chemical monitoring and management notes

8/12/2019 Chemical Monitoring and Management Notes

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Chemical Monitoring and Management. Construct word and balanced formulae equations of all chemical reactions as they are encountered in this

module: EQUATIONS to remember:

o Different products under different conditions:o Completecombustion:

propane + oxygen carbon dioxide + water C3H8 (g)+ 5O2 (g) 3CO2 (g)+ 4H2O(g)

o Incompletecombustion: propane + oxygen carbon + carbon monoxide + water C3H8 (g)+ 3O2 (g) C(s)+ 2CO(g)+ 4H2O(g)

o Haber Process:o nitrogen + hydrogen ammonia + heato N2 (g)+ 3H2 (g) 2NH3 (g) H = -92 kJ/mol

o Sulfate Content in Fertilizer:o barium chloride + sulfate barium sulfate + chlorideo BaCl2 (aq)+ SO42-(aq) BaSO4 (s)+ 2Cl-(aq)

o How Ozone Protects Us From UV Radiation:o Oxygen reacts with UV, forming 2 radicals:

O2+ UV radiation 2Oo Radical reacts with oxygen, forming ozone:

O + O2 O3o Ozone reacts with UV, forming oxygen and a radical:

O3+ UV radiation O + O2o

Radical reacts with ozone, creating oxygen: O + O3 2O2

o All the CFC-Related Equations:o Formation of chlorine radical:

CCl2F2 (g)+ UV radiation Cl(g)+ CClF2 (g)o Reaction of ozone:

Cl(g)+ O3 (g) ClO(g)+ O2 (g)o Regeneration of chlorine:

ClO(g)+ O(g) Cl(g)+ O2 (g)o Removal of chlorine radical:

Cl(g)+ CH4 (g) HCl(g)+ CH3 (g)o Removal of chlorine monoxide radical:

ClO(g)+ NO2 (g) ClONO2 (g)o Formation of molecular chlorine:

HCl(g)+ ClONO2 (g) Cl2 (g)+ HNO3 (g)o Decomposition of molecular chlorine:

Cl2 (g)+ UV radiation 2Cl(g)o The Heavy-Metal Sulfide Test:

o The sulfide-test is based on the following equilibrium: S2-(aq)+ 2H3O+(aq) H2S(aq)+ 2H2O(l)


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1. 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 the chemical principle that the chemist uses:

Dr John Chapman: see assignment

1.2:Identify the need for collaboration between chemists as they collect and analyse data: As chemistryis such a broad field of knowledge, people tend to specialise within a particular branch,

such aspolymerchemistry or analyticalchemistry.

However, in real-life situations, many chemical problems require expertise and in depth knowledgefrom a wide range of chemical branches.

Hence, collaboration between chemists is essential for solving chemical issues, or when dealingwith large amounts of data being collected, as the chemists provide input and expertise from their

own particular field, for a common goal.

As chemists often work in teams, collaboration and communication is required to collectivelybenefit the team, as they collect and analyse information.

o EG: An industrial process would require collaboration between physical chemists (forequilibrium considerations), organic chemists (for how the reaction occurs) and analytical

chemists (for monitoring products).

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:

Combustion:o Chemical reactions can form different products under different conditions.o Take, for example, the combustionof a simple hydrocarbon, propane.o In an environment with adequate amounts of oxygen, propane combusts completely,

forming only carbon dioxide and water:

propane + oxygen carbon dioxide + water C3H8 (g)+ 5O2 (g) 3CO2 (g)+ 4H2O(g)

o In an environment with insufficient oxygen, propane combusts incompletely, and can form arange of different products, such as carbon (soot), carbon monoxide, carbon dioxide and

water.

propane + oxygen carbon + carbon monoxide + water C3H8 (g)+ 3O2 (g) C(s)+ 2CO(g)+ 4H2O(g)

Monitoring:o Hence, under different conditions, chemical reactions can proceed in different ways, as seen

by the combustion reaction above.

o However, in certain situations (such as in car engines), only one reaction is desired. Thus,the reaction conditions must be monitored to ensure that only (or mostly) the wanted

reaction occurs.

o Carbon monoxide is a poisonous gas and can affect human health negatively. Carbon (soot)is carcinogenic to humans and can be irritating to the lungs. Both of these alternative

products can also signal a decrease in fuel efficiency and result in a reduced energy yieldfrom the fuel.


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Complete combustion Incomplete combustion

Products formed Carbon dioxide and water Water and any combination of

carbon monoxide, carbon (soot)

and unburned hydrocarbons

Relative ratio of oxygen to fuel Unlimited (excess) oxygen

available (high air to fuel ratio)

Insufficient oxygen for the

amount of fuel. (low air to fuel

ratio)Relative amount of energy

released

Maximum energy Much less energy obtained from

fuel.

Environmental effects Greenhouse gas, carbon dioxide,

produced

Much more polluting as CO is very

toxic, hence, harmful to humans

and animals. Carbon (soot)

particles from the air are

carcinogenic and irritating to the

lungs. Other greenhouse gases

may be produced.

1.4:Gather, process and present information from secondary sources about the work of practising

scientists identifying:-

o the variety of chemical occupations:o a specific chemical occupation for a more detailed study:

THE VARIETY OF CHEMICAL OCCUPATIONS:o The large rangeof jobs available in the chemical industry includes:

Analytical chemistry. Bio-molecular chemistry. Colloid and surface science chemistry. Environmental chemistry. Industrial chemistry. Inorganic chemistry. Electrochemistry. Organic chemistry. Physical chemistry.

Polymer chemistry . A SPECIFIC CHEMICAL OCCUPATION:

o A summary of the job of an environmentalchemist: Job includes reviewing operation of effluent water treatment systems and ensuring

compliance with government environmental regulations. Reviewing industrys

compliance with government environmental noise standards. Assessing levels of

potential contamination in wastes (e.g. soil) intended for landfill disposal and

classifying them in accordance with government guidelines. Managing disposal of

contaminated wastes. Investigating reports of contamination in soil or groundwater

to determine source and then arranging to correct it. Determining whether gas stackemissions contain unacceptable levels of regulated materials. Advising


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engineers/managers of corrective actions needed if any of the above parameters

show faults in systems. Answering public or professional enquiries or complaints

regarding environmental performance.

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

2.1: identify and describe the industrial uses of ammonia

Ammonia(NH3) is a colourless, toxic gas with a pungent odour The industrial uses of ammonia:

o Solid and liquid fertilisers (through a reaction with sulfuric acid, nitric acid or phosphoricacid to form ammonium sulfate fertiliser, ammonium nitrate fertiliser or ammonium

hydrogen phosphate fertiliser). The nitrogen in the ammonia is an essential plant nutrient.

o Production of chemicals: Nitric acid (through the Ostwald Process) which in turn is used to manufacture

synthetic fibres such as nylon and explosives such as TNT.

Cyanideused in plastics manufacture and gold extractiono Cleaning agent: ammonia solution (ammonium hydroxide) destroys bacteria so it is a

component of many household cleaners such as floor and bathroom cleaners.

o Weak base: ammonia is used to safely neutralise acidic by-products in petroleum refiningand in acid spills. Being a weak base, it generates heat slowly during neutralisation (an

exothermic process) so does not cause further burning.

o Manufacture of some pharmaceuticals (i.e. sulphonamides) and refrigerants.2.2: identify that ammonia can be synthesised from its component gases, nitrogen and hydrogen

The synthesis of ammonia from hydrogen and nitrogen:o N2(g)+ 3H2(g) 2NH3(g)

For the synthesis of ammonia, nitrogen is obtained by fractional distillation of liquefied air andhydrogen is obtained by the reaction of steam with methane obtained from natural gas.

o CH4(g)+ 2H2O(g) H2(g)+ CO(g)o The carbon monoxide gas can either be liquefied, reacted with a base (i.e. CaOH) or undergo

the following reaction with water:

o CO + H2O CO2+ H22.3: describe that synthesis of ammonia occurs as a reversible reaction that will reach equilibrium

TERMINOLOGY:o a reversible reactionis a reaction that can proceed in both directionso equilibrium is a reversible reaction proceeding in a closed system and with the rate of the

forward reaction equal to the rate of the reverse reaction

THE SYNTHESIS OF AMMONIA:o Hydrogen and nitrogen react very slowly to form ammonia, and at the same time, the

ammonia decomposes into nitrogen and hydrogen. Thus, the reaction is reversible:

nitrogen + hydrogen ammonia N2 (g)+ 3H2 (g) 2NH3 (g)


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o In a closed system, equilibriumwill be reached when the rate of the forward reaction is thesame as the rate of the reverse reaction. However, for this reaction the equilibrium is slow

to be reached and lies to the left.

o The synthesis of ammonia has a high activation energy because a lot of energy is needed tobreak the covalent bonds between the hydrogen molecules and the nitrogen molecules and

form atoms that can rearrange to form ammonia.

Nitrogen and hydrogen do not exist as single atoms; they both exist as diatomicmolecules held together by strong covalent bonds.

Nitrogen molecules are held together by very strong triple covalent bonds and thesingle covalent bond between hydrogen atoms is also quite strong.

2.4: identify the reaction of hydrogen with nitrogen as exothermic

The reaction of hydrogen with nitrogen (Haber Process) can be represented as:o N2 (g)+ 3H2 (g) 2NH3 (g) H = -92 kJ/mol

From the equation we can see that H is negative; hence, the reaction is exothermic. Overall energy is released in the reaction of hydrogen with nitrogen to form ammonia. There is less

chemical energy in the product than in the reactants. The energy needed to break the bonds in

hydrogen and nitrogen is less than the energy given out when the new bonds in ammonia are

formed. The bends in ammoniua are weaker than the bonds in the reactants.

2.5:explain why the rate of reaction is increased by higher temperatures

RECALL:o Before any chemical reactions can occur, there must be an energy input.o The activation energyof a reaction describes the minimum amount of energy input

necessary for that reaction to occur.

The rate of reactionis a term used to describe how FAST a reaction occurs. There are 2 reasons why higher temperatures result in a higher rate of reaction:

o As temperature is increased, energyis delivered into the reaction as thermal energy. Thisthermal energy is converted into kinetic energy, and particles begin to move faster. This

causes more collisions between particles, and hence more reactions occur.

o Also, if the temperature is higher, there is more chance that colliding particles will have thenecessary activation energyfor the reaction to take place.

For the Haber process (and all reversible reactions in general), at higher temperatures, the rate ofreaction of both theforwardand reversereactions are increased, and hence equilibrium is reached

faster.

2.6: explain why the yield of product in the Haber process is reduced at higher temperatures using Le

Chateliers principle

Le Chateliers principlestates if a chemical system at equilibrium is subjected to a change inconditions, the system will readjust itself to partially counteract that change

In terms of industrial reversible reactions, the term yield of productdescribes how much productis formed at the point of equilibrium:

o It has nothing to do with RATE of reaction.


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Since the reaction is an exothermic reaction, applying Le ChateliersPrinciple we can deduce that:o If an increase in temperature is imposed onto the system (the reaction) then the system

will shift itself to counteract this imposed change.

o Since the system will want to coolitself, to oppose the heating, the reaction that isendothermicwill be encouraged.

o The forward reaction is exothermic; hence, the reverse reaction is endothermic.o Thus, at higher temperatures, the reverse reaction occurs moreo But this produces reactants, not products; thus the yield of products reduces.

Thus, high yields of ammonia favour lower temperatureso However, at low temperature, the reaction rate is too slow to produce ammonia at a

reasonable rate

o ammonia to be obtained at a satisfactory rateo In practice, temperatures of about 400oC are used

2.7:explain why the Haber process is based on a delicate balancing act involving reaction energy,

reaction rate and equilibrium In order for the Haber process to be economically viable, we need to consider yield of products,

rate of reaction, as well as costs.

Hence, a compromise (balancing act) of all the above must be made:o Temperature: Higher temperatures will produce ammoniafaster, but lower temperatures

will produce moreammonia. Hence a moderate temperature of about 400-500C is used,

together with the iron/iron-oxide catalyst.

o Pressure: Increased pressure will produce moreammonia, alsofaster, but it will beexpensive to build and maintain high-pressure equipment. The benefits of high pressure

outweigh the costs, and so a pressure of 250-350 atmospheres is used.

EXTRA: Another step taken to encourage the economic formation of products is the continuousliquefaction and removal of ammonia as it is produced. This reduces the concentration of ammonia,

and hence encourages the forward reaction, according to Le Chateliers principle.

2.8: explain that the use of a catalyst will lower the reaction temperature required and identify the

catalyst(s) used in the Haber process

A catalystis a substance that increases the rate of reaction of a chemical reaction, but does notitself take part in the reaction.

Catalysts work by reducing the activation energy of reactions and hence allow the reaction toproceed more quickly and at lower temperatures.

The Haber process uses the catalyst iron oxide (magnetite; Fe3O4). The catalyst is finely ground, to produce a large surface area, and has its surface partly reduced to

elemental iron.

How the use of a catalyst in the Haber process lowers the reaction temperature required:o The Haber process involves a reversible, equilibrium reaction.

N2(g)+ 3H2(g) 2NH3(g)H= -92kJ mol-1o The forward reaction is exothermic, so the high temperature needed to produce a fast

reaction rate would push the equilibrium to the left and result in a lower yield.


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o The reaction rate for both forward and reverse reaction is increased by using a catalyst. Alower temperature can be used with the catalyst to achieve a faster reaction rate. This helps

in the delicate balance between the effect of temperature on rate and the effect on

equilibrium position.

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

The Haber process involves the synthesis of nitrogen gas and hydrogen gas to form ammonia:o N2(g)+ 3H2(g) 2NH3(g)

According to Le Chateliers principle, increasing thepressure will favour the side that will reduce thepressure (i.e. has LESS moles of gas):

o In this reaction, there are less moles of gas on the product side (gas ratiois 4:2) and henceincreasing the pressure will encourage the forward reaction.

o In addition, higher pressures also increase the reaction rate because the gas molecules arecloser and at higher concentrations.

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

Monitoring is needed to maintain optimum conditions for maximum yield with the least possiblewaste.

Getting maximum yield of ammonia from the Haber process involves balancing reaction energy,reaction rate and equilibrium. A compromise is reached, and the reaction is monitored, maintaining

the following conditions in the reaction vessels to ensure optimum yield:

o nitrogen and hydrogen are fed into the reaction chamber in a ratio of 1:3o a pressure of 250-350 atmosphereso a temperature of 400-500oCo iron oxide (Fe3O4) catalyst lowers the activation energyo unused gases are returned to the reaction vesselo ammonia is constantly removed as a liquid

Cool the mixture and liquefyas they have different boiling points, they will turninto liquid at different temperatures. If all components are liquefied, they can be

separated by fractional distillation.

2.0.1: 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

The development of the industrial synthesis of ammonia:o Fritz Haber:

Haber succeeded in making small amounts of ammonia from hydrogen andatmospheric nitrogen in the laboratory.

He discovered a catalyst for the reaction and worked out the conditions oftemperature and pressure that allowed a reasonable yield.


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o Carl Bosch: Bosch developed the process to an industrial scale, including inventing the necessary

high pressure technology that would enable the process to be carried out on a large

scale. Germany had succeeded in implementing this process by 1913.

The conditions used by Haber and Bosch to allow the production of commercial quantities ofammonia:

o Nitrogen and hydrogen used in ratio of 1:3o 250-350 atmospheres pressureo about 450oC temperatureo catalyst of finely divided iron or iron oxideo ammonia liquefied and removed as it is produced

The significance of the industrial synthesis of ammonia:o Before the invention of the industrial Haber process in 1913, the global source of nitrates

(for fertilisers and explosives) came from saltpetre(bird poo/guano)from Chile.

o During WWI, Germanys supplies of nitrogen compounds were cut off by the British; thisthreatened to cause widespread starvation, as well as cause Germany to rapidly lose thewar (they relied on saltpetre to make explosives).

o Historians believe that Germany would have run out of nitrates by 1916 if it had notdeveloped the Haber process. On the other hand, the Allies had to rely on Chilean nitrates,

which became more expensive as the war progressed.

o However, with the invention of the Haber process, Germany (and later the rest of the world)had a cheap source of nitrates from elemental nitrogen and hydrogen.

o Thus, the Haber-Bosch process had a significant impact on the course of history during theearly 20

thC as it allowed Germany to continue the war for much longer than otherwise

would have been possible.


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3. Manufacture products, including food, drugs and household chemicals, are analysed to determine or

ensure their chemical composition:

METHODS OF DETERMINING CONCENTRATION:o Concentration is defined as the amount of solute in a specified amount of solvent. There are

many ways of expressing concentration depending on the purpose and circumstances.

o Mass per unit volume (grams/litre) used when describing solubility or making solutions involving dissolving a solid in a

solvent, usually water

i.e. 2g fertiliser is dissolved in enough water to make a 50mL solution m = 2g, V = 0.050L

o Per cent by mass, % (w/w) uses a comparison of weight of solute compared to weight of solution, converted to

per cent for ease of comparison

household cleaners often express concentrations of active ingredients in this way

i.e. 35g NaCl is dissolved in 100g water msolute= 35g, msolution= 100 + 35 = 135g

o Per cent by volume, % (v/v) used when liquids are dissolved in other liquids alcohol concentration in drinks is expressed in this way

i.e. 2.5mL hydrogen peroxide is dissolved in enough water to make 50mL of solution vsolute= 2.5mL, vsolution = 50mL

o Parts per million (ppm) means parts of a particular solute per million parts of mixture often used in environmental contexts when the concentrations are very small,

especially when considering pollutants

i.e. if the maximum allowable concentration of DDT in beef is 1.5ppm, would a 500gsample of beef containing 0.075g of DDT be acceptable?

mDDT= 0.075g, mbeef= 500g

The beef is not acceptable as this is 100 times the allowable limit


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

Ions that are being tested:o Cations: Ba2+, Ca2+, Pb2+, Cu2+, Fe2+and Fe3+o Anions: PO43-, SO42-, CO32-and Cl-

Test Result Ions present

Add KI Yellow precipitate Lead

Add OH- ions, drop wise Deep blue precipitate that

dissolves in excess hydroxide

Copper

Spray into flame Apple green colour Barium

Add AgNO3 White precipitate that darkens in

exposure to sunlight

Chloride

Add dilute HCl Gas produced that turns

limewater milky

Carbonate/hydrogen

When givena flowchart, it is very easy to deduce the ion(s) present. However, you need to memorise the tests for the above ions. We useprecipitationreactions to identify ions in solution. There are 2 situations possible: when there is only one ion present in a sample, or when there is a

mixture of ions in a sample.

CATIONS (when only oneion is present):o To determine the ion present, HCl, H2SO4and NaOH is added in that order, and the

formation of a precipitate would indicate which ion it is:

o Firstly, HCl(Cl-ions) is added to the sample. If a white precipitate forms, then the unknownion is LEAD (Pb

2+); the precipitate is lead chloride (PbCl2).

To verify, add a few drops of potassium iodide (KI) to a fresh sample. Pb2+ions form avibrant yellow precipitate with iodide (I

-) ions.

o Next, H2SO4(SO42-ions) is added to a FRESH SAMPLE. If a precipitate forms, the unknownion is eithercalcium (Ca

2+) or barium (Ba

2+):

To distinguish the two ions, add a few drops of sodium fluoride (NaF) to a newsample. Ca

2+forms a precipitate with fluoride (F

-), but Ba

2+does not.

o Lastly, NaOH(for OH-ions) is added to a fresh sample. If a precipitate forms, the ion is eithercopper (Cu2+), iron(II) (Fe2+) or iron(III) (Fe3+):


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If the precipitate is blue then the ion is Cu2+. To further verify that it is copper,dissolve the precipitate in ammonia (NH3), and if it is Cu(OH)2it will form a deep-blue

solution.

If the precipitate is NOT blue, then the ion is either Fe2+or Fe3+. Using a fresh sample,add:

A few drops of potassium thiocyanate (KSCN) solution. Fe3+reacts withthiocyanate ions (SCN

-

) to form a bloodred precipitate. A few drops of PURPLE potassium permanganate (KMnO4) solution. Fe2+

decolourises the permanganate ion (MnO4-), changing the solution from

purple to colourless.

CATIONS (when there is a mixtureof ions):o When there is a mixture of ions, there is the risk that the test for one ion will interfere with

the test for another ion.

o Once a precipitate is formed, the reagent is added until no more precipitate will form (this isto remove all traces of a specific cation).

o The mixture is then filtered or centrifuged to remove the precipitate, and then further testsare performed on the remaining solution.

o Theprocedurefor identifying ions in a mixture: Add HCl solution; if a precipitate forms, Pb2+is present in the mixture. Keep adding

HCl until no more precipitate forms, then filter.

Divide the filtrate into 2 portions: Add NaFto one portion; precipitate indicates the presence of Ca2+. Add H2SO4to the other portion; if a precipitate forms, Ba2+or Ca2+ions are

present in the mixture. Completely precipitate out all the barium and calcium

ions, then filter.

Add NaOHsolution; if there is a precipitate, mix NH3into the solution and filter. Apresence of any blue precipitate indicates Cu

2+, while any green or brown precipitate

indicates iron ions (to distinguish iron(II) and iron (III), use thiocyanate and

permanganate tests on new samples).

ANIONS (when only oneion is present):o Carbonate(CO32-):

Add dilute nitric acid (HNO3); if bubbles of a colourless gas form (that when passedthrough limewater turns it cloudy) carbonate is present.

If the solution has a pH of 8-11 then carbonate is likely present.o Sulfate(SO42-):

If the addition of Ba(NO3)2(barium nitrate) in to an acidified sample produces a thickwhite precipitate, then sulfate is present:

Acidify solutions using dilute nitric acid (does not form precipitates). If acidification and addition of Pb(NO3)2(lead nitrate) produces a white precipitate,

then sulfate is present.

o Phosphate(PO43-):

If the addition of Ba(NO3)2(barium nitrate) to an ALKALINE sample produces a whiteprecipitate, phosphate is present.


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Use ammonia (NH3) to make solutions basic. If acidification followed by the addition of (NH4)MoO4(ammonium molybdate)

solution produces a yellow precipitate, phosphate is present.

o Chloride(Cl-): If the addition of AgNO3(silver nitrate) to an acidified sample produces a white

precipitate that dissolves in ammonia solution and darkens in sunlight, then chloride

is present. ANIONS (when there is a mixtureof ions present):

o Again, care must be taken not to cause interference between tests:o The procedure:

Add nitric acid; any bubbling indicates the presence of carbonate. Keep adding aciduntil all bubbling stops.

Acidify solution with more nitric acid. Add Ba2+(through barium nitrate). If aprecipitate forms, sulfate is present. Filter solution.

Make the filtrate alkaline by adding ammonia. Add more Ba2+ions. If a precipitateforms, phosphate is present. Filter solution.

Acidify solution again and add Ag+ions; precipitate indicates Cl-ions.


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3.0.1:PRACTICALPerform first-hand investigations to carry out a range of tests, including flame tests, to

identify the following ions:-

Cations: Barium, calcium, lead, copper and iron:Anions:Phosphate, sulfate, carbonate and chloride:

In this practical, students were given vials of unknown solutions; vials were labelled as mixtures ofions or only one ion.

Using both precipitation and flame tests, the contents of the vials were determined. Precipitation Tests:

o Please see ABOVE for a very in-depth coverage of precipitation tests used to determineanions and cations present in a sample.

Flame Tests:o Flame tests were only used to identify cations.o Anions cannot be identified by flame tests.o Out of the given list of cations, only barium, calcium, and copperproduce a distinctive flame

colour when sprayed into a flame:

Ba2+gives apale-greenflame. Ca2+gives a brick-redflame. Cu2+gives a blue-green flame.

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 trace elements:

ATOMIC ABSORPTION SPECTROSCOPY: A method of quantitatively determining the concentrations of metal ions in solutions; it is

extremely sensitive and measures in ppm (usually) or ppb (if a graphite furnace is used).

Developed by Australian scientist, Alan Walsh, and his CSIRO team in early 1950s. HOW AAS WORKS:

o A hollow-cathode lamp containing the element being analysed generates wavelengths oflight specific to the metal ion being tested for. (for example, if cobalt is being tested for, a

cobalt lamp is used, where the cathode in the lamp is cobalt metal).


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o A solution test sample being analysed is fed into a nebulizer where the liquid solution ismade into a spray or mistwhich is then mixed with a fuel and its oxidant (usually a mixture

of oxygen and acetylene).

o The flame vaporises the atoms in the mixture.o The light beam is then passed through the sample which absorbs some of the light. (The

more concentrated the sample, the greater intensity of light that is absorbed).

oThis changed light is passed into the monochromator which selects that specificwavelength(s) which have been absorbed, and compares it to a reading without the

flame/atoms to determine a reading called absorbance.

o By measuring the fraction of the light at a specified wavelength that is absorbed, we candetermine the concentration of the element; absorbance is proportional to concentration,

and hence the unknown concentration of the element is determined.

Absorbance is an arbitrary unit, so the AAS device must be calibrated using standard solutions(solutions of an element of known concentration):

prior to the unknown sample being tested, standard solutions of known concentrationareaspirated one at a time, and the light absorbed by each solution is measured and recorded. Theabsorbance of the light is then graphed against the concentration of the samples. This process is

calibrating the AAS.

USES OF AAS:o It is used to monitor concentrations of heavy-metals in the environment as well as in food,

for health and safety reasons. AAS is used as even at low concentrations these metals can

be very dangerous.

o It is used to measure concentrations of micronutrients in soils.o Used to measure levels of pollutants in water, soil and air.o It can determine the concentration of trace elementsin living things and hence determine

the cause of deficiency-related diseases.

The Impact of AAS On Understanding of Trace Elements:o Trace elementsare elements that are needed in very small amounts by living things (in the

range of 1-100 ppm).

o Trace elements are needed in minute quantities for the proper growth, development, andphysiology of organisms.

o Common trace elements in humans are: zinc cobalt copper nickel molybdenum iodine, and selenium.

o Before the invention of AAS, analytical methods were not sensitive enough to measure theconcentration of trace elements in organic samples.

o The presence of these elements were often unnoticed, and the causes of diseases relatingto trace-element deficiency (such as goitre; iodine deficiency) were unknown.


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o AAS showed that not only that there were trace amounts of elements in all organisms, butthat these were also essential for their well-being.

o Hence, AAS had a great impact on the understanding of trace elements:o Examples of AAS use related to trace elements:

In coastal SW Australia, animal health was very poor even though they were grazedon seemingly good pasture. AAS showed that there were cobalt deficiencies in the

soil and the pasture, and this was corrected. Arid areas of Victoria could not support legume crops until molybdenum deficiencies

were detected and rectified.

Before the 1930s large areas of Australia couldnt be farmed very well, even whenheavily fertilized with superphosphate. If the grass grew, sheep that fed on it grew

very patchy wool. Research using wet methods of chemistry showed that the soils

were deficient in trace elements such as Cu, Zn, Mn and Mo. As soon as these

elements were provided, farming could be established. AAS has allowed the levels of

trace elements in our soils to be more readily monitored.

3.0.5:Gather, process and present information to interpret secondary data from AAS measurements and

evaluate the effectiveness of this in pollution control:

AAS is an extremely effective tool in pollution monitoring and management. It can be used to measure levels of pollutants in the soils, food, water and has many other

applications in relation to pollution control.

EG:o AAS was used in Bangladesh to monitor levels of arsenic in drinking water.o Arsenic is a serious pollutant as it is extremely toxic.o The following AAS absorbance data was obtained by using standard solutions of arsenic of

known concentration:

Total Arsenic Concentration Absorbance

50 g/L 0.12

100 g/L 0.23

150 g/L 0.35

This data was then graphed on a calibration curve:


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Samples of drinking water were taken and their absorbances were measured:Sample Absorbance

1 0.28

2 0.13

3 0.31

These absorbances were then plotted on the graph, and from there the arsenic concentrationswere estimated:

o Sample 1 (124 ppb)o Sample 2 (61 ppb)o Sample 3 (163 ppb)

Arsenic levels higher than 100 ppb were considered polluted. Hence, AAS is a very effective tool in pollution monitoring and control.

3.0.2:Gather, process and present information to describe and explain evidence for the need to monitor

levels of specific ions in substances used in society:

Lead:o Lead needs to be monitored because it is a severe neurotoxin.o It retards intellectual development in young children, causes brain damage and can lead to

neurological disorders.

o Until recently, lead was widely used as an additive in petrol; it was released in greatquantities to the atmosphere in vehicle exhausts and deposited in the environment near

highways.

o Lead also used to be found in many paints, as these were often lead-based pigments; thislead was released into waterways, the soil and air when old houses were demolished.

o Monitoring of lead concentrations of soil near highways, in water and in the atmosphere isessential to ensure that people are not exposed to harmful levels of toxic lead ions.

Phosphate:o Phosphate occurs in natural waterways at low concentrations and is essential for normal

aquatic plant growth.

o However, if phosphate levels become too high, it could set off and algal bloom; this willchoke the entire waterway, as the waterway will be completely surrounded by algae and

drained of oxygen.

o This has many detrimental effects on the ecosystem living in the water.o Hence, by monitoring the levels of phosphates in waterways and in consumer goods that

reach waterways (e.g. detergents), scientists can guard against the development of algal

blooms.

Summary of information gathered

Identify the ion chosen Lead

Why the ion needs to be monitored Lead is a toxic, heavy metal and a neurotoxin Can cause damage to all organisms in the body,

especially the brain, kidneys and reproductive

system. It disrupts enzyme systems and causes

anaemia as it inhibits the formation of red blood


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cells.

Causes brain damage and retards intellectualdevelopment in young children.

Lead bioaccumulates and is difficult to eliminate Bioaccumulation occurs along the food chain so

levels can build up in animals at the end of

chains, i.e. humansHow the ion is monitored Lead is readily detected and its concentration is

measured by AAS

Substances monitored for this ion atmosphere waters food human tissues soil

Sources of the ion in these substances Mining and refining of ores containing lead (i.e.copper smelters)

Paints containing leadreleased as itdeteriorates or is sanded or burnt

Lead glazing of pottery Corrosion of plumbing materials containing lead Car batteries Burning of rubbish

Incidents involving this metal Higher concentrations of lead in the atmosphere

along major roads, when lead was allowed in petrol,and around mining towns and copper smelting,

caused lead poisoning. Children with higher than

normal lead concentrations in blood after eating

flaking paint in their homes.

3.0.3:PRACTICALIdentify data, plan and select equipment and perform first-hand investigations to

measure the sulfate content of lawn fertiliser and explain the chemistry involved:

In this practical, the sulfate content of a lawn fertiliser was calculated. This is an example of gravimetric analysis; it is a quantitative analysis. METHOD:

o In a dry beaker, 5 grams (0.01%) of fertilizer was electronically weighed.o All the fertilizer was carefully transferred to a mortar and pestle, where it was ground into a

fine powder.

o The powder was transferred into a beaker; using a wash bottle with distilled water, all theresidue was washed into the beaker up to the 200 mL mark.

o 50 mL of 0.1 M hydrochloric acid was added, and the mixture stirred until all of the fertilizerdissolved.


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o The mixture was then heated to its boiling point; the flame was turned off, and bariumchloride was added in drops, which formed a precipitate:

BaCl2 (aq)+ SO42-(aq) BaSO4 (s)+ 2Cl-(aq)o Barium chloride was added until no more precipitate formed.o The mixture was digested(heated just below boiling point) for 30 minutes, stirring every

now and then, and then the precipitate was allowed to settle.

oThe beaker and its contents were then cooled in an ice-bath.

o Using a sintered-glass crucible (which had its mass recorded), connected to a vacuum pump,the mixture was filtered.

o The crucible was washed with water, and then ethanol, and then dried in an oven to aconstant mass.

o The difference between the crucibles original weight and weight after drying (which wasthe mass of BaSO4) was found to be 5.92 g.

CALCULATING SULFATE CONTENT:massof BaSO4formed = 5.92 g

percentageof sulfate in BaSO4 = molar mass sulfate / molar mass BaSO4

= (32.1 + 416.0) / (137.3 + 32.1 + 416.0)

= 41.2 %

mass of sulfate in BaSO4 = 5.92 41.2 %

= 2.44 g

percentage of sulfate in fertilizer = mass of SO4/ mass of fertilizer 100

= 2.44 / 5.0 100

= 48.9 %

3.0.4:Analyse information to evaluate the reliability of the results of the above investigation and to

propose solutions to problems encountered in the procedure:

RELIABILITY:o The use of a very precise electronic scale ensured accurate measurement.o The fertilizer was ground into a powder to ensure that all of it dissolved; if some sulfate

stayed in solid form, the measurements would be inaccurate.

o The washing of the mortar and pestle into the beaker was to ensure all of the fertiliser wastransferred into the beaker.

o Hydrochloric acid was added to aid in the dissolving of the fertiliser.o Slowlyforming precipitates (using a dropper) at a hightemperature ensures the formation

of large particles.

o Also, the mixture was digested for half an hour to allow the particles to grow.o Large particle size meant fewer loses of BaSO4through the filter.o The mixture was cooled in ice-water to greatly reduce the solubility of BaSO4to ensure that

virtually the entire sulfate precipitated out.

o A sintered-glass crucible was used instead a filter-paper as filter paper pores are too large;they allow an unacceptable level of BaSO4through.

o The washing with water and ethanol removed any traces of contaminants.


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SOLUTIONStoProblems Encountered:o Human errors in measurement were the main source of inaccuracies; more careful

measurement of fertilizer mass, would ensure better results.

o There were small losses of barium sulfate due to its very small solubility. This was why thebeaker was cooled in ice-water before filtering (solubility decreases at low temperatures).

However, due to time constraints, cooling did not occur to a great extent.

o Longer digestion times would allow larger particles to form, and less loss of barium sulfatethrough the filter would occur.

o There was possibly some barium sulfate left on the beaker walls before filtering; this wouldbe solved by washing out the beaker with distilled water.

o An incomplete drying of the sintered glass crucible (due to moist environment, as well astime constraints) would be solved by a longer period of heating, as well as by using a

desiccator.

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

4.1:describe the composition and layered structure of the atmosphere

Name of layer Minimum and

maximum distance from

the surface of the Earth

Composition Temperature

Troposphere 0approximately 15km Contains 90% of

atmospheric gases. 78%

N2, 21% O2, 0.9% Ar,

small amounts of other

gases such as CO2, Ne,

He and pollutants such

as methane and oxides

of sulfur and nitrogen.

Variable. This is where

weather is determined.

For every rise in altitude

of 1km, the temperature

drops by around 5oC

Stratosphere 1550km Contains 9% of

atmospheric gases.

Nitrogen (N2), Oxygen

(O2) and Ozone (O3) and

-50oC to 30

oC at the top.

Temperature increases

largely because of

ozone, which absorbs


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other gases in the

troposphere

some thermal energy

from the suns radiation.

Ionosphere (made up of

the two layers called the

mesosphere and

thermosphere)

50150km (atmosphere

gradually fades away

there is no sharp upper

boundary)

Contains 1% of

atmospheric gases. The

spacing between

molecules is even

greater at thesealtitudes; the gas

particles include ions

(i.e. O2+, NO

+) together

with atoms (such as O)

and free electrons that

would not be stable at

higher altitudes.

Mesosphere:

temperature decreases

with increasing altitude

to about -120oC.

Thermosphere:temperature increases

with increasing altitude.

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

Pollution refers to an undesirable change in the physical, chemical, or biological characteristics of the naturalenvironment, brought about by man's activities.

The main pollutants found in the lower atmosphere and their sources:Pollution Artificial Source Natural Source

Nitrogen oxides (NOx, i.e. NO,

NO2)

Motor vehicles, energy

production, jet engines

Biomass burning, lightning, soil

bacteria

Volatile organic compounds Unburnt fuel, solvents and paints Emitted by vegetation, i.e.

eucalypts

Carbon monoxide (CO) Motor vehicles, incomplete

combustion of fuels

Biomass burning, volcanoes,

decomposition of plants and

animals

Carbon dioxide (CO2) Combustion of fossil fuels in

motor vehicles and electricity

production

Biomass burning, volcanoes,

decomposition of plants and

animals

Sulfur dioxide (SO2) Electricity production, smelting

metal sulfide ores, combustion of

fossil fuels, sulfuric acid plants,industries, i.e. paper and food

processing

Bacteria, volcanoes, hot springs

Particles (soot, asbestos etc) Combustion of fossil fuels,

mining, construction, incinerators

Biomass burning, soil (wind

erosion), pollen, spores

Lead Motor vehicles (with leaded

petrol), smelting metal ores,

incinerators, paint,

manufacturing, i.e. batteries

Erosion of lead ores

Chlorofluorocarbons (CFCs) Formerly in spray cans,refrigerant/air conditioner


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coolant, foaming agent

Ozone High voltage equipment Lightning, the reaction between

hydrocarbons and the oxides of

nitrogen under the influence of

UV light.

GAS MIXING:o Hot air rises and cold air falls.o For the troposphere, its bottom is warmer than its top (because temperature decreases as

altitude increases); hence, the air from the bottom is always rising to the top. That is, there

is constant mixing of gases (convection).

This means that pollutants released at the Earths surface by human activity arerapidly dispersed throughout the stratosphere.

This is what causes the lower atmosphere to be so rapidly polluted.o For the stratosphere, its bottom is colder than its top (because temperature increases as

altitude increases); hence, there is little movement of gases. The cold air at the bottom and

hot air at the top simply stays there.

This protects the stratosphere from pollutants released at the surface, as gasmixing stops at the tropopause. The only way pollutants enter the stratosphere is by

slow diffusionof gases.

Pollutants are very minor constituents in the troposphere and their concentrations are usuallymeasured in ppm.

Pollution interferes with ecosystems and our health and quality of life:o Sulphur dioxide: irritates the respiratory system, causes lung damage and may cause asthma.

It also contributes to acid rain.

o Nitrogen oxides: contribute to acid rain and photochemical smog; they decrease lungfunction, increase susceptibility to respiratory infections and sensitivity to asthma.

o Particles: settle in the lungs and cause irritation, reduce visibility and some are carcinogenic.o VOCs: contribute to photochemical smog and many carcinogenic.o Carbon dioxide: greenhouse gas, contributes to global warmingo Carbon monoxide: toxic, combines with haemoglobin better than oxygen, causing

asphyxiation

o CFCs: ozone depletion in the atmosphere4.3:describe ozone as a molecule able to act both as an upper atmosphere UV radiation shield and a lower

atmosphere pollutant

The action of ozone (as well as its value) depends greatly on where it is located. In the upper atmosphere (stratosphere) ozone is found as the ozone layer. It is extremely crucial

part to life on Earth.

However, in the lower atmosphere (troposphere), ozone is a serious air pollutant. Ozone in the Stratosphere:

o Ozone in the stratosphere, in the form of an ozone layer,protects us from harmfulultraviolet radiation (UV light):

There are 3 forms of UV light; UV-A, UV-B and UV-C.


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The ozone-layer blocks the harmful UV-B and UV-C rays from passing through theatmosphere; these can cause many cancers and severe sunburn.

The useful UV-A (needed for photosynthesis) can still pass through. Ozone layer in the stratosphere absorbs 97-99% of the Suns UV light

o The following equations show how ozone is formed and destroyed as well as how it protectsus from harmful UV radiation:

O2+ UV radiation 2O

O + O2 O3 O3+ UV radiation O + O2 O + O3 2O2

o Every time an oxygen/ozone reacts with UV light, it absorbs it.o Hence ozone can be said to be an upper atmosphere UV radiation shield.

Ozone in the Troposphere:o However, when ozone is found in the lower atmosphere (troposphere), it is considered a

serious air pollutant.o This is because ozone can cause serious health and environmental problems.o HEALTH ISSUES:

Ozone is poisonous to humans; as a strong oxidant, it can react with body tissue,especially with sensitive mucous membranes when breathed in.

Ozone causes breathing difficulties, aggravates respiratory problems and producesheadaches and premature fatigue.

o PHOTOCHEMICAL SMOG: When ozone is found as a component of smogit is a serious pollutant, and can be

very hazardous for health.

Sunlight splits nitrogen dioxide and the free radical produced joins with oxygen toform ozone: NO2 NO + O. Also, hydrocarbons and PAN (peroxyacyl nitrates)

can be present in the smog.

Thus ozone is both as a major pollutant, and a UV radiation shield.o Fortunately, most ozone is located in the stratosphere.

4.4:describe the formation of a coordinate covalent bond

Non-metallic compounds contain covalent bonds. A covalent bondis a shared pair of electrons thatkeeps two atoms together. Normally one atom contributes one electron and the other joined atom

contributes the other shared electron.

A coordinate covalent bond is formed when one atom donates both the electrons in the sharedpair. A lone pair from one atom forms the bond.

o Once the coordinate bond has formed, cannot be distinguished from other covalent bonds.4.5:demonstrate the formation of coordinate covalent bonds using Lewis electron dot structures

RECALL:


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o In LEWIS electron-dot structures, atoms are represented by their chemical symbol,surrounded by only valenceelectrons; e.g. oxygen will be represented as an O surrounded

by 6 electrons (see ABOVE).

o Use different symbols for the electrons of different atoms (e.g. crosses/dots). A coordinate-covalentbond involves one atom donating a pair of electrons to the other to form a

bond, so both can have an octet; all the electrons in the bond come from one atom:

o EXAMPLES:o In the OZONE (O3) molecule, one of the oxygen atoms forms a coordinate covalent bond

with an oxygen atom:

o Ions, such as the hydronium H3O+and the ammonium NH4+, contain a coordinate covalentbond. In the formation of the hydronium ion, one of the non-bonding electron pairs on the

oxygen atom is used to form a covalent bond between the hydrogen ion H+(which has no

electrons) and the oxygen atom.

o Formation of a coordinate covalent bond in the hydronium ion:

o Formation of a coordinate covalent bond in the ammonium ion:

o TIPWhen asked to draw a Lewis diagram of ozone, check that all oxygen atoms have only6 electrons of their own, but 8 electrons bonded altogether:

Left: 4 unbonded electrons + 4 electrons in covalent bond = 8 Middle: 2 unbonded + 4 in covalent bond + 2 in coordinate covalent = 8 Right: 6 unbonded + 2 in coordinate covalent = 8

4.6:compare the properties of the oxygen allotropes O2and O3and account for them on the basis of molecular

structure and bonding

Allotropesare different forms of an element made of the same type of atom, but with atomsarranged differently. Allotropes have the same chemical properties but different physical properties.

o For example, allotropes of carbon are graphite, diamond and fullerenes. Both oxygen gas and ozone are composed of oxygen atoms, but they are arranged differently.

Oxygen is a diatomic molecule with two atoms joined by double covalent bonds. Ozone molecules


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have three oxygen atoms, two of them joined by double covalent bonds and one joined to the

central atom by a single coordinate bond.

Property O2(oxygen gas) O3(ozone) Explanation

State and colour Colourless gas Pale blue gas No explanation

Odour Odourless Sharp, pungent odour No explanation

Reactivity Moderately reactive.

Decomposed by highenergy UV light.

Highly reactive.

Decomposed bymedium energy UV

light.

To decompose oxygen, its double bond

has to be broken; this requiresconsiderable amounts of energy.

However, the single bond (coordinate

covalent bond) in ozone requires much

less energy to be broken, and hence

ozone is much less stable (readily

decomposes to O2).

Oxidation ability Moderately strong

oxidising agent

Very strong oxidising

agent.

The oxidising strength of ozone comes

from the weakness of the single bond; it

easily releases an oxygen atom which

can then oxidise a compound.

e.g. reaction with metals: oxygen forms

the oxide as the only product whereas

ozone reacts more readily producing the

metallic oxide and an oxygen molecule.

Solubility in water Slightly soluble 15 times more soluble

than oxygen

Non-polar O2does not form strong

intermolecular forces in the polar water.

Ozone has a bent structure, which

provides for some polarity of the

molecule in its interaction with water.

Effect on humans Essential for life Lethal to

microorganisms.

Causes coughing,

chest pain and rapid

heartbeat. Irritates

eyes and airways.

At concentration > 1

ppm it is toxic.

Melting point and

boiling point

MP: -218.75oC

BP: -182.96oC

MP: -192.5o

C

BP: -110.5oC

The boiling point of diatomic oxygen is

lower than that of the ozone as diatomicoxygen has a lower molecular mass

requiring less energy in the boiling

process.

Structure and

bonding

Diatomic molecule

two oxygen atoms held

together with a covalent

double bond.

Three oxygen atoms

held together with 1

double covalent bond

and 1 single

coordinate covalent

bond

Shape Molecule is linear

shape. Thus, non-polar.

Molecular shape is

bentpolar molecule


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

A free radical is a reactive particle that contains one or more unpaired electrons in its outer shell. EG: The oxygenfree radical:

o The oxygen free radical has two pairs of electrons, as well as two unpairedelectrons (seediagrams); these unpaired electrons are highly reactive.

o It is basically an oxygen atom; they have the same electron configuration. The oxygen free radical can be made either by passing electrical current through oxygen gas to

decompose it, or by exposure to U.V. radiation:

o O2 2O

o the energy absorbed in the splitting of oxygen, and the unpaired electrons, make the freeradical very reactive.

COMPARISON:o O2, O3and the oxygen free radical (O) are all forms of the element oxygen, but the free

radical is much more reactive and the most toxic. O2and O3are relatively stable in the

atmosphere unless acted upon by UV, but the free radical only lives briefly, once formed it

immediately reacts.

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

Chloroflurocarbons (CFCs) are halogenated alkanes with all hydrogens substituted with chlorineand fluorine atoms, i.e. dichlorofluromethane and 1,1,2,2-tetrachloro-1,2-difluroethane.

o they are man-made (synthetic) chemical compounds.o DO NOT CONTAIN HYDROGEN AT ALLo CFCs were introduced in the 1930s (known asfreons) as replacements for ammoniain

refrigeration:

This was because had the required pressure-dependent properties that refrigerantsneeded, as well as that they were odourless, non-flammable, non-toxic and inert,

much unlike the toxic, foul-smelling ammonia.o CFCs were very widely used as:

Refrigerants in fridges and air-conditioners Propellants in aerosol spray cans Foaming agents in the manufacture of foam plastics like polystyrene Cleaning agents in electronic circuitry Solvents in dry cleaning

o These many uses released CFCs directly into the lower atmosphere.o As they were very inert and insoluble in water (rain), they remained in the troposphere,

where air convection spread them throughout the atmosphere.


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o Very slowly, the CFCs began to diffuse through the tropopause and into the stratosphere,where problems began to occur.

Halons are halogenated alkanes with hydrogens substituted with bromine in addition to chlorineand fluorine atoms, i.e. bromotrifluromethane, bromochlorodifluromethane.

o They are dense, non-flammable liquids that were widely used as effective fire-extinguishers(called BCF fire-extinguishers) because of their excellent fire retardant properties.

o As they were used onto fires, the halons were released directly into the atmosphere, wherethey too slowly diffused into the stratosphere.

o Halon use has been dramatically reduced because the bromine molecules are even moreeffective than chlorine atoms in the chain reactions that lead to the depletion of the ozone

layer.

Because both halons and CFCs are so inert, they remain in the atmosphere unchanged for manyyears.


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4.9:identify and name examples of isomers (excluding geometrical and optical) of haloalkanes up to eight

carbon atoms

A haloalkaneis an alkane with one or more halogen(elements in group 7) atoms replacinghydrogen atoms.

Naming Haloalkanes:o Use prefixes for the halogen groupi.e. fluro-, chloro-, bromo-, iodo-o If more than one type of halogen atom is present, list them in alphabetical ordero Use di, tri, tetra when there is more than one atom of any halogeno Number the carbon chain, giving the lowest set of numbers to the halogens presento If the numbers are the same from both ends of the chain, then give the first named halogen

the lowest number

Isomers:o Isomersare compounds that have the same molecularformula, but a different structural

formula (different arrangement of atoms).

o Carbon compounds, such as haloalkanesare able to form many different isomers: Molecules of alkanes and alkenes containing less than 4 carbon atoms can only

assume one possible structure.

Molecules larger than and including butane and butane have various isomersthenumber of which increases with increasing molecular size.

o Due to the differences in the arrangement of the atoms, isomers have different chemicaland physical properties, and hence it is vital that these differences in structure are reflected

in systematic names.

o EG: Draw 4 isomers of C4H7ClF2and name them using IUPAC nomenclature:

2-chloro-1,3-difluorobutane.



1-chloro-1,1-difluoro-2-methylpropane.


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4.10:discuss the problems associated with the use of CFCs and assess the effectiveness of steps taken to

alleviate these problems

CFCs were widely used for 50 years The biggest problem associated with the use of CFCs is the destruction of stratospheric ozone (i.e.

depletion of the ozone layer) and the greenhouse effect:

o CFCs are very inert, and are not washed out by rain.o CFCs remain in the troposphere for many years, because they are very stable, and

eventually diffuse into the stratosphere.

CFCs are broken down by the presence of UV radiation in the atmosphere (photodissociation), releasing halogen free radicals.

These free radicals can then react with ozone, destroying it.o This increases the UV radiation penetrating the Earth, leading to:

increases in sunburn and skin cancer damage to plants possible harmful effects on sensitive ecosystems, such as those found in the

Antarctic the breaking down of chemical bonds, in particular in biological polymers like DNA

and proteins, causing considerable damage to living systems

increases in eye cataracts increased rate of deterioration of synthetic polymers left in the sin damage to aquatic plants and animals decreases in phytoplankton decreases in crop productivity

o The production and destruction of ozone is an equilibrium processuntil the release ofCFCs

o CFCs catalyse the destruction of ozonedepleting the layer faster than it can be madenaturally, and hence they decrease the amount of shielding against UV radiation.

How CFCs Destroy The Ozone Layer:o Firstly, short wavelength UV radiation (that has not been removed by the ozone layer)

attacks the CFC molecule and breaks off a chlorine atom:

CCl2F2 (g)+ UV radiation Cl(g)+ CClF2 (g)o The chlorine radical reacts with ozone, forming oxygen gas, and a chlorine monoxide radical:

Cl(g)+ O3 (g) ClO(g)+ O2 (g)o The chlorine monoxide radical then reacts with an oxygen radical, and the chlorine radical is

regenerated:

ClO(g)+ O(g) Cl(g)+ O2 (g)o The net result is that an ozone molecule and an oxygen radical have been converted into 2

oxygen molecules AND the chlorine has not been used up.

o The chlorine radical can then attack another ozone molecule and repeat the whole processthousands of times; this is a chain reaction.

o Thus, a very small amount of CFC in the stratosphere can do significant damage. How Chlorine Radicals Are Removed:

o According to the above, theoretically, a single chlorine atom could destroy the entire ozone-layer; however certain natural reactions remove this radical.


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o The chlorine atom reacts with stratospheric methane, ending the chain reaction: Cl(g)+ CH4 (g) HCl(g)+ CH3 (g)

o Neither HCl nor the methyl-radical has any effect on ozone.o Another important reaction for stopping ozone depletion involves the ClO species reacting

with nitrogen dioxide, forming chlorine nitrate:

ClO(g)+ NO2 (g) ClONO2 (g) The Greenhouse effect:

o The greenhouse effect is the heating of the Earth as a consequence of some gases in theatmosphere which absorb and emit infrared radiation. Without these gases, heat would

escape back into space and Earths average temperature would be much colder. Because of

how they warm our world, these gases are referred to as greenhouse gases.

o CFCs are greenhouse gaseso Many people are worried that all of the extra greenhouse gases being generated because of

human activities might increase the greenhouse effect causing more heat to be retained by

the Earth, leading to global warming

The Antarctic Spring Ozone Hole:o There is a serious periodic depletion of the ozone-layer that occurs every spring over

Antarctica; it is called the Ozone Hole.

o This is due to the conditions of Antarctica in winter, as well as spring.o Antarctic wintersare perpetually dark; the cold conditions, as well as solid particulate

catalysts in the air, encourage the following reaction to occur:

HCl(g)+ ClONO2 (g) Cl2 (g)+ HNO3 (g)o This has zero effect on ozone levels during the winter.o However during early spring, the Sun begins to rise, and the situation changes dramatically;

sunlight is able to split chlorine molecules:

Cl2 (g)+ UV radiation 2Cl(g)o Hence in spring there is another source of chlorine radicals to destroy more ozone; the

concentration of ozone is reduced dramatically, causing a hole.

o Eventually, the fixed amount of Cl2created over the winter is blown away by Antarctic windsand the ozone layer slowly regenerates.

Dealing With The CFC Problem:o The only way to stop ozone depletion is to STOP releasing CFCs of any form.o INTERNATIONAL AGREEMENTS:

The main way the CFC problem is being dealt with is by international agreementsbased on the common goal of phasing out CFCs.

The Montreal Protocolon Substances That Deplete the Ozone Layer (1987) is aninternational treaty designed to protect the ozone layer by phasing out the

production of a number of substances believed to be responsible for ozone

depletion.

Its goals included ceasing the manufacture, and banning the use, of CFCs and certainhaloalkanes by 1996, the end of halon use by 1994, the phasing out of HCFCs, as well

as the provision of financial assistance to developing nations in order to help them

reach the goals of Montreal.


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o CFC REPLACEMENTS: Finding alternative compounds to fulfil the roles of CFCs is a major step forward in

preventing ozone depletion.

Alternatives include: Replacing CFC aerosols propellants with hydrocarbons and the use of normal

pressure packs

Alternative chemicals:o HCFCsare less damaging to the ozone layer than CFCs because they

have more reactive carbon-hydrogen bonds and so react before they

can diffuse into the stratosphere. HCFCs that do diffuse into the

stratosphere will be a source of chlorine radicals

o HFCsdo not contain chlorine and so do not deplete the ozone layereven if they are released into the stratosphere. HFCs are the best

chemicals to replace CFCs.

o they also contribute less to global warmingo Dealing With Increased UV Radiation:

Increasing UV levels have meant that more UV inhibitors need to be included inpolymers (such as PVC) and Cancer Councils have advised the use of only sunscreens

with a rating of SPF 30+ or greater.

Effectiveness of These Solutions:o The Montreal Protocol is only effective if member nations ratify the protocol and adhere to

its regulations; so far, the Montreal Protocol has been a huge success in international

agreement and environmental health.

o Certain CFC replacements are not as effective as the CFCs themselves; future technologicaladvancement hopes to find better replacements.

o There are still, however, significant levels of CFCs in the atmosphere, and currenttechnology has no way of removing them.

4.0.1: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

All the CFC-related equations from above:o Formation of chlorine radical:

CCl2F2 (g)+ UV radiation Cl(g)+ CClF2 (g)o Reaction of ozone:

Cl(g)+ O3 (g) ClO(g)+ O2 (g)o Regeneration of chlorine:

ClO(g)+ O(g) Cl(g)+ O2 (g)o Removal of chlorine radical:

Cl(g)+ CH4 (g) HCl(g)+ CH3 (g)o Removal of chlorine monoxide radical:

ClO(g)+ NO2 (g) ClONO2 (g)o Formation of molecular chlorine:

HCl(g)+ ClONO2 (g) Cl2 (g)+ HNO3 (g)o Decomposition of molecular chlorine:


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Cl2 (g)+ UV radiation 2Cl(g) Since the chlorine atom is not being used up in the above reactions, it is able to attack more ozone

molecules, and continue breaking ozone up indefinitely. This continues like a chain reaction until

the chlorine reacts with nitrogen or hydrogen forming compounds such as ClONO2and HCl

4.11:analyse the information available that indicates changes in atmospheric ozone concentrations,

describe the changes observed and explain how this information was obtained How Are Ozone Levels Measured?

o Stratospheric ozone levels are measured from ground-based instruments, from instrumentsin satellites and from instruments in weather-balloons.

Ozone levels are measured in Dobson Units (DU)the lower the DU, the less ozoneis present/the lower the concentration of ozone

One Dobson Unit is equivalent to about 2.69 1016 ozone molecules in a columnwith a cross section of 1 square centimetre.

The instrument that measures ozone concentrations in Dobson units is called theDobson spectrophotometer. It works by measuring the intensity of sunlight at twowavelengths that are absorbed by ozone, and two that aren't.

o The measurements made indicate that changes in ozone levels have occurred.o GROUND-BASED:

The ground-based instrumentsused are UV spectrophotometers that are able tomeasure the intensity of light at specific wavelengths.

These instruments are pointed directly upwards towards the sky and are set tomeasure light intensity at the wavelengths of light at which ozone absorbs (such as

UV-B and UV-C) and at wavelengths on either side (for light which ozone does not

absorb).

A comparison of these 2 measurements gives a measure of the total ozone in theatmosphere per unit of area of Earth surface at that location.

o BALLOON-BASED: These spectrophotometers can also be placed in high-altitude weather balloons that

can rise above the stratosphere.

The instruments are pointed downwards, and measure ozone from above.o SATELLITE-BASED:

TOMS (total ozone mapping spectrophotometers): used on board probe satellites They measure the total ozone in a column of atmosphere below it by

comparing the UV radiation coming from the column of atmosphere below

with the UV radiation directly coming from the sun. The data is usually

presented as a computer generated colour map.

TOMS are able to scan the entire globe and measure ozone concentrations asa function of altitude and geographical location.

TOMS are no longer used since a failure in 2006, OMI is now used

OMI (Ozone Mapping Instrument) modified spectrophotometer


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The Changes Observed:o Measurements of the total amount of ozone in a column of atmosphere have been

recorded since 1957.

o The main depletion of ozone has occurred over the Antarctic.o Scientists identified that a dramatic decline in springtime ozone occurred from the late

1970s over the entire Antarctic. The decline reached approximately 30% by 1985. In some

places, the ozone layer had been completely destroyed.

o The ozone decline over Antarctica during springtime is now not so dramatic, but oftenexceeds 50%.

4.0.2:gather, process and present information from secondary sources including simulations, molecular

model kits or pictorial representations to model isomers of haloalkanes

In this experiment, molecular modelling kitswere used to show different isomers of a haloalkane. The class was divided into groups, and each group was provided with a kit. Each group was provided with a haloalkane, which they were require to draw structural formula for,

and then using the kit, 3 different isomers were formed.

JUSTIFY the method:o The models created a good visual 3D representation of a chemical property; that is,

isomerism. RESULTS:

o Four isomers of C4H7ClF2with their IUPAC names:

o 2-chloro-1,3-difluorobutane.

o 4-chloro-1,1-difluorobutane.


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o 1-chloro-1,1-difluoro-2-methylpropane.

4.0.3: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

Ammonia:o Large scale (industrial) refrigeration has reverted back to using ammoniaas a refrigerant, as

was done prior to the discovery of CFCs.

o However, great care is exercised, as ammonia is dangerous and toxic. HCFCs:

o Hydro chlorofluorocarbons are CFCs that contain hydrogen.o These were the first replacements for CFCs.o HCFCs contain CH bonds that are susceptible to attack by reactive radicals in the

troposphere and so are decomposed rapidly to a significant extent.

o This means that only a very small proportion ever reaches the stratosphere.o HCFCs replaced CFCs in domestic refrigeration, as propellants in spray cans, as an industrial

solvent and as a foaming agent.

oEffectiveness:

Small amounts of HCFCs do reach the stratosphere, and hence they are also ozone-depleting (10% the ozone-depleting potential of CFCs).

They are seen as only a temporary solution. HCFCs also contribute massively to the greenhouse effect, and so their use is being

phased out (complete ban by 2030).

HFCs:o Hydro fluorocarbonsare compounds that contain only carbon, hydrogen and fluorine (NO

chlorine or bromine).

o They are widely seen as a viable CFC and HCFC alternative, as they contain reactive CHbonds (so they degrade in troposphere) as well as the fact that they do not contain any

chlorine (and hence cannot form Cl radicals).

o Their ozone depleting potential is zero.o HFCs are very widely used in refrigeration and air-conditioning applications.o Effectiveness:

As they have zero ozone-depleting potential, HFCs are a good alternative to usingCFCs in terms of atmospheric health.

However, they are not as effective refrigerants as CFCs, and are slightly moreexpensive.

They are also strong greenhouse gases, and so further research is required.


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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

5.1: identify that water quality can be determined by considering: concentrations of common ions, total

dissolved solids, hardness, turbidity, acidity, dissolved oxygen and biochemical oxygen demand

Water quality can be determined by considering the following factors:o Concentrations of common ions:

CATIONS: Most common cations in water: Na+, Mg2+, Ca2+, K+, Sr2+, Fe3+ Other metal ions are analysed routinely, like Al3+, which is mobilised by

increased acidity, toxic heavy metals, like Hg2+

, Pb2+

, and Cd2+

, and As

(arsenic) in its various forms.

AAS is the preferred method for determining the concentrations of most ofthese ions.

ANIONS: Most common anions in water: Cl-, SO42-, HCO3- Chloride: gravimetric analysis is used to determine chloride levels by

precipitation as AgCl. Alternatively, volumetric analysis can be used by

titration with AgNO3solution.

Sulfate: concentration usually determined gravimetrically as BaSO4 Hydrogen carbonate: concentration determined volumetrically by titration

with standard HCl

Relative concentrations of ions in water depend on three factors: their prevalence in the Earths crust their solubilities, and the degree to which they are extracted from the water by living things

Factors affecting solubility of substances in water: the nature of the soluteionic, covalent network, covalent molecular either

polar or non-polar (water is a good solute for ionic and polar substances)

temperaturethe solubilities of most solids increase with increasingtemperature; the solubilities of gases decrease with increasing temperature

gas pressurethe solubilities of gases are directly proportional to thepressure of the gas above the water

The concentrations of sodium and chloride are important indicators of the salinityofthe water system; any significant change in salinity (increase or decrease) can greatly

affect aquatic life.

Magnesium and calcium ions are measured to indicate water hardness, which iscovered in more detail below.

Phosphate and nitrate ions are essential to aquatic life; however, excess levels theseions leads to eutrophication and algal blooms, destroying waterways.

o Total dissolved solids TDS are usually ionic salts TDS is commonly referred to as measuring the salinity of the water


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high concentrations are usually uninhabitable for many species contrastingly, somespecies can only live in a marine or brackish environment

MEASURMENT: TDS determined by evaporation of a filtered sample and weighing the

remaining solidsconcentrations measured in ppm or mg L-1

alternative method: measure the electrical conductivity of the water using aconductivity meter and estimate the TDS based on a series of standards

o Hardness: hard wateris water that contains significant concentrations of calcium and

magnesium ions together with hydrocarbonate, sulfate and chloride ions

temporary hardness: hardness that can be removed by boiling the water. It iscaused by the presence of calcium and magnesium hydrogen carbonate.

These form the insoluble carbonate when heated, thus removing calcium ions

from the water.

permanent hardness: caused by the presence of heat stable salts such assulphates. These cannot be removed by boiling. Permanently hard water can

be softened by adding sodium phosphate (calogen) or sodium carbonate

(washing soda).

Advantages of hard water: the scum that builds up inside pipes helps prevent metals leaching from old

pipes or joints into the water supply

some industries, such as the brewing industry, prefer hard water Cafor growth of strong bones and teeth

Disadvantages of hard water: difficult to lather, leaving scum on the washing calcium carbonate deposits inside hot water systems and pipes, eventually

blocking the flow of water

How to turn hard water into soft water: ion exchange process in an ion exchange process hard water is passed through a bed of sodium

zeolite and calcium and magnesium ions in the water are removed and

replaced by sodium ions in the zeolites, leaving soft water. A deioniser is an

ion exchanger containing zeolites that softens water by replacing either

calcium and magnesium ions with hydrogen ions or negative ions with

hydroxide ions.

NOTE desalination is a technique that may also be used but is not currentlyviable due to the excessive amount of energy required

MEASUREMENT:

concentrations of calcium and magnesium ions in a water sample can bedetermined by volumetric analysis by titration with ethylenediaminetraacetic


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acid (EDTA)the EDTA forms stables complexes with calcium and

magnesium ions

o hardness of water is usually reported as mg L-1or ppm CaCO3assuming all the calcium ions are present as calcium carbonate and no

magnesium ions are present

can also be assessed qualitively using height of the lather head techniqueo Turbidity

turbidity is a measure of suspended solids in water sources of suspended solids include clay, silt, plankton, industrial wastes, sewage high turbidity is a problem:

reduces the penetration of sunlight, reducing the effectiveness of aquaticplants photosynthesis, affecting oxygen concentration and pH

suspended sediment can carry nutrients and pesticides into waterways small particles in the upper layers of a water body can absorb infra-red

radiation from sunlight, raising water temperature

suspended solids also affect animals i.e. they smother oysters, clog fish gillsand make it difficult for predators to find food

MEASUREMENT can be measured visibly (qualitive test) can be measured using a turbidity or Secci diskthe disk is lowered into the

body of water until the cross or mark can no longer be seen; the greater the

concentration of the suspended solids in the water, the more quickly the

mark will disappear as the disk is lowered

can be measured by pouring water into a turbidity tube which allowsturbidity to be measured in NTU. Potable (drinking water) needs to have a

reading lower than 3 NTU

o Acidity the pH of an aquatic system depends on the source of the water, the geology of the

catchment and levels of biological activity within the system

good indicator of the water bodies health changes in acidity/alkalinity affect the usability of the water MEASUREMENT

pH probe or universal indicator may be used potable water needs to have a pH range between 6.5 and 8.5

o Dissolved oxygen the concentration of dissolved oxygen in an aquatic ecosystem is an excellent

indicator of its healthdissolved oxygen is sensitive to temperature, the presence of

organic wastes and the overall health of the system

imperative because aquatic organisms require oxygen to survive two main sources of dissolved oxygen:

dissolved from the atmosphere which is mixed through the water body byturbulence created by wind, water flow and thermal currents


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oxygen produced by photosynthesis by aquatic plants, algae andphytoplankton

low levels of dissolved oxygen are often an indicator of pollution MEASUREMENT:

Winkler methodtitration (quantitive) meter with calibrated O2sensitive electrode (quantitive) special tablets can be used that dissolve in water and change colour

depending on the level of dissolved oxygen (qualitive)

o Biochemical oxygen demand (BOD) BOD is a method of assessing the capacity of the organic matter in a water sample to

consume oxygen

also in indirect measure of organic waste present in the water MEASUREMENT

assessing the quantity of oxygen used up in decomposing the organic matter the BOD test uses anaerobic organisms to decompose (oxidise) the organic

matter over a five day period at 25oC

o the difference between the dissolved oxygen levels atcommencement and at the end of the five day period represents the

BOD of the sample

o water samples in excess of 4ppm are regarded as being likely pollutedo Nitrogen to phosphorus ratio:

Because of the excessive nutrient inputs into our aquatic systems, it is imperative forchemists to regularly monitor their levels and identify their major sources.

Both nitrogen and phosphorous are essential for the growth of plants and plantsdiffer in their requirements for these elements. If the N:P ratio is >10:1, or if N and P

respectively > 1 and 0.1 ppm, then eutrophication tends to occur.

Thus, the NSW EPA recommends a N:P ratio of >10:1, total nitrogen in therange of 0.1-1 ppm and total phosphorous in the range 0.01-0.01 ppm

MEASUREMENT: Nitrate and other ionic forms of nitrogen (inc. NO2-and NH4+) are generally

analysed by visible spectrometry following the addition of particular reagents

Alternatively, (school lab) drop a few drops of sulfuric acid and a small pieceof copper foil to 1mm of the sample. This is then heated gently in a fume

hood and brown fumes of noxious nitrogen dioxide should result.

Phosphate analysed by visible spectrometry; depends on the addition of aparticular reagent that forms a coloured complex in the presence of a

phosphate ion.


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5.2:identify factors that affect the concentrations of a range of ions in solution in natural bodies of water

such as rivers and oceans

Ion concentration in solutions of natural water bodies (i.e. rivers, lakes, oceans) are affected by anumber of factors, both natural and unnatural

o Natural Sources of Ions: rocks and soils of over which the river flows. i.e. water which contains dissolved

carbon dioxide will be acidic enough to dissolve carbonates from rocks such aslimestone:

CaCO3(s)+ 2H2CO3 CO2(g) + H2O(l)+ Ca(HCO3)2(aq) If rain falls on bushland, and then runs-off into streams and rivers, it will only pick up

small amounts of nitrates and phosphates from surface nutrients, as well as some

Mg2+ and Ca2+ from minerals; TDS will be low (50).

If rain soaks into the ground and flows into aquifers (layers of permeable rock) andthen into rivers, the water will have increased levels of Ca2+, Mg2+, Cl-, SO42- and

CO32- which are dissolved from the soils and rocks the water flows through. TDS will

be moderate (200). If water seeps down into rocks (percolates) in deep underground basins (artesian

basins) and only reaches the surface centuries later, then the levels of the above ions

will increase massively, as may contain other ions (such as Fe3+, Mn2+, Cu2+ and

Zn2+. TDS values are very high (>1000).

o Land Clearing: When land is cleared of vegetation, the soil loses the stabilising effects of plant roots

and so soil is easily moved and displaced.

If rain flows over cleared land, it will disturb dirt and sediment and carry it into thewater body it flows into (this will greatly increase TURBIDITY).

The level of dissolved solids and ions (TDS) will increase, due to high levels of mineralions in the soils (such as Na+, K+ etc.)

o Agriculture: When rain flows over land used for the growing of crops and pasture-land it leads to

increased levels of phosphates and nitrates due to fertilizer run-off.

The turbidity will also increase, as well as the BOD, as organic matter (such as animalfaeces) enters the water-ways.

o Raw Sewage and Other Effluents: Raw sewage, if discharged directly into the water, will greatly increase the levels of

many ions (especially nutrient ions such as nitrates and phosphates).

Sewage can increase a water-ways TDS by 200 or more; it also greatly increasesturbidity, BOD and pathogen levels.

Stormwater run-off in urban areas can also carry high levels of ions. Industrial effluent as well as leaching from rubbish dumps can increase the levels of

dangerous HEAVY-METAL ions in water (such as Hg2+ and Cd2+).

o Other factors: Discharge of wastes from mines, power stations and other industries Increased soil salinity due to irrigation, clearing of land, water logging of soil and

rising water tables


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Solubility of a substance. The solubility of most substances increases withtemperature and can vary with pH (i.e. aluminium becomes more soluble in acidic

water)

Rate of river flow Gases from the atmosphere dissolving in falling rain

5.3:describe and assess the effectiveness of methods used to purify and sanitise mass water supplies TREATMENT OF DRINKING WATER: Monitoring Catchment:

o The first step to ensure water used for human use is clean is to ensure that the area thewaterflows over (the CATCHMENT area) is kept clean.

o This involves banning any land-clearing, swimming, boating, industry and agriculture in theentire catchment area, to prevent sediment, animal waste or bacteria to build up in water

supplies.

o EFFECTIVENESS: This is a very cheap and effective way of ensuring the purity of water for human use;

by removing the sources of contamination, purity is ensured.

Screening:o Before the water from catchment areas is allowed to enter treatment plants or storage

dams, it is passed through metal screens that remove large debris such as sticks, leaves,

trash and other large particles which may interfere

chemical monitoring and management notes

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