peak chemical monitoring and management

8/10/2019 PEAK Chemical Monitoring and Management

1/30

Roy Fu

HS

CCHEM

ISTRY

MODU

LETHR

EE

Roy Fu

Chemical Monitoring

and Management

The chemical industry

The Haber process

Monitoring ions

Atmospheric chemistry

Monitoring water quality


2/30

The chemical industry

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. (1.1.1)

Gather, process and

present information

from secondary

sources about the

work of practising

scientists identifying:

- the variety of ----

--chemical =---------

--occupations

- a specific chemical -

--occupation for a-----

--more detailed study

(1.2.1)

- There are many different branches of chemistry including:

Analytical chemistry; the determination of what substances are in a sample

and how much of each is present.

Physical chemistry; the study and measurement of physical aspects of

compounds and reactions such as rates of reaction/kinetics and the

structure and bonding in compounds. Environmental chemistry; the study of how substances interact in the

environment and the monitoring of pollutants in air, water and soil.

Polymer chemistry; the development of new polymers, working out how

polymerisation occurs and how to make it more efficient and studying the

properties of polymers.

Nuclear chemistry; the production and uses of radioisotopes for medicine

and industry and the study of the fundamental nature of nuclear reactions.

- Luke (not his real name) is an analytical chemist at Qenos, an Australian chemical

manufacturing company in Botany Bay.

-

This company makes ethylene by the thermal cracking of ethane and thenpolymerises it to form polyethylene. It also sells some ethylene to other companies

that make ethylene oxide, ethylene glycol, non-ionic surfactants and other plastics.

- Luke has many roles as an analytical chemist. He must:

Monitor the quality of ethylene and polyethylene products, particularly

checking the nature and amount of any impurities present.

Monitor waste water and gaseous emissions to ensure environmental

standards are met.

Collaborate with process engineers at the cracking furnace to adjust

operating conditions for yield optimisation.

Ensure instruments are calibrated and are operating properly.

- Gas-Liquid chromatography(GLC) is a chemical principle used by Luke in his

analysis. This technique involves a gas mobile phasebeing vaporised into a stream

of Hecarrier gas that flows over a liquid stationary phasecoated onto the GLC

column.

- The gaseous components will dissolve in the stationary phase and then evaporate

back out of it at differing rates. The solubility of the gas will depend on its polarity

relative to the stationary liquid.

- More soluble components will have longer retention times through the column as

they move through the column more slowly.

- A separation is achieved and a detector measures the amount of each component

as it emerges from the GLC column. A graph or chromatogram is produced whichcan be analysed.


3/30

- The height of the peak and the area under the peak/integral provides a measure for

the relative proportions of each component.

Identify the need for

collaboration

between chemists as

they collect and

analyse data. (1.1.2)

- Since chemistry is such a board discipline, chemists will specialise in particular

branches of chemistry. However, many chemical problems in the real world require

expertise from many branches of chemistry and science.

- Solving complex problems will require chemists with different specialities and thus

it is essential that chemists collaborate andcommunicatewith each other.

- For example, environmental chemists may collaborate with analytical chemists to

monitor pollutant levels and if there are excessive levels, they may collaborate to

deduce a possible source of the contamination such as an industrial plant. They may

then collaborate with industrial chemists to reduce these excessive emissions.

Describe an example

of a chemical reaction

such as combustion,

where reactants form

different products

under different

conditions and thus

would need

monitoring. (1.1.3)

- Combustion reactions produce different products under different conditions.

- In a plentiful supply of oxygen, complete combustionoccurs which produces carbon

dioxide and water only.

-If there is insufficient oxygen, incomplete combustionwill occur which produces

any combination of water, carbon monoxide and soot.

Carbon monoxideis a toxic gas even at low ppm concentrations as it

combines preferentially with haemoglobinsin the red blood cells 200

times better than oxygen. This reduces the efficiency of the red blood cells

ability to carry oxygen, leading to suffocation.

Soot is carcinogenic; it may cause cancer.

- Because of the toxic nature of these 2 products, combustion reactions must be

monitored to ensure that there is an ideal air : fuel ratio so that the production of

these substances is avoided.- Combustion can also release acidic oxides such as sulfur dioxide, unburnt

hydrocarbons, particulates and lead. The emission of these substances must also be

monitored for environmental and health reasons.

- Finally, since incomplete combustion releases less energy than complete

combustion, it is necessary to monitor combustion reactions to ensure that the

maximum energy output from the reaction is achieved.


4/30

The Haber process

Identify and describe

the industrial uses of

ammonia. (2.1.1)

- Ammoniais used to make:

Fertilisers in the form of ammonium nitrate or ammonium sulfate as a

source of nitrogen for plants.

Nitric acidfrom the Ostwald process which is used for explosives such as

TNT, synthetic dyes, fibres and plastics.

Sodium carbonatefrom the Solvay processwhich is used to make glass. Household cleaners anddetergents

Identify that ammonia

can be synthesised

from its component

gases, nitrogen and

hydrogen. (2.1.2)

Describe that

synthesis of ammonia

occurs as a reversiblereaction that will

reach equilibrium.

(2.1.3)

Identify the reaction

of hydrogen with

nitrogen as

exothermic. (2.1.4)

Explain why the yield

of product in theHaber process is

reduced at higher

temperatures using Le

Chateliers principle.

(2.1.6)

- Ammonia can be produced in an exothermic equilibrium reaction:

At ordinary temperatures and pressures, this equilibrium lies well to the left.

- When the temperature is increased, Le Chateliers principle predicts that the

equilibrium will shift left towards the heating absorbing endothermic reaction in an

attempt to decrease the temperature. Thus, the yield of ammonia is reduced.

Explain why the rate

of reaction is

increased by higher

temperatures. (2.1.5)

- The collision theorypredicts that the rate of a reaction depends on the frequency

of successful collisionsbetween reactant particles. Successful collisions involve

the reactants particles colliding with enough KE to overcome activation energy so

that products can be formed.

-

Higher temperatures results in an increase in the average KE of the reactantparticles. This in turn leads to an increased reaction rateas the frequency of

collisions will increase and the proportion of reactant particles colliding with

will also increase.


5/30

Explain that the use of

a catalyst will lower

the reaction

temperature required

and identify the

catalyst(s) used in the

Haber process. (2.1.8)

- A catalyst increases the rate of reaction by providing an alternative reaction

pathway with lower , sometimes via the formation of an intermediate.

- By increasing the rate of reaction with a catalyst, lower temperaturescan be used

in the Haber process.- The catalyst used in the Haber process ispowdered magnetite(fused

with, and.

Analyse the impact of

increased pressure on

the system involved in

the Haber process.

(2.1.9)

- When the pressure on the system is increased, Le Chateliers principle predicts that

the equilibrium will shift right to produce less moles of gas in an attempt to

decrease gas pressure. Thus, the yield of ammonia increases.

- Higher pressures alsoresults in an increased reaction rate since the number of

reactant particles per unit volume will increase, allowing for more successful

collisions to occur between reactant particles.

- Thus, high pressures favour both yield and reaction ratein the Haber process.


6/30

Explain why the Haber

process is based on a

delicate balancing act

involving reaction

energy, reaction rate

and equilibrium.

(2.1.7)

Explain whymonitoring of the

reaction vessel used

in the Haber process

is crucial and discuss

the monitoring

required. (2.1.10)

Gather and process

information from

secondary sources to

describe theconditions under

which Haber

developed the

industrial synthesis of

ammonia and

evaluate its

significance at that

time in world history.

(2.2.1)

- Compromise conditions are used in the Haber process in order to achieve a high

yield of ammonia relatively quickly at a reasonable cost. Most of these conditions

can be predicted using Le Chateliers principle and the collision theory:

Moderate temperatures(450C)is used to give moderate yieldsmoderately quickly. If temperatures are too high, there will be a fast

reaction rate BUT the yield of ammonia will be compromised and the

catalyst may get damaged. Conversely, if temperatures are too low, there

will be a high yield BUT the rate of reaction will be too slow.

High pressures (25 MPa) are used to improve yield and kinetics. Eventhough it is preferable to have pressure to be as high as possible, this is not

done due to economic and safety considerations.

Apowdered magnetitecatalystfused with, andis used toincrease the rate of reaction. Sulfur compounds, and may poisonthe catalyst so it is essential to ensure the input gases are not contaminated

with these compounds. It is also important to monitor the particle size of

the catalyst to ensure it has a high SA so that it can make contact with the

reactants.

A 3:1 stoichiometric ratio of is used so that left-over reactants canbe recycled without the build up of one reactant over another. This

maximises the efficiency of the process.

Ammonia product is liquefied under pressureupon formation to drive the

equilibrium towards the right to increase the yield of ammonia.

Heat released by the reaction is recycled by using it to heat up any

incoming reactants to minimise energy costs. This also prevents the catalyst

from overheating and losing activity.

- Eventually, about 98% of the reactants are converted into ammonia with these

conditions.

- Chemical engineers need to perform a vast range of monitoring activities to ensure

quality control. The temperature, pressure, supply of nitrogen and hydrogen,

removal of ammonia, heat exchange and activity of the catalyst must be monitored

to ensure the plant is functioning efficiently and safely.

- The Haber process was first developed by Fritz Haberin 1905. Using lower

temperatures, high pressure and an osmium catalyst, Haber was able to produce

100 g of ammonia. Carl Boschlater scaled the process up to industrial levels.

-The Haber process was extremely significantduring this time.

The rising world populationhas caused an increase in demand for nitrogen

based fertilisers to increase agricultural crop yields but there was a limited

and dwindling supply of natural fertilisers such Chilean saltpetre and guano.


7/30

With the Haber process, synthetic fertilisers could be readily produced and

this allowed for sufficient food production to sustain the growing

population.

Early in WW1, the Allied naval blockaded the Atlantic sea routes from Chile

and this prevented Germany from importing Chilean saltpetre for use in

agriculture and in the manufacture of explosives and gunpowder.

Consequently, the Haber process allowed synthetic fertilisers to be

produced to grow the crops needed to sustain the German population

during WW1. Furthermore, the Haber process paved the way for efficientnitric acid productionwhich allowed Germany to manufacture explosives

for its war effort. Indeed, the Haber process may haveprolonged WW1,

resulting in more deaths.


8/30

Monitoring ions

Deduce the ions

present in a sample

from the results of

tests. (3.1.1)

Perform a first-hand

investigation to carry

out a range of tests,

including flame tests

to identify the

following ions:

- phosphate

- sulfate

- carbonate

- chloride

- barium

- calcium

- lead

- copper

- iron

(3.2.1)

- There are 3 qualitative teststhat can be done to identify ions; colour of solution,

flame tests and precipitation tests. These tests can only identify the species present

in a sample.

Colour of solution

- The colour of solutioncan be used to quickly make a reasonable guess on which

ions are present.

Ion Colour of solution

Blue Pale green (may be colourless if dilute) Yellow brown (nearly colourless if dilute)

, , Colourless

- This test is generally not very reliable because many salt solutions are colourless.

Flame Tests- Some cations produce distinctive colours when their salts are volatilised in a blue

Bunsen flame. This flame test can be used to identify the presence of certain

cations.

Ion Flame colour

Blue green Brick red Apple green Yellow Light purple

- The following method can be used to perform a flame test:

1. Clean a Pt wire by dipping it in HCl and heating it with a Bunsen flame.2. Repeat step 1 until no colour comes from the wire. This must be done to

remove any which produces an intense yellow flame colour that may maskother colours.

3. Dip the Pt wire into the sample.

4. Place it into the Bunsen flame and observe the colour of the flame.

-Advantages of the flame test includes:

Quick and cheap to do.

Helps confirm precipitation test.


9/30

- Disadvantages:

Only gives qualitative information.

Can only be used to identify certain cations and is completely useless on

anions.

Cannot distinguish between ions of the same element (eg. and).

Not suitable for assessing solutions with more than 1 cation as the

contamination will make it difficult to identify individual cations.

Cannot be used to identify toxic heavy metals like lead due to safety issues.

- The reason why cations produce characteristic flame colours lies in the electron

shell structure of an atom. When a sample is vaporised in a flame, the outershell

electrons of the cation may absorb a quantum of energyand are excited to

higher energy levels. Excited electrons are unstable and they release energy as light

with a particular frequency when they return to the ground state. Atoms of each

element have different energy levels and the frequency of the light emitted by an

element is given by with

Precipitation tests

- Precipitation tests can be used to identify the ions in a solution. These tests revolve

around the formation of distinctively coloured precipitates or metal complexes.

- The solubility rules are required here.

Insoluble

,

,

- If the unknown solution contains more than 1 cation/anion, we must prevent the

ions from cross reacting; for example, both give a white precipitatewith

. Once an ion forms a precipitate and is identified, it must be removed

by precipitating it to excess and then filtering it out to ensure it will not interfere

with subsequent tests. Further tests are then performed on the filtrate.

Cations

- To identify the cations present in a solution, the following sequence may be

followed:


10/30

- Further confirmatory tests can also be used:

will form a canary yellow precipitate with solution

decolourises acidified potassium permanganate () forms a blood red complex ion with potassium thiocyanate ()

Anions- To identify anions in a solution, the following sequence may be used:

- Note: While can precipitate with either or

, it will not precipitate

with under acidic conditions.


11/30

- Further tests can also be used here:

A solution with

will have pH > 7.

If effervescence of gas does occur after the first step, whether or not the

gas is can be confirmed with limewater. turns limewater fromcolourless to milky due to the formation of a precipitate.

Acidified

forms a canary yellow precipitate with ammonium

molybdate.

precipitate dissolves in excess to form a colourless complex ion.

- Advantages of precipitation tests:

Can identify both cations and anions.

More reliable than simple flame tests.

- Disadvantages:

Only gives qualitative information.

Very time consuming and cumbersome.

Need to have appropriate reagents available.

Gather, process and

present information

to describe and

explain evidence for

the need to monitor

levels of one of the

above ions in

substances used in

society. (3.2.2)

- Leadis a toxic heavy metalthat can cause a vast range of adverse health effects if

exposed to it:

The effects of acute lead poisoningincludes: muscle weakness, loss of

appetite, abdominal pain, nausea and constipation.

Chronic lead poisoning may lead to anaemia, kidney disease, impaired

memory and concentration peripheral neuropathy.

In children, it may also cause retarded intellectual development and

behavioural problems.

Because of these health effects, it is essential to monitor the levels of Pb in

substances used in society to ensure that people are not exposed to harmful

concentrations of Pb.-

The main exposures to Pb includes:

Lead-based paints in older homes.

Soil and water that has been contaminated by old leaded petrol.

Smelting of lead ores.

- According to the NHMRC, the recommended blood lead levels is less than 0.1 ppm

and drinking water should have less than 0.01 ppm of Pb.

Identify data, plan,

select equipment and

perform first-hand

investigations tomeasure the sulfate

content of lawn

fertiliser and explain

the chemistry

involved. (3.2.3)

Analyse information

to evaluate the

reliability of the

results of the above

investigation and topropose solutions to

problems

encountered in the

procedure. (3.2.4)

- Determining amounts of concentrations of specific substances in a sample is called

quantitative analysis.

- Gravimetric analysisis a form of quantitative analysis which involves the weighing

of materials and determining the percentage composition (by mass) of elements incompounds or components of a mixture.

- In the context of ions, gravimetric analysis is basically a quantitative extension of

precipitation tests.

FHISulfate content in a fertiliser

- Aim: To determine the sulfate content of a fertiliser by gravimetric analysis.

- Safety Issues: is a toxic solution and HCl is highly corrosive.- Method:

1. Accurately weigh out 0.60 g of powdered fertiliser into a beaker.

2. Pour distilled water into the beaker and stir until the fertiliser is dissolved.

3.

Add 10 drops of concentrated.4.

Heat the mixture with a hotplate until it just boils.

5.

Slowly add excess dropwise into the beaker. Stir with a glass rod aftereach addition and note any cloud formation as strikes the solution.

6. Gently re-boil the mixture for 5 minutes to coagulate the precipitate.


12/30

7. Allow the mixture to cool.

8.

Weigh some dry filter paper and record the mass obtained.

9.

Set up a filtration apparatus and filter off the precipitate. Alternatively, a

sintered glass cruciblemay be used.

10.

Ensure all the precipitate is transferred by rinsing the beaker with water.

11.

Rinse the precipitate with distilled water and ethanol.

12.

Dry the precipitate in a drying oven until constant mass is attained and thenweigh it.


13/30

- Results:

Fertiliser Glass sintered crucible Glass sintered crucible

with dried precipitate

Mass (g) 0.5010 20.2052 20.7351

- Analysis:

The precipitation reaction that occurs is represented by:

(

)

-Discussion:If the method was followed carefully, both accurate and valid results should be

obtained. To assess the reliability of the results, the method should be repeated

several times to see if consistent results are obtained.

- Problems and solutions:

Underestimation of sulfate content:

can form as very small particlesthat can pass through the filter. Toovercome this problem, the precipitate was formed slowly in a hot solution

which causes the particles to be large. The particle size was then further

increased by digesting the mixture. Finally, the solution was cooled

before the filtration step to increase the insolubility of the precipitate. Some may be lost by dissolution if the volume of wash water is too

great.

can also be lost via spillage when transferring from beaker to funnel.

- Overestimation of sulfate content:

may be contaminated with adsorbed impuritiesdue to the large SAof the small particles. HCl is added initially to prevent any

and/or

from precipitating with . Also, the precipitate is rinsed with

distilled water after filtration to remove any excess impurities. The precipitate may not have completely dried so it may still contain

water when it is weighed. To prevent this error, the precipitate was dried toa constant mass in a drying oven.

- Conclusion: The percentage by mass of sulfate in a fertiliser was found to be

43.54%.

Describe the use of

atomic absorption

spectroscopy (AAS) in

detecting

concentrations of

metal ions insolutions and assess

its impact on scientific

understanding of the

effects of trace

- Atomic absorption spectroscopy(AAS) is a very sensitive instrumental technique

that can measure the concentration of ions in a sample.

- The key principle of AAS is that each element only absorbs and emits specific

wavelengths of light.

- The sample that is being analysed is vaporised in flames to convert molecules,

compounds and ions into atoms. A hollow cathode ray lamp is then used to emitspecific wavelengths of light that are known to be absorbed by the element being

measured. The lamp uses the element itself as the cathode to produce a set of

unique emission wavelengths. As the sample absorbs the specific wavelengths of

light emitted by the lamp, the light intensity will drop. A filter selects 1 wavelength


14/30

elements. (3.1.2)

Gather, process and

present information

to interpret

secondary data from

AAS measurements

and evaluate the

effectiveness of thisin pollution control.

(3.2.5)

of light to analyse and the intensity of the light detected is measured with and

without the sample in the flame. This ratio is used to calculate absorbance.

- Absorbance is directly proportional to the concentration of the metal ion in the

sample. - To obtain the concentration of the metal ion, a calibration curve is constructed

using a series of standard solutions.

(ppm) 1 5 10 25 50Absorbance

(dimensionless)

0.0065 0.0275 0.0555 0.1395 0.2790

The concentration of the metal ion can then be determined by interpolation from

the calibration curve.It is also possible to extrapolate the graph to obtain a concentration but this may

result in an invalid concentration since it assumes that the graph will continue to

have the same trend. It is more preferable to simply use a wider range of standard

solutions so interpolation can be done.


15/30

- AAS can be used to monitor toxic heavy metal pollutionin soil and water. AAS is

extremely effectivehere since toxic heavy metals such as Pb, Hg and Cd are often

present at only minute levels. This helps to ensure public health as it prevents

poisonings (eg. the Minamata disease which occurred due to the release of Hg in

industrial wastewater that accumulated in seafood).

- AAS can also be used to monitor essential trace elements.

- Trace elements are elements that are required by living organisms in very small

amounts (typically 1-100 ppm). Any deficiencies may lead to diseases. Common

trace elements in humans include Fe for haemoglobin production and function, Cofor DNA synthesis, Zn for enzyme functions and DNA binding proteins and I for

thyroid hormone production.

- Older analytical techniques such as gravimetric analysis and volumetric analysis

were not sensitive enough to measure the concentration of trace elements. In fact,

before AAS was invented, deficiency diseases could not be explained. For example,

people suffering from iron deficiency anaemia had symptoms including fatigue, hair

loss and dizziness but these symptoms could not be explained. Since AAS is much

more sensitive and specific compared to these older analytical techniques, it has

greatly developed the scientific understanding of trace elementsin living

organisms:

It has helped to identify trace elements and elucidate their biological roles.Any deficiencies can be detected in blood or urine and then rectified.

AAS has also improved agricultural productivity as it can be used to identify

soils and pastures that lack micronutrients such as Mn, B and Mo. Trace

elements can then be included in fertilisers to improve crop growth and

animal health.

- While AAS has the advantage of being very accurate and sensitive, there are some

limitations:

The AAS machine is expensiveand lacks portabilitywhich is required for

field testing.

Different lampsare required for each element so the cations of interest

must be known. Generally cannot be used to analyse anions.

Cannot differentiate between ions of the same element (eg. and).


16/30

Atmospheric chemistry

Describe the

composition and

layered structure of

the atmosphere.

(4.1.1)

- The atmosphere is the thin layer of gases that surrounds the Earth.

- The composition of the atmosphere is essentially constant at all altitudes:

Gas Concentration (%v/v)

Nitrogen 78.1

Oxygen 20.9Argon 0.93

Carbon dioxide 0.037

- The atmosphere consists of 5 layers. From Earths surface outwards, these are the

troposphere, stratosphere, mesosphere, thermosphere and exosphere.

The boundaries between each layer are marked by changes in the temperature

gradient.

-

The troposphere is the region of the atmosphere closest to Earth in which

temperature decreases as altitude increases. It extends from sea level to an altitude

of about 15 km. In the troposphere, gases are well mixed due to convection

currents and this gives rise to weather.

- Thestratosphereextends from an altitude of about 15-50 km and here,

temperature increases as the altitude increases. In the stratosphere, there is limited

vertical mixing of gases so it is very dry and very stable. It contains the ozone layer

which is most concentrated at an altitude of around 25 km. Gas diffusion into and

out of the stratosphere via the tropopause is very slow.- The thermosphereand the mesosphereare the 2 outer layers of the atmosphere

and they have very low gas pressures. They both contain the ionospherewhere

many atoms and molecules are ionised into gaseous ions.

Identify the main

pollutants found in

the lower atmosphere

and their sources.

(4.1.2)

d

Pollutant Sources

Carbon monoxide Incomplete combustion in motor vehicles, bushfires

and cigarettes.

Volatile organic

compounds

Unburnt fuels from vehicles, industry.

Ozone Formed as part of photochemical smog.


17/30

Describe ozone as a

molecule able to act

both as an upper

atmosphere UV

radiation shield and a

lower atmosphere

pollutant. (4.1.3)

- In the troposphere, ozone is apollutant. Ozone is very toxic at concentrations

greater than 20 ppm. It is a very powerful oxidising agent and thus can disrupt

biochemical reactions in the body by attaching oxygen free radicals to unsaturated

biological molecules. It causes eye irritation, breathing difficulties, headachesand

premature fatigue. Ozone is also poisonous to plants and readily attacks plastics

and rubber, causing them to deteriorate.

- In the stratospherehowever, ozone isprotectiveas it acts as a radiation shield that

prevents damaging short wavelength UV radiation from reaching Earths surface.

Describe the

formation of a

coordinate covalent

bond. (4.1.4)

Demonstrate the

formation of

coordinate covalent

bonds using Lewis

electron dot

structures. (4.1.5)

-

A coordinate covalent bondis a covalent bond in which both of the shared

electrons came from the same atom. Once formed, a coordinate covalent bond is

identical to a normal covalent bond.

- When a coordinate covalent bond is formed, there is a partial transfer of charge

from one atom to another.

-

A covalent bond symbol with an arrow tip () can be used to designate acoordinate covalent bond.

- The formation of a coordinate covalent bond can be demonstrated with Lewis dot

diagrams:

-

Ozone contains a coordinate covalent bond and there are 2 possible Lewis

structures for it:

-

The 2 bonds in ozone are actually identical. The actual structure of ozone is a hybrid

of the resonance structures above:

Compare the

properties of the

oxygen allotropes

and andaccount for them on

the basis of molecularstructure and

bonding. (4.1.6)

- Allotropes are different structural forms of an element in the same state.

- Oxygen exists in 2 allotropic forms; (diatomic oxygen) which is an odourless andcolourless gas and (ozone) which is a pale blue gas with a sharp odour.

- Ozonehas a bent shape and contains dipolesdue to its coordinate covalent bond;

it is apolar molecule. On the other hand, diatomic oxygenis linearand does not

contain dipoles so it is a non-polar molecule. Thus, ozone contains dipole-dipoleattractions whereas diatomic oxygen only contains weak dispersion forces. This

results in diatomic oxygen and ozone having different physical properties; ozone

has a much higher MP/BPand is much more soluble in waterthan diatomic

oxygen. Also, ozone is denserthan oxygen because it is 1.5x heavier than oxygen.


18/30

- The double bond in diatomic oxygen has a high bond energy; it is very strong.

-

The bond dissociation energy in ozone is much lower so the OO bond in ozone is

labile.

Because of this diatomic oxygen is much less reactive and more stable than ozone.

Compare theproperties of the

gaseous forms of

oxygen and the

oxygen free radical.

(4.1.7)

-

Afree radicalis a neutral atom or molecule with one or more unpaired valenceelectron.

- The dot notation () can be used to represent a free radical.

- The oxygen free radicalis formed by the splitting of diatomic oxygen.

- The oxygen free radical is very reactive and unstablecompared to diatomic oxygen

because of the presence of an unpaired electron and an incomplete valence shell. In

fact, the oxygen free radical is even more reactive than ozone.

Identify the origins of

chloroflurorcarbons

(CFCs) and halons in

the atmosphere.

(4.1.8)

- A haloalkane is a compound in which one or more hydrogen atom of an alkane has

been replaced by a halogen atom.

- Chloroflurocarbons(CFCs) are haloalkane molecules in which all the hydrogen

atoms have been replaced by fluorine and/or chlorine atoms.

- Halons are haloalkane molecules in which all the hydrogen atoms have been

replaced by bromine, chlorine and/or fluorine atoms.

- CFCs were originally used to replace toxic ammonia gas as a refrigerantin fridges

and air conditioners. They were also used aspropellantsin spray cans, blowing

agentsto make expanded plastics and solventsfor cleaning electrical circuit boards.

In many of these uses, CFCs were released directly into the atmosphere since it was

believed they were safe due to their inert and non-toxic nature.

-

The properties of CFCs that made them so useful includes: very inert, low solubilityin water, low MP/BP, readily liquefies upon compressions, non-toxic and

non-flammable.

- Halonswere used infire extinguishersdue to their fire retardant properties. They

are dense, non-toxic and non-flammable liquids.


19/30

Identify and name

examples of isomers

(excluding

geometrical and

optical) of

haloalkanes up to

eight carbon atoms.

(4.1.9)

- Isomers are compounds with the same molecular formula but different structural

formula.

- An example is :

- When dealing with isomers, focus on arranging the halogen substituents. Also, be

wary that isomers with 4 or more carbons are not all linear.

- To name haloalkanes, IUPAC nomenclature rulesare used:

Count the longest carbon chain.

Name all substituents using prefixes where necessary and arrange in

alphabetical order.

Add numbering positions such that the sum is minimised. If the same sum is

obtained despite using different numbering positions, give the lowest

number to the halogen that is cited first as a prefix.

Discuss the problems

associated with the

use of CFCs and

assess the

effectiveness of steps

taken to alleviate

these problems.

(4.1.10)

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.

(4.2.1)

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. (4.2.3)

- The inertnessand low water solubilityof CFCs that made them useful has become a

major problem. Because of these 2 properties, CFCs are not destroyed in the

troposphere and are not washed out by rain. Instead, they slowly diffuse into the

stratosphere where high energy UV radiation initiates reactions that destroy ozone.

The produced essentially acts as a catalyst for the destruction of ozone.

is then regenerated when reacts with an oxygen free radical in the

stratosphere. This precipitates a chain reaction.

One can destroy thousands of ozone molecules before it is removed from thestratosphere by other processes. These series of reactions were proposed by

Rowland and Molina, hence the Rowland-Molina hypothesis.

- Similar reactions occur with halons involving - CFCs and halons have high ozone depletion potential(ODP).

- Depletion of the ozone layer is a major concern since it will lead to more UV-B and

UV-C reaching the Earths surface. These high energy photons would cause many

issues:

Sunburns and skin cancers due to DNA damage.

Cataracts due to the breakdown of lens proteins.

Suppressed immune responses and so more diseases in general.

Reduced growth in some plants.

Damage to polymers like PVC.

- The only way to stop ozone destruction by CFCs is to stop releasing them into the

atmosphere since it is practically impossible to remove them. Because CFCs can no

longer be used, alternative substances have been made to replace them.

- Hydrochloroflurocarbons (HCFCs) were the first replacement to CFCs. These

compounds contain CH bonds which make them more readily broken down in the

troposphere by free radicals and atoms. Only a small portion of HCFCs can reach the

stratosphere so they have much a lower ODP than CFCs. Nevertheless, their ODP is

still relatively significant since they contain CCl bonds and thus they are only

temporary replacementsfor CFCs. An example of a HCFC is .


20/30

- Hydrofluorocarbons(HFCs) are regarded as the long term CFC replacementsand

are now widely used as refrigerants. Like HCFCs, they are also broken down in the

troposphere but in addition, they have an ODP of zerosince they contain no CCl

or CBr bonds. An example of a HFC is .- Unfortunately, HFCs are more expensive than CFCs and both HCFCs and HFCs are

potent greenhouse gases. Despite this, both are extremely effective replacements

for CFCs as they have similar properties to CFCs but have much lower ODPs due to

their structure.

- The Montreal Protocol (1987) was the first international treaty to phase out CFCs

and other ozone depleting substances (ODS).

- Many targets have been met even ahead of time because of the widespread

adoption and global cooperation. This has allowed for various amendments to be

made to accelerate the phase out.

- While it will start take several decades for ozone levels to recover, the Montreal

Protocol has been very effectiveas the use of ODS is dropping and the ozone hole is

starting to stabilise.

Analyse the

information availablethat indicates changes

in atmospheric ozone

concentrations,

describe the changes

observed and explain

how this information

was obtained. (4.1.11)

- There are many instruments that can be used to measured ozone levels in the

stratosphere.- Ground based UV spectrophotometers point vertically upwards towards the

atmosphere. It then measures the intensity of light at a wavelength known to be

absorbed by ozone and then compares this to the intensity of light at wavelengths

that are not absorbed by ozone. This comparison gives a measure of the total ozone

per unit area of Earth surface at that location in Dobson units(DU).

- The total ozone mapping spectrophotometer (TOMS) and ozone mapping

instruments (OMI) are satellite based spectrophotometers that work similarly to

ground based UV spectrophotometers. However, these devices are placed on board

a satellite where it scans through the atmosphere as the satellite orbits to measure

ozone levels as a function of altitude and geographical location.

-Aerial spectrophotometers can also be used. Instruments are carried up to thestratosphere on a He balloon where the concentration of ozone is measured as a

function of altitude.

- There is direct evidencethat indicates ozone levels are dropping:

The British Antarctic Survey at Halley Bay noted a 10% drop in stratospheric

ozone levels in spring 1976 and a 50% drop by 1985.

The evidence above correlates with independent data measured by TOMS.


21/30

- There is also indirect evidence:

Levels of were measured in theAirborne Antarctic Ozone Experimentin 1987. This experiment identified a significant correlation between the

formation of and a decline in ozone levels; it was consistent with theRowland-Molina hypothesis.

The Montreal Protocoland its amendments have caused ODS such as CFCs

to be replaced with non-ozone depleting substances. This has resulted in

the partial recovery of the ozone hole so it indicates that substances like

CFCs have indeed caused the destruction of ozone.

Studies of skin cancer shows that in the period 19872000, there has been

a 66% increase in skin cancerin the second half of this interval compared to

the first half. This correlates with the 56% reduction of ozone recorded over

the same period.


22/30

Monitoring water quality

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

(5.1.1)

Perform first-hand

investigations to use

qualitative and

quantitative tests to

analyse and compare

the quality of water

samples. (5.2.1)

- In scientific terms, the criteria used to assess water quality include: concentration of

ions, total dissolved solids, hardness, turbidity, pH, dissolved oxygen and the

amount of biochemical oxygen demand.

Concentration of common ions

- The most common cationsin water are

. There are also

some trace metals (eg. , ) and heavy metals (eg. , ).- These ions can affect water taste, hardness and toxicity.

- AASis widely used to monitor these cations; gravimetric analysis and volumetric

analysis are generally not used since they are not sensitive enough.

- The most common anions in water are

. These can

affect water taste and pH.

- Gravimetric analysis can be used to monitor these ions.

can be used to precipitatewhile can be used toprecipitate

.

The precipitate formed is then weighed and the concentration of the ioncan be calculated.

- Volumetric analysiscan also be used.

can be titrated with using a indicator.

can be titrated with standardised HCl.

- Alternatively, ion-selective electrodes can be used. The voltage measured by these

galvanic cells is related to the concentration of a particular ion in the water.

Total dissolved solids

- Total dissolved solids (TDS) is the mass of dissolved solids per unit volume of water.

- Most of the dissolved solids in water are ionic compoundsso TDS can be a measure

of salinity.- TDS can affect water taste, use of water for irrigation, survival of fish and DO levels.

- High TDS in waterways can result from waterways being too close to the ocean or

from human activities that lead to rising water tables and soil erosion such as

farming practices, land clearing and over-irrigation.

- The TDS in a water sample can be measured by first filtering off any suspended

solids and then evaporatingthe water to dryness and weighing the residue left

behind. This method tends to be unreliable with clean water.

- Modern instrumental techniques use a conductivity probe and meter to measure

the electrical conductivity of a water sample to approximate TDS. The probe and

the meter must be calibrated with standard solutions before it is used. This method

gives a reasonable approximation of the TDS in a water sample since most of thedissolved solids will be ionic compounds. While this technique is faster and

portable, it becomes less accurate at higher TDS levels.

Hardness

- Water with appreciable amounts of and/or is called hard water. Waterwith very low concentrations of these 2 ions is called soft water.

- The and in hard water precipitates with soap molecules forming ascumthat sticks to clothes and sinks. This effectively removes soap from solution

and hence disrupts its cleaning action.

- A qualitative test for hardness involves the use of soap. Soap is added to a water

sample and then shaken in a stoppered test tube. This is then compared topositiveand negative controls(2 shaken test tubes containing soap and water that is known

to be soft or hard). The amount of lather formed is a qualitative indicator of the

hardness of the sample; the more lather formed, the softer the water.


23/30

- Alternatively, hardness can be monitored quantitatively via titration with EDTA

solution. In a buffer solution, EDTA reacts with both and in

a 1:1 ratio. Eriochrome BlackT is used as the indicator in this titration.

Because there is no distinction between and with this method, hardnessis expressed as equivalent in.

- AAS can also be used to monitor hardness by measuring and individually. Note that the concentration obtained for with AAS will be lowerthan the one obtained by EDTA titration since EDTA solution also reacts with.

Turbidity

- Turbidity is a measure of the cloudiness or lack of transparency in a water body. It is

measured in nephelometric turbidity units (NTU).

- Turbidity occurs due to small insoluble suspended solidsin the water that scatters

light and makes the water appear cloudy.

- High levels of turbidity will give the water an unpleasant appearance and taste.

- It also reduces the penetration of sunlight through the water which is essential for

aquatic plants for photosynthesis.

- Increased levels of turbidity can arise naturally from soil erosion especially after

heavy rainsand floods. This natural process is greatly accelerated by human

activities such as land clearing, farming practices and mining.- Secchi diskscan be used to measure relative turbidity of water. The disk is lowered

into the water sample until it just becomes invisible. The dept at which this occurs is

an inverse measure of the turbidity of the water; the shorter the length of the

string, the higher the turbidity.

- Turbidity tubescan also be used. The sample of water is slowly added to the tube

until the mark at the bottom of the tube just becomes invisible. The turbidity can

then be read off the tube.


24/30

- Gravimetric analysiscan also be used to measure the total suspended solids and

hence turbidity. The suspended solids in a sample of water are filtered off and the

dry mass of the residue is then measured. This is quite effective on dirty water in

the environment but it is not practical on drinking water because it contains

particles that are too small to be filtered off.

- A more exact measure of turbidity uses a nephelometer. This instrumental

technique measures the intensity of light scattered at to the incident light. Themore turbid the water, the more scattering occurs. Turbidity is then measured

relative to distilled water (0 NTU) and formazin (100 NTU) standards.

Acidity

- Water is considered to be polluted if thepH is outside the range of6.5 8.5.

- The pH of the water may disrupt the acidbase balance in aquatic organisms and

may lead to death if severe.

- Possible sources of too acidic water include industrial waste, acid rain, fertiliser run-

off and sulfide ore mines.

If the water is too basic, the cause may be industrial wastes or nearby limestone

rocks.

- Narrow range universal indicator pH papers can be used to approximate the pH of

water.

- Alternatively, a calibratedpH meter is used which gives an exact pH value.

Dissolved oxygen

- Dissolved oxygen (DO) is the amount of oxygen (mg) dissolved in 1 L of water at a

fixed temperature.

- Aquatic plants undergo photosynthesis to produce oxygen which can then dissolve

in the water.

Some oxygen also dissolves into the water directly from the atmosphere. This

process is assisted by turbulent water flow.

- High DO levels are vital for the survival of aquatic organisms. It is required for the

respirationof aquatic organisms and for the decomposition of organic matter by

aerobic bacteria. If DO levels get too low (less than 45 ppm), aquatic organisms

will experience metabolic stressand anaerobic bacteria will decompose organic

matter into toxic and malodorous products.

- The main cause of low DO levels in natural water is high organic waste discharges.

This includes poorly treated sewage and wastes from farms and meat processing

plants. Other causes may be high salinity, high water temperatures due to thermal

pollution or eutrophication.

- The Winkler titration method can be used to determine the DO in a water sample.

The 1:4 ratiobetween and

can then be used to calculate DO.


25/30

- Alternatively, an electrolyticDO sensorcan be used. Dissolved oxygen from the

sample diffuses across a membrane and is reduced to water at the platinum

cathode. At a constant voltage, the current flow through this cell is proportional to

the DO concentration.

Biochemical oxygen demand

- The biochemical oxygen demand(BOD) of a water body is the amount of DO

required by aerobic bacteria to completely break down the organic matter in the

water.

- BOD is a measure of organic waste pollution. In general, a waterway is considered

to be polluted if the BOD > 45 ppm.

- To monitor BOD, the 5-day BOD testcan be used. A water sample is divided into 2

samples. The DO of the 1st

sample is measured while the 2nd

sample is incubated in

a dark air-free container at for 5 days. 5 days is usually sufficient for natural

organic waste to be decomposed in non-polluted water ways. Also, the sample isheld in the dark to prevent any photosynthetic algae from producing oxygen. The

DO of the 2nd

sample is then measured and the BOD can be calculated using:

- If the water is polluted, the above method will not work because all the available

DO will be consumed in less than 5 days. Polluted water samples are analysed by

either diluting the sample with a standard nutrient solution with a known orby re-aerating the sample with oxygen gas periodically and then measuring the new

DO each time.

Identify factors that

affect theconcentrations of a

range of ions in

solution in natural

bodies of water such

as rivers and oceans.

(5.1.2)

- The ion concentrations in a water body can be affected by the following factors; the

pathway from rain to water body, frequency and volume of rain, characteristics ofthe water, nearby human activities and the type of water body.

Pathway from rain to water body

- Rain contains some

. When rain runs off bushland into

streams, some

and

can be picked up from natural nutrients on the

surface and perhaps some and from decomposing minerals.- Rain can also percolate to underground aquiferswhere it will dissolve even more

ions such as and .

Frequency and volume of rain

-Heavy or more frequent rain will carry more ions into the water body though theextra volume of water may cause ion concentrations to decrease.


26/30

Characteristics of the water

- More acidic rain can cause the leaching of ions such as and from soils andbedrocks into the water body.

- Waters with higher temperatures will cause more minerals to dissolve.

- Higher rates of water evaporation will increase ion concentrations.

Nearby human activities

- Land clearing and mining generally leads to more water rapidly running across

disturbed lands and into water bodies. This facilitates the dissolution of a variety ofions.

- The use of fertilisers in farms may lead to fertiliser run-off when rainwater carries

this fertiliser form the soil into water bodies. This often increases the levels

of,

and .

- Discharges of raw and/or treated sewage will increase the concentration of many

ions, particularly

and

. Industrial effluents and rubbish dumps may be

a source of heavy metal ions.

Type of water body

- Oceans are less affected by changes in ion levels than smaller water bodies due to

the large volume of water present.

Gather, process and

present information

on the range of tests

used to:

- identify heavy metal

--pollution of water

- monitor possible --

--eutrophication of ---

--waterways

(5.2.2)

Heavy metals

- Heavy metalsare metals with high atomic masses such as Pb, Hg and Cd.

- They bioaccumulate up the food chain within tissues of living organisms and are

generally toxic.

- The common sources of heavy metals are industrial wastes (eg. Pb paints and Hg

cell) and runoff from contaminated soils near roads and landfills.

- To monitor heavy metals, the following sequence may be used:

- Alternatively, instrumental techniques can be used which are generally more

sensitive and accurate. These includeAAS, ion-selective electrodesand mass

spectrometry.


27/30

Eutrophication

- Eutrophicationoccurs when a water body is enriched with nutrients to the point

where rapid proliferation of algae/plant life occurs (an algal bloom).

- Eutrophication mostly occurs due to high levels ofphosphate and nitrate. These 2

ions are the growth liming nutrients for plants.

- Common sources of nitrates and phosphates include excess fertiliser run-off from

farms, animal wastes, phosphate builders in laundry detergents and raw sewage.

- Algal blooms are not only aesthetically unpleasant but they also cause DO levels to

drop dramatically: The green scum reduces UV penetration so there will be less

photosynthesis.

Algal blooms hinder the diffusion of oxygen from the air to the water.

On the death of the algae, oxygen is used by aerobic bacteria to decompose

their remains.

Other adverse effects include:

Algae may clog up irrigation pumps and give the water an unpleasant taste.

They lead to the build-up of sediments in the water body due to dead algae.

Bluegreen algae called cyanobacteria can produce toxins that can kill

livestock and cause serious illness in humans.

-To monitor eutrophication, phosphate and nitrate levels are monitored by a

colorimetric method. Colorimetry involves measuring the absorbance of light at a

certain wavelength passing through a solution.

To monitor phosphate, acidified ammonium molybdateis added to a water

sample. If phosphate is present then a canary-yellow precipitatewill form.

A quantity of ascorbic acid is then added to the precipitate to form an

intense blue complex. The concentration of phosphate is then determined

by colorimetryrelative to standards.

To monitor nitrate levels, the water sample is passed through a tube of

granulated Cd/Cu to reduce nitrate ions into nitrite ions. Sulfanilamide andN-napthalenediamine is then added to the solution to form an intense

pink purple azo-dye. The concentration of nitrate is then measured

colorimetrically against known standards.

- DO and BOD levels can also be measured to monitor eutrophication; low DOand

high BOD levels may indicate possible eutrophication but these tests should be

used in conjunction with the phosphate and nitrate tests.

Describe and assess

the effectiveness of

methods used to

purify and sanitisemass water supplies.

(5.1.3)

Gather, process and

present information

on the 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----

- Water purificationis done to remove contaminants from raw water to produce

water suitable for human use.

- There are 2 major goals in water purification:

Clarification; making the water clear, colourless and odourless. Sanitation; removing harmful microbes from the water.

- The steps are as follows:

1. Screening: Large objects such as fish and plant debris are removed using screens

that act as sieves.

2. Aeration: Air is bubbled into the water to help remove colour and odour by

oxidising and to insoluble products.3. Lime softening: Lime (CaO) is added so that the water becomes slightly alkaline for

the next step. Soda ash () is then added to soften the water by removingand by precipitation reactions.

4. Flocculation: or are added as coagulants to create a gelatinous

precipitate to help remove suspended solids. The suspended particles adsorb onto the precipitate and form flocs. This process

is aided by the addition of cationic polymers.

5. Sedimentation: The water is then transferred into the settling tanks where the flocs


28/30

--and 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

(5.2.3)

settle to the base of the tank to form a sludge. These are periodically removed.

6. Filtration: Water is filtered through layers of sand and gravel to remove any

remaining particulates. Crushed anthracite coal can also be used as a filter to

adsorb organic matter and improve the odour and taste of the water.

7. pH adjustment: The pH is readjusted with hydrated lime or soda ash to prevent the

scaling and corrosion of water distribution pipes.

8. Disinfection: The filtered water is disinfected with 1-2 ppm of .

The produced hypochlorous acid kills bacteria and some viruses and protozoa.

Sometimes, ammonia is then added to produce monochloramine, which is a longer

lasting disinfectant.

In rare cases, ozone can also be used which is very effective against both bacteria

and viruses.

9. Fluoridation: About 1 ppm of fluoride (in the form of ) is added to

strengthen tooth enamel and reduce tooth decay.

- Screening, the second part of flocculation, sedimentation and filtration are the

physical processesused to purify water.

- Aeration, lime softening, the first part of flocculation, pH adjustment, disinfection

and fluoridation are the chemical processesused to purify water.

- Overall, these methods are very effective for purifying water since ADWG criteria is

consistently met.

- The screens remove large objects quickly, coagulants and sand filters removes

colours, odours and most suspended particles and chlorination removes almost all

bacteria and some viruses.

- There are some problems though. Chlorination is NOT foolproof; it may not kill

extremely fine pathogens. The Giardia and Cryptosprordium outbreakin 1998 isproof of this. Also, adding to water will decrease its pH and excessive amountscan affect human health so levels must be closely monitored.

- Taking all factors into consideration however, the water purification process is

generally both fast and reliable. With better catchment management and consistent

monitoring, the present treatment methods should be sufficient to produce water

suitable for human use.

- A catchmentis the drainage area for all the rainfall going into a water body or a

storage reservoir.

- The Sydney catchment covers over 16000 to the south and west of Sydney

and consists of 5 major systems, each with its own reservoir and water filtrationplant.

- The largest reservoir in Sydney is Warragamba Dam. Warragambas catchment

covers 9050 and has Coxs and Wollondilly as 2 major rivers. Areas closest tothe dam, making up 30% of the total catchment, are restricted special areasof


29/30

unspoilt bushland. Most of the rest of the catchment consists of cleared farming

land and some small and large towns.

- Sources of contamination includes:

Agriculture; water run-off from agricultural lands can contain fertiliser,

faecal matter and organophosphate/organochlorine pesticides.

Mining; water can flow into abandoned mines where it will leach ions such

as and. Animals; native and feral may contaminate the water with their faeces or by

dying and decaying within the water. This leads to the contamination of the

water with pathogens and parasites.

- The contaminants can be monitored with chemical tests that have already been

described.

Describe the design

and composition of

microscopic

membrane filters and

explain how they

purify contaminated

water. (5.1.4)

- A microscopic membrane filter is a thin film of synthetic polymer with uniformly

sized pores.

- The common polymers used for these filters are polypropylene,

polytetrafluoroethylene and polysulphone.

- Microscopic membrane filters are an alternative method for purifying water supply.

They can be produced in sheet or capillary forms.

-Advantages of microscopic membrane filters include:

They have uniform holes that reliably filter out very small particles such as

pathogens that are not killed by chlorination.

They filter out water fairly quickly as the membranes are thin and can

withstand high pressures.

They can be cleaned easily by black-flushing and then reused.

- Disadvantages:

They are very expensiveso it cannot be used to purify mass water supplies.

Pleated sheet membrane filter

- This consists of a 100 membrane that isfolded or spirally woundedaround acentral core. It is help in place with mesh and plastic outer casing to form a

cartridge.

- The cartridge is mounted in a water pipe where water will flow across the

membrane(NOT perpendicularly) to avoid the clogging up of the pores.

-

Since the pores are very tiny (0.2 ), larger particles and pathogens cannot passthrough the filter.

- High fluid pressures(2-5 atm) are maintained to accelerate the filtration process.


30/30

Capillary membrane filters

- These consists of porous material made into hollow capillarieswith an outer

diameter of 500 , an inner diameter of 200 and pore sizes of around0.2-0.5 .

- For each capillary, dirty water flows along the outside through the wall of the

capillary and clean water transverses the pores and emerges inside.

- Many capillaries are bundled together to make a filtering unit with a large SA.

peak chemical monitoring and management

Documents