment covers 16 000 square kilometres and its capacity is greater than 2.4 million mega litres. Special Areas protect our water supply by acting as a buffer zone to help stop nutrients and other substances that could affect the quality of water entering the storages. Sydney Catchment Authority uses a multi-barrier approach to ensure the quality of Sydney’s water supply by taking actions across various points in the system.

Possible sources of contaminants to waterways: Agriculture (crops and animals)

o Pesticides and fertilisers – algal blooms, eutrophication, increased BODo Bank erosion and manure – increased TDS and nutrients and turbidity

Natural bushlando Leaves, twigs, branches

Urban developmento Stormwater (incl. detergents, faecal coliforms and rubbish) – increased bacteria

and BOD, phosphates and algal bloomso Road runoff – petrol, greases, oils

Industrial developmento Coal mining, quarrying – increased heavy metals and toxicity, dust and turbidityo Old mines – acidic and soil runoff, increased TDS, turbidity and heavy metalso Abattoirs – increased organic material, TDS and BOD