2009_chemistry_notes

5/24/2018 2009_Chemistry_Notes

1/14

Chemical Monitoring and Management

Identify the need for collaboration between chemists as they collect and

analyse data

Collaboration The sharing of ideas or methodology.

Chemists often work in teams and since each of them specialise in a particular area of

chemistry, they need to collaborate in order to provide maximum benefits for their

organiation. The benefits include!

" #ider range of in"depth knowledge is available.

" Increases accuracy and validity of data results, as the chemists verify and collaborate

with each other.

" More efficient productivity and less environmental problems.

$escribe an example of a chemical reaction such as combustion, where

reactants form different products under different conditions and thus would

need monitoring

" Combustion reactions have a number of states, depending on the amount of oxygen

provided in the reaction.

" The combustion of petrol %primarily octane& in a car's internal combustion engine is

a reaction where different products are formed in different conditions.

" If there is an excess of oxygen in the reaction, complete combustion occurs

producing carbon dioxide and water only.

2 C8H18+ 25 O218 H2O + 16 CO2

" If there is an insufficient supply of oxygen in the reaction, incomplete combustion

occurs, producing carbon monoxide and carbon soot.

2C8H18(l)+ 8O2(g) 7CO (g)+ 9C(s)+ 9H2O(l)

" Carbon monoxide is a poisonous gas and carbon soot is a ma(or contributor to

pollution, and thus the combustion of octane in petrol needs to be monitored, in order

to reduce the occurrence of incomplete combustion.

Identify and describe the industrial uses of ammonia

)mmonia is vastly produced worldwide, because it has a number of uses, such as!

" *roduction of fertilisers %sulfate of ammonia, ammonium nitrate, urea&

" *roduction of fibres and plastics %rayon, acrylics, nylon&


2/14

" *roduction of nitric acid, which in turn is used to make fertiliser %ammonium

nitrate&, dyes, fibres, plastics and explosives such as ammonium nitrate, T+T and

nitroglycerine %in dynamites&.

" ousehold cleaners

" $etergents %non"ionic ones&

Identify that ammonia can be synthesised from its component gases, nitrogen

and hydrogen

" In -/0, the 1erman, 2rit aber developed a method of synthesising ammonia

from its elements.

" In --3, Carl 4osch successfully converted it into an industrial process.

" 5nder pressure and heat, ammonia can be synthesised from its components,

hydrogen and ammonia.

N2 (g) + 3H2 (g) 2NH3(g) + 92 kJ mol-1

$escribe that synthesis of ammonia occurs as a reversible reaction that will

reach e6uilibrium

" The synthesis of ammonia occurs as a reversible reaction, meaning that reactions

occur spontaneously in both directions. The forward reaction produces ammonia from

nitrogen and 7 hydrogen. The reverse reaction produces hydrogen and nitrogen fromammonia.

" )n e6uilibrium is reached when the rate of forward reaction is the same as the rate

of the reverse reaction.

" )t ordinary pressures and temperatures, the e6uilibrium lies well to the left.

Identify the reaction of hydrogen with nitrogen as exothermic

The forward reaction of hydrogen and nitrogen is exothermic as 8 k9 mol "- of heat is

released in the reaction.

:xplain why the rate of reaction is increased by higher temperatures

" igher temperatures increase the kinetic energy of molecules, which allows them to

move faster, thus increasing the fre6uency of the collisions. Thus the rate of reaction

is increased.

" Most of the increased rate of reaction comes from more of the colliding particles

exceeding the activation energy needed for the reaction to occur.


3/14

:xplain why the yield of product in the aber process is reduced at higher

temperatures using ;e Chatelier's principle

" If the temperature is lowered the e6uilibrium will move in the direction, which tendsto increase temperature %release heat&.

" )ccording to ;e Chatlier's principle, increasing the temperature will cause the

e6uilibrium to shift to the left since the reaction is exothermic< to counteract the

change, and thus the yield of ammonia is reduced, as it decomposes.

:xplain why the aber process is based on a delicate balancing act involving

reaction energy, reaction rate and e6uilibrium

" ;owering the reaction temperature will cause the e6uilibrium to shift to the right,increasing the yield of ammonia. The flaw is that, the reaction will take a very long

time to react.

" Increasing the reaction temperature will cause the e6uilibrium to shift to the left, but

increasing the rate of reaction, as more energy is available to exceed the activation

energy. The flaw involved is the decrease in the yield of ammonia.

" The need for a compromise is evident and the following conditions are used!

-. Temperature of about 3// oC

8. Total pressure of 8=/ atmospheres>. 5se of a catalyst to increase reaction rate

:xplain that the use of a catalyst will lower the reaction temperature re6uired

and identify the catalyst used in the aber process

" The catalyst lowers the activation energy barrier by providing an alternate, lower

activation path. This means that more molecules will be able to react, so the

temperature re6uired is lower.

" The catalyst used in the aber process is a porous structure of 2e?2e >@3. It is used

because it has a large surface area, which increases the amount of gas able to adsorb

onto the surface.

Catalysed reaction has a

lower :)


4/14

)nalyse the impact of increased pressure on the system involved in the aber

process

" )ccording to ;e Chatlier's principle, an increase in the pressure of the system will

result in the e6uilibrium moving in the direction, which tends to reduce pressure. That

is the direction, which corresponds to a decrease in moles of gas.

" Thus in the aber process, the reaction moves to the right if the pressure is

increased.

4 moles2 moles

" igh pressures increase the reaction rate because more effective collisions occur, as

the particles are closer together.

" igh gas pressures increase yield as the e6uilibrium shifts to the right to counteractpressure increases.

:xplain why monitoring of the reaction vessel used in the aber process is

crucial and discuss the monitoring re6uired

4ecause many different conditions must be maintained for efficient and safe operation

of the aber process, monitoring is essential. The following need to be monitored!

" Temperature and pressure must be monitored to keep them in the range for optimum

conversion of reactants to products. :xcessive temperatures can damage catalysts.

" The incoming gas stream of hydrogen and nitrogen need to be kept at a ratio of >!-.

" That oxygen is not present.

" Catalyst effectiveness

" The build up of unreactive gases need to be removed.

1ather and process information from secondary sources to describe the

conditions under which aber developed the industrial synthesis of ammonia,

and evaluate it's significance at that time

" The aber process, the reaction of nitrogen and hydrogen to produce ammonia, was

first developed by the 1erman, 2rit aber in -/ in 1ermany.

" )t the start of the 8/thcentury, nitrates were high in demand for both agricultural

fertilisers and for nitric acid, used to produce explosives. owever the only source of

nitrates was from natural deposits, such as those available in Chile.

" It was a time of war, with the blockade of nitrates to 1ermany< it was high in

demand as it was essential for the production of fertilisers and explosives. To satisfy


5/14

this demand, 2rit aber developed the method of synthesising ammonia in the

laboratory.

" In his book of thermodynamics of technical gas reactions, aber recorded the

production of small amounts of ammonia from hydrogen and nitrogen gas at

temperatures of about -/// oC with the help of iron as a catalyst. 5pon attemptinglarge"scale synthesis, aber developed the process of circulating nitrogen and

hydrogen over the catalyst at a pressure of -=/"8// atmospheres at a temperature of

about =// oC.

" The aber process provided a solution to the shortage of fixed nitrogen not only to

1ermany, but the rest of the world. $uring the ##- period, 1ermany was in

desperate need of ammonia in nitrogenous fertilisers to supply food during the war

period. Anowing this, the 4ritish +avy prevented the import of nitrogen compounds

into 1ermany.

" +itrogen compounds were also re6uired by 1ermany during the war. $uring thewar, the ammonia produced was oxidised for the production of nitric acid in the

@swald process, and the nitric acid was used for the production of various explosive

nitro compounds used in munitions.

" There were also many disadvantages of the aber process. @ne significant

conse6uence is that it prolonged the war, which meant that more lives were lost.

)nother problem was the effect that the nitrogenous compounds had on the water in

run"off. The nitrate atoms and nitrate ions became overabundant and can make the

water toxic to children. The algae can multiply, causing low"lying algae to die, thus

causing oxygen to be used up leading to the death of fish and other marine creatures.

" In terms of economics, the aber process established industries and provided

employment during the start of the twentieth century. The aber process also resulted

in political (ealousy, as the 1ermans were advantaged throughout the war.

$educe the ions present in a sample from the results of tests

Metallic Ion Flame Colour

Ba2+ Apple-green

Ca2+

Brick redCu2+ Green

$escribe the use of the atomic absorption spectroscopy %))B& in detecting

concentrations of metal ions in solutions and assess its impact on scientific

understanding of the effects of trace elements

" )tomic )bsorption Bpectroscopy detects minute concentrations of elements in a

sample solution. :ach element has it's own characteristic absorption spectrum that is

related to its electron energy levels. ))B is measured in parts per million %***&.


6/14

" If atoms of an element are irradiated with light of a wavelength, which is known to

be absorbed by those atoms, and then the fraction of light, which is absorbed,

measured, then the concentration of can be calculated.

" This is how ))B works. The sample to be tested is fed into a flame, which

vapories it and converts molecules and ions into atoms. ) lamp emitting a specific

wavelength for each different element passes light through a flame onto a prism and a

photo multiplier detects how much light has been absorbed. Measurements are very

accurate and measures concentration in ppm in small samples.

" Trace elements are elements that are re6uired in very small amounts by living

organisms. ))B has allowed the measurement of many trace elements in plants andanimals and has allowed scientists to work out how these trace elements helped the

functioning of organisms %previously undetectable&. 4ecause of ))B, trace elements

in organisms can be monitored i.e. deficiencies in soil of Mn, Cu, 4, Mo, and n may

lead to ill health.

$escribe the composition and layered structure of the atmosphere

The atmosphere is a layer of gas, which surrounds the earth. It consists of four parts!

" Troposphere! ;ies about -= km above sea level. The temperature falls as you climb,

reaching 8= oC at the top. Contains D=E of earth's gases by mass. It is where all the

whether takes place. Common particles include< +8, @8, 8@ and )r.

" Btratosphere! lies from -= km to =/ km above mean sea level. The temperature rises

with altitude to 8=FC at the top. *ressure is much lower due to greater spacing

between particles. ) thin oone layer is found in the top of this layer, which absorbs

harmful 5.G radiation from the sun. +8, @8 and oone are found in this region.

" The Mesosphere and Thermosphere form a combined region called the Ionosphere.

These regions extend from =/ km to 0= km for the Mesosphere and over 0= km for

the thermosphere. The temperature ranges from 8= oC to -//oC for the mesosphere

and -// oC to 8= oC for the thermosphere. The spacing between molecules is

greater. 1as species include ions %eg. @8H, +oH&.


7/14

Identify the main pollutants found in the lower atmosphere and their sources

Pollutat !ou"#e

Carbon monoxide Cars, incomplete combustion, cigarettes,

bushfires, slow combustion stoves

@xides of nitrogen %+@, +@8& Cars, power plants, high temperature

furnacesGolatile organic compounds Bolvents and unburnt fuels

ydrocarbons Gehicles and factories using solvents

%petrol and fuels, mainly octane&

)irborne *b ;eaded fuel and old house paint

*articulates Incomplete combustion, earthmoving and

agricultural dust

@one *hotochemical smog formed when

sunlight acts on car exhaust gases

containing +@8

$escribe oone as a molecule able to act both as an upper atmosphere 5.Gradiation shield and a lower atmosphere pollutant

" In the upper atmosphere, the @one acts as a 5G radiation shield for the plant,

preventing 5G rays from reaching the surface, where it is possible for them to cause

cancer and sunburn in animals and humans.

" @one is considered a pollutant in the lower atmosphere, produced in photochemical

smog from nitrogen oxides and volatile compounds such as xylene.

NO2 + !ul$g%t & NO + O

O + O2 & O3

@one is produced naturally in the stratosphere.

O2(g) + '& 2O(g)

O2 (g) + O(g) & O3

It can cause breathing difficulties such as asthma, and can, after prolonged exposure,

cause scarring of the lungs.

$escribe the formation of a co"ordinate covalent bond

" ) coordinate covalent bond forms when one atom in a species %a molecule or ion

containing non"metallic atoms& provides both electrons in the covalent bond.

" @nce formed this coordinate bond is indistinguishable from other covalent bonds.

$emonstrate the formation of coordinate covalent bonds using ;ewis electrondot structures


8/14

Compare the properties of the oxygen allotropes @8 and @> and account for

them on the basis of molecular structure and bonding

P"oe"t* O*ge O,oe

Symbol

@8 @>

Melting point "8- "-0>

Boiling point "-> "---

Odour @dourless Bharp irritating electric

odour

Colour Colourless *ale blue

Liquid density -.-= -.-

Stability Btable 5nstable dissociatesreadily to form @8

Reactivity ighly reactive %oxidising

agent& with many metals

and non"metals %MgH, BH&

Gery reactive %oxidising

agent will oxidise all

common metals except )u

and *t. )ttack double

bonds in alkenes and

deteriorates textiles and

rubber&.

Uses "Bustaining life

%respiration&

" In hospitals for patient

breathing problems.

" Combustion of fuels for

energy

" Industrial manufacture of

8B@3

" Bterilisation of water

supplies and swimming

pools kills bacteria andviruses.

" Bterilisation of stagnant

air in slaughter rooms.


9/14

Test

1lowing splint Characteristic odour, IJ

spectroscopy

" @>has a higher boiling and melting point than @8because it has a higher molecular

mass.

" @>is less stable than @8because of the reactivity of the coordinate covalent bond in

@>.

Compare the properties of the gaseous forms of oxygen and the oxygen free

radical

Free radicals atoms?molecules that have at least one unpaired electron.

" #hen an oxygen molecule is split into two oxygen atoms by high energy 5G, the

oxygen atoms produced have additional energy and two unpaired electrons.

" The energy absorbed in the splitting and the unpaired electrons make the free radical veryreactive.

" @8is moderately reactive but the oxygen free radical, like oone is highly reactive.

Identify the origins of Chlorofluorocarbons %C2C's& and halons in the

atmosphere

" C2C's are artificial compounds, containing only chlorine, fluorine and carbon.

" alons are synthetic compounds containing only bromine, chlorine, fluorine and

carbon.

" C2C's do not occur naturally, their emission into the atmosphere is entirely the

result of human activity. C2C's were originally developed as a non"toxic, unreactive,

alternative to refrigerant in ammonia. They were released into the atmosphere from its

use in propellants in spray cans, as solvents for cleaning, electronic solvents and from

leakages from its use as a coolant in air conditioners and refrigerants.

" 2or example, trichlorofluoromethane %C2C"--& was used in making plastic

insulators, whilst dichlorofluoromethane %C2C"-8& was used as a working fluid in

refrigeration and air conditioning. )s C2C products were used, gaseous C2C's were

released into the atmosphere.


10/14

" Bince C2C's are inert, they do not react in the troposphere, instead they gradually

make their way into the stratosphere.

" alons are released into the atmosphere from use in fire extinguishing systems. 2or

example, bromofluoromethane was used in fire extinguishers.

Identify and name examples of isomers %excluding geometrical and optical& of

halogens up to eight carbon atoms

*resent information from secondary sources to write the e6uations to show the

reactions involving C2C's and oone to demonstrate the removal of oone

from the atmosphere

@one is formed and destroyed by 5G lights this is how oone absorbs 5G light. It

is formed though this series of reactions!

O2(g) + ' l$g%t2O(g)

O(g) + O2(g)O3(g)

It then absorbs 5G light during its destruction, as shown below!

O3(g) + ' l$g%tO2(g) + O(g)

2O(g)O2(g

C2Cs produce the ClK free radical when they are hit by a 5G light photon. 2or

instance, C2C"-- decays like!

CCl3.(g) + ' l$g%tC.3(g) + Cl(g)


11/14

These ClK radicals then destroy @> molecules in a cycle, where the radical is not

actually consumed.

Cl(g) + O3(g)ClO(g) + O2(g)

ClO(g) + O(g)Cl(g) + O2(g)

$iscuss the problems associated with the use of C2C's and assess the

effectiveness of steps taken to alleviate these problems

" There are many problems associated with the use of C2C's including, oone

depletion, increased penetration of 5G radiation and an enhanced greenhouse effect.

" Mario Molina, Bherwood Jowland and *aul Cruten, showed that chemically inertC2C's could be transported to the stratosphere where they cold photo dissociate to

produce reactive free radicals that would destroy oone.

" ) chain reaction occurs and thousands of oone molecules can be destroyed by one

chlorine atom, significantly decreasing oone concentration. 2urthermore, C2C's are

not easily removed from the atmosphere as they are insoluble in water, and will thus

not be washed out through the rain.

" @n an annual global basis, C2C's have caused > to 0E decrease in the amount of

oone in the stratosphere and a more dramatic =/E to /E decrease in oone levels

over the )ntarctic during spring.

" )s a conse6uence of C2C's depleting the atmosphere, the amount of 5G radiation

reaching earth has increased. This increases the chances of cancer in living organisms

as 5G radiation has sufficient energy to break bonds and thus alter the molecular

structure in biological molecules such as proteins and $+), which may lead to

cancer. It can also cause an increased brittleness of plastics.

" The use of C2C's has also led to an enhanced greenhouse effect. In the stratosphere,

C2C's absorb heat rays emitted from the earths surface, instead of allowing them to

be released into space, thus trapping heat and raising overall temperatures, leading to

the deaths of organisms.

" ) 5nited +ations Convention in -0D established the M@+TJ:); *J@T@C@;,

which, aimed to restrict and control global emissions of oone destroying chemicals

and to protect the oone layer.

" The AL@T@ *J@T@C@; in -D re6uired all halon production to cease by 8/-/.

" The 5B and twelve nations in :urope agreed to ban all use and production of C2C's

by 8///. This is highly significant because these countries produce three 6uarters of

the C2C's in the world.


12/14

" owever the effectiveness of the steps are limited, as some nations have hindered

attempts to restore the balance of oone by refusing to approve of the agreement.

" @ther steps used to alleviate the problems caused by C2C's, include increased

research and development into new forms of 5G protection, such as sunscreens.

" These steps have proven to be somewhat effective as a recent assessment in 8//8,showed that the release of C2C's has decreased.

*resent information from secondary sources to identify alternative chemicals

used to replace C2C's and evaluate the effectiveness of their use as a

replacement for C2C's

" C2C's have been replaced by compounds with significantly lower oone depletion

potentials %@$*&. The first replacement compounds were C2C's %hydro

fluorocarbons&. C2C's contain C" bonds which are relatively reactive and easily

broken up by reactive radicals and atoms in the troposphere, therefore preventing the

ma(ority of C2C's from reaching the stratosphere, where it is dangerous.

" 2or example, C2C"-8> %C2>CCl8& is oxidised in the troposphere by hydroxyl

radicals %@& to form C>CCl8, which in turn is oxidised by oxygen to form carbon

dioxide, water and hydrogen halides.

" The use of C2C's as an alternative to C2C's is effective to some extent as it has a

much lower oone destroying capacity. The most common C2C, C2C"-- has an @$*

of -, whereas C2C"-8> has an @$* of /./=. @ne of the problems in using C2C's

is that their toxicity to humans is unknown.

" 2C's %ydrofluorocarbons& are the most widely used replacement of C2C's. Bince

they do not contain any chlorine atoms, they have an @$* of /. 2or example, 2C"

->3a, known as -,-,-,8"tertafluoroethane is widely used in refrigeration and air

conditioning as a replacement of C2C's. owever 2C's are more expensive and less

efficient than C2C's. 2C's are also significant greenhouse gases.

" )lternative compounds to C2C's in 2C's and C2C's are effective in that they

reduce the @$*, but they are ineffective in that they pose a problem as a greenhouse

gas.

Identify factors that affect the concentrations of a range of ions in solution innatural bodies of water such as rivers and oceans

Pat!ays "rom rain te natural !aters Jain contains very few ions %eg. C@>8", +aH&.

#hen it runs off bushland into streams, it picks up nitrates 7 phosphates.

p# o" te rain )cid rain can better leach out certain cations in Ca 8Hand Mg8Hfrom

the soil it passes, increasing their concentrations.

$ature and amount o" uman activity in te area ;and clearing leads to more rapid

run"off into streams and so sediments increasing dissolution of ions eg. +aH, Ca8H,

Mg8H. )gricultural activity often leads to fertiliser run off, eg. *@ 3>".


13/14

%""luents discarged into te !ater bodies $ischarge of raw or treated sewage into

rivers or oceans, increase the concentration of ions, e.g. phosphates and nitrates.

Industrial effluents if not monitored, can discharge heavy metal ions e.g. *b 8H, g8H,

Cd8H, n8H.

$escribe and assess the effectiveness of methods used to purify and sanitisemass water supplies

&eration Bpray water into the air to increase concentration of dissolved oxygen.

Flocculation )luminium sulfate %)l8B@3& is often added to lime %Ca%@&8& to

produce a gelatinous precipitate of )luminium hydroxide. The )luminium hydroxide

attracts suspended solids, precipitated iron and some bacteria that coagulate into

heavier particles in a process called flocculation.

/l3+ + 3H2O /l(OH)3 + 3H-

Sedimentation The settling of flocculation where the water is left to stand in a

settling tanks, and the flocculated particles settle out as sludge at the bottom.

Filtration The water from the settling tank is filtered through granular filters, often

containing sand, gravel and anthracite coal. These filter out any remaining particles.

Clorination Chlorine is added to destroy any bacteria and to prevent the growth of

algae in pipes. Chlorine gas reacts with water.

Cl2(g) + H3O(a0)HOCl(a0) + H+

(a0) + Cl-(a0)

The hypochlorous acid %@Cl& mainly kills the bacteria. )utomatic metering devices

are often used to constantly alter the amount of chlorine added.

2locculation processes are very effective at removing fine suspended particles that

attract and hold bacteria and viruses to their surface. Jesearch has shown that this

process alone is capable of removing up to . E of the bacteria and E of the

viruses from the water supplies.

#hile chlorination of water is a cost effective way of removing most disease causing

products, it can result in the formation of haardous disinfectant by"products such astrihalomethanes. There are flaws in the methods used to purify and sanitise mass

water supplies as contamination can still occur, as shown with the contamination of

Bydney's water supplies in -0.

1ather, process and present information on the range and chemistry of the

tests used to!

" Identify heavy metal pollution of water

" Monitor possible eutrophication of waterways

:utrophication is a process where bodies of water, such as lakes, rivers or wetlands,

become enriched in mineral nutrients, including nitrogen and phosphorous. The

sources of these nutrients include!


14/14

" fertiliser runoff

" plant and animal waste

" Industrial waste

" Bewage, human waste, detergents and shampoos

:utrophication leads to algal blooms, which is the rapid an excessive growth of algae.The side effect is that atmospheric oxygen is prevented from mixing with the water

due to algal scum on surface. The blockage of the sun can also lead to the deaths of

water life.

The methods used for monitoring possible eutrophication of waterways include!

testing for nitrates and phosphates as these are key nutrients, which cause

eutrophication< measuring for dissolved oxygen< and observing for the presence of

algae.

The'(eldal metod measures the level nitrogen present in organic material. In the

reaction, nitrogen is converted into ammonium sulfate by boiling with concentratedsulfuric acid. :xcess alkali is added and the ammonia formed is distilled off and

allowed to react with known amount of standard acid. 4y back titration, the amount

of ammonia is determined. Total nitrogen of - ppm indicates possible eutrophication.

The phosphorous content of water can be determined by first treating the water

sample with a strong oxidant %nitric acid&to ensure that all phosphorous present is

present as phosphate. The molybdenum blue method is then used. ) solution of

ammonium molybdate %+3&8Mo@3is added to the sample, producing a pale yellow

*hosphomolybdate complex. Then solid ascorbic acid is added to the solution,

forming an intense blue colour. This is then compared calorimetrically to samples thathave a predetermined phosphorous concentration. *hosphorus concentrations greater

than =/ppm may cause eutrophication.

eavy metals are those with high atomic mass, such as lead, cadmium, mercury,

cobalt, silver, etc. They can be detected in water via many ways.

" The water can be tested by adding sodium sulfide %+a8B&. 2irst, the water is

acidified, and then +a8B is added. If a precipitate forms, then one of the following is

present! *b8H, )gH, g8H, Cu8H, )s>H. If a precipitate does not form, the water should be

made basic.

" )tomic )bsorption Bpectroscopy can used to identify heavy metal pollution in

water. It uses the fact that the metals absorb certain wavelengths of light, and exploits

this by shining light through a flame, where the water sample is sprayed. )ny heavy

metal ions will get exited and absorb the wavelengths.

2009_chemistry_notes

Documents