chemical monitoring and management ash morgan
DESCRIPTION
ChemTRANSCRIPT
1 HSC STUDY BUDDY
‘Much of the work of chemists involves monitoring the reactants and products of reactions and managing reaction conditions’
1.1: outline the role of a chemist employed in a named industry or enterprise, identifying the branch of chemistry undertaken by the chemist and explaining a chemical principle that the chemist uses. 1.4: present information about the work of practicing scientists identifying the variety of chemical occupations, and a specific chemical occupation for detailed study. Analytical Chemist Works for Sydney Water Monitoring Services
-‐ Environmental and water monitoring services to protect the environment and public health. -‐ Monitoring includes: monitoring all influent into wastewater, stormwater, effluent from
those systems and the measure of impacts on receiving environments. -‐ Water monitoring of raw water, treated water and recycled water -‐ Chemists role: routine monitoring for hundreds of potential contaminant in the water, eg.
Carbon compounds, viruses, bacteria, micro-‐organisms. -‐ Equipment: AAS, gas chromatography, emission and mass spectroscopy precise/ sensitive
readings of level of contaminants. -‐ Results are reported to a senior analytical chemist, who monitors the water as a matter of
urgency, and informs the government/ Environmental Protection authority if contamination is harmful.
Polymer Chemist -‐ Work in industry manufacturing synthetic fibres, packaging materials, agricultural
chemicals, rubber, biodegradable polymers. -‐ They produce new products/ materials. Synthesise/ study physical and chemical properties
of polymers. They also must ensure that the product meets the customers’ requirements. -‐ Use analytical methods such as: X-‐ray diffraction, mass spectroscopy (chemical/ structural
characteristics), strength/ hardness tests, reactivity with acids/ bases, biocompatibility, mp bp.
-‐ Case study: use of gas liquid chromatography to test for volatile material. Chemical principle used= each volatile substance has a unique retention time in the GLC column
1.2: identify the need for collaboration between chemists as they collect and analyse data
-‐ Different types of chemists have specialised skills and expertise, and can bring different information into problem solving/ understanding.
-‐ Increases the accuracy/ validity of data as chemists share their outcomes -‐ Chemists keep up to date with new developments in the field via communicating
1.3: describe an example of a chemical reaction such as combustion, where reactants form different products under different conditions, and thus would need monitoring Reasons for Monitoring and Management:
-‐ Efficiency -‐ Minimal pollution, few pollutants produced -‐ Limited damage to the environment/ society’s health -‐ Maximise the amount of desired product/ optimum yield is achieved -‐ Reactions are energy efficient
Note: In combustion reactions, the process must be monitored to ensure that combustion is COMPLETE, as this releases the largest amount of energy, produces CO2 instead of CO (toxic). If not monitored a number of results could occur
• COMPLETE: 2C8H18(l) + 25O2(g) 16CO2(g) + 18H2O(l) • INCOMPLETE:
o 2C8H18(l) + 17O2(g) 16CO (g) + 18H2O(l) o 2C8H18(l) + 9O2(g) 16C(s) + 18H2O(l) [yellow flame + soot]
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o 2C8H18(l) + 13O2(g) 8CO(g) + 8C(s) + 18H2O(l) [yellow + blue flame] • Incomplete combustion= a problem for the environment, as it produces CO and C.
o CO= toxic gas, bonds with haemoglobin, therefore starving the body of oxygen. o C= doesn’t look appealing, when inhaled cause respiratory problems
• Incomplete combustion produces less energy than complete, therefore it isn’t as energy efficient. Therefore it needs to be monitored!!
Monitoring and Management of: Dehydration/ Hydration of Ethylene/ Ethanol:
-‐ C2H4(g) + H2O(l) C2H5OH(aq) EXO -‐ To achieve highest yield of desired product:
o Increase yield= concentration/ amount of reactants need to be increased o Concentrated H2SO4 is used as a catalyst to speed up the reaction, creating a more
efficient process o Need to manage: temperature, concentration, pressure and catalyst depending on
which reaction is used. Eg. To move reaction forward (hydration), decrease temp slightly, increase
pressure, increase concentration, use a catalyst. LINK TO LE CHATELIERS PRINCIPLE
Esterification -‐ Any example! Eg. CH3COOH9G) + CH3OH(g) CH3CH2COOCH3(g) + H2O(l) ENDO -‐ To achieve maximum yield
o Control heat to speed up reaction. Heat is required to change reactants to gases in order to react
o Increase concentration of reactants o Catalyst is required to absorb water and force reaction forwards o Higher temp= greater yield
‘Chemical processes in industry require monitoring and management to maximise production’ 2.1: identify and describe the industrial uses of ammonia -‐ Fertilisers (ammonium sulphate, ammonium nitrate and urea) -‐ Plastics (rayon, acrylics, nylon) -‐ Nitric acid (can be used to make explosives TNT -‐ Dyes -‐ House cleaners -‐ Detergents Therefore it is widely used in industry 2.2: identify that ammonia can be synthesised from its component gases nitrogen and hydrogen
Magnetite (Fe3O4) 2.3: describe that synthesis of ammonia occurs as a reversible reaction that will reach equilibrium 2.4: identify the reaction of hydrogen with nitrogen is exothermic
Magnetite (Fe3O4)
The Haber Process (producing ammonia through the use of a catalyst-‐ iron) With metal catalysts, reactant particles collide with the surface of the metal, and some may become attached. These molecular rearrangements make it more likely that following collisions will be
successful. A catalyst such as iron is used to speed up reactions by lowering the activation energy, so that bonds can be broken.
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The Process: This process combines nitrogen (from air), with hydrogen (from natural gas-‐ methane), to form a yield of approximately (10-‐20%) ammonia under conditions of optimum temperature and pressure. This is a reversible (equilibrium) and exothermic reaction. A mixture of nitrogen and hydrogen are put into a reactor in a ratio of 1:3, this means that there is 1 molecule of N to 3 molecules of H. The temperature in the reactor is raised to 400-‐450˚ to speed up the reaction in order to produce higher proportions of ammonia in a shorter period of time. The pressure is also raised to 200 atm. This brings the molecules closer together, and increases the chances of molecules hitting and sticking to the iron where they can react (increased rate of reaction). The hydrogen and nitrogen pass over beds of iron oxide (which is prepared by reducing magnetite Fe3O4), where some are bound to the surface of the iron as separate atoms. The broken bonds are then reformed into NH3. The temperature is then cooled so that the ammonia can be liquefied, and leftover gases are reused. As a result this reaction releases 92.4 kJ/mol of energy at 298K (25˚C).
N2(g) nitrogen
+ 3H2(g) hydrogen
heat, pressure, catalyst <------------------------------------->
2NH3(g) ammonia
Optimum Temp: 400-‐500˚C Optimum pressure: 200 atm Importance of process: Ammonia is difficult to produce on an industrial scale, but is extremely important as it generates fertilizer that is responsible for sustaining 1/3 of the Earth’s population. Using a catalyst means that production is quicker, easier and cheaper. 2.5: explain why the rate of reaction is increased by higher temperatures
-‐ Increasing the temperature speeds up the reaction by giving the particles greater kinetic energy, so they move faster and collide with greater energy. Therefore lowering the activation energy.
-‐ however if the temp is too high the catalyst will be damaged 2.6: explain why the yield of product in the Haber process is reduced at higher temperatures using Le Chatelier’s principle Le chatelier’s principle: if a system in equilibrium is disturbed, the system will adjust itself to minimise the disturbance
-‐ Due to the reaction being exothermic, if heat is increased the reaction will be forced to the left (reverse), therefore favouring the products side and decreasing the yield produced. Therefore increased temp= decreased yield
2.7: explain why the Haber process is based on a delicate balancing act involving reaction energy, reaction rate and equilibrium
-‐ The Haber process needs to be monitored/ managed in order to promote the most efficient process that will produce the most yield on an industrial scale, with limited resources
-‐ To create an efficient process, heat can be used to speed up the reaction by increasing the kinetic energy and in turn particle collisions. This in turn would increase the reaction rate
-‐ However, the Haber process is an exothermic reaction. If heat is increased, the reaction will be forced in reverse, favouring a higher proportion of reactants
-‐ Therefore increasing the temp may help to increase the rate of reaction, however due to equilibrium, it doesn’t increase the yield.
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-‐ In order to create an efficient industrial process, whereby the reaction proceeds at a fast rate, and a high yield is produced, the process must be monitored, and a number of factors balanced.
-‐ COMPROMISE: o use of a catalyst, o high pressure 250atm, o medium temp 500 degrees
2.8: explain that the use of a catalyst will lower the reaction temperature required and identify the catalysts used in the Haber process Catalyst in Haber process= magnetite (Fe3O4) or Osmium Catalysts lower the activation energy and in turn increase the reaction rate. It allows the N and H bonds to be more easily broken, allowing it to occur at lower temps and thus favours the forward reaction. 2.9: Analyse the impact of increased pressure on the system involved in the Haber process
• For every 4 moles, 2 moles of NH3 are produced • Increasing pressure forces the reactants into a smaller volume, pushing the moles closer
together and increasing the chance of collisions • Therefore increasing pressure will favour the forward reaction, as a result of the equilibrium,
and so will increase the yield • This will also increase the reaction rate, as more collisions will be occurring at a faster rate. • However increasing pressure is an expensive industrial process.
2.10: explain why monitoring of the reaction vessel used in the Haber process is crucial and discuss the monitoring required
-‐ The Haber process needs to be constantly monitored and managed for effective and optimal production of ammonia. If it isn’t monitored, a change in the reaction could result in decreased yield or a slow reaction which in turn will affect productivity and cost the firm money and time
-‐ Monitoring: o Feedstock (N +H) must be pure, otherwise it will impact on yield and ruin catalyst o Ratio of N:H (1:3), avoid build up of one decrease production o Temp + Pressure optimum production. Too high temp= damage catalyst. Too high
pressure= damage vessel o Build up of gases in plant o Remove ammonia, ensure no impurities o Structural integrity of vessel
2.11: describe the conditions under which Haber developed the industrial synthesis of ammonia, and evaluate its significance at that time in world history
-‐ His first experiments produced small yields of ammonia, when nitrogen and hydrogen were combined at 1000˚C over an iron catalyst
-‐ He tested numerous catalysts, osmium was the best but was expensive -‐ Further experiments showed that pressure needed to be raised, but temp lowered to
increase yield. -‐ He could synthesise 100g of ammonia -‐ Carl Bosch modified this process to an industrial level (500˚, 200atm) -‐ Significance of process at the time: production of fertilisers needed for agriculture, and to
sustain the growing population. Used for gunpowder and explosives for WWI, sustained troops. It prolonged the war by assisting Germany’s efforts.
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‘Manufactured products, including food, drugs and household chemicals, are analysed to determine or ensure their chemical composition’
3.1: deduce the ions present in a sample from the results of tests 3.3: first hand investigation to test/ identify phosphate, sulphate, carbonate, chloride, barium, calcium, lead, copper, iron Anions (negative)
-‐-‐-‐-‐-‐-‐-‐-‐-‐ CO3 2-‐ + 2H+ CO2 + H2O
-‐-‐-‐-‐-‐-‐-‐-‐-‐ 2PO4 3-‐ + 3Ba2+ Ba3(PO4)2 (s)
-‐-‐-‐-‐-‐-‐-‐-‐-‐ SO4 2-‐ + Ba 2+ BaSO4 (s)
Cl-‐ + Ag+ AgCl (s) -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐
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Cations (positive)
-‐-‐-‐-‐-‐-‐-‐-‐-‐ Pb 2+ + 2Cl-‐ PbCl2 (s)
-‐-‐-‐-‐-‐-‐-‐-‐-‐Ba 2+ + SO4 2-‐ BaSO4 (s)
-‐-‐-‐-‐-‐-‐-‐-‐-‐Ca2+ + SO4 2-‐ CaSO4 (s)
Cu 2+ + 2OH-‐ Cu(OH)s (s)-‐-‐-‐-‐-‐-‐-‐-‐
Fe 2+ + 2OH-‐ Fe(OH)2 (s)-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐
Fe 3+ + 3OH-‐ Fe(OH)23 (s)-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐
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3.2: 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
• This technique is very sensitive and can measure in ppm Uses: test purity of mined samples, monitor pollution, detect harmful levels, quality control Steps:
1. A sample thought to contain a metal atom is heated in a flame 2. Species in this sample are converted to gases in the flame 3. If light of a frequency known to be absorbed by this chemical passed from the light source
through the heated sample, the element in the sample will absorb some of the light 4. The proportion of light energy absorbed by the sample (absorbance) is proportional to the
concentration of the substance How AAS can be used to determine which metal ions are in a solution and their concentration
-‐ A separate light source must be used for each metal ion to be tested (each metal ion has its own unique emission and absorption spectrum)
-‐ A frequency which is characteristic and unique for the element to be tested must pass through the heated sample, and the proportion of light absorbed can be measured
-‐ Concentration is determined by comparing the absorbance of the sample with absorbance of standard solutions of known concentrations.
Trace Elements -‐ Elements required by living things in very small quantities (1-‐100ppm) -‐ In humans:
o Zinc (needed to help enzymes function), cobalt, nickel, iodine, selenium -‐ In plants:
o Manganese, copper, boron, zinc -‐ Selenium: in animals (protect against harmful exposure to mercury, regulate male
hormones, support prostategland, enhances immune function, anti-‐cancer nutrient -‐ Zinc: Animals (metabolism of amino acids and in energy production (homeostasis), immune
response, oxidative stress). Plants (regulates plant growth hormones) Impact of AAS on scientific understanding of the effects of trace elements
-‐ Before AAS, scientists used techniques such as gravimetric/ volumetric analysis, which was an invalid method as it cannot measure very small concentrations (ppm) of trace elements. Therefore it wasn’t accurate.
-‐ Assessment: The development of AAS has allowed scientists to understand the effects of trace elements, has furthered our understanding, and is more accurate and valid. Allowed the impact of deficiencies in metal ions to be investigated and allowed the testing of foods to determine the levels of essential vitamins/ minerals.
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3.4: describe and explain evidence for the need to monitor levels of one of the above ions in substances used in society
-‐ It is important to monitor levels of ions as some in high concentrations are harmful to humans.
-‐ Lead ions-‐ cations o Lead is a poison o Effects: retard intellectual development in young children, brain/ neurological
disorders o Lead was originally used in petrol and paint. o Due to their original use, there is still some lead compounds in the soil, around
industrial sites, paint factories etc. lead compounds in petrol were released into the atmosphere
o AAS is used to monitor soil samples, and is more efficient and sensitive then previous techniques. Pollution and manufacturing of goods containing lead is illegal, so it is important that monitoring of lead ion concentrations are conducted.
-‐ Phosphate ions-‐ anions o Found in waterways (naturally) o Essential for normal aquatic growth. o If concentration becomes too high= algal bloom make water unusable,
degradation of lake. Loss of oxygen results in death of fish etc, build up of sediments. EUTROPHICATION
o Phosphate ions are derived from sewage, fertilisers, detergents. o Monitoring is required as a predictor of Eutrophication. o Colorimetric method is used (very sensitive), molybdenum blue test,
spectrophotometer. 3.5: first hand investigation to measure sulphate content of lawn fertiliser. Explain the chemistry involved. Ba 2+(aq) + SO4 2-‐ (aq) BaSO4 (aq) See separate sheet! 3.6: evaluate the reliability of the results of the above investigation and propose solutions to problems encountered in the procedure
-‐ Heating will coagulate the precipitate, ensuring it is collected -‐ Use samples of fertiliser with a greater mass will lessen % error in accuracy -‐ Quantitative filter paper has very fine pores, no solid will escape -‐ Improve reliability by repeating or using a glass filter. -‐ Experiment assumes that ppt is only barium sulphate, without any impurities like ions/
water 3.7: interpret secondary data from AAS measurements and evaluate the effectiveness of this in pollution control See bronwyns book! And sheet
-‐ Detect presence of heavy metals and concentrations eg. mercury, lead, cadmium, arsenic -‐ EPA monitors and evaluates levels protects environment by controlling and minimising
pollution/ waste. -‐ AAS is quantitative, and can determine concentrations. Without it pollution would go
undetected. -‐ However it has limitations, it tests for a range of metals but must be done separately.
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‘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’
4.1: describe the composition and layered structure of the atmosphere
Layers of the Earth This Module Sucks Terribly 4.2: identify the main pollutants found in the lower atmosphere and their sources
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4.3: describe ozone as a molecule able to act both as an upper atmosphere UV radiation shield and a lower atmosphere pollutant
Why does concentration of gases (oxygen and nitrogen) decrease as altitude increases: force of gravity pulls gases towards the earth’s surface, therefore concentration decreases as altitude increases Why is there more ozone in the stratosphere than there is in the troposphere?
-‐ Ozone is made when oxygen is broken into free radials using energy from Uv light. Intensity of short wave length UV light, needed to break up O molecules is greater in the stratosphere than in the troposphere.
-‐ O2 (g) 2O. (g) O2 (g) + O. (g) O3 (g) Ozone concentration is low/ stable in the troposphere. Why is this so?
UV 1. O2 (g) → 2O• (g) 2. O2 (g) + O• (g) → O3 (g) 3. O3 (g) → O2 (g) + O• (g) 4. 2O• (g) → O2 (g)
The overall equation: 1. 2O3 3O2 -‐ Oxygen free radicals react with O to form ozone -‐ Ozone decomposes to form O -‐ Reverse reactions keep concentration of ozone fairly stable in the stratosphere, unless
pollution caused by high temp combustion to form NO2 increases -‐ O free radicals are formed by Uv or O or NO2
Presence of pollutants eg. NO2 in lower atmosphere promotes the formation of ozone. UV
NO2 (g) NO (g) + O• (g) O2 (g) + O• (g) O3 (g) Ozone in troposphere= BAD Ozone in stratosphere= GOOD
-‐ In troposphere: (electrical energy from storms provide energy for decomposing O2). Ozone is poisonous, causing the breakdown of biological molecules due to ozone reacting with carbon compounds. In turn causing respiratory problems, fatigue, lowers resistance to infection, disrupts biochemical reactions (strong oxidising agent). Therefore it is a pollutant
-‐ In stratosphere: (provides energy to decompose O2 ozone), ozone protects the earth from radiation by absorbing high energy UV, allowing low energy UV to reach earth. High energy UV, could cause cancer (skin). Want to trap UVB and UVC
4.4: describe the formation of a coordinate covalent bond Coordinate covalent bond: formed by non-‐metal atoms sharing electrons, when one atom (donor atom) contributes both electrons into the pair of electrons holding the atom together
-‐ Every acid-‐base reaction involves the formation of a co-‐ordinate covalent bond, since hydrogen ion does not contribute any electrons when it bonds to the non-‐bonding pair on the base.
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4.5: demonstrate the formation of coordinate covalent bonds using Lewis electron dot structures Hydronium ion Ammonium ion
Ozone
Carbon monoxide
4.6: compare the properties of the oxygen allotropes O2 and O3 and account for them on the basis of molecular structure and bonding Allotrope: different forms of the same element. They have the same atoms, but different bonding
Differences in physical properties: ozone is bigger, heavier, with more electrons. Therefore greater molecular interaction. Ozone has stronger dispersion forces therefore higher mp/bp. Greater mass= greater density. 4.7: compare the properties of the gaseous forms of oxygen and the oxygen free radical Oxygen molecule: stable form of the element. All electrons are paired and stable. Oxygen free radical: can be formed when UV splits oxygen. It is very reactive, unstable, 2 unpaired electrons. They want to from covalent bonds therefore doesn’t stay as a free radical for long. Combines to form ozone, NO NO2.
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4.8: identify the origins of CFCs, and halons in the atmosphere Haloalkanes: an alkane in which one or more H atoms are substituted by halogen atoms. Chlorofluorocarbons (CFCs): Haloalkanes, when all Hs are replaced by F or Cl. Compounds containing only Cl, F or C.
-‐ Features : Odourless, non-‐toxic, non-‐flammable, inert substances -‐ Origin : developed as a replacement for ammonia in refrigeration, used as aerosol spray
propellants, foaming agents. -‐ Example: CCl3F (trichlorofluoromethane), CCl2F2 (dichlorodifluoromethane)
Halons: haloalkanes where all Hs are replaced by Cl, F or Br (Carbon, bromine and other halogens) -‐ Features: dense, non-‐flammable liquids -‐ Origin: fire extinguishers -‐ Example: CBrClF2 (bromochlorodifluoromethane) or CBrF3
CFCs are no longer produced. However CFCs used in air conditions prior to 1987 still release CFCs. 4.9: identify and name examples of isomers of haloalkanes up to 8 carbons long
4.10: discuss the problems associated with the use of CFCs and assess the effectiveness of steps taken to alleviate these problems
-‐ In the troposphere, CFCs are inert, non-‐toxic, insoluble. They are dense and slowly diffuse into the stratosphere stability causes them to persist for decades
-‐ In Stratosphere, problems= CFCs are broken down by UV to produce Chlorine free radicals, which react with ozone and remove it from the atmosphere. Depletion of ozone= increased levels of UV
-‐ Compounds which break down in troposphere (HCFCs) or have no Cl (CFCs) can be used as a replacement
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4.11: analyse information that indicates changes in atmospheric ozone concentrations, describe the changes observed and explain how this information was obtained
-‐ graph shows a decrease in levels of CFCs, and has begun to stabilize
-‐ level of ozone concentration was obtained by instruments in satellites such as UV spectrophotometers
o these measure the intensity of light received at a wavelength at which ozone absorbs and then at wavelengths either side of this, that ozone doesn’t absorb -‐-‐. Comparison gives total concentration
o measured in Dobson units o balloons can be used to carry
instruments into the atmosphere 4.12: write equations to show the reactions involving CFCs and ozone to demonstrate the removal of ozone from the atmosphere
UV 1. CCl3F → Cl• + CCl2F•
2. Cl• + O3 → ClO• + O2 (breaks down ozone)
3. ClO• + O• → Cl• + O2 Steps 2 and 3 can continue again and again to form a chain reaction The net result of these last 2 reactions is the conversion of O3 O2 4.13: model isomers of haloalkanes using simulations, molecular model kits or pictorial representations 4.14: identify alternative chemicals used to replace CFCs and evaluate the effectiveness of their use as a replacement for CFCs Uses of CFCs: refrigerants solvents, propellants in aerosol cans Reasons: non-‐toxic, inert Problems with use: stable CFCs reacg upper atmosphere where they destroy ozone
1. HCFCs (hydrochlorofluorcarbons) -‐ More reactive than CFCs due to higher reactivity of C-‐H bonds, therefore majority
are destroyed in troposphere -‐ Temporary substitute for CFCs until better compounds are found long term
toxicity to humans is unknown 2. HFCs (hydrofluorocarbons)
-‐ Contain no Cl -‐ More expensive and less effective as refrigerants, but don’t react with ozone
3. Hydrocarbons to a lesser extent eg. Butane -‐ Used as aerosol propellants -‐ Problems-‐ flammable, release hydrocarbons into atmosphere -‐ React to form photochemical smog
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Why it is unlikely ozone concentration in stratosphere will change significantly in the next few years
-‐ CFCs= inert, non-‐toxic, insoluble. Relatively dense gas molecules and diffse slowly into stratosphere.
-‐ Stability n troposphere means they aren’t destroyed and persist for decades -‐ Steps to alleviate problems with CFCs appear to be effective as levels of ozone have
stabilized -‐ Decades before CFCs/ halons are eliminated as one Cl free radical can cause
breakdown of 1000 ozone molecules. Why ozone concentration in stratosphere is at its lowest in spring over polar regions. Explain processes which contribute to the ozone holes at these times The chain reaction of chlorine free radicals with ozone can be terminated by 2 different reactions.
-‐ The chlorine free radical can react with methane to form hydrogen chloride gas and a CH3.
Neither of these products reacts with ozone. Cl• + CH4 → HCl + CH3
-‐ The ClO• reacts with nitrogen dioxide gas in the stratosphere to remove the free radical. The product does not release the Cl• on exposure to UV light. ClO• + NO2 → ClONO2
-‐ In winter, at the poles, atmosphere is cold/ dark and the air patterns do not allow mixing of the air over the poles with other air. Under these conditions, the products of the termination reaction can react and release chlorine into the atmosphere. HCl + ClONO2 → Cl2 +HNO3
-‐ During winter, the chlorine in the stratosphere has no effect on the ozone level. However, in spring, when sunlight returns to the pole, there is a dramatic breakdown of the chlorine molecules into chlorine free radicals. The concentration of ozone drops dramatically, creating an ozone hole over the polar regions in spring (October – November) in the southern hemisphere.
‘Human activity also impact on waterways. Chemical monitoring and mgmt assists in providing safe
water for human use and to protect the habits of other organisms’ 5.1: identify that water quality can be determined by considering: concentration of common ions, total dissolved solids, hardness, turbidity, acidity, dissolved oxygen and biochemical oxygen demand
Factor Definition Causes How it is measured Common ions Chlorine, sulfate salinity of water
Carbonate: cause pH to increase (carbonates= bases), may affect plant growth Ca and Mg: indicate hardness of water Phosphate: excessive= can cause algal blooms, predictor of algal blooms Nitrate: indication of sewage/ fertilisers
AAS for metals, gravimetric analysis
Turbidity Degree of transparency of water. Determined by the presence of suspended solids
Presence of suspended solids that can’t be filtered. Eg. Clay, silt, industrial solids, bacteria, faecal matter,
Gravimetric analysis Meter tube Secchi disk Turbidity meter
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algae TDS (total dissolved solids)
Total amount of dissolved solids, mass of solids dissolved per unit of volume
Presence of dissolved solids eg salt Rocks minerals in soil
Gravimetric chemical analysis (ppt then separate) Conductivity meter
DO (dissolved oxygen)
Amount of oxygen dissolved in water
Depend on salinity, temp, conc of dissolved/ suspended pollutants. High temp= low O Rate of flow Amount of O used in respiration
Calibrated oxygen sensor electrode titration
BOD (biochemical oxygen demand)
Quantity of oxygen needed by aerobic bacteria to break down all the organic matter in a water sample
Pollution/ waste. Higher the pollution= higher the BOD
DO sensor Seal/ incubate 5 days Measure DO Calculate BOD
pH Acidity of water Presence of CO2/ pollution
pH meter indicator
hardness Hard water= wont lather with soap. Contains Ca, Mg
Presence of Ca, Mg Titration (stoichiometry)
5.2: identify factors that affect the concentrations of a range of ions in solution in natural bodies of water such as rivers/ oceans 1. Pathways from rain to water body
-‐ if rain passes quickly to water body, TDS will generally be small and main ions will b NO3, PO4, CO3, Ca, Mg. if rain soaks in underground water, it will contain increased ions -‐ if water flows into deep aquifers contain heavy metals (Fe, Mn Cu, Zn)
2. pH of rain -‐ more acidic the rain, more likely it is that ions/ minerals will dissolve in it from rocks/ soil 3. Nature of human activity in catchment area
-‐ Agriculture. Land clearing increase run off of sediments and therefore increase the amount of material that is able to dissolve in water
4. Effluent discharged into water bodies -‐ includes sewage, stormwater run off, and industrial effluents 5. Leaching from rubbish dumps -‐ heavy metals eg. Cadmium, Hg, Pb, Zn, NO3, PO4 (Eutrophication in excessive amounts). 5.3: describe and assess the effectiveness of methods used to purify and sanitize mass water supplies
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Screening aeration Flocculation Sedimentation Filtration chlorination pH adjustment(stabilization) fluoriationstorage reservoir Treating waste water Primary treatment: screened, solids removed, chlorinated Secondary: treated further, remove organic solids Tertiary: colloidal particles/ mineral ions are removed.
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5.4: describe the design/ composition of microscopic membrane filters and explain how they purify contaminated water
-‐ thin film of synthetic polymer, which has small pores of uniform size
-‐ Prose sizes range from 0.2-‐ 0.5 micrometers (10^-‐6). These pore sizes are big enough for water molecules to pass through but small enough to trap microorganism and some viruses
-‐ Membrane filters are used in industries-‐ bottle water, soft drink ,beer Advantages:
o Filter smaller particles than other filters
o A thin-‐liquid flows through them rapidly
o Strong, can withstand pressure o Can be cleaned and reused
-‐ Microfiltration membranes: remove microscopic parasites Giardia, viruses -‐ Ultrafiltration membranes: remove particles from 100 nanometers to 2 nanometers. Paint
particles, organic molecules -‐ Nanofiltration membranes: less than 1 nanometer, remove ions from water.
5.5: first hand investigation to use qualitative/ quantitative tests to analyse and compare quality of water samples Qualitative: description/ use of words Quantitative: use of numbers and statistics Test Method Qualitative/ Quantitative Concentration of ions AAS
Flame test ppt
Quantitative Qualitative Quantitative
Insoluble solids Filter measured sample, dry and weigh residue
Quantitative
TDS Filter, evaporate a measured amount, dry and weigh residue
Quantitative
Hardness Ppt tests to determine Ca Ability to lather with soap
Quantitative Qualitative
Turbidity % light transmitted through depth at which lines can be seen
Quantitative
Acidity Indicators Data logger with probe
Qualitative Quantitative
DO Data logger with O probe Quantitative BDO Difference between initial and
final DO after 5 days in dark Quantitative
Phosphate Colorimetric-‐ add ammonium molybdite, measure depth of colour when a blue compound forms
Quantitative
SEE PRAC SHEET
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5.6: information on the range and chemistry of the tests used to identify heavy metal pollution of water, monitor possible Eutrophication of waterways Nitrogen-‐to-‐phosphorus ratio: measurement associated with water quality
-‐ Conc of NO3 and PO4 ions are important predictors of algal blooms. Both these are essential nutrients for algal growth but in excess can lead to Eutrophication and degradation of water
-‐ Ratio o N to P has an impact on algal growth -‐ Diff species require diff ratios -‐ High N:P promotes blue-‐green algae -‐ Low N:P promotes green algae -‐ To avoid algal blooms, EPA has recommended levels. Total N= 0.1-‐1ppm, Total P= 0.001-‐
0.1ppm Heavy Metals: transition metals and lead, Arsenic.
-‐ In water, heavy metals can be damaging to health. Monitoring conc is vital -‐ AAS can be used -‐ Lead: poison, retards intellectual development in children, brain damage, -‐ Mercury: pollutant, toxic, bioaccumulative. Damages nervous system, death in fish/ animals.
Unborn children are affected if mothers eat contaminated fish. Algal Blooms: excessive growth of algae which covers streams/ dams with geen sludge unstable for people
-‐ Factors: temp (warm), rate of flow (still), level of UV (high), concentration of nutrients (high) fertilizers, sewage
Eutrophication: process by which a water body becomes enriched by nutrients eg. PO4, NO3, making algal blooms highly likely.
-‐ Tests for monitoring Eutrophication: o Monitoring presence of PO4, in waterways is used as a predictor o Colourimetric method needs to be very sensitive to pick up low concentrations o Molybdenum blue test o Spectrophotometer, which measures the absorbance of light at a particular
frequency . o Absorbance test of the sample is compared with absorbance of standard phosphate
solutions 5.7: information on features of the local town water supply in terms of: catchment area, possible sources of contamination in this catchment, chemical tests available to determine levels/ 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 SEE SHEET Catchment area:
-‐ 5 major systems form the Sydney catchment area -‐ 16000 sq km. to south and west of Sydney -‐ Warragamba system -‐ Upper nepean -‐ Woronora system -‐ Blue Mountains system -‐ Shoalhaven system -‐ All have rivers, lakes, dams, reservoirs, pumping stations, filtration plants, pipes
Contamination: -‐ Turbidity: rub off from bushland, grazing land -‐ High levels of iron/ manganese:high natural levels leached from the soil and rock
19 HSC STUDY BUDDY
-‐ Treated/ untreated sewage -‐ Microbes -‐ Pesticides -‐ Mining: zinc, copper, lead -‐ Grazing/ native/ feral animals
Chemical tests for contaminants -‐ Contamination with acids and bases: pH meter -‐ Metal ions: EDTA titration, lather with soap(hardness) -‐ Salt: AAS, flame photometry, volumetric analysis -‐ Nitrogen/ phosphorus: colourimetrically
Purifying water Physical processes: screening, coagulation, sedimentation, filtration Chemical processes: aeration to oxidize iron, manganese, oxidation, lime softening to ppt, CaOH addition (raise pH), pH adjustment, addition of Cl and NH3 to kill microbes, addition of F (dental health)