Monitoring The Environment

HHSSCC CChheemmiissttrryy TTooppiicc 33 ““CChheemm MMoonniittoorriinngg && MMaannaaggeemmeenntt””CCooppyyrriigghhtt ©© 22000055-22000099 kkeeeepp iitt ssiimmppllee sscciieenncceewwwwww..kkeeeeppiittssiimmpplleesscciieennccee..ccoomm..aauu

keep it simple science®

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1

but first, an introduction...

HSC Chemistry Topic 3

CHEMICALMONITORING & MANAGEMENTWhat is this topic about?To keep it as simple as possible, (K.I.S.S.) this topic involves the study of:1. WHAT CHEMICAL SCIENTISTS DO

2. INDUSTRY CASE STUDY: AMMONIA PRODUCTION3. TECHNIQUES IN CHEMICAL ANALYSIS

4. ATMOSPHERIC CHEMISTRY & OZONE5. MONITORING & MANAGING

WATER SUPPLIES...in the context of Chemistry’s importance to environment & society.

Chemistry’s “Bad Press”Chemical Science has an image problem. Everyday, in thousands of locations around the world,Chemical Scientists carry out routine tests tomonitor and manage processes that are of vitalimportance to:

• Industrial production of important substances we need.

• Ensuring that quality & safety standards are met.

• Protecting the environment from pollution.

• Ensuring that the air we breathe, andour water supplies are clean & healthy.

However, when something goes wrong andthere’s a chemical spill, or industrial fumes

make people sick,It’s Big News

In this topic, youwill firstly look atsome of the thingsthat real ChemicalScientists do.

Then you will study oneof the most important

processes in theChemical Industry...

Production of Ammonia,

NH3You will study what’s good,and what’s not good about

OZONEin the air

and finally,study aspects of the management of your community’s

Water Supply System

You willlearn more

aboutsome of

thetechniques

of

CChheemm

iiccaall

AAnnaall

yyssiiss

To many people, “Chemistry” is a dirty word!

Generally, no-onenotices all the

millions of testsand management

decisions thatachieve the goals

of safety,productivity andefficiency, day-in,

day-out.




2

QuantitativeLaboratoryAnalysis of an Ion

QualitativeTests

for Ions

ChemicalOccupations

The Need toMonitor a Chemical

Process

Purifying &

Sanitisingwater

Supplies

Measuring Heavy Metals

&Eutrophication

Tests for Water

Quality

TheAtmosphere

CFC’s&

OzoneDepletion

Propertiesof

O2 & O3

The Need forMonitoring

Uses ofAmmonia

CHEMICALMONITORING & MANAGEMENT

CONCEPT DIAGRAM (“Mind Map”) OF TOPICSome students find that memorising the OUTLINE of a topic helps them learn and remember the concepts and important facts. As you proceed through the topic,

come back to this page regularly to see how each bit fits the whole. At the end of the notes you will find a blank version of this “Mind Map” to practise on.

AtomicAbsorption

Spectrometry

The HaberProcess

CoordinateCovalentBonding.

Formationof Ozone

Haloalkanes.Structure &

Naming.

Isomers

What Chemical

Scientists doProduction

ofAmmonia

Techniquesin Chemical

Analysis

AtmosphericChemistry

&Ozone

Monitoring &

ManagingWater Supplies

Variety of Chemical OccupationsSince every substance on Earth is a chemical,then every human endeavour which deals withsubstances will, sooner or later, use theservices of a Chemical Scientist.

Chemists may be involved in:

• soil, water or air analysis• developing new materials, or managing

production in- chemical industry - pharmaceuticals- foods - agricultural products- metals - fuels- plastics ... and many more.

• criminal investigation• pollution and corrosion control• materials for electronics and the

electro-chemical industries• environmental science and protection• quality assurance, in a wide range of industries

Specific Duties of a Laboratory Toxicologist

The UK-based company Altrix provides drug-testing services to Government and corporateemployers who need to screen (for example) jobapplicants for evidence of drug abuse or certaindiseases, such as hepatitis.

The company has developed a detectionmethod, based on a non-invasive mouth-swabor hair sample, which can identify a wide rangeof drugs of abuse, such as cocaine or cannabis.

Their laboratory uses high-tech methods ofChemical Analysis, such as gaschromatography and mass spectrometry.

The company employs Chemical Scientists tocarry out all the technical and scientific aspectsof the operation.

As well as carrying out the chemical analyses,the scientists report the results back to theclients, and need to be prepared to appear as“expert witnesses” should any matter end in alegal challenge.

Gas ChromatographyThe sample to be analysed is vaporized andinjected into a stream of inert “carrier” gas suchas helium.

As the mixture flows through the“Chromatography Column” different moleculesadsorb to the coating according to the polarity,shape and size of each molecule. Eachsubstance keeps moving through the column,but at different rates, so each “fraction”emerges separately and is picked up by asensitive detector.

In the case of drug-screening, the detector issensitive to the tiny amounts of drug residuesthat remain in the body for months after usingheroine, cocaine, cannabis, etc.

The Need for CollaborationThe image of the solitary, mad-genius Scientistworking in his (they’re always male!) secretlaboratory to make brilliant-but-misguidedbreakthroughs, began with the “Frankenstein”story 200 years ago, and persists still.

This image couldn’t be further from the truth.Real Science is a team effort, and real Scientistsmust co-operate, communicate and collaboratewith their colleagues and clients.

For example, a scientist working for Altrix must:

• compare analysis results from other tests doneby other workers, to confirm the validity of aclient’s screening.

• discuss results and conclusions with otherprofessionals.

• collaborate on the usage of equipment, thescheduling of tests to be completed and thedeadlines for completion.

• keep up to date with new developments in thefield, by communicating with other scientistsand attending seminars and conferences.

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1. WHAT CHEMICAL SCIENTISTS DOkeep it simple science

®


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ssaammppllee

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““CChhrroommaattooggrraapphhyy CCoolluummnn”” iiss aa lloonngg ttuubbee,, ccooaatteedd wwiitthh

cchheemmiiccaallss ttoo wwhhiicchhmmoolleeccuulleess ““aaddssoorrbb””,, oorr cclliinngg..

Photo by Dain Hubley


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The Need to Monitor a Chemical Process

Many chemical processes are very sensitive toany change in the conditions of the reactioninvolved.

For example, most reactions will run at adifferent rate if the temperature changes. Achange in pressure could cause an equilibriumto shift, according to Le Chatelier’s Principle,and affect the yield of a reaction.

As a specific example, consider the effect ofoxygen availability on a combustion reaction,such as the burning of natural gas, which ismostly methane gas:

If there is a good supply of oxygen, and thereactants mix well, the products are carbondioxide and water vapour.

Complete Combustion

CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

This combustion reaction could be part of anindustrial process such as:

• heating a furnace or kiln for making bricks or ceramics.

or• boiling water for steam supply to

an industrial complex.

However, if there is a shortage of oxygen, theproducts can include carbon monoxide, or evencarbon (soot).

Incomplete Combustion

CH4(g) + 3O2(g) CO(g) + 2H2O(g)2

CH4(g) + O2(g) C(s) + 2H2O(g)

Incomplete combustion is undesirable because:• less energy is released per unit of fuel used.• carbon monoxide is toxic.• soot can build up in equipment,

causing problems.

In any industrial application, it is vital to ensureefficient, economical operation withoutemission of toxic fumes, or extra maintenanceproblems caused by incomplete combustion.

To manage this process, it would be importantthat someone (e.g. a Chemical Engineer)monitors the combustion by regularly

• measuring the flow, and mixing of fuel and air.• measuring the temperature within the

combustion area.• measuring the composition of the exhaust

gases.



Practical, Applied Chemistryis all about

Monitoring & Management

The Uses of AmmoniaAmmonia, NH3, is one of the most importantindustrial chemicals in the world. Its production ismeasured in millions of tonnes, and its uses arevery widespread, including the manufacture of:

• fertilizers (urea and ammonium compounds)• nitric acid, which in turn is used to make:

- explosives- dyes and pigments - fibres and plastics

• household cleaners and detergents

For example, to make the common fertilizer“sulfate of ammonia”, ammonia is reacted withsulfuric acid in a simple acid-base reaction:

2NH3 + H2SO4 (NH4)2SO4

History: Ammonia SynthesisPrior to World War I, the manufacture offertilizers and explosives was largely dependanton the supply of “saltpetre” (sodium nitrate)from natural deposits in Chile.

In 1908, the German Chemist Fritz Haber,developed a method to make ammonia from itselements, nitrogen and hydrogen, using an ironcatalyst. Later, Carl Bosch developed theprocess to an industrial scale.

Nitrogen + Hydrogen AmmoniaN2(g) + 3H2(g) 2NH3(g)

Since nitrogen makes up about 80% of air, andhydrogen can be obtained from hydrocarbons inpetroleum, this process did away with thedependance on mining and shipping from adistant country.

This was a hugelysignificant developmentat that time. Europe wason the brink of war, withexplosives and foodsupplies (needing fertilizers) about to becomecritically important.

ShippingfromChilecould bestoppedby theenemy,but theHaber-Bosch process allowed Germany to be self-sufficient in fertilizers and explosives madefrom ammonia.

Industrial Production of Ammonia by the Haber Process

One hundred years after it was developed, themanufacture of ammonia by the Haber processis one of the most important industrial chemicalprocesses in the world.

The reaction is not an easy one: it is exothermic,but at ordinary temperatures the reaction ispainfully slow, and the equilibrium lies well tothe left, with a very low yield of ammonia.

Speeding Up A ReactionYou learnt in an earlier topic that the rate of anyreaction depends on the reactant moleculescolliding with enough energy (“activationenergy”) to start the process of breaking oldbonds and making new ones.

Basically, there are 3 ways to increase the rateof reaction:

Increase the TemperatureAt higher temperatures the molecules movefaster. They collide more often and with moreenergy.

Increase Concentration of ReactantsIf the concentration is higher, the “density” ofmolecules is higher and so the chance of acollision is greater. More collisions gives ahigher reaction rate.

In gases, increasing the pressure increases theconcentration of molecules by forcing themcloser together.

Using a CatalystCatalysts have the effect of reducing theactivation energy of the reaction. At any giventemperature, a catalyst makes it more likely thatcolliding molecules will have enough energy toreact, so the rate increases.

Fritz Haber was an educated Chemist... he knewall these things. His discovery of the processwhich bears his name was no accident, but theresult of applying chemical knowledge to solvethe problem of supply that his country, and theworld, faced in the early 20th century.

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2. INDUSTRIAL CASE STUDY: AMMONIA PRODUCTIONkeep it simple science

®


N2(g)+ 3H2(g) 2NH3(g) ∆∆H= -92 kJmol-1

++ heat

At ordinary temperature & pressure,the Equilibrium, and the Rate of Reaction,does not yield much ammonia




6

The Haber Process Explained

PPUUMMPP

PPUUMMPP

Mixture of H22 & N22(in ratio 3:1)

pumped in underpressure of

300 atmospheres

HeaterUnit

Temp400ooC

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sseess

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LiquidAmmoniaout

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HH2 && NN2

UUnnrreeaacctteedd HH2 && NN2rree-pprreessssuurriisseedd

aanndd rreettuurrnneedd ttoo

rreeaaccttiioonn vveesssseell

REACTION VESSEL

Since the reaction is Exothermic

N2(g)+ 3H2(g) 2NH3(g) + heat

by Le Chatelier’s Principlelower temperatures would drive the equilibrium right,

and increase the yield of ammonia

BUT...The higher the temperature, theFASTER the RATE of reaction.

SO...400oC is a COMPROMISE

The reaction is exothermic, so heat is produced constantly

For maximum efficiency, thereactant gases are mixed in theMOLE RATIO of the balanced

equation

N2(g) + 3H2(g) 2NH3(g)

High Pressurecauses the equilibrium to shift

right increasing the yield of ammonia

N2(g)+ 3H2(g) 2NH3(g)

4 moles 2 moles of gas of gas

By Le Chatelier’s Principle,increasing the pressure causesthe equilibrium to shift right, inan attempt to create less gas

and a lower pressure.

Constantly removing Ammoniafrom the mixture causes theequilibrium to shift to the

right, which increases the yield

The use of a catalyst lowers the activation energy,and increases reaction rate.

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rreedduucceedd ttoo aa llaayyeerr ooff eelleemmeennttaall iirroonn..

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eeccoonnoommiiccaall tteemmppeerraattuurree..

The Need to Monitor The Haber process is based on a delicate balancing actbetween reaction energy, reaction rate and equilibrium.It needs constant monitoring of:• the ratio of reactant gases.• temperature & pressure (each affects the other) which

must be optimal to ensure efficiency and yield.• levels of contaminating gases (such as carbon

monoxide and sulfur compounds) which could“poison” the catalyst.


The reactant gases are mixed in the ratio 3 partsr)............................. to 1 parts)................................. and combined at apressure of t)..................... atmospheres. Thishigh pressure forces the equilibrium to theu).............................

The reaction mixture is heated to approximatelyv)............. oC. This temperature is a compromisebetween increased w)............................. and thex)................................., which shifts left at highertemperatures.

A catalyst of y)....................... lowers thez)............................ energy and speeds up therate. This allows a aa).............................., moreeconomical temperature to be used.

The reaction mixture flows out of the reactionchamber to a ab).................................... whereammonia is ac)......................... Unreactedhydrogen & nitrogen are ad)...................................................................

To ensure efficient production, monitoring of thereaction mixture ratio, ae)............................ and................................ is required. The presence ofcontaminating gases (such asaf)................................... and ................................)is important too, since these couldag).................. the catalyst, if allowed to build up.

1. List 6 industries which rely on the services ofChemical Scientists.

2. As an example of a specific job, list 3 duties ofa Laboratory Toxicologist.

3. Explain the basic scientific principle ofchemical analysis using the technique of GasChromatography.

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Copying is permitted according to the Site Licence Conditions onlykeep it simple science®

Worksheet 1 What Chemical Scientists Do Student Name..........................................4. List 3 reasons why a Laboratory Toxicologistwould need to collaborate with his/hercolleagues.

5. With reference to a combustion reaction in anindustrial setting:a) explain how the reaction conditions can affectthe products of the reaction.

b) Explain the need for monitoring the reaction,and list 2 factors which might be monitored.

Worksheet 2 Ammonia ProductionFill in the blank spaces Student Name..........................................Ammonia is used in the manufacture ofa)............................. for agriculture, and forb)...................... acid. This, in turn, is used tomanufacture c)..........................., ......................and ..................................

Until the early 20th century, manufacturing thesethings depended on the supply ofd).................................. mined in natural depositsin e)......................... In 1908, Fritz f)........................developed a method to make ammonia fromg).................................. and ..............................This was enormously significant for Germanywhich could continue making h)............................and ........................... during World War I.

The reaction to make Ammonia is not an easyone. At room temperature and pressure, thereaction rate is very i)....................., and theequilibrium lies well to the j)......................,favouring the k)..............................

l)....................... temperatures increase thereaction rate, but also shift the equilibrium to them)...................., because the reaction isn)............-thermic.

The modern production of ammonia by theo)...................... Process is a balancing actbetween reaction energy, reaction p)....................and the q).............................., to achieve efficientand economical production.

Chemical AnalysisOne of the key processes in Chemical Monitoring andManagement is the analysis of samples to detectand/or measure the levels of a chemical of interest.

In this section, you will study some examples ofchemical analysis, at 2 different levels:

Qualitative Analysis identifies a chemicalspecies, but does not measure quantity.

Quantitative Analysis measuresthe amount or concentration of a chemical.

The syllabus requires that you study techniquesto detect and/or measure 9 specific ions. Thereare many other ions and compounds that needmonitoring in industry or in the environment.

The Need to Monitor Levels of Some Ions

There are certain human activities which canrelease dangerous or harmful ions into theenvironment. Monitoring the levels of these inair, water, soil or food is essential to help protectpeople, and the environment, from harm.

Two important examples are:

Phosphate IonsPhosphate ions (PO4

3-)are a normal and healthypart of the natural environment at normalconcentrations.

However, human activities can increase thelevels of phosphate ion in water environments.This leads to Eutrophication; a process wherewater plants and algae are “over-fertilized” andgrow excessively. This clogs waterways, andleads to masses of dead, rotting algae whichtakes all oxygen from the water so fish and otheranimals die.

The human activities responsible are mainlyagricultural fertilizer run-off from farmland, anddischarge of human sewerage into waterways.Taking water for irrigation also reduces waterflow and makes the problem more likely.

Lead IonsLead is a toxic “heavy metal” which is notpresent in the natural environment in significantamounts. Even very low levels are dangerousbecause it can accumulate in the body until itreaches toxic levels.

Lead poisoning in an adult leads to chronicneurological disease. In children it can causepermanent brain damage.

In the past, lead compounds were included in avariety of products including house paints(banned years ago) and “super” petrol (nowreplaced by ULP...”unleaded petrol”). Thesechanges were made specifically to reduce thelead levels in the environment.

Perhaps themain concernsabout lead arefading nowthat leaded-petrol is nolongerpumping lead-laden fumesinto the air, butlead persistsin theenvironmentfor centuries,so monitoringof previouslypolluted areasis still needed.

It is also necessary to monitor for leademissions from industries which produce oruse lead, such as lead smelters, or car batterymanufacturers.

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3. TECHNIQUES IN CHEMICAL ANALYSISkeep it simple science

®


The ions specified by the syllabus are

CATIONS (+) ANIONS (-)

Barium PhosphateCalcium SulfateLead CarbonateCopper ChlorideIron

Photo by Ken Kiser

PPhhoottoo bbyyPPaamm rrootthh


9

Qualitative Identification of IonsThe simplest laboratory methods for detecting andidentifying the ions being studied, are to usePrecipitation Reactions and Flame Tests.

You will have done a series of laboratory exercises tofirstly, familiarise yourself with the tests themselves,and then to use the tests to identify some “unknown”samples.

Precipitation ReactionsYou were introduced to these in the PreliminaryTopic, “Water”.

Most ionic compounds are soluble in water, butsome have extremely low solubility. If certaincombinations of cation and anion are mixedtogether in a solution, they may form aninsoluble solid and precipitate from solution.

You previously studied these reactions to learnabout the “Solubility Rules”. A knowledge ofthese “rules”, and of the common precipitatecolours can now be used to test a solutioncontaining “unknown” ions.

Flowcharts for Identifying Cations & Anions



Dropper bottles of soluble ionic compounds

Spot Test PlateCertain combinationsof ions will formcoloured precipitates

Solution Containing One CationBa2+ Ca2+ Pb2+ Cu2+ Fe2+ or Fe3+

Add Cl-((aaqq))

Green Precipitate,turns brown

Brown Precipitate

Blue Precipitate

Use a Flame Test todecide. (next page)

White Precipitate

No Reaction

NNoo RReeaaccttiioonn



White Precipitate

PPbb2+

CCaa2+

CCuu2+

BBaa2+

FFee2+

FFee3+

Add SO4422-

((aaqq))

Add OH-((aaqq))

or

Solution Containing One AnionCl- SO4

2- CO32- or PO4

3-

Add Acid

Green Precipitate

White Precipitate.Darkens in sunlight

Thick WhitePrecipitate

No Reaction

If No Reaction, “target”anions not present

Gas Bubbles Form((CCOO2 ggaass))

CCOO32-

CCll-

SSOO42-

PPOO43-

Add Ba22++((aaqq))

Add Ag++((aaqq))

Add Fe22++((aaqq))

Note: If the sample contains a mixture ofmore than 1 cation and 1 anion, these simple

schemes may need to be modified.


10

Flame TestsWhen atoms absorb energy, electrons may“jump” up to a higher energy level (a higher,unoccupied orbit). Usually, they will immediatelydrop down to a lower level again, and in theprocess they lose the excess energy by emittinglight rays at a precise set of frequencies.

...thiscan beused foridentification.

In the flowcharton the previouspage, the ionsCa2+ and Ba2+

both gave thesame results forprecipitationreactions.

They can beeasilydistinguished if asample of eachsolution is“flamed” in abunsen.

Each one“flares” brieflywith a distinctandcharacteristiccolour.

Of the ions inour list to be studied, 3 give flame test coloursthat are useful for analysis.

Flame Test ColoursIon Flare ColourBarium lime greenCalcium orange-redCopper blue

As you will see next, the principle involvedhere, can be used for quantitative analysis aswell...

Atomic Absorption Spectroscopy (AAS)

When a small sample of atoms are energised so theyemit light, as shown at the left, the amount of lightemitted is too small for measuring the amount orconcentration.

However, the exact frequencies of light that aparticular type of atom will emit, are also the samefrequencies that that atom will absorb strongly, andthis time it is more easily measured.

AAS is a technique of beaming light through avapourized sample, and measuring the amountof the light (of the appropriate frequencies forthe “target” atoms) that is absorbed. Theamount of light absorbed is in direct proportionto the amount of “target” atoms present, so itmeasures them quantitatively.

Each type of atom has its own unique set ofabsorption frequencies (see next page), so AAScan positively identify each atom, and measureits concentration accurately.

The process was invented and developed inAustralia in the 1950’s and is sensitive toextremely low concentrations of atoms, mainlymetals. It has become very important forchemical analysis of “trace elements” in soil orwater.

When substances are present in extremely lowconcentrations they are often measured in unitsof “parts per million” (ppm). For example, ifthere was one atom of Radon gas for everymillion atoms in the air, its concentration wouldbe 1 ppm.

AAS can routinely measure concentrations ofover 60 elements at levels of only 0.01 ppm andless.



eelleeccttrroonnss jjuummppttoo hhiigghheerr oorrbbiitt

LLiigghhtt eemmiitttteedd aass tthheeyyddrroopp ddoowwnn aaggaaiinn

In many cases, thelight emitted

requires specialequipment to

detect.

However, in thecase of a few

common ions thelight is bright and

visible to thenaked eye...

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SSaammppllee vvaappoorriizzeeddiinn ggaass ffllaammee..

““TTaarrggeett”” aattoommssaabbssoorrbb ssoommee lliigghhtt

ffrreeqquueenncciieess

BBeeaamm oofflliigghhtt

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AAS

The technique of AAS has revolutionised the study of “trace” elements and their

effects. Examples next page.


11

Emission & Absorption SpectraYou should be familiar with the idea of a“spectrum” of light. For example, if “white” lightis passed through a prism, the differentfrequencies are separated, and the familiarrainbow colours appear.

(use your imagination... we can’t print colours)

If the light emitted by atoms of a particularelement is put through a prism, the spectrumshows very narrow bright lines on a darkbackground, because only certain frequenciesare given out. The pattern of lines ischaracteristic for each element.

If the same element absorbs light it will be atexactly the same characteristic frequencies. Thespectrum will have dark lines on a brightbackground.

The following diagram shows 3 ficticiouselements, just to give the general idea.

In AAS, the optical system allows the measurement ofabsorption of light of specific frequencies whichcorrespond to the spectrum of a particular element.

The amount of this light absorbed by a sample is indirect proportion to the concentration of that type ofatom.

By measuring the absorption of light of knownconcentration standard solutions a “calibrationgraph” can be constructed. When the absorption ofthe same frequencies by test samples has beenmeasured, the concentration of the target elementcan be read from the calibration graph. (example atright)

Examples of the Use of AASThe value of AAS lies in its ability to measurequantities of elements that are too low to bedetected by the “normal” laboratory chemicalanalyses.

Essential Trace Elements in SoilA famous case occurred in Western Australia inthe 1950-60’s. In one region of the state manysheep farmers found their animals werechronically unhealthy, despite apparently goodpastures and disease control.

Using the newlydevelopedtechnique ofAAS, the CSIROfound that thesoil (and thenthe plants andthe sheep) werelacking tinyamounts of theelement cobalt.Further study revealed that all mammals need“trace” amounts of cobalt for one particular,important enzyme in their cells. In the cobalt-poor area the sheep were unhealthy becausethey could not make the vital enzyme.

Once this was understood, the sheep were givena slow-release cobalt “pill”, and a multi-milliondollar industry was rescued from trouble.

Monitoring Lead PollutionAAS is ideal for measuring extremely smalllevels of pollutant chemicals, such as lead, in(say) the soil. By measuring the absorption oflight (at lead’s frequencies) by AAS, the sort ofdata discovered was:

It was data like this, from AAS analysis, that wasimportant in the decision to stop using leadedpetrol, since it revealed the amount of leadpollution occurring in heavy-traffic areas.

AAS data is vital for monitoring pollutants likelead.



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12

Quantitative Laboratory AnalysisYou will have carried out a practical analysis tomeasure the sulfate content of a lawn fertilizer.

A productcommonly testedis shown.

The simplestmethod to use isGravimetricAnalysis (collect asolid and weigh it)following an ionicprecipitationreaction.

As covered earlier,sulfate ions can beidentified (an inthis case collectedquantitatively) byprecipitation using Ba2+ions.

An outline of a typical procedure (and exampleresults and analysis) is at the right.

Below is a discussion of some of thecommonly encountered difficulties with thisanalysis.

Reliability of the ResultsThe “reliability” of any analysis can be assessed byhow close (or otherwise) the results are when theprocedure is repeated. In a class situation, a numberof different groups usually carry out the sameanalysis. If the various group results are in closeagreement, then the procedure can be considered“reliable”.

Common DifficultiesThe major problem with this analysis is that theBaSO4 precipitate is notoriously difficult to collect byordinary filtration because it is very fine-grained and alot gets through the filter paper.

It is better to use a sintered glass crucible & vacuumfilter.

Typical Results and AnalysisMass of fertilizer sample = 2.34 g

Mass of dried precipitate (BaSO4) collected = 2.67 g

moles of BaSO4: n = m/MM MM= 233.4g= 2.67/233.4= 0.01144 mol

∴∴ moles of sulfate = 0.01144 mol (ratio 1:1)

mass of sulfate: m = n x MM MM(SO4)= 96.1g

= 0.01144 x 96.1= 1.10 g

∴∴ % sulfate in sample = 1.10 x 100 = 47.0%2.34

Accurately Weigh a Sample of Ferilizer

(approx 2 grams is suitable)

Dissolve in about 100mLdilute HCl

Filter to remove any insoluble material

Slowly add an excess of Ba22++

and stir well

(about 40mL of 0.5 molL-11

BaCl22((aaqq)) is suitable)

Ba2+(aq) + SO4

2-(aq) BaSO4(s)

Filter to collect solid barium sulfate

Dry the residue in an oven and weigh

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Suction

Filtrate

SSiinntteerreedd ggllaassss ffiilltteerr((ppoorroouuss))

aalllloowwss wwaatteerr tthhrroouugghh,, bbuutt ttrraappss ffiinnee ssoolliiddss

Mixture

Qualitative Analysis means toa).............................. a chemical species.To analyse quantitatively means tob).................................................................

Some human activities releasedangerous ions (or harmful amounts)into the environment. For example,phosphate ions can cause the processof c)......................................... to occur inwater environments. This is when thereis d)............................................................Later, the dead, rotting vegetatione)................. .................................... fromthe water. The main sources of extraphosphate are f)................................ and.......................................

Lead ions can g).............................. in thebody and cause h)......................................................... in children. Untilrecently, the main source of leadpollution was from the use ofi).................................................................

The simplest qualitative tests to identifyions is to use j)..................................reactions and k)............................ tests.

A simple scheme to identify the 6syllabus cations is:1. Add l)............................. ion. A whiteprecipitate indicates the presence ofm).................................

2. Add n)............................ ion. A whiteprecipitate indicates eithero)....................... or ..........................These can be differentiated by ap).......................................

3. Add q)............................ ion. A blueprecipitate indicates r).............................while a brown precipitate indicatess)..............................., and a greenprecipitate (which slowly goes brown)indicates t)...............................

To identify the 4 syllabus anions:1. Add u)............................. If carbonateions are present you will seev)...........................................

2. Next, add w)............................ ion. Ifsulfate ions are present you will seex).........................................................

3. Add y)........................... ion. A whiteprecipitate (which darkens in sunlight)indicates z)........................................

4. Finally, add aa)................. ion. A greenprecipitate indicates ab)...........................

Of the 6 syllabus cations, 3 givedistinctive colours in a flame test: barium flares ac)............................, calcium flares ad)................................ and copper flares ae).......................

AAS stands for af)........................................................................ Thistechnique is able to quantitativelymeasure extremely smallconcentrations of an element. Basically,it works by measuring the amount ofag)............................. absorbed by atomsin a vaporized sample. Each elementhas its own unique absorptionah)................................ The AASequipment is able to select theai)................................... of light whichcorrespond to the aj)..............................spectrum of the element beinganalysed.

AAS has made it possible to study“ak).......................” elements whichcould not be previously analysed. In afamous case, AAS analysis solved amajor problem in a sheep-farming areaby detecting a deficiency ofal)................................. which wasmaking the sheep sick. AAS also makesit possible to monitor pollutants such asam)..........................., which isdangerous even at low levels in theenvironment.

13



WHEN COMPLETED, WORKSHEETSBECOME SECTION SUMMARIES

Worksheet 3 Chemical AnalysisFill in the blank spaces Student Name..........................................

Each of the following describes a series of testscarried out on an “unknown” ionic solution.Name the ion(s) identified in each case.

Sample a)• added acid: no reaction• added Ba ion: no reaction• added Ag ion: white precipitate

Sample b)• added Cl ion: no reaction• added sulfate ion: white precipitate• flame test flared orange-red colour

Sample c) • added Cl ion: no reaction• added sulfate ion: no reaction• added hydroxide: green precip., went brown

Sample d) • added acid: bubbles formed

Sample e)• added acid: no reaction• Added Ba ion: no reaction• added Ag ion: no reaction• added Fe2+ ion: green precipitate

Sample f)• added Cl ion: no reaction• added sulfate ion: no reaction• added hydroxide: blue precipitate

14



Worksheet 4 Practice Problems Identifying Ions Qualitatively Student Name..........................................

Worksheet 5 Practice ProblemsQuantitative Analysis Student Name..........................................1.Two different lawn fertilizers were analysedgravimetrically by dissolving a sample in dilutehydrochloric acid, adding excess Ba2+ ion, thencollecting the BaSO4 precipitate, drying andweighing.

Fertilizer A: sample mass = 4.46gmass of BaSO4 collected = 3.27g

Fertilizer B: sample mass = 1.93gmass of BaSO4 collected = 2.66g

Calculate the % by mass of sulfate in eachfertilizer.

2.To measure the amount of chloride ion in asample of sea water, and excess of silver ions(in silver nitrate solution) was added.

a) Write an equation for the reaction betweensilver and chloride ions.

b) From a 50.0g sample of seawater, the massof dried precipitate collected was 3.42g.Find % by mass of chloride ion in the sample.

Multiple Choice1. The need to monitor a chemical process isbecause even slight changes in conditionscould alter:A. the pathway and products of the reaction.B. the rate of reaction and energy change.C. the equilibrium position and yield.D. all of the above.

2.The industrial production of ammonia involvesthe reaction:N2(g) + 3H2(g) 2NH3(g) ∆∆H = -92kJ/mol

Increasing the temperature would be expectedto:A. increase the yield and speed up the reaction.B. decrease the yield and speed up the reaction.C. increase the yield and slow down the

reaction.D. decrease the yield and slow down the

reaction.

3. Samples of a solution known to contain oneionic compound were tested as follows:

added ResultCl- no reactionSO4

2- no reactionOH- blue precipitateacid no reactionBa2+ white precipitate

The solution contains the compoundA. barium hydroxideB. iron(II) sulfateC. copper(II) sulfateD. lead(II) chloride

4. A flame test on a sample containing barium ionswould be expected to flare:A. brick redB. lime-greenC. yellowD. blue

5.The analytical technique known as AAS wouldbe suitable for measuring:A. trace amounts of the element arsenic in the

hair of a murder victim.B. drug residues in the saliva of a sports person.C. the yield of ammonia in an industrial plant.D. the mass of lead in a bullet from a crime

scene.

Longer Response QuestionsMark values shown are suggestions only, and are togive you an idea of how detailed an answer isappropriate. Answer on reverse if insufficient space.

6. (4 marks)With reference to a specific job as a ChemicalScientist, outline 3 reasons for collaboration betweenscientists.

7. (7 marks)In the Haber process for the industrial production ofammonia:a) explain why hydrogen and nitrogen gases aremixed in a ratio of exactly 3:1. Include an equation inthe explanation.

b) explain why the reactants are combined under ahigh pressure of about 300 atmospheres.

c) name the catalyst employed, and explain how itcontributes to the process.

d) explain why the reaction temperature (about400oC) is considered a “compromise”.

8. (5 marks)In a qualitative analysis scheme for the cations Ba2+ Ca2+ Pb2+ Cu2+ Fe2+ and Fe3+, and forthe anions Cl- SO4

2- CO32- and PO4

3-, the following results were obtained for an ionicsolution:

Added Resulti) sulfate ion no reaction

ii) hydroxide ion green precipitate, turned browniii) barium ion no reactioniv) silver ion white precipitate, darkened.

a) What is meant by a “qualitative” test?

b) For each test i)-iv) described above, state what thisshows as either a positive, or negative, conclusion.

9. (7 marks)In a gravimetric analysis of the purity of anammonium sulfate fertilizer, a 5.47g sample wasdissolved in dilute hydrochloric acid and filtered toremove insoluble solids.An excess of barium chloride solution was added,and the precipitate collected by filtration. The driedresidue had a mass of 9.15g

a) Write a balanced equation for the precipitationreaction.

b) Calculate the % by mass of ammonium sulfate inthe fertilizer.

c) Describe one of the difficulties this analysis maypresent, and suggest how to overcome it.

15



Worksheet 6 Test Questions sections 1,2,3 Student Name...............................

Structure of the AtmosphereThe atmosphere is composed of a number of layers,although these different layers cannot be seen. Theair within each layer rarely crosses the boundary tothe next layer (i.e. each is more or less a separatebody of gas) and each layer has certain differences intemperature profile and chemistry. It is only thelowest 2 layers you need to know about.

Composition of the AtmosphereWater vapour in the air varies from about 0.5 -5%, but all the other gases of the air areremarkably constant:

Nitrogen 78.1% (% of dry air)Oxygen 20.9%Argon 0.9%

99.9%

Another dozen or more gases make up theremaining 0.1%Their concentrations are best measured in partsper million (ppm). The most significant are:

Carbon dioxide 380 ppm (and rising!)Inert gases ≅≅ 30 ppm Methane 1-2 ppm

OZONE 0.02 ppm (at ground level)up to ≅≅ 8 ppm (in stratosphere)

Air Pollutant ChemicalsOne of the main indicators of human economicand technological development over the last200 years or so, is the release into theatmosphere of a range of substances which are

• toxicand/or • environmentally damaging.

Pollutant Human Activities ResponsibleCarbon monoxide Incomplete combustion in

CO vehicle engines, fires.

Sulfur dioxide Fossil fuels (S impurities burn).SO2 Smelting of sulfide ores.

Hydrocarbons Unburnt fuels, solvents, spills.CnHm

“NOx gases” High-temp. combustions in NO & NO2 engines & power stations.

Particulates Combustions, e.g. burning-off, dust, ash, smoke agriculture, mining.

Ozone, O3 Photochemical smog.

More About OzoneWay back in Preliminary Topic 1, you wereintroduced to the concept of “Allotropes”;different forms of the same element, such asgraphite and diamond, the allotropes of carbon.

Ozone: allotrope of oxygen.

Ozone in the lower atmosphere is a toxicpollutant. At concentrations as low as 0.2 ppm itcauses lung damage, and aggravates otherbreathing problems. For people who haveasthma, for example, ozone is a life-threateningsubstance.

Ozone in the upper atmoshere is animportant shield against dangerous U.V.radiation from the Sun. In the Stratosphere,where ozone concentrations are as high asabout 8 ppm, up to 90% of the damaging UV isabsorbed by ozone molecules.

16


4. ATMOSPHERIC CHEMISTRY & OZONEkeep it simple science

®


O22

O33

Always good!

up high : good!down low : bad!

Ironically, human activities produce ozone in the Troposphere

and destroy ozone in the Stratosphere!

The Atmosphere

AAllttiitt

uuddee

((kkmm

))1100

2200

3300

44

00

55

00

MMtt EEvveerreessttTroposphere

Stratosphere

BByy 11

0000kkmm

uupp,,

yyoouu

aarree

vviirrtt

uuaallllyy

iinn ss

ppaaccee

,, aalltthh

oouugghh

ssoomm

ee aaii

rreexx

tteenndd

ss oouu

tt ttoo

aabboouu

tt 550000

kkmm

AAllll oouurrwweeaatthheerr aanndd

7755%% ooff tthhee aaiirr

Zone of highest concentration of Ozone

EEvveenn aatt iittss hhiigghheesstt ccoonncceennttrraattiioonn,, tthhee aaiirr ooff tthhee““oozzoonnee llaayyeerr”” iiss oonnllyy aabboouutt 00..00000088%% oozzoonnee..

HHoowweevveerr,, tthhiiss iiss eennoouugghh ttoo bblloocckk 9900%% ooffiinnccoommiinngg ssoollaarr UUVV..

PPrreessssuurree((aattmmooss))

0.001

0.1

1.0




17

Coordinate Chemical BondingYou are already familiar with “normal” covalentbonding, and you should be able to describe theO2 molecule using a Lewis formula.

To form an ozone molecule, another oxygenatom must bond to the O2, and the way thisoccurs is an example of a

“Coordinate Covalent Bond”

Once a coordinate covalent bond has formed, itis indistinguishable from a “normal” covalentbond.

Other Examples of Coordinate Covalent Bonding

You can now understand the formation of somechemical species which previously couldn’t beexplained.

Sulfur Trioxide, SO3Notice in the Lewis formula for SO2, the sulfuratom still has another unshared pair of electronsavailable. Under the right conditions, anotheroxygen atom can bond there, again by forminganother coordinate covalent bond.

2 SO2 + O2 2SO3

Sulfate Polyatomic Ion, SO42-

Notice that in SO3 the sulfur atom has just 6electrons in the outer shell. The “rule of 8” is notalways obeyed.

But, what if 2 extra electrons were added? (They might comefrom a metal atom, forexample.) There is roomfor them in the sulfuratom’s orbit, and then theycan be shared with a 4thoxygen atom.

All the polyatomic ions areformed in a similar way,and many covalent compounds involvecoordinate covalent bonds. That’s why it canbe difficult to predict formulas for covalentcompounds.

O O

2 Oxygen atomsEach has 6 electrons

in outer shell

O O

O2 molecule2 pairs of electrons

shared

Structural formula

OO==OOModel

O O

CoordinateCovalent Bond

O O O O

O2 molecule

O3 moleculeOzone

O atom

Structural formulaOO==OO-OO

Model

TThheessee ssiinnggllee eelleeccttrroonnss wwiillll bbee sshhaarreedd,, iinn ppaaiirrss

TThhiiss uunnbboonnddeedd ppaaiirr iiss aabboouutt ttoo bbee ““ddoonnaatteedd””

ttoo bbee sshhaarreedd wwiitthh tthhiiss ssiinnggllee OO aattoomm

The O33 molecule is bent, due to theelectron pairs all getting as far away from

each other as possible

SO

O

SO

O

SSuullffuurr aattoomm && 22 ooxxyyggeenn aattoommss,,

wwiitthh aallll eelleeccttrroonnss iinn ppaaiirrss

TThhee ssuullffuurr aattoommssuupppplliieess aallll tthhee

eelleeccttrroonnss ttoo sshhaarree iinntthheessee ccoooorrddiinnaatteeccoovvaalleenntt bboonnddss

O

SO

O

O

O

SO

O

22 eexxttrraa iioonniicc eelleeccttrroonnss cchhaarrggee

2-

A Coordinate Covalent Bond forms when boththe shared electrons come from the same atom

Properties of O2 and O3 ComparedLike all allotropes, O2 and ozone show quite differentproperties. For example:

Property O2 O3boiling point (oC) -183 -111density of liquid (g/cm3) 1.2 1.6smell odourless strong

chemical reactivity reactive highly(e.g. combustion) reactive

chemical stability stable highlymolecule unstable

It is the chemical properties that are of most significance.

Explaining the DifferencesThe properties are the result of structure andbonding.

The differences in physical properties are due simplyto the O3 molecule being larger and heavier, whichincreases the dispersion forces between molecules.

The O=O double bond in O2 is quite strong. It requiresalmost 500 kJ of energy per mole of bonds, to break.In contrast, it only takes about 100 kJ/mole to breakone of the bonds in O3. This is why ozone is unstableand very highly reactive... the molecule’s bonds aremore readily broken, so the activation energy for anyreaction is quite low, and ozone readily entersoxidation reactions.

Sulfur Dioxide, SO2


18

Oxygen Free-RadicalsHow can an ozone molecule be formed in the firstplace?

Up in the high Stratosphere, conditions are verydifferent to down here at the bottom of theatmosphere. It’s cold, the air pressure is extremelylow and there is a lot of high energy radiation from theSun.

Oxygen doesn’t absorb U.V. radiation verymuch, but occasionally a U.V. ray scores a directhit and smashes the molecule into 2 separateoxygen atoms.

These are called “oxygen free-radicals”.

Oxygen free-radicals are extremely reactive, butwhat is there to react with in the highatmosphere?

The most common substances up there are:• nitrogen, (N2) which is very stable and

chemically unreactive.• oxygen molecules, (O2) which are fairly

reactive.• argon, (Ar) which is totally inert.

So, the free-radical atoms tend to react withoxygen molecules:

O2 + O O3

This is how ozone is formed in the upperatmosphere. Although it is unstable and highlyreactive, there is virtually nothing up there for itto react with, and the air of the Stratospherehardly mixes with the Troposphere, so it buildsup to a concentration of up to about 8 ppm.

It’s interesting to note, that the U.V. rays whichcreate the oxygen free-radicals and thus createozone, are strongly absorbed by the ozone. Lessthan 10% of the dangerous, incoming U.V.penetrates to the surface, thanks to ozone.

Depletion of the Ozone LayerFor over 100 years, scientists have been sendinghigh-altitude balloons up into the Stratosphere tocollect information and air samples, so the presenceof ozone has been known for many years, and its roleas a U.V. shield has been recognised since the 1920’s.

How Ozone Levels are Measured• Automatic chemical analysis units are sentaloft in high altitude balloons. Direct chemicalmeasurements of ozone concentration can becollected at any desired altitude.

• The “Dobson Spectrophotometer” is a groundbased instrument (invented 1925) whichmeasures the amount of several differentfrequencies of U.V. light reaching the surface.

By comparing the level of a U.V. frequencyknown not to be absorbed by ozone, with afrequency that is strongly absorbed by ozone, acalculation gives the amount of ozone in the“total column” of air above the instrument.

• Similar instruments are carried by satellites inorbit. They measure the UV scattered fromdifferent layers of the atmosphere, and so canmeasure a “profile” of ozone concentrations atdifferent altitudes.

Evidence for Ozone DepletionRegular measurements of ozone concentrationhave been made since 1925, and intensivemeasuring has been going on since the 1970’s.

A world wide decline in Stratospheric ozonelevels of about 10% has been recorded. Moreimportantly, it has been found that every springover Antarctica, a “hole” develops in the ozonelayer. A vast area of the Stratospheretemporarily loses up to 90% of its ozone forseveral months each year. The size of this“hole” varies, but some years it expands tocome very close to populated areas.

So What?The problem with ozone depletion is that (forexample) a 30% decrease in ozoneconcentration would mean a 50% increase in thelevel of dangerous U.V. radiation reachingground level.

U.V. radiation is known to cause sunburn, eyedamage and increased incidence of deadly skincancers in humans. Plant studies indicate that largeincreases in U.V. could seriously disrupt crop growth,possibly leading to a food supply crisis.

Before learning about how ozone is beingdestroyed, you need to know about another typeof carbon compound...

the Haloalkanes.



O=O bond broken

U.V. Rays

2 separate oxygen

atoms

“oxygen freeradicals”

Chemical Reactivity Comparison

Oxygen O2 Ozone O3 O free-radicalChemically VERY active ExtremelyActive Active

+


19

Haloalkanes“Halo-” refers to the “Halogens”... the generalname for the elements of group 7 of the PeriodicTable; fluorine, chlorine, bromine and iodine.

Haloalkanes are alkane molecules in which oneor more hydrogen atoms have been replaced byhalogen atoms.

The simplest example is a methane moleculewith one of its hydrogens replaced by (say) achlorine atom.

If, instead of chlorine, the replacement was:

• fluorine... CH3F = fluoromethane.• bromine... CH3Br = bromomethane.• iodine... CH3I = iodomethane.

What if 2, or more, hydrogens were replaced bychlorine atoms?

Prefixes to use for the number of halogenatoms:1 = no prefix 4 = tetra2 = di 5 = penta3 = tri 6 = hexa

What if there is more than one type of halogenatom substituted? They must be orderedalphabetically by halogen name... (not by anyprefixes used, though).

This little beauty, CBrClF2is called

“bromochlorodifluoromethane”

IsomersWhen the molecule gets bigger, another variation thatcan occur is in the position of the various atoms.

For example, these 2 molecules are ethane, with2 chlorines substituted for hydrogens.

Both Cl atoms attached Cl atoms attached toto same carbon. different carbon atoms.

1,1-dichloroethane 1,2-dichloroethane

These molecules have the same molecularformula (C2H4Cl2) but have a different structure,and are different compounds. Their m.p. & b.p.,density, and other properties would be slightlydifferent. We must give them a different name.

This is done by numbering the carbon atoms(from whichever end gives the smallest result)and stating the position number for everyhalogen atom present.

More Examples of Naming Haloalkanes:

C4H5Cl3F2

Best to number thecarbons from the right.

1,2,2-trichloro-1,3-difluorobutane

C5H5Br3F4

Best to numberfrom the left.

2,3,4-tribromo-1,1,1,5-tetrafluoropentane



Cl

HH

H

C CH3ClChloromethane

CH2Cl2Dichloromethane

CHCl3Trichloromethane

CCl4Tetrachloromethane

Cl

ClH

H

C

Cl

ClCl

H

C

Cl

ClCl

Cl

C

Cl

BrF

F

C

ISOMERShave the same molecular formula,

but different structures.They are different compounds,

with different properties.

F Br Br

HHF

F

C C CBr

HC

HF

H

C

H F Cl

ClH

H

H

C C CCl

HC F

WORKSHEET at the end of section


20

The Chlorofluorocarbons (CFC’s)One particular class of haloalkanes have becomenotorious as ozone destroyers... the “CFC’s”.

CFC stands for “chlorofluorocarbon”. These arealkane molecules in which ALL the hydrogenshave been replaced by chlorine and fluorineatoms.

Three of the most used CFC’s were:

CCl3Ftrichlorofluoromethane

Trade name “Freon-11”

CCl2F2dichlorodifluoromethane


C2Cl3F31,1,2-trichloro-

1,2,2-trifluoroethane


These compounds (in general):• have boiling points near room temperature.• are very stable, and chemically unreactive

and inert.• are non-toxic, non-inflammable and

non-corrosive. (i.e. very safe)

This set of properties made the CFC’s ideal as:• the “working fluid” in refrigerators.• propellant gas in aerosol cans.• the gas to “blow up” foam plastics.• small fire extinguishers, cleaning sprays

and solvents.

From about the 1930’s, CFC’s began to be widelyused, reaching a peak in the 1970’s. The methods ofusage meant that the CFC’s were eventually releasedinto the atmosphere.

Although the air of the Troposphere does not mix withthe Stratosphere much, the CFC’s released havegradually diffused into the upper atmosphere. Thismight take 20 years, but these chemicals are verystable and easily last that long.

Once there, we now know that they cause aseries of reactions which destroys ozone.

By international agreement, production and useof CFC’s is now banned. However, all themillions of tonnes released back in the 1950-70’sis still up there, doing its thing...

What CFC’s Do to OzoneRemember how ozone is formed? The first stepis the production of an “oxygen free-radical”when U.V. strikes an oxygen molecule.

A similar thing can happen to a CFC molecule:

A likely product of this is a chlorine free-radical;a loose atom of chlorine, which is even morereactive than an oxygen free-radical. We usethe symbol “Cl•” to represent the free-radical.

What happens next:

Reaction 1

chlorine + ozone chlorine monoxide + oxygenfree-radical free-radical

Cl• + O3 ClO• + O2

Meanwhile, the U.V. has just busted an oxygenatom and formed an oxygen free-radical too.Normally this might make another ozonemolecule, but if the ClO• radical finds it first:

Reaction 2

chlorine monoxide + oxygen oxygen + chlorinefree-radical free rad. free rad.

ClO• + O• O2 + Cl•

If you add reactions 1 and 2 together, severalspecies “cancel out”:

Cl• + O3 ClO• + O2ClO• + O• O2 + Cl•

O3 + O• 2 O2

The “net equation” shows that overall, ozonehas been converted to oxygen, and the oxygenfree-radicals (which potentially could haveformed more ozone) have been “mopped up”.

Notice also, that the Cl• free-radical isregenerated by reaction 2, and can do it all

over again... it is acting as a catalyst.

A little CFC can destroy a lot of ozone.



Cl

ClF

Cl

C

Cl

F

Cl

C

Cl

ClF

F

C

F

Cl

F

C

FF

CCll

CCll

CCll

CCll

FF

CCll

CCll

U.V. light

Molecular fragments are highlyreactive “free-rradicals”

ttrriicchhlloorroofflluuoorroommeetthhaannee

CCCC


21

What’s Been Done About CFC’s?

CFC’s are also potent “Greenhousegases”, although their contribution toGlobal Warming is minor compared totheir impact on the ozone layer.

Between 1987-1994 a series ofinternational agreements have bannedthe manufacture and use of CFC’s,although some developing countrieshave been given a little more time tocomply.

CFC’s have been replaced by:

For some uses, CFC’s have beenreplaced by HFC’s. These arehydrofluorocarbons, containinghydrogen, fluorine and carbon, but nochlorine. These are being used inrefrigeration, foam plastics, etc. HFC’sare more expensive, and slightly lessefficient than CFC’s.

However, HFC’s mostly decompose inthe Troposphere, and if any does reachthe Stratosphere it is “ozone-friendly”because it contains no chlorine.

The main HFC being used in Australia is

1,1,1,2-tetrafluoroethane, C2H2F4

Can the Ozone Layer Recover?The answer is yes. Although CFC’s are verystable, they cannot last forever, and once theirconcentration begins to fall, the normal ozoneproduction in the Stratosphere will restore thenormal balance.

The CFC’s released back in the 1970’s are stillreaching the Stratosphere, and so ozonedepletion is serious. However, this should peakin the next 10-20 years and then the recoverywill begin. It is estimated that ozone levels willbe back to normal in 50-100 years.

In the meantime, governments must:

• continue to comply with, and enforce the banon CFC’s, and maintain pressure on othernations to comply.

• financially support the continued monitoring ofozone concentrations.

• educate people about the dangers of U.V. andthe ways to protect themselves from it.

You need to realize that you will live in a high-UVworld for the next 50 years or so... basically foryour lifetime.



Hydrocarbons, for example,

as propellantsin aerosol

cans.Hydrocarbons

areinflammable,so this is less

safe thanusing CFC’s,but it savesthe ozone.

F

F

F

C

H

F

H

C

Dobson Spectrophotometer in actionmonitoring Ozone levels

The lowest layer of the atmosphere is thea)....................................... Above that, extending up toabout 50km, is the b)................................... The airconsists of the 3 main gases, c)..............................,..................................... and ....................................which combined make up d)..................%.

Significant pollutants in the atmosphere includee)................................... (CO) from incompletecombustion, sulfur dioxide, from f)..........................................................., “NOx” gases fromg)........................... ................................ and ozone,formed in petrochemical “h)....................”

At ground level, ozone is a dangerous pollutant whichcan cause i)............................ ...............................However, up in the Stratosphere, ozone is veryimportant because it absorbs j).....................................

Ozone forms by “k).................................. covalentbonding”, which is when both the electrons beingshared l).............................................. All the“m)......................................... ions”, and many covalentcompounds are formed by this type of bonding.

O2 and O3 are n)........................... of oxygen. They havequite different properties, but it is theiro)............................... properties which are mostsignificant. Compared to O2, ozone is much morep).............................................. because the molecule isquite q)................................ While the bonds in O2require 500 kJ/mol to break, the bonds in O3 need onlyabout r)................. kJ/mol.

Ozone forms in the upper atmosphere when U.V.radiation strikes an s)............................ molecule andsplits it into 2 t).......................... ........................ Theseare extremely reactive, and can react with an O2molecule to form u).................................... Theconcentration of ozone can be measured by sendingup analysis devices in balloons, or by using av)..................... .....................................

This measures different frequencies ofw).................................. and from this, the amount ofozone can be calculated. Measurements made overthe past 80 years reveal that, since the 1970’s, ozonelevels have declined about x)...................% generally,but that a huge “y)............................................” formstemporarily over z)........................................ everyspring. Potentially, even partial destruction of theozone layer can result in increased exposure to U.V.,leading to aa).......................................... and increased............................................... There is also a potentialfor disrupted plant growth, leading toab)............................................

“Haloalkanes” are ac)................................. moleculesin which one or more hydrogen atoms have beenreplaced by atoms of ad)...........................,............................, ....................... or ...............................which collectively known as theae)........................................

A type of haloalkane, the af)...................................................... (CFC’s) are believed to beresponsible for ozone depletion in the Stratosphere.CFC’s were widely used for ag)........................................................................, but have nowbeen banned. CFC molecules released at ground levelgradually make their way up into the Stratosphere. Ifstruck by U.V. radiation, a ah)........................ free-radical can be formed. This can act asai).......................... in a series of reactions which turnozone into aj).............................

CFC’s have now been replaced by hydrocarbons andak).............................................................. These are notas efficient, but are “ozone-friendly”. The ozone layeris expected to continue to degrade for some years,but then slowly recover within aboutal)........................... years.

22



Worksheet 7 Atmospheric Chemistry & OzoneFill in the blank spaces Student Name..........................................

2. Name each of the following compounds.

3. Isomersa) Draw structural formulas for 3 different isomers oftrichloropropane. Name each correctly.

b) Draw structural formulas for 4 different isomers ofbromochlorobutane. Name each correctly.

Worksheet 8 Practice Problems Co-ordinate Bonding + Haloalkanes Student Name..........................................1. a) Construct a Lewis Formula for carbon, with its 4electrons in pairs. Add an extra pair. Now attach 3oxygen atoms in coordinate covalent bonds. Write aformula, and name, for the polyatomic ion.

b) As above, but begin with nitrogen (5 electrons).Add 1 extra electron, then 3 oxygens by coordinatecovalent bonding. Formula and name?

c) Construct a Lewis Formula for a water molecule.Now add a hydrogen ion (H+) so it forms a coordinatecovalent bond with the oxygen atom. Formula andname?

a) Br

HCl

H

C

b) F F Cl

HH

F

H

C C CCl

HC H

c) F

ClBrI

C

d) Br H Cl

HH

Br

H

C C C Cl

Multiple Choice1.The 4 most abundant gases in normal dry airare:A. nitrogen, oxygen, argon & carbon dioxide.B. oxygen, carbon dioxide, nitrogen & ozone.C. nitrogen, helium, oxygen & ozone.D. carbon dioxide, oxygen, argon &

sulfur dioxide.

2. At ground level, ozone is a pollutant gasassociated with:A. incomplete combustion of fuels.B. smelting of metal ores.C. photochemical smog.D. emissions from chemical industries.

3.Oxygen and ozone are examples of:A. isotopes.B. different elements.C. isomersD. allotropes.

4.Which of the following chemical species is likelyto form by coordinate covalent bonding?A. polyethyleneB. potassium sulfideC. ammonium ionD. carbon dioxide

5.Which list places the 3 chemical species inincreasing order of chemical reactivity?A. O2, O3, O•B. O•, O2, O3C. O3, O•, O2D. O3, O2, O•

6.The compound shown would be called:A. 1,1-chloro-2-fluoroethaneB. 1-fluoro-2,2-chloroethaneC. 1,1-dichloro-2-fluoroethaneD. 1-fluoro-2,2-dichloroethane

7.CFC’s are thought to cause ozone destruction inthe Stratosphere because, when struck by U.V.rays, the CFC molecule:A. absorbs the U.V. so it does not penetrate

to the ground.B. breaks apart, releasing a chlorine free-radical.C. attaches to an ozone molecule and

immobilizes it.D. converts to different isomer.


8. (4 marks)A Scientist was overheard to say: “Ozone... good up there, bad down here”.Explain in more detail what was meant by thiscomment.

9. (5 marks)a) Give a definition for “Coordinate CovalentBond”.

b) Using Lewis Formulas, explain the formation of an ozone molecule.

c) Contrast the chemical reactivity and stabilityof the O2 and O3 molecules, and account forthese differences.

10. ( marks)a) Outline 2 different methods used to monitorozone concentrations in the upper atmosphere.

b) Give 2 significant findings that have comefrom ozone measurements taken over the past30 years.

c) Discuss briefly 2 potential consequences thatcould arise from a continuation of the trendsmentioned in part (b).

11. (8 marks)Draw structural formulas for, and givesystematic names of, four different isomers ofdichloropropane.

12. ( marks)a) Write a series of equations (including a netequation) to show how ozone is destroyed by achlorine free-radical.

b) Explain how the Cl• acts as a catalyst in thisprocess.

23



Worksheet 9 Test Questions section 4 Student Name...............................

Cl

H

Cl

C

F

H

H

C



Measuring Water QualityOne of the most fundamental requirements of anycommunity is to have a supply of healthy drinkingwater.

More than that, our communities expect that thewater will not only be safe, but will taste good, lookcrystal clear, will not clog pipes with mineraldeposits, will allow soap to lather-up readily, and willmake a really nice cup of tea!

To ensure that the water supply is of high qualityrequires constant monitoring and measurement ofsuch qualities as:

TurbidityThis is a measurement of “cloudiness” or lackof clarity. Turbidity is related to the presence ofsuspended solids.

Total Dissolved Solids (TDS)This measures the solids dissolved in the water.

Concentration of Common IonsWhile the TDS measures all dissolved solids, itis also possible to measure particular commonions. For example, measuring chloride ion (Cl- )is a simple way to assess the level of salt (NaCl)present.

Hardness“Hard” water has significant amounts of Ca2+ andMg2+ ions dissolved. These cause mineral deposits tobuild up inside water pipes (eventually blocking themand requiring expensive replacement) and alsointerfer with the lathering of soap.

AcidityPure water has a pH = 7, but normal goodquality drinking water is often slightly belowthat (e.g. pH = 6.5) due to the natural dissolvingof CO2. Polluted water can have values morethan 2 pH units either above or below neutrality.

Dissolved Oxygen & Biological Oxygen Demand (BOD)This measurement is the most importantmeasurement for assessing safety of the waterfor drinking. Low oxygen levels mean the wateris “stagnant”. This might be safe to drink, butusually tastes unpleasant, so is not acceptable.

BOD measures whether the dissolved oxygenchanges over time in a sealed container. If it does,this is a strong indication of living things presentand growing, in the water. This is very dangerousto the community since the micro-organisms couldbe disease-causing pathogens.

24


5. MONITORING & MANAGING WATER SUPPLIES

Practical Work: Qualitative & Quantitative Water TestsYou may have carried out a series of analyses onwater samples, to experience making some of theassessments described above. Typically, you mighthave tested

• your local tap water ) for• samples of sea water ) comparison• samples from a creek or bore )

Total Dissolved SolidsTraditionally, this ismeasured by evaporating awater sample in a pre-weighed evaporating dish,and weighing the residue.You may have done thiswith a sea water sample andmeasured about 30 gramsof salt per litre.

However, tap water has solittle TDS (< 0.1g/L) that it isdifficult to measure byevaporation.

Another way is shown. Thisprobe actually measureselectrical conductivity, butthis relates to TDS becausethe dissolved solids areusually ionic, and increasethe conductivity of thewater.

Turbidity This is usually measured by thedepth of water required before ahighly visible mark becomesinvisible. You may have used adevice similar to the diagram. Asyou look down the tube at the crossdrawn on the bottom, water isslowly poured in at the top.

Dirty creek water will obscure thecross within a few centimetres.

With good quality tap water thecross may still be visible when thetube is nearly full.

The tube is marked with ameasuring scale, but the numbersdon’t relate to any chemicalmeasurement and really are forcomparison only.

Turbiditymeasuring tube

More Water Tests Next Page...



Qualitative & Quantitative Water Tests (continued)

Concentration of Common IonsThe same precipitation reactions learnt earliercan be used qualitatively to detect specificions. For example, if chloride ion is present,the addition of silver nitrate solution will cause:

Ag+(aq) + Cl-(aq) AgCl(s)

The solid silver chloride causes a visible“cloudiness” (turbidity).

Using a sample of sea water you could collectthe solid by filtration, and measure it bygravimetric analysis.

In tap water there is usually such a smallquantity that quantitative measurement byweighing a precipitate would be difficult, butyou might have done a “semi-quantitative”estimation as follows:

Silver chloride is not totally insoluble, so invery dilute solutions (like tap water) the“cloudiness” depends on concentration. If youhave dilute solutions of silver nitrate (0.01molL-1 and 0.0001 molL-1) and add one drop tocertain volumes of water samples, whether ornot a visible “cloudiness” appears gives anestimate of chloride ion concentration.

For example: Goes cloudy Not cloudy• 1 drop 0.01 molL-1 > 0.2 < 0.2

in 10 mL sample(values are mg/L of Cl- ion, approx.)

• 1 drop 0.0001 molL-1 > 200 < 200in 100 mL sample

25


Water HardnessTo measure Ca2+ and Mg2+ ions quantitatively

requires a complicated titration involving the reagent “EDTA”.

A simple, qualitative test is toplace shaved soap pieces in a

bottle with some water andshake vigorously.

“Hard” water (try sea water)will hardly foam at all, and mayform a “scum”on the surface.

“Soft” water will foam-up.

For comparison tests, be sure to keep theexperiment “fair” by using exactly the same

quantities of soap, water and shaking.

AcidityUse “pH paper”

(Universal indicator) and a colour comparison chart,

or use a pH meter.

It is vital that any glasswareused is perfectly clean and

preferably rinsed withwater from the source

about to be tested.

Dissolved O2 and BODData to

Computer

Water Sample

Data-llogger O22 probe,measures O22 concentrationby electronically measuringa REDOX reaction between

its silver and platinumelectrodes

Using the equipment shown, instantaneousreadings of dissolved oxygen levels can beobtained.

To measure BOD, 2 samples are needed.

• one is measured immediately, and valuerecorded.

• the other must be kept in a sealed container(with no air bubbles) in the dark (so algae cannotgrow) for 5 days, then measured again.

If the reading is lower than the original, it meansthat something has used up the oxygen in thewater sample.

This could indicate not only the presence of livemicrobes in the water, but also that there must beorganic matter for them to feed on...

This indicates polluted water!


26

Factors That Affect the Concentration of Ions in Water

All our water supplies originally fell as rain or snow.When this hit the ground it was virtually pure water,but by the time it reaches the river or lake it may havepicked up a variety of dissolved ions. Which ones,and at what concentration depends on factors suchas:

• Pathway. If the rainwater flows across the surface ofnatural bush and forest it will dissolve only smallamounts of ions such as Na+, Cl-, SO4

2-, etc.

If it flows into and through underground aquifers itmay dissolve much more material (higher TDS),including ions like Ca2+ and Fe3+. Ground water isoften very “hard”.

• Type of soil and rock the water flows through.

• pH of the water. Generally, the more acidic (lowerpH) the water, the more ions it will dissolve.

• Nature of human activities in the catchment.Water which drains from agricultural land maydissolve ions from farm fertilizers and animal dung,such as phosphate and nitrate ions.

Water flowing through a garbage dump could pick upions of heavy metals (e.g. lead, mercury from oldbatteries).

Human activities might actually discharge extra ionsinto the water catchment, such as phosphates andnitrates from sewerage treatment works, or heavymetal ions from factories, mines, and storage dumps.

Heavy Metal Pollution of WaterOf all the possible ions that might end up in our water,the heavy metals like lead and mercury are the mostdangerous to human health.

To detect and monitor these ions in water, gravimetricanalysis using precipitation reactions will not work,because these metals are dangerous at levels too lowto be detected and analysed gravimetrically.

A suitable method has already been discussed earlierin this topic... Atomic Absorption Spectroscopy (AAS)

Monitoring EutrophicationThe process of “Eutrophication” was describedbriefly earlier in this topic.

Nitrate and phosphate ion concentrations in watercan rise when water flows through farm land andpicks up fertilizers, or when treated sewerage isdischarged into waterways.

These ions act as fertilizers for water plants andalgae, leading to over-growth. This can clog streamswith water plants and produce “algal blooms” of toxicalgae. Later, as the mass of plant material dies, therotting process absorbs oxygen from the water (i.e.BOD becomes extreme) and aquatic animal life maysuffocate.

Quite apart from ecological damage, water fromstreams with eutrophication is quite unsuitable forhuman consumption, due to the high load ofmicrobes present.

Potential Eutrophication problems can be predictedby measuring the phosphate concentration of thewater. Once again, the simpleprecipitation/gravimetric tests learnt earlier are notsensitive enough.

Measuring Phosphate Ion by Photometry

One way to measure phosphate levels is to reacta water sample with the reagent ammoniummolybdate (NH4)2MoO4, then add ascorbic acid(vitamin C).

A reaction occurs with phosphate ions whichforms an intense blue-coloured solution.

The more phosphate present, the deeper theblue colour. This is measured by a photometer,a simple device which electronically measuresthe amount of light which passes through thesolution to a photoelectric cell detector.

Known concentration PO43- solutions are used

as “standards” and reacted and measured thesame way to produce a “calibration graph”. Theconcentration of the “unknown” sample is readfrom the graph according to how much lightpasses through it.



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27

Purifying and Sanitising Water Supplies

The best way to survive a car accident is to drivecarefully so as not to have one, and the best wayto purify and sanitise water supplies is to collectgood clean water to start with.

All water supply authorities will attempt to dothis, but in practice the water in the mainreservoirs is not good enough to simply pumpout to peoples’ homes. It is usually needspurifying and sanitising by:

Flocculation of Suspended SolidsThis achieved by adding Fe3+ ions which reactwith water forming highly insoluble iron(III)hydroxide, Fe(OH)3. The fine particles of Fe(OH)3tend to join together and to adsorb particles ofother fine suspended materials. This joiningtogether is called “flocculation” and results inthe suspended solids being in larger particleswhich either settle out, or can be filtered out,more quickly and efficiently.

FiltrationMany water supplies are filtered through beds ofsand and carbon granules. This traps most ofthe flocculated solids, and the carbon tends toadsorb any organic chemical which can causeunpleasant odours and tastes.

ChlorinationAfter flocculation and filtration, the water isusually quite clean and clear, but may still carrysmall numbers of dangerous microbes.

To kill these, the usual practice is to addchlorine (Cl2) to a concentration of about 2 ppm,which is sufficient to sanitise it. Lower levelsmight not kill all the microbes, and higher levelshave a noticeable “chlorine taste”.

Effectiveness of TreatmentsOur water supply systems deal in millions of litres ofwater per day and there is always a compromisebetween meeting the needs of the community, andmeeting quality and safety standards, and keepingthe cost to a minimum.

Generally, the processes of filtration and sanitationseem to work effectively. In NSW, the number ofhealth problems resulting from sub-standard water iszero in most years. Compared to the amount of illnessand death occurring in parts of Africa where peopleare forced to use untreated water, we would have toconclude that our systems are very effective.

However, they are not infallible. In 1998 there was anoutbreak of disease in the Sydney area, caused by apathogen which survived the treatment processes.The actual number of cases was very low, but thepublic alarm (and media panic) was such to convincethe authorities to do a better job.

Microscopic Membrane FiltersUsing plastics such as polypropylene, it ispossible to make filters with extremely smallpores in the material, as small as about 0.1µµm.(1 µµm = 1/1000 mm)

This is so fine that virtually all suspendedparticles (including living microbe cells andmany viruses) can be filtered out of the water.

The usual system is to make the filtermembranes into very fine, hollow “capillarytubes” (only 0.2 mm diameter). Although each istiny, a bundle of thousands of them has a largesurface area, and the strength of the polymermeans that the water can be filtered under highpressure to speed up the throughput.

Generally, the “dirty” water is forced through thematerial from the outside, and a flow of cleanwater collected from the inside of the capillarytubes.

Membrane filters are very expensive comparedto the existing sand filters, but very effective. InSingapore, a country with very limited watersupplies, treated sewerage water is beingfiltered by microscopic membrane filters soeffectively that it can be returned to the generalwater supply for re-use. In Australia, membranefilters are used mainly for filtering high qualitybottled mineral waters.



““Dirt

y” w

aater

u

nder

pre

ssur

e, oo

n oou

tsid

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mem

bbraan

e

ccaap

illaar

y

tubb

e

FFiinnee ppaarrttiicclleess ttrraappppeedd oonnoouuttssiiddee ooff mmeemmbbrraannee

Clean water flowsdown inside of tube

Fine pores inmembrane material

Cut-aaway view ofone membranecapillary tube

To monitor and ensure the quality ofwater supplies, a number ofmeasurements and tests are useful:

• Turbidity is a measure ofa)...................................... This is relatedto the presence of b)................................solids in the water. This is oftenmeasured by pouring water into a talltube and observing c)...........................................................................................

• TDS stands for d).................................................. It can be measuredby evaporating a sample ande)................ ..........................................Electronic probes which measuref).............................................. can also beused for quick and accurate readings.

• “Hardness” is caused by dissolvedg)............ and .............. ions. Hard watercauses h)...................................................in water pipes and prevents soap fromi)................................. This can be usedas a qualitative test. Hardness can beassessed by the amount ofj)................................ formed when somesoap and water samples are shaken.

• Acidity can be measured byk)........................ or ....................................Unpolluted water should have a pHabout l)................ Polluted water mayhave values m)................. or more pHunits above or below this.

• BOD stands for n)................................................ This measures thechange in o).................................... whena sample is stored for 5 days. A largechange indicates that p).......................................................................... and thismeans the water probably containsq)....................... ................................

A number of factors influence which ions, andwhat concentrations, are dissolved in water.

• The Pathway. If water flows across naturalbushland it will r)........................................................ If it flows underground,it may dissolve s)........................................................ and reach higher t)....................readings.

• The type of u)................. and ................. thewater flows over or through.

• The v)............... of the water. If water is morew)................................... it will generally dissolvemuch more material.

• Human activities. If water flows throughfarmland it may dissolve a lot ofx)........................... and ......................... ions fromy)............................................. Water seepingthrough a garbage dump could dissolvez)................ metals, such as aa)................... and...............................

A method suitable to detect and measure evensmall quantities of heavy metals is AAS whichstands forab)..............................................................

“ac)..............................................” refers to whathappens to waterways if too much phosphateand nitrate get into them. These ions acts aad).................................... causing plants andalgae to ae).................... ....................................and clog waterways. Then, when masses ofplants die, the rotting process causesaf)...........................................................

Generally, every water supply system treats thewater to purify and ag)............................... it. Thefirst step is often to“ah).............................................” suspendedsolids. This means to make them “clumptogether” into larger particles. These are thenremoved by ai).......................... the waterthrough beds of aj)..................... and ....................Any remaining microbes are killed by treatingthe water with ak)......................................

An alternative treatment is toal)................................ the water throughMicroscopic am)....................................................... which can remove suspended solidsand virtually all microbes.

28



WHEN COMPLETED, WORKSHEETSBECOME SECTION SUMMARIES

Worksheet 10 Monitoring & Managing Water SuppliesFill in the blank spaces Student Name..........................................

Multiple Choice1.Water that is suitable for human consumptionshould have:A. very low BOD and turbidity.B. high dissolved oxygen and high BOD.C. low pH and high dissolved oxygen.D. high turbidity and high pH.

2.A simple test for water “hardness” is to:A. taste it.B. add silver ions, and look for a precipitate.C. measure the pH.D. see if soap will lather in it.

3.The addition of chlorine to water supplies is to:A. prevent tooth decay.B. flocculate suspended particles.C. test for the presence of silver ions.D. sanitize the water.


4. (8 marks)a) Describe in outline, how a BOD water test iscarried out.

b) State the expected results you might obtainon a i) sample of pure, healthy drinking water.

ii) water from a lake suffering “eutrophication”.

c) Explain what is meant by “eutrophication”,including mention of the usual chemical causeand its source(s).

5. (4 marks)Our water supplies may have certain chemicalsubstances added to them. Explain thereason(s) for adding:a) iron(III) chloride.

b) chlorine.

29



Worksheet 11 Test Questions section 5 Student Name...............................

ABN 54 406 994 557

PO Box 2575PORT MACQUARIE NSW 2444

(02) 6583 4333 FAX (02) 6583 9467www.keepitsimplescience.com.au [email protected]

kkeeeepp iitt ssiimmppllee sscciieennccee

Need to contact us?

®


30



CONCEPT DIAGRAM (“Mind Map”) OF TOPICSome students find that memorising the OUTLINE of a topic

helps them learn and remember the concepts and important facts. Practise on this blank version.

CHEMICALMONITORING & MANAGEMENT


31

Answer SectionWorksheet 11. pharmaceutical, food, metallurgy, fuels, plastics,environmental, criminal investigation... (more)

2. Carrying out analyses using Gas Chromatographyand Mass Spectrometry.Reporting analysis results to clients.Giving evidence as an “expert witness” in legalcases.

3. Different molecules in a vaporized sample areseparated by adsorption as they flow through achromatography tube. Different molecules travelthrough at different rates and are detected separatelyas they emerge.

4. To compare and discuss analysis results.To arrange for the use of equipment, schedules, etc.To keep up with new developments by attendingconferences and seminars.

5. a) In a combustion, the amount of oxygen can affectwhether the product is CO2, CO or soot.b) Incomplete combustion is inefficient anduneconomical, so it is necessary to monitor fuel/airmixtures, temperature and exhaust gases.

Worksheet 2a) fertilizers b) nitricc) explosives, pigments, fibres/plasticsd) saltpetre (sodium nitrate)e) Chile f) Haberg) hydrogen & nitrogen h) explosives & fertilizersi) slow j) leftk) reactants l) higherm) left n) exothermico) Haber p) rateq) equilibrium r) hydrogens) nitrogen t) 300u) right v) 400w) reaction rate x) equilibriumy) iron z) activation energyaa) lower ab) condenserac) liquifiedad) pumped back into the reaction chamber.ae) temperature & pressureaf) carbon monoxide and sulfur compoundsag) poison

Worksheet 3a) detect/identifyb) measure quantity or concentrationc) eutrophication d) excessive plantgrowthe) removes the oxygen f) sewerage & fertilizersg) accumulate h) permanent brain damagei) leaded petrol j) precipitationk) flame l) chloridem) lead n) sulfateo) barium or calcium p) flame testq) hydroxide r) copper s) iron(III) ion t) iron(II)u) acid v) bubbles of CO2w) barium ion x) thick, white precipitatey) silver z) chloride ionsaa) iron(II) ab) phosphateac) lime-green ad) brick-red

ae) blueaf) Atomic Absorption Spectroscopyag) light ah) frequencies/spectrumai) frequencies aj) absorptionak) trace al) cobaltam) lead

Worksheet 4Identifying Ionsa) chloride b) calcium c) iron(II) d) carbonatee) phosphate f) copper

Worksheet 5Quantitative Analysis1.Fertilizer A: moles of BaSO4: n = m/MM MM= 233.4g

= 3.27/233.4= 0.0140 mol

∴∴ moles of sulfate = 0.0140 mol (ratio 1:1)mass of sulfate: m = n x MM MM(SO4)= 96.1g

= 0.0140 x 96.1= 1.35 g


Fertilizer B:moles of BaSO4: n = m/MM MM= 233.4g

= 2.66/233.4= 0.01140 mol

∴∴ moles of sulfate = 0.01140 mol (ratio 1:1)mass of sulfate: m = n x MM MM(SO4)= 96.1g

= 0.01140 x 96.1= 1.10 g


2.a) Ag+

(aq) + Cl-(aq) AgCl(s)

b)moles of AgCl: n = m/MM MM= 143.3g= 3.42/143.3= 0.02387 mol

∴∴ moles of chloride = 0.02387 mol (ratio 1:1)mass of chloride: m = n x MM MM(Cl-)= 35.45g

= 0.02387 x 35.45= 0.846 g

∴∴ % chloride in sample = 0.846 x 100 = 1.69%50.0

Worksheet 61. D 2. B 3. C 4. B 5. A

6.A Toxicologist employed to carry out screening testsfor drug residues would need to compare and discussanalysis results done by others, to confirm the finalconclusions. He/she needs to collaborate on sharingequipment, scheduling and deadlines. To keep upwith new developments there is a need to attendconferences and seminars and share and discusswith other scientists.




32

Worksheet 6 (cont)7.a) N2(g) + 3H2(g) 2NH3(g)

The reactants are mixed 3:1 (by volume) because thisis the mole ratio in which they react, so this is themost efficient mixture.b) High pressure shifts the equilibrium to the right,increasing the yield of ammonia.c) Catalyst is iron. (usually iron ore, with the surfacereduced to elemental iron)Catalyst speeds up the rate of reaction by loweringthe activation energy.d) Higher temperatures speed up reaction rate, butreduces the yield of ammonia, because the reaction isexothermic (equilibrium shifts left at higher temps).400oC is a compromise giving reasonable rate andreasonable yield.

8.a) A qualitative test can detect and identify a chemicalspecies, but does not measure the amount orconcentration.b)

i) no barium or calcium ions present.ii) iron(II) ions present.

iii) no sulfate ions present.iv) chloride ion is present.

9. a) (NH4)2SO4(aq)+ BaCl2(aq) BaSO4(s)+ 2NH4Cl(aq)

b) moles of BaSO4: n = m/MM MM= 233.4g= 9.15/233.4= 0.03920 mol

∴∴ moles of (NH4)2SO4 = 0.03920 mol (ratio 1:1)mass of (NH4)2SO4: m = n x MM MM = 132.1g

= 0.03920 x 132.1= 5.178 g


c) The precipitate of barium sulfate is very fine-grained and often passes through a normal filterpaper. It is better to use a sintered glass crucible filter,and use vacuum filtration.

Worksheet 7a) Troposphere b) Stratospherec) nitrogen, oxygen, argond) 99.9%e) carbon monoxide f) fuel impurities/smeltingg) engines & power stations h) smogi) lung damage & breathing difficultiesj) U.V. radiation k) coordinatel) come from same atom m) polyatomicn) allotropes o) chemicalp) chemically reactive q) unstabler) 100 s) oxygent) oxygen free-radicals u) ozonev) Dobson Spectrophotometerw) U.V. radiation x) 10%y) hole in the ozone layerz) Antarctica

aa) sunburn, eye damage & increased skin cancersab) crop failure/food shortagesac) alkanead) fluorine, chlorine,bromine, iodineae) halogens af) chlorofluorocarbonsag) refrigeration, aerosol propellant, foam plasticsah) chlorine ai) catalystaj) oxygenak) hydrofluorocarbons (HFC)al) 50-100

Worksheet 81. Coordinate Covalent Bondinga) CO3

2-

carbonate ion

b) NO3-

nitrate ion

c) H3O+

hydronium ion

2. Naming Haloalkanesa) bromochloromethaneb) 3,4-dichloro-1,1,2-trifluorobutanec) bromochlorofluoroiodomethaned) 1,1-dibromo-3,3-dichloropropane

3. Isomers

1,1,1-trichloropropane 1,1,3-trichloropropane

1,2,3-trichloropropane

(several others)

1-bromo-1-chlorobutane 1-bromo-2-chlorobutane

1-bromo-3-chlorobutane 2-bromo-3-chlorobutane (lots more)



O

O

CO

22 eexxttrraa iioonniicc cchhaarrggeeeelleeccttrroonnss

2-

O

O

NO

Cl Cl Cl

HH

H

H

C C C H

Cl H Cl

HH

Cl

H

C C C H

Cl H H

HH

Cl

Cl

C C C Ha)

b) Cl H H

HH

Br

H

C C CH

HC H

H H Cl

HH

Br

H

C C CH

HC H

H Cl H

HH

Br

H

C C CH

HC H

H Br Cl

HH

H

H

C C CH

HC H


33

Worksheet 91. A 2. C 3. D 4. C 5. A 6. C 7. B8.Ozone at ground level is a serious pollutant, createdin photochemical ‘smog”. It can cause lung damageand breathing difficulties at concentrations as low as2 ppm. In the Stratosphere, ozone is greatly beneficial,because it absorbs certain frequencies of U.V. andacts as a shield against dangerous radiation from theSun.

9.a) This is when the 2 electrons being shared bothcome from the same atom.b)

c) The O2 molecule is stable, and moderatelychemically active. For example, is involved incombustion reactions.Ozone is very unstable, and readily decomposes. It isalso much more reactive than O2, and will rapidlyattack many substances. (That’s why it’s dangerousto living things, and can be used as a germ killer andbleach.)

The reason for this difference is that it takes about500kJ/mol of energy to break the O2 bond, but onlyabout 100kJ/mol to break a bond in O3. This meansthe activation energy for any ozone reaction is verylow, so it reacts readily.

10.a) Automatic chemical analysis devices can be sentup in balloons to sample and measure ozoneconcentrations.The “Dobson Spectrophotometer” is a ground-baseddevice which measures U.V. penetration through theatmosphere. By comparing readings for frequenciesthat ozone does not absorb, with those it doesabsorb, it can measure the total ozone content of thecolumn of air above that point.b) 1. Average ozone concentrations have declined byabout 10% globally since the 1970’s.2. Each spring over Antarctica, a huge “hole”develops in the ozone layer.

c) Continued depletion of ozone could result in asignificant increase in the U.V. radiation reaching thesurface. This would cause extra sunburning, eyedamage and skin cancers. It could also interfer withcrop growth, possibly leading to food shortages.

11.

1,1-dichloropropane 1,2-dichloropropane

11. (cont)

1,3-dichloropropane 2,2-dichloropropane12.

Cl• + O3 ClO• + O2ClO• + O• O2 + Cl•

net equation: shows ozone is converted to oxygen.O3 + O• 2 O2

The 2nd equation shows that the chlorine free-radicalis regenerated, so it can begin the process again.Since it is involved in the reactions, but not beingused up by them, it is acting as a catalyst.

Worksheet 10a) cloudiness/lack of clarity b) suspended c) the depth required to obscure a mark on the bottomd) total dissolved solids e) weighing the residuef) electrical conductivity g) Ca & Mgh) mineral deposits i) latheringj) foam/suds k) indicators or pH meterl) 6.5 m) 2n) Biological Oxygen Demando) dissolved oxygen p) something is using the O2q) organic matter/microbes r) dissolve only a few ionss) different ions t) higheru) rock and soil v) pHw) acidic x) phosphate and nitratey) fertilizers z) heavyaa) lead & mercuryab) Atomic Absorption Spectroscopyac) Eutrophication ad) fertilizer ae) over-growaf) oxygen depletion / animal suffocationag) sanitize ah) flocculateai) filtering aj) sand & carbonak) chlorine al) filteram) membrane filters

Worksheet 111. A 2. D 3. D25. a) BOD involves taking 2 water samples andtesting one immediately for dissolved oxygen levels.The other sample is kept for 5 days (in dark, nocontact with air) then its dissolved oxygen ismeasured.b) i) There should be no change in dissolved O2. ii) The dissolved O2 reading will drop significantlyfrom first measurement, and the 5-days-later sample.c) Eutrophication is caused by extra phosphate andnitrate ions getting into a stream. This fertilizes thewater plants and algae, leading to over-growth and“algal blooms”. When the algae dies, the rottingvegetation takes all the oxygen from the water, soaquatic animal life suffocates.The sources of the phosphate and nitrate is usuallyfrom farm fertilizers or discharge of treated sewerage.26.a) The iron(III) ions react with water forming highlyinsoluble iron(III) hydroxide. This precipitate causesother suspended solids to “flocculate” or clumptogether in larger particles. These are more efficientlyremoved by sedimentation or filtration.b) Chlorine is added to sanitise the water by killingany “germs”.



O O

CoordinateCovalent Bond

O O O OO2 molecule

O3 moleculeOOxxyyggeenn ffrreeee-rraaddiiccaall

+

Cl H H

HH

Cl

H

C C C HH Cl H

HH

Cl

H

C C C H

H H H

HH

Cl

H

C C C Cl

H Cl H

HCl

H

H

C C C H

keep it simple science Photocopy Master Sheets

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