Module 3; Chemical Monitoring and Management;

1. Much of the work of chemists involves monitoring the reactants and products of reactions and managing reaction conditions;

1. Outline the role of a chemist employed in a named industry or enterprise, identifying the branch of chemistry undertaken by the chemist explaining a chemical principle that the chemist uses;

‘and’1. Gather, process and present information from secondary sources about the work of practising scientists identifying;

The variety of chemical occupations A specific occupation for a more detailed study

Variety of chemical occupations

Roles of chemists are becoming increasingly diverse and important Chemists may be involved in:

Soil, water or air analysis Developing new materials, or managing production in:

o Pharmaceuticalso Foodso Agricultural productso Metalso Fuelso Plasticso Electronics and electro-chemical industries

Criminal investigation Pollution and corrosion control Environmental science and protection Quality assurance

Specific occupation

Drug research chemist: o Role: development of new pharmaceuticals to improve treatment

of diseases or medical conditionso Branch of chemistry: mostly organic chemistry

o Chemical principle – chemical synthesis (pain relievers) Involves testing substances designed for specific purposes

→ E.g. using AAS for determining amounts of ions present in samples and also performing titrations to monitor the concentration of substances in a sample

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

All scientists must work in teams Team of chemists may have some members who specialise in different fields

or have prior knowledge from past experience This means that collaboration is a vital aspect of the collection and analysis

of data

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

Oxygen availability in combustion reactions

Good supply of oxygen = complete combustion – CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (g)

Shortage of oxygen = incomplete combustion – CH4 (g) + 3/2O2 (g) → CO (g) + 2H2O (g)

Incomplete combustion is undesirable because: Less energy is released per unit of fuel used Carbon monoxide is toxic

Therefore, a chemist may be employed to monitor the combustion process by regularly:

Measuring the fuel: oxygen ratio Measuring the composition of exhaust gases

2. Chemical processes in industry require monitoring and management to maximise production;

1. Identify and describe the industrial uses of ammonia;

There are a variety of industrial uses of ammonia: Production of fertilisers, e.g. ammonium sulfate Production of nitric acid which is used in making explosives such as

TNT Ingredient in cleaning agents

2. Identify that ammonia can be synthesised from its component gases, nitrogen and hydrogen;

‘and’3. Describe that the synthesis of ammonia occurs as a reversible reaction that will reach equilibrium;

‘and’4. Identify the reaction of hydrogen with nitrogen as exothermic;

Ammonia can be synthesised from its component gases, nitrogen and hydrogen→called the Haber process

The reaction is reversible and reaches equilibrium

The forward reaction is exothermic

5. Explain why the rate of reaction is increased by higher temperatures;‘and’

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

At higher temperatures, there is:o Less yield (favours reverse reaction according to Le Chatelier’s

principle)o Higher rate of reaction

Particles have more energy – higher tendency to collide

At lower temperatures, there is:o More yield (favours forward reaction, according to Le Chatelier’s

principle)o Lower rate of reaction

Particles have less energy – less collisions/slower reaction

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

The conditions under which Haber process is carried out must be carefully chosen

A balance must be struck between yield and rate of reaction

→i.e. raised temperature will decrease yield but increase rate of reaction

A balance is struck at about 500oCo 30-40% yieldo Rate of reaction is satisfactory

8. Explain that the use of a catalyst will lower the reaction temperature required and identify the catalyst(s) used in the Haber process;

The catalyst used in the Haber process is a finely ground iron-oxide catalyst which absorbs the nitrogen and hydrogen molecules on its surface, rearranging them to form ammonia

Lowers the activation energy necessary for the reaction to occur This means lower temperatures are able to be used, favouring yield

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

The forward reaction results in less molecules of gas Le Chatelier’s Principle says that higher pressures favour the reaction which

produces less molecules of gas Therefore higher pressures increase yield, thus a pressure of 345

atmospheres is used

High pressures also favour the rate of reaction There is higher concentration of reactants and more chance of successful

collisions occurring to form ammonia molecules

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

Reaction prevented from reaching equilibrium by removing product, ammonia (increases yield by favouring products)

It is separated from unreacted hydrogen and nitrogen by liquefying it under pressure

o Unreacted H2 and N2 recirculated into reaction chamber to be used again

o Recycling improves efficiency of process Heat released is removed to maintain temperature at around 500°C

→recycled to heat up gas mixture entering reaction chamber 

Optimal conditions include careful control of: o Temperatureo Supply of nitrogen and hydrogen (in mole ratio of balanced chemical

equation – hydrogen: nitrogen in ratio of 3:1)o Removal of ammoniao Pressureo Activity of the catalyst

Production will decrease if these aren’t at optimum level

Chemical engineer must ensure variables are monitored and controlled to keep plant functioning economically and efficiently

Safety issues arise when operating a chemical plant using gases under pressure

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

Haber was a German scientist at the time of WWI Germany was highly dependent on overseas supplies of nitrate for agriculture

and manufacture of explosives→much of the fertiliser was from Chile and Peru

Naval blockade of Germany by allied forces blocked this supply route for nitrate and other materials needed for the war effort

Haber supported his country’s war effort – realised production of ammonia was vital

His synthesis of ammonia facilitated manufacture of fertiliser for continued food production

Also, ammonia could be oxidised to nitric acid to produce explosives and other ammunition

Haber had considerable significance at that time in world history o Germans used the process to make explosives in WWI (after supplies

from Chile cut off)o Ultimately lengthened the war

 

3. Manufactured products, including food, drugs and household chemicals, are analysed to determine or ensure their chemical composition;

1. Deduce the ions present in a sample from the results of tests;

Determining unknown cations ;

Reaction table;

Cation 1. Add dilute HCl 2. Add dilute H2SO4 3. Add dilute NaOHPb2+ White/yellow ppt [lead (II)

chloride]- -

Cu2+ - - Blue ppt [copper (II) hydroxide]Fe2+ - - Pale green ppt [iron (II) hydroxide] NB:

turns brownFe3+ - - Brown ppt [iron (III) hydroxide]Ca2+ - White ppt [calcium sulfate] -Ba2+ - White ppt [barium sulfate] -

Flame tests;

Metal ColourBarium Yellow-greenCalcium Red

Determining unknown anions ;

Reaction table;

Anion 1. Add AgNO3 2. Add dilute HNO3 to pptCO3

2- Yellow ppt [AgCO3] Yellow ppt dissolves + CO2 bubbles form

Cl- White ppt [AgCl2] Ppt does not dissolve – white ppt remains

PO43- Yellow ppt [Ag3(PO4)2]] Yellow ppt dissolves

SO42- No ppt -

1. Perform first-hand investigations to carry out a range of tests, including flame tests, to identify the following ions;

Cations; o Bariumo Calciumo Leado Coppero Iron

Anions; o Phosphateo Sulfateo Carbonateo Chloride

2. Gather, process and present information to describe and explain evidence for the need to monitor levels of one of the above ions in substances used in society;

Water supply companies (e.g. Sydney Water) constantly monitor the concentration of phosphate ions in inland lakes/rivers, derived from industry/agricultural run-off:

o Provide excess nutrients causing algal blooms which lead to eutrophication of waterways

o Starve water of oxygen causing death of other marine species

2. Describe the use of atomic absorption spectroscopy (AAS) in detecting concentrations of metal ions in solutions and assess its impact on scientific understanding of the effects of trace elements;

AAS detects minute concentrations of an element in solution Each element has own characteristic absorption spectrum related to

electron energy levels;

AAS process;o Metal ion solution sprayed into flame creating vapour of atomso A light beam, frequency of which is matched to metal’s absorption

spectrum, is passed through flameo Flame containing vaporised sample absorbs some of light as it passes

througho Detector records intensity of emergent beam/calculates absorbance

of solutiono Using calibration curve formed by standard solutions of known

concentration, concentration of metal ion in solution can be deduced

Impact on scientific understanding; AAS reveals the effect of minute amounts of certain elements within

biological systems:o Agriculture;

Learned presence of trace elements in soil affect plant growth

Implications for continued production of sufficient food to feed earth’s growing population

Other applications;o Monitoring pollutants in air and watero Detecting metal content in mineral sampleso Testing blood/urine samples for excess/deficiency of particular

elements, e.g. irono Testing for toxic metals in food/drink

Assessment; AAS technology – wide application within natural/industrial worlds Significant impact on scientific understanding of effects of trace elements

in biological/mechanical systems Detect/rectify many issues

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

Calculations;

If ask for concentration of metal in solution;o Simply read absorbance/concentration off graph

If ask for concentration of metal in dilute sample;1. Read absorbance/concentration off graph. Express

concentration (ppm) in mgkg-1. [note: 1ppm = 1mgkg-1]2. Calculate mass of metal in volume of solution. Concentration

(mgkg -1 ) x mass of solution (kg) [note: given volume assume 1mL = 1g]. Express solution in mg.

3. Calculate concentration of metal in sample. Mass of metal in solution (mg) / mass of sample (kg). Express answer in mgkg-1 and ppm.

To convert from ppm to mol/L ppm = mg/kg divide by 1000 to get g/kg to get from g → moles – divide by molecular mass of substance (n = m(g)/MM)

Note: mol/kg = mol/L

Also, note dilution factor

Evaluation of effectiveness in quality control;

Compared to previous and existing technologies AAS is very effective in quality/pollution control

Trace elements in pollution would have otherwise gone unnoticed

AAS useful in monitoring concentration of heavy metals in food:o Seafood such as mussels and oysters tend to bioaccumulate heavy

metals quite readily, potentially harmful if ingested, therefore AAS is very important

Advantages; AAS made possible for low concentrations of many different trace

elements to be detected in various environments before pollution accumulateso i.e. atmosphere, soil, water, food and living organisms

Precision of equipment (i.e. measuring concentrations to ppm/ppb)o Responsible for accuracy of results and effective detection of

pollutants which would otherwise go unnoticed

Due to quick, accurate and cheap process, authorities can receive immediate results and hence take quick action in detecting source of/controlling pollution

Disadvantages; AAS equipment can only test for single ion at any given time Equipment very expensive to purchase/set up

Overall

The study of the concentration of pollutants in our environment has been greatly enhanced and is more accurate and reliable since the development of AAS.

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

Gravimetric analysis:o Dissolve ammonium sulfate fertiliser in watero Add barium chloride to precipitate BaSO4 (s) out of solution

(NH4)2 SO4 (aq) + BaCl2 (aq) → BaSO4 (s) + 2NH4Cl (aq)

o Pass through fine scintillation filter

Calculations; Mass of barium sulfate; # moles of barium sulfate;

o # = m/mm # moles of sulfate = # moles of barium sulfate Mass of sulfate;

o m = # x mm Percentage of sulfate;

o = mass of sulfate/mass of fertiliser x 100

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

Reliability – ability of experiment to yield similar results each time it is performed

Repeat expt minimum of 3 x to improve reliability Ensure all ammonium sulfate fertiliser dissolved in water:

o Heat for one houro Magnetic stirrero Addition of HCl (helps dissolve further)

All sulfate from fertiliser must be removed by precipitation – ensure reaction goes to completion

% sulfate too high if:o Precipitate contaminated with other ions present in fertiliser –

adsorbed from solution during precipitationo Precipitate not thoroughly dried – still contains water

% sulfate too low if:o Filtration incompleteo Some precipitate lost through spillageo Filter paper used instead of scintillation filter – some BaSO4 pass through

Human activity has caused changes in the composition and the structure of the atmosphere. Chemists monitor these changes so that further damage can be

limited;

1. Describe the composition and layered structure of the atmosphere;

Atmosphere is thin layer of gases that surrounds earth

Composed of gases held towards earth by gravity;o Nitrogen- 78.1%o Oxygen- 20.9%o Argon- 0.9%o Carbon Dioxide- 0.036%o Other < 0.1%

Consists of 4 layers marked by changes in temp/pressure at different altitudes

Troposphere (0-12km) Contains most of atmosphere’s mass (i.e. 90% atmosphere’s gases) Temperature decreases with altitude Highest pressure

Stratosphere (12-50km) Temperature increases with altitude ‘Ozone layer’ at 25km

Mesosphere (50-80km) Temperature decreases with altitude

Thermosphere (80-120km) Temperature increases with altitude Lowest pressure Contains ionosphere;

o Reflect radio waves (i.e. important for long distance radio communications)

Note: pressure decreases exponentially with altitude

2. Identify the main pollutants found in the lower atmosphere and their sources:

Carbon monoxide: Direct poison (i.e. readily combine with haemoglobin/prevent regular

oxygen uptake) Source – fuels burnt in limited oxygen supply (i.e. incomplete

combustion);

o e.g. car engines

Lead: Poisonous heavy metal Source – leaded fuels, metal extraction and leaded paints

Sulfur oxides: Cause smog/acid rain Source – burning of fossil fuels, smelting of sulfide ores;

Nitrogen oxides: Cause photochemical smog/acid rain Source – high temperature combustion environments such as car engines

Ozone

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

Troposphere – pollutant

Present in limited amounts due to instability and reactivity relative to O2

Component/indicator of photochemical smog;

o NO2(g) + UV → NO(g) + O*o O2(g) + O* → O3 (g)

Respiratory irritant;o Causes irritation of airwayso Contributes to increased prevalence and severity of respiratory

conditions (e.g. asthma) Poisonous at > 20ppm

Strong oxidant – change cell structure + disturb functioning of living things

Stratosphere – UV radiation shield

Formation in stratosphere:o Slow diffusion from troposphereo O2 gas + high energy UV light

O2 (g) + UV → 2O* O* + O2 (g) → O3 (g)

Absorbs UV radiation and decomposes:

O3 + UV → O2 + *O Decomposition products react back to form ozone:

O2 + *O → O3

Protects skin from damaging effects of excessive UV exposure:o Can break bonds in important molecules (e.g. proteins, DNA)o Can lead to sun burn, skin cancer and cataracts

4. Describe the formation of a coordinate covalent bond:‘and’

5. Demonstrate the formation of a coordinate covalent bond using Lewis dot structures:

A coordinate covalent bond;o Occurs when one atom provides both electrons in a covalent bondo Is indistinguishable from regular covalent bonds once formedo Is represented using an arrow (e.g. ozone: O←O = O)

e.g. O3 molecule Lewis dot structure:

e.g. formation of ammonium ion - Lewis dot structure:

Other examples

Formation of hydronium ion Carbon monoxide

6. Compare the properties of the oxygen allotropes O2 and O3 and account for them on the basis of molecular structure and bonding:

‘and’7. Compare the properties of the gaseous forms of oxygen and the oxygen free radical:

Property Oxygen: O2 Ozone: O3 ExplanationMelting/boiling point Lower Higher Ozone has stronger intermolecular forces which

require more energy to break;o i.e. Ozone is polar – more readily forms dipole-

dipole bonds, O2 is straightSolubility in water Less soluble More soluble Oxygen is non-polar – does not form strong bonds

with polar H2OOzone is polar – forms stronger bonds with polar H2O

Reactivity Less reactive (highly reactive oxidising agent)

More reactive (very highly reactive oxidising agent)

Single covalent bond in O3 requires less energy to break than double covalent bond in O2

Chemical stability More stable Less stable Based on reactivity

Toxicity Non-toxic More toxic O2 – required for respiration O3 – respiratory irritant/poisonous

Oxygen free radical (O*):

Formed when O2 is decomposed by UV radiation;o Energy released as 2 electrons un-pair to form oxygen radicals

O2(g) + UV → 2O*(g)

More reactive than gaseous forms of oxygeno Has 2 unpaired electrons in valence shell

More toxic than the gaseous forms of oxygen:o Readily reacts with organic molecules in living cells

Less stable than the gaseous forms of oxygen:o Very highly reactive (i.e. exists only briefly, reacts immediately after

formed)

Note: Allotropes are forms of the same element which exhibit different physical properties

8. Identify the origins of chlorofluorocarbons (CFCs) and halons in the atmosphere:

Chlorofluorocarbons (CFCs) are haloalkanes in which all hydrogen atoms are replaced by fluoro- and chloro- functional groups

Origins of CFCs:o Refrigerants in air conditioning/fridgeso Propellants in spray canso Blowing agents for expanded plastic products

Halons are haloalkanes in which all hydrogen atoms are replaced by bromo-, chloro- and/or fluoro- functional groups

Origins of Halons:o Previously used in fire extinguishers

1. Present information from secondary sources to write the equations to show the reactions involving CFCs and ozone to demonstrate the removal of ozone from the atmosphere

CFCs released Unreactive in lower atmosphere (inert/low boiling point) 3-5 years move into stratosphere/ozone layer

o Undergo photodissociation – UV light decomposes CFC forming Cl free radicals

e.g. CCl3F(g) + UV → CCl2F(g) + Cl•(g)

o Cl free radicals catalyse removal of ozone

i.e. O3 (g) + Cl• (g) → O2 (g) + ClO (g)

o ClO then reacts with O free radicals forming Cl free radicals + O2, producing a chain reaction

i.e. ClO (g) + O•(g) → Cl•(g) + O2(g)

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

‘and’2. Gather, process and present information from secondary sources including simulations, molecular model kits or pictorial representations to model isomers of haloalkanes:

Haloalkanes are carbon compounds that contain one or more halogen atom(s) attached in place of hydrogen atoms in hydrocarbons

Isomers – same molecular/different structural formula

IPUAC nomenclature system:o Prefix: abbreviated halogen name

fluorine – fluoro chlorine – chloro bromine – bromo iodine – iodo

o Suffix: name of appropriate hydrocarbon 1 – methane 2 – ethane 3 – propane 4 – butane 5 – pentane 6 – hexane 7 – heptane 8 – octane

o Note: number required to indicate position of halogen

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

‘and’3. Present information from secondary sources to identify alternative chemicals used to replace CFCs and evaluate the effectiveness of their use as a replacement for CFCs:

Problems: Use of CFCs has created holes in the ozone layer;

o Decreased ozone concentration has allowed more UV radiation to reach earth’s surface

Human health: Can break bonds in DNA/protein molecules Increase risk of sun burn, skin cancer and cataracts

Environmental: Kill phytoplankton/zooplankton;

o Disrupt delicate marine food chain Detrimental to crop production

o Excess UV radiation disturbs photosynthesis of plants

Industrial: Increased deterioration of synthetic polymers

o Additives now used to protect from UV radiation

Steps taken to alleviate problems:

1. Montreal Protocol (1987) International treaty designed to gain cooperation for global

reduction in production of CFCs and Halons

2. Identification/introduction of alternative chemicals Hydrocarbons now used as propellants in spray cans Hydrochlorofluourocarbons (HCFCs), Hydrofluorocarbons (HFCs)

o Replace CFCs in refrigeration and air conditioningo Lower ozone-depleting potential (ODP) than CFCs as react

more readily in lower atmosphere

Assessment/evaluation of effectiveness:

Moderately successful;o Size of Antarctic hole decreased slightly since above three measureso Although, CFCs take 3-5 years to reach stratosphere and remain there

for 150 years – little improvements thus far

o Little research conducted regarding long term effects of alternative chemicals – accurate assessment/evaluation on their effectiveness cannot be made

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

Observed changes: Ozone levels have decreased in stratosphere

o Ozone concentration over Antarctica decreased by 50% between 1975-1985

o 40% thinning in Arctic ozone layer by late 1990’so 3% loss in ozone world-wide over last 20 yearso Presence of ozone holeo Measurement of harmful radiation reaching earth’s surface

How information obtained:

1. Total Ozone Measuring Spectrometer (TOMS)

Base station – satellite Measure UV from sun (satellite/balloon) and compare with that being

reflected back from earth (on ground) Calculate absorption and hence, ozone concentration

2. UV spectrophotometers

Measure intensity of UV from sun at frequencies absorbed/not absorbed by ozone

Comparison allows calculation of ozone concentration in atmosphere

Note: located on ground, in balloons and in satellites

5. Human activity also impacts on waterways. Chemical monitoring and management assists in providing safe water for human use and to protect the

habitats of other organisms;

1. Perform first-hand investigations to use qualitative and quantitative tests to analyse and compare the quality of water samples:

‘and’1. Identify that water quality can be determined by considering:

Water quality must be monitored/managed regularly:o Domestic use (i.e. limit of 500ppm dissolved solids);

Palatable Ensure not harmful to health

o Natural aquatic systems Ensure concentrations sufficient/not harmful to ecosystem

Concentrations of common ions;o Cations:

Na+, Mg2+, Ca2+, K+, Sr2+, Fe3+

AASo Anions:

Cl-, SO42-, HCO3

-

Gravimetric/volumetric analysis

Total dissolved solids;o Salinity

Dissolved salt content of a body of water Usually ionic salts, e.g. NaCl

o Gravimetric analysis: Filtered sample evaporated Remaining solid weighed

o Calibrated conductivity metre: Electric current passed through sample Determine quantity of ionic salts (i.e. TDS) based on series of

samples

Note: Solubility of solids increase with increasing temperature Solubility of gases increase with decreasing temperature and proportional

to pressure of gas above water

Hardness;o Hardness = excess concentrations of Ca2+ and Mg2+ ionso Undesirable for domestic use:

Ca2+ and Mg2+ react with anions in soap forming insoluble salt – soaps do not lather effectively

Ca2+ react with HCO3- or SO4

2- at high temperatures producing insoluble build up on inside of kettle

Express hardness in mg Ca CO3 / L (ppm)

o Quantity of Ca2+ and Mg2+ cations determined by volumetric analysis – titration with EDTA

Turbidity;o Measure of suspended solids that make water appear cloudy

o Sources of suspended solids include: Clay Silt Industrial wastes Sewage

o Problems associated with high turbidity: Insufficient sunlight able to penetrate water for

photosynthesis Solid sediment carry imbalance of nutrients/toxic pesticides

into waterways Particles absorb infra-red radiation + raise water temperature

o Quantity of suspended solids determined by: Secchi disk;

Disk lowered into water until cross/mark disappear Depth recorded/calibrated against series of standards

Turbidity tube; Sample added to tube until cross/mark at bottom

disappears Volume recorded/calibrated against series of standards

Gravimetric analysis – filtration; Filter sample through fine pores Mass of filtered solids recorded

Acidity;o pH too high/low (2 above/below neutrality):

Domestic use – unpalatable (drinking water pH 6.5-8.5) Damaging to aquatic ecosystems

o pH of water body dependent on: Source of water Geology of catchment

e.g. limestone soils (alkaline) → pH > 7 Biological activity within system Human activity/pollution

e.g. acid rain/exposure to sulfide ores → acidic pH < 7

o pH measured by: pH meter Universal indicator

Dissolved oxygen and biochemical oxygen demand;

Dissolved oxygen:o 2 sources of oxygen;

O2 dissolved from atmosphere O2 produced by photosynthesis of aquatic plants

o 2 processes of oxygen reduction; Respiration by aquatic plants/animals Decomposition of organic matter

o Low levels of dissolved oxygen indicative of; Heat pollution Addition of organic wastes (decomposition uses up oxygen) Eutrophication (excessive growth of plants → increased

decomposition processes → increased oxygen demand)

o Quantity of dissolved oxygen measured by; Dissolved oxygen meter – calibrated oxygen-sensitive

electrode Winkler method/back titration:

Dissolved oxygen react with iodine to form yellow chemical

Solution titrated with sodium thiosulfate Each oxygen molecule associated with one iodine

molecule – able to calculate quantity of oxygen

Biochemical oxygen demand (BOD):o BOD = capacity of organic matter in water sample to consume oxygen

o Measured by;1. DOM measure dissolved oxygen quantity at day zero2. Sample left for five days in sealed container at 25oC – aerobic

bacteria decompose/oxidise organic matter (consume O2)3. DOM measure dissolved oxygen quantity at day five

Difference in two readings = BOD of sample ˃ amount of organic waste = ˃ BOD

2. Identify factors that affect the concentration of a range of ions in solution in natural bodies of water such as rivers and oceans:

Concentration of ions in oceans remains constant

Concentration of ions in rivers/freshwater lakes vary due to following factors;o Pathway of rainwater run-off

Collect different types/amounts of ionso Rate at which rainwater enters body of water

Dilute/reduce concentration of ionso Type of soil/rock water flows through

Different minerals/solubilitieso pH of rain/groundwater

more acidic → more ions dissolveo Nature of human activity near/in catchment area

Agricultural practices → ammonium/nitrate ions from fertilisers/manure

Industries/mines → discharge of waste solutionso Ability of aquatic organisms in extracting ions from water by natural

processes Reduce concentration of ions

2. Gather, process and present information on the range and chemistry of the tests used to:

Identify heavy metal pollution of water;

o Human activity/industrial waste release heavy metals (e.g. lead, mercury and cadmium) into waterways

o Can bioaccumulate in aquatic organisms and travel up food chain – highly toxic

o Main test used to identify heavy metal pollution = AAS Determine type/quantity of heavy metal present Preferred procedure due to low concentrations of heavy

metals in water

Monitor possible eutrophication of water ways;

o Eutrophication process: Excess nitrate/phosphate ions enter body of water High nutrient levels stimulate algal blooms Reduced light penetration → reduced photosynthesis →

reduced dissolved O2

Lower level plants/algae die → decompose → further reduce dissolved O2

Body of water unable to support life

o Tests to monitor concentration of nitrate and phosphate ions in waterways:

Phosphate Molybdenum colorimetric procedure;

Nitrates Kjeldahl colorimetric procedure;

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

Description of methods:

Screeningo Remove large debris

Aeration;o Spraying to convert iron salts into insoluble iron oxides for later

removal Flocculation;

o Chemicals added to cause coagulation/form flocs (i.e. easier to filter) Sedimentation;

o Flocs deposit to form a sludgeo Sludge dried – used for composting

Filtration;o Water passed through sand/gravel beds

Chlorination;o Water disinfected/microorganisms killed using chlorine

gas/hypochlorites pH adjustment (stabilisation);

o Buffering chemicals (e.g. carbonates) added to achieve pH 7-8 Note: water naturally acidic due to dissolved CO2 therefore

base added (e.g. lime) Fluoridation;

o Flouride compounds added (1ppm) to help prevent tooth decay

Assessment of effectiveness: Sydney’s/NSW water treatment is very effective;

o Evident in minimal health problems resulting for sub-standard water

4. Describe the design and composition of microscopic membrane filters and explain how they purify contaminated water:

Microscopic membrane filters:

Membrane consists of;

o Polymers (e.g. cellulose, PVC) made into bundle of fine capillary tubeso Polymers have very small/fixed pore sizes

Liquid forced through membrane by gravity, vacuum, pressure pumps or centrifugal force

Impurities physically too big to pass through tiny pores in polymer membraneo Removed → pure water flow out of filter

3. Gather, process and present information on the features of the local town water supply in terms of:

Catchment area;o Dams, rivers and freshwater lakes

Possible sources of contamination in this catchment;

o Sources of contaminants in catchment area; Sewage leaks – aerobic bacteria Agricultural run-off – NO3, PO4

Industry run-off – heavy metals Thermal pollution Run-off through natural formations – solid particles, ions

Chemical tests available to determine levels and types of contaminants;

See previous

Physical and chemical processes used to purify water;o Physical:

Screening Sedimentation Filtration Microscopic membrane filters

o Chemical: Aeration Flocculation Chlorination pH adjustment/stabilisation Fluoridation

Chemical additives in the water and the reasons for the presence of these additives;o Chlorine:

Water disinfected/microorganisms killed using chlorine gas/hypochlorites

o Flouride: Helps prevent tooth decay