Cambridge IGCSE Chemistry 3rd Edition

11 AIR AND WATER

• Water pollution and
treatment

An ad equate supply o f water is essential to the health Figure 11.38 Thislakeisusedasasourceofdrinkingwater.
and well-bein g of the world 's populatio n. Across the
planet, bi o logical and ch emical pollutants arc affecting A lo t o f drinking water is o btained fro m lakes and
the qu ality o f o ur water. An ad equate supply o f fresh rivers where the po lluti on levels are low (Figure 11.38 ).
drinking water is need ed fo r everyon e o n the planet. Undesirable m aterials rem oved fro m water include :
Lack of availability of fresh water leads to watcrbornc
diseases, such as cho kra and typhoid , and to diarrhoea , • collo idal clay (clay particles in th e water )
which is o ne of the biggest killers across the world. • bacteria
• chemicals which cau se the water to be colo ured
Agriculture need s a water supply in ord er to
irrigate crop s, especially in areas o f th e wo rld with and fo ul tasting
h ot climates. The produ ctio n o f m o re and mo re • acids, which are neutrali sed.
crops fo r the ever-increasing po pulatio n is essential.
Making wat e r fit t o d rin k
Water is very good at dissolving substances. Tlrns,
it is very unus ual to find really pure water o n this The treatm ent n eed ed to m ake water fit to drink
planet. As water fall s throll gh th e atmosphere, o n to depends on the source o f the water. Some sources,
and then th roug h the surface o f th e Earth , it dissolves for example m o untain streams, may be almost
a trem endou s variety o f substances . C h emical pure and b oilin g may be en o ug h to kill any micro-
fertilisers washed o ff surrounding land will add o rg ani sm s present. H owever, others, such as slow-
nitrate ion s ( N03- ) and ph osphate io ns ( PO/ - ) to fl owin g rivers, may be contamin ated. The o bject o f
the water, owing to the u se o f artificial fertili sers such treatin g contaminated water is to rem ove all mi cro -
as ammo nium nitrate and ammo nium phosphate. o rg ani sm s th at may cause disease.

The nitrates en courage th e growth o f algae which Th e process o f water treatment involves b oth
eventu ally die and d ecay, rem oving oxygen fro m the filtrati on and chl orinatio n and is summarised in
water. It may also contain human waste as well as
insoluble impurities su ch as g rit and bacteria, and
o il and lead 'dust ' ( to a decreasin g extent) fr om the
exhau st fum es o f lorries and cars ( Fi gure 11.37) .

Figure1 1.37 A badly polluted river. 1 Impure water is passed throu gh screens to filter out
fl oatin g d ebris.
All th ese artificial, as well as natural, impurities must
be rem oved fro m th e water before it can be u sed . 2 Aluminium sulfate is added to coag ulate sm all
Recent regulation s in many countries have imposed particles o f clay so that they fo rm larger clumps,
stri ct guidelines o n the am ounts o f vario u s substances which settle mo re rapidly.
all owed in drinking water.
3 Filtratio n through coarse sand traps larger, insoluble
0 particles. The sand also contains specially grown
micro bes which rem ove som e o f the bacteria .

4 A sedimentatio n tank has ch emicals known as
fl occulants, fo r example aluminium sulfate, add ed
to it to make th e smaller particles (which remain in
the water as collo idal clay) stick togeth er and sink
to the bottom of the tank.

5 These particl es are rem oved by furth er filtrati on
thro ugh fin e sand. Som etimes a car bon slurry is
used to rem ove unwanted tastes and odours, and a
lime slurry is u sed to adju st the acidi ty.

1 Water pollution and treatment
water passed through screen
cove red
2 sto rag e
aluminium sulfate added tank

pump sulfur
dioxide
added

4 5 6
sedimentatio n fine sand chlorin e added
t a nk filt er

Figure 11.39 Theprocessesinvolved inwatertreatment.

6 Fin ally, a little chl o rin e gas is added , which Sewage treatment
sterilises th e water and kill s an y rem aining bacteria .
Excess chlorine can b e rem oved by th e additio n After we have u sed water, it must be treated again
of sulfur dioxid e gas . The additi o n of chlorine gas before it can b e returned to rivers, lakes and seas .
m akes the water mo re acidi c and so app ropriate This multi-stage p rocess kn own as sewage treatment
am o unts o f sodium hyd roxide solutio n arc added. is shown in Fig ure 11.41.
Flu o rid e is som etimes added to water if there
is insufficient occurrin g naturally, as it helps to ~ge
preve nt tooth d ecay.

The 'iron problem' ,~-------

Ifthc acidity level o f the treated water is no t sludge
controlled , problems occur due to the precipitati o n (for either dumping
ofi ron(m) hyd roxid e. These include: or co nversio n t o f ertiliser)
and methane gas
• vegetables turning brown
• tea havin g an inky appearance and a bitter taste grave l
• clothes sh owing rusty stains after washing
4
(Fig m e 11.40). treated water is chlorinated
and return ed t o th e river
Figure 11.41 The processes involved in sewage treatment.

Figure 11.40 The rusty stains on this pillowcase are due to iron(•) U sed water, sewage, co ntain s waste pro ducts such
compounds in the water. as human waste and washin g -up d ebris as well as
everything else th at we put d own -a drain or sink.
The processes that arc involved in its treatment arc
as foll ows .

1 Large screen s rem ove large pieces o f rubbish .
2 Sand and grit arc separated in large sedimentati o n

tanks. The p rocess is speed ed up b y addin g
aluminium sulfatc, which helps the solids to

11 AIR AND WATER

coagulate into larger particl es that separate m o re VVa tcr is a ren ewable resource but care mu st b e
rapidly. The sand and grit often contain large taken to avo id excessive water po lluti o n , as this
am oun ts o f u seful chemicals which , by th e actio n o f could cau se seri o u s hea lth issu es such as t ypho id
sck ctcd microbes, can be u sed as fe rtilisers. o r cholera.
3 Tht: impure water is then rem oved and sent to a
trickling filter, where it is allowed to drain th rough Questions
g ravd o n whi ch microbes have been d eposited.
These kill o ff any rem aining bacteria in th e water 1 Make a list of four major water pollutants and explain
by aerobic processes. This stage is known as
bio logical filtratio n. where they come from. What damage can these pollutants
4 The treated water is then chlo rinated and returned
to a river, after checking. do?
5 Anaero bi c bacteria digest what rem ains fr om the
o ther stages. M ethane gas is produ ced , which can 2 In the treatment of water for public use, state the purpose
be u sed as a foci.
of the addition of:

a aluminium sulfate c sodium hydroxide

b chlorine d sulfur dioxide.

3 Many industries use water as a coolant. Suggest the sorts

of problems that may be created by this 'thermal pollution'.

A summ ary o f the main sources o f atm ospheric and
water po llutio n is shown in T ab le 11 .9.

Tabl e 11.9 Main sources of atmospheric and water p:>llution.

Pollutant Source Effects

Carbondioxide,C02 Complete combustion of fossil fuels (p. 92) Contributes to global warming (p. 212)
CHig) + 202{g) ----> co,(g) + 2H,D(1)

Carbon monoxide, CO Incomplete combustion of fos.sil fuels (p. 95) Poisonous, colourless, odourless gas

Oxides of nitrogen, NO~ Car exhaust fumes (p. 182) Oxides of nitrogen cause photochemical smog
N2(g) + O,(g) ----> 2NO(g) 2NO(g) + Oi{g) ----> 2NOi{g)

Particulates, carbon C Incomplete combustion of fos.sil fuels (p. 95) Covers surfaces 'Nith carbon particles

Lead and lead oxides Car batteries Lead and its compounds are toxic and particularly
affect the nervous system

Lead compounds Lead additives are added to petrol (use is decreasing), Lead and its compounds are toxic
resulting in exhau st fumes

Chlorofluorocarbons (CFCs) Aerosol sprays and refrigerators (p. 221) Destroy the layer of ozone around the Earth

Nitrates N03- and phosphates Po/- Fertilisers {p. 180) Eutrophication*
Eutrophication*
Sodium phosphate Detergents and water softeners

DDT* Insecticides Accumulates in food chain till eventually kills top
predators

Paraquat *andglyphosate Herbicides Kill harmless plants

*DDT is an organochlorin e herbi cide. It has high toxi city t o insects but has low t oxicity to mammals. However, it is very chemica lly stable
so it accumulates in th e environment and ca n become more concentrat ed in food chains. Fo r this reason it is banned in many co untries.
However, as it is cheap many developing co untries continue t o use it.

*Paraquat is a t otal herbi cide. It destroys all g reen plant mat erial. Paraquat is inactivat ed as soon as it t ouches th e soil but it does kill any
plant w hose leaves itto uches.

*Gl yphosate is a herbicide sprayed o nto th e o uts ide of leaves and it th en spreads thro ugh th e plant t o the root s. It is no n-selective and
kills usefulpl antsaswe ll aswee ds.

*Eutrophicati on occurs w hen fertiliser drains into lakes and rivers, ca using algae to multiply rapid ly and th e wa ter t o turn g reen. It results
in fi sh and other organisms suffoca tin g and dy ing th ro ugh lack of oxygen in wat er.

Checkfis t

Checklist • Nitrogen fixation The direct use of atmospheric nitrogen
in the forma t ion of important compounds of nitrogen.
After studying Chapter 11 you should know and understand Bacteria present in root nodules of certain plants are able to
the following terms. take nitrogen directly from the atmosphere to form essential
protein molecules.
• Artificial fertiliser A substance added to soil to increase
the amount of elements such as nitrogen, potassium and • Optimum temperature A compromise temperature used
phosphorus. This enables crops grown in the soil to grow in industry to ensure that the yield of product and the rate
more healthily and to produce higher yields. at which it is produced make t he process as economical as
possible.
• Atmosphere (air) The mixture of gases that surrounds
the Earth . • Ozone (trioxygen) A colourless gas produced in the
stratosphere by the action of high-energy ultraviolet
• Bulk chemical A chemical that. because of its large usage radiation on oxygen gas, producing oxygen atoms. These
across a range of uses, is produced in large quantities. oxygen atoms then react with fu rther oxygen molecules to
produce ozone. Its presence in the stratosphere acts as a
• Carbon dioxide A colourless, odourless gas, soluble in screen (ozone layer) against dangerous ultraviolet radiation.
water, producing a weak acid called carbonic acid. It makes
up 0.04% of air. It is produced by respiration in all living • Particulates Very small particles found in the atmosphere,
things and by the burning of fossil fuels. It is taken in by such as certain types of smoke emitted from diesel engines,
plants in photosynthesis. as well as dust.

• Chemical equilibrium A dynamic state. The • Photosynthesis The chemical process by which green
concentrations of the reactants and products remain plants synthesise their carbon compounds from atmospheric
constant because the rate at which the forward reaction carbon dioxide using light as the energy source and
occurs is the same as that of the back reaction. chlorophyll as the catalyst.

• Eutrophication A process that occurs when fertil iser • Pollution The modification of the environment caused by
drains into lakes and rivers, causing algae to multiply rapidly human influence. It often renders the environment harmful
and the water to turn green. it results in fish and other and unpleasant to life. Atmospheric pollution is caused by
organisms suffocating and dying through lack of oxygen in gases such as sulfur dioxide, carbon monoxide and nitrogen
the water. oxides being released into t he atmosphere by a variety of
industries and also by the burning of fossil fuels. Water
• Flue gas desulfurisation (FGD) The process by which pollution is caused by many substances, such as those found
sulfur dioxide gas is removed from the waste gases of in fertilisers and in industrial effluent.
power stations by passing them through calcium hydroxide Raw material A basic material from which a product is
slurry. made. For example, the raw materials for the Haber process
are nitrogen and hydrogen.
• Fractional distillation of air The process used to extract
individual gases from the air. Air is a major raw material. The • Removal of hardness Temporary hardness is removed
mixture of gases is separated by first liquefying the mixture by boiling. Both temporary and permanent hardness are
at low temperature and high pressure. The temperature is removed by:
then allowed to rise and the gases collected as they boil off. • addition of washing soda (sodium carbonate)
The gases so produced have many and varied uses. • ion exchange
• distillation.
• Haber process The chemical process by which ammonia
is made in very large quantities from nitrogen and • Reversible reaction A chemical reaction which can go
hydrogen. both ways. This means that once some of the products have
been formed they will undergo a chemical change once
• Hardness of water This is caused by the presence of more to re-form the reactants. The reaction from left to
calcium (or magnesium) ions in water, which form a 'scum' right. as the equation for the reaction is written, is known
with soap and prevent the formation of a lather. There are as the forward reaction and the reaction from right to left is
two types of hardness: known as the back reaction.
• temporary hardness - caused by the presence of
dissolved calcium (or magnesium) hydrogencarbonate • Stratosphere A layer of the atmosphere above the
• permanent hardness - this results mainly from dissolved troposphere in which the ozone layer exists.
calcium (or magnesium) sulfate.
• Transpiration The process of evaporation of water from
• Hydrogen bond A weak intermolecular force (bond) that leaves.
occurs between water molecules because the bonds within
the molecules are polar. It is the strongest of these weak • Troposphere A layer of the atmosphere closest to
forces. the Earth which contains about 75% of the mass of the
atmosphere. The composition of dry air is relatively constant
• limestone A form of calcium carbona te (CaC03). Other in this layer of the atmosphere.
forms include chalk, calcite and marble.
• Water cycle The cycle by which water circulates around
• Nitrogen cycle The system by which nitrogen and the Earth. The driving force behind the water cycle is the
its compounds, both in the air and in the soil, are Sun.
interchanged.

Q Air and water

• Additional questions 4 Use the words below to complete the fo llowing
p assage abo ut limesto ne and its u ses.
1 The apparatus shown o n p. 174 , Figure 11.6, was
used to estim ate the proportio n o f oxygen in the :ibundant chlorine nitrates
a t m o sp h e re. monitored coobnt fertilisers re:ictions
A volume o f dry air (2 00 cm3 ) was passed pure cl:iy solvent essential
backwards and fo rward s over heated copper until
no furth er ch ange in volume took place . The Water is for all life o n Earth. It is th e
apparatu s was then allowed to cool d own to room
temperature and the fin al volume reading was then m ost substance o n Earth. Water is no t
taken . Som e typical results arc shown bdow.
o nly used fo r drinking and washing but also:
Volume of gas before = 200cm 3
Volum e o f gas after= 157 cm 3 • in ch emical _ _ _ , fo r example in the
produ ctio n o f ethano l fro m cthcnc
During the cxpn im cnt the copper slowly turned
bl ac k . • as a _ _ _ to dissolve things
• as a _ _ _ in som e ch emical p rocesses.
a Why was the apparatus all owed to cool back
to room temperature b efore the fin al volume For us to drink it, water must b e relatively _ _.
reading was taken ?
T o make the water drinkable, any undissolved solids
b Using the in fo rmatio n given above, calculate th e
percentage volume redu ctio n which has taken arc rem oved throu gh filtrati on bed s. Aluminium
p la ce.
sulfatc is added to rem ove sm all particles o f
c Explain briefly why th ere is a ch ange in vo lume. _ _ _ _ _ _ _ is added to kill bacteria.
d W hat o b servati o n g iven above suppo rts your
Water is continu ou sly _ _ _ _ becau se there
explanatio n in d Write a balan ced ch emical
equation fo r any reaction which h as occurred. arc certain substances that eventually find their
e Give the nam e o f the m ain residual gas at the
end of the experiment. way into the water supply. For example, artificial
f Would you exp ect th e copper to have increased
o r d ecreased in mass during the ex perim ent? arc washed off farmland and this can
Explain your answer.
cause th e water supply to be contamin ated with
2 :i Oxygen has an ato mic number o f 8 and mass
number 16. \,Vh at is the elect ron structure o f the nitrates. arc harmful to babies.
oxygen atom?
5 a E xplain what is m eant by the term ' po llutio n '
b H ow many electro n s, neutron s and pro to n s arc with referen ce to air and water.
there in the oxygen atom i
b (i) Name an air pollutant produced by the
c O xygen m olecules arc diatomic. Explain the burning of coal.
meaning of this term.
(ii) N am e a different air pollutant prod uced b y
d Draw a diagram o f th e oxygen m olecule sh owing the combustio n o f p et ro l in a car eng ine.
the o uter shell o f elect rons o nly. W hat typ e o f
bo nding d ocs the molecule contain ? c Som e o f our drinking water is o btained by
puri fy ing river water.
3 E xplain the following. (i) Would distillatio n o r filtrati o n produce the
:i Ai r is a mixture o f elem ents and com pounds. purest water fro m river water? Give a reason
b The percentage o f carbo n dioxide in th e fo r your answer.
atmosphere d ocs n ot sig nificantly vary fr o m (ii) W hich process, distillatio n or filtratio n , is
0 .04%. actually used to produce drinking water
c Power statio n s arc tho ug ht to be a m ajo r ca use fr o m river water? Comment on your an swer
o f acid rain . in comparison to your an swer in c (i).

d Power statio ns produ ce warm water. This cau ses
th ermal pollutio n as this warm water is pumped
into nearby rivers.
(i) W h y d o power statio n s prod uce such large
quantities of warm water?
(ii) W hat effect d ocs this warm water have o n
aquatic litc?

Additional questions

6 Fert ili ser Formu la %n it rogen !:~ :·::
NH 0 82.4
Ammonia solution Ca(N0~2 17.1
Calcium nitrate NH4N03 35.0
Nit ram NaN03
Sodium nitrate KN03 5 30
Potassium nitrate ~ 20

550°(

a Copy and complete the above table by 0
calculating the percentage of nitrogen in the
fertilisers sodium nitrate and potassium nitrate. -.~ 10
(Ac' H~ I; N ~ 14; 0 ~ 16; N, ~23; K ~ 39;
CF40) ·~

b Including the data you have just calculated, '#. 0 100 200 300 400
which of the fertilisers contains: pressure/atm
(i) the largest percentage of nitrogen?
(ii) the smallest percentage of nitrogen? a VVrite a word and balanced chemical equation
for the reversible reaction between nitrogen and
c Give the chemical name for the fertiliser that hydrogen to produce ammonia using the Haber
goes by the name Nitram®. process.

d Ammonia can be used directly as a fertiliser but b What is meant by the term 'reversible reaction'?
no t very commonly. Think of two reaso ns why c Use the graphs to say whether more ammonia is
ammonia is not often used directly as a fertiliser.
produced at:
e Nitram® fertiliser is manufu.chtred by the (i) higher or lower temperatures
reaction of nitric acid with ammonia solution (ii ) higher or lower pressures.
according to the equation: d What is the percentage yield of ammonia if the
conditions used to run the process arc:
NH3(,q) + HN03(,q) - NH4N03(,q) (i) a temperature of350°C and a pressure of

A bag ofNitram® may contain 50kg of 100 atmospheres?
ammonium nitrate. What mass of nitric acid (ii) a temperature of550°C and a pressure of
would be required to make it?
350 atmospheres?
7 Ammonia gas is made industrially by the Haber e The conditions in industry for th e production
process, which involves the reaction between
the gases nitrogen and hydrogen. The amount of ammonia arc commonly of the order of
of ammonia gas produced from this reaction is 200 atmospheres and 450 °C. What is the
affected by both the temperature and the pressure percentage yield of ammonia using these
at which the process is run. The graph shows how conditions?
the amount ofammonia produced from the reaction f \iVhy docs industry use the conditions stated in
changes with both temperature and pressure. part e if it is possible to obtain a higher yield of
The percentage yield of ammonia indicates the ammonia using different conditions?
percentage of the nitrogen and hydrogen gases that
arc actually changed into ammonia gas. 8 Explain the following.
a Industry normally requires water which has been
softened.
b Hard water is good for the promotion of healthy
bones and teeth.
c Hard water causes kettles to fur. This ' fur' can be
removed by using a dilute acid.
d Hard water wastes soap.
e Hard water can coat lead pipes and reduce the
possibility of lead poisoning.

11 AIR AND WATER

9 The results o f testing five samples of water from 10 A town 's water s upply is o btained b y purif)1ing
river water.
diftCrcnt areas arc shown in the table below. The a What arc th e A and B in the diag ram of th e
soap solutio n was g radually added to 25 cm 3 of each water cycle below?
sample o f water with sluicing until a permanent
lather (om:: which lasts fo r 20 seconds) was obtained.

i ,. t--. ,rainA
Ill( '
Water sample/ Vo lume of soap solution added/cm3
25cm3
Before boiling After boiling

12

13

11 11

14 rivers lakes and seas

16 16

a (i) Which sampks arc permanently hard ? b (i) Filtrati o n or distillatio n - which o f these
(ii) Which samples arc temporarily hard ? processes would prod uce the purest water
(iii)Which sample contains both temporary and fro m river water? Give a reason fo r your
permanent hardness?
(ii) Filtration or distillatio n - which o f these
b N am e a compo und which could be present in processes is u sed in this country fo r
sample D but not in sample E . produ cing drinking water fr om river
water1
c Name a compo und which could be present in
sample E but no t in sample D. c In recent years po llutio n o f rivers and lakes
has becom e a serio us pro blem. State two m ain
d Explain how th e compound you have named in c sources o f river pollution.
get s into the w ater.
d In so me areas water is ' recycl ed ' W hat d ocs
e Sample E was distilled. The water collected recyclin g mean and why is it n ecessary?
was tested with soap solutio n. 'vVhat volume o f
soap solutio n mig ht you expect to be add ed to
produce a permanent lather? Comment on your

@ Sulfur

Sulfur - the element Sulfurk add
Usesofsulfur Industrial manufacture of sulfuric acid - the Contact process
Chemical properties of sulfur Usesofsulfuricacid
Properties of sulfuric acid
Sulfur dioxide
Acid rain Checklist

• Sulfur - the element Additional questions _/

Sulfur is a yellow no n-m etallic clem ent. It is fo und Sulfur is fo und in large quantities b ut in vario ll s
in G roup VI of th e Periodic T ab le. It is a brittle, fo rms throu gh o llt the world . It is fo LJnd in metal
non-conducting solid with a fairl y low melting po int o res su ch as copper pyrites or chalcopyritc (C uFcS2 )
( 11 5 °C ). Sulfur will not dissolve in water but will and zinc blend e ( Z nS) and in volcanic regio ns o f
dissolve in solvents such as car bon disulfid e and the world. N atural gas and o il contain sulfur and
m cthylbcn zcnc ( to lu ene). Like car bon , sulfur has its com po llnds, but the m ajority o f this sulfur is
allo tropcs. Its m ain allo t ropcs arc call ed rho m bic rem oved as it wollld cau se enviro nmental problem s.
sulfur and monoclinic sulfor (Figure 12 .1). Sulfur obtained fro m these so urces is kn own as
' recovered sulfur' and it is an important source o f th e
clem ent. It is also fo und as elem ental sulfur in sulfur
beds in Po land, Ru ssia an d the US ( Louisiana ). These
sulfur bed s arc typically 200 m below th e ground.
Sulfur fr o m these beds is extracted u sing the Frasch
process, nam ed after its invento r H ermann Frasch.

Uses of sulfur

Sulfm has a very im portant role in th e chemical
indust ry. The vast majority o f sulfur is used to
produ ce perhaps the most im portant indust rial
ch emical, sulforic acid . Sulfur is also LJscd to
vulcanise rubber, a p rocess which makes the ru bber
h arder and increases its elasticity. Relatively sm all
am o unts arc u sed in the manu facture o f m atch es,
fir eworks and fun g icides, as a sterilising agent and in
m edicin es .

Chemical properties of sulfur

Sulfm will react with both metals and no n-m etals.

• It reacts with m agn esium metal to fo rm magn esium
sulfid c.

m agn esium + sulfur ---> magnesium sulfidc

Mg(s) + S(s) - MgS (s)

• It reacts with oxygen to produce sulfur di oxide gas.

sulfur + oxygen ---> sulfur d ioxide

S(s) + 0 2(g) - S02(g)

Figure 12.1 Sulfur - rhombic (lop) and monoclinic.

12 SULFUR

• Sulfur dioxide

Sulfur diox ide is a colo urless gas prod uced when
sulfur or substan ces containing sulfur, fo r example
crud e o il or natural g as, arc burned in oxygen gas . It
has a ch o kin g smell and is extremely p o isono us. The
gas dissolves in water to p rodu ce an acidic solutio n o f
sulfu rous acid.

sulfur di oxide + water ~ sulfu rous ;1cid
SO,(g) + H,O(i) c= H,so ,(,q)

This solution turns m oist uni versal indicator paper Figure 12.3 This forest has been devastated byac:id rain.
red. It is on e o f the maj or pollutant gases and is th e
gas principally resp onsible fo r acid rain. H owever, it in acidity has led to extensive dam age to fo rests
d ocs have so me u ses: as a bleaching agent fo r paper (Fig ure 12.3), lakes and m arine life.
m anufacture, in fumigan ts and in the preservatio n o f
food by killing bacteria. In additio n it has led to the in creased corrosio n
o f exposed m etals and to damage to buildings and
Sulfur dioxid e will turn acidified potassium statues m ad e fro m lim esto n e or marble (Fig ure 12.4).
m anganatc(vn) solutio n fro m purple to co lo urless The sulfu rous acid in rainwater oxidises to sulfuric
(Figure 12.2). acid. The sulfuric acid reacts with the lim eston e,
whi ch is eaten away by the chemical process .

limesto ne + sulfuric acid ---+ calcium + wat er + carbon

sulfate di o xide

CaCOis) + H 2S0 hq) ---+ CaSO h) + H 20 (1) + CO i(g)

Figure 12.2 Testforsulfurdioxide.

Question Figure 12.4 Acid rain is responsible for much of the damage to this
temple on the Acropolis in Athens.
1 'Sulfur is a non-metallic element.' Discuss this statement,
giving physical and chemical reasons to support your The am o unt o f sulfor dio xid e in the atm osphere h as
increased dramatically over recent years. There h as
Acid rain always been som e sulfur dioxide in the atmosphere,
fro m natural processes su ch as volcanoes and ro tting
Rainwater is naturally acidic since it dissolves carbo n vegetatio n. O ver Euro pe, h owever, around 8 0%
dioxide gas fro m the atm osphere as it fall s. N atural o f the sulfor di oxid e in the atm osphere is fo rmed
rainwater has a pH o f about 5 .7. In recent years, fro m the combustion o f fuel s containing sulfur
especially in central Europe, the pH o f rainwater has (Figure 12. 5 ). After dissolving in rain to produce
fall en to between pH 3 and pH 4 .8 . This in crease sulfurous acid , it reacts furth er with oxygen to fo rm
sulfuri c acid.

Sulfuric acid

metal salts

pow~
stations
60'>1

Figure 12.5 Sourcesofsulfurdioxide.

Nitric acid (H N0 3 ) in the atmosp here , fo rmed fr om
N0 2 gas dissolving in the rainwater, also contributes
to th e productio n of acid rain .

Questions

1 How could the amount of sulfur dioxide being produced by
the above sources be reduced?

2 Devise an experiment which you could carry out in the
school laboratory to determine the amount of sulfur in two
different types of coal.

• Sulfuric acid

Industrial manufacture of sulfuric
acid - the Contact process

The major use of sulfur is in the productio n of
sulfuric acid. This is probably the most important
industrial chemical, and the qmntity of it produced
by a country has been linked with the economic
stabili ty of the country. In excess of 150 millio n
to nnes of sulfuric acid arc produced worldwide each
year. lt is used mainly as the raw material fo r th e
production of man y substances (Fi gure 12.6).

The process by which sulfuric acid is produced is
known as the C o ntact process (Figure 12.7 ).

Figure 12.6 Productsmadefromsulfuric acidincludedetergents,paints
and pigments.

12 SULFUR

Figure 12.7 A Contact process plant used for making sulfuric acid. o f m olecules o f gas, it will be fa voured by a
hig h pressure. In reality, the process is run at
The process has the fo llowing stages. atmospheri c pressure. Under th ese conditio ns,
about 9 6% o f the sulfur dioxide and oxygen arc
• Sulfor dioxide is first produ ced , primarily by th e con verted into sulfur trioxide. Th e heat produced
reactio n o f sulfor with air. by this reactio n is used to heat the incoming gases,
thereb y saving m o ney.
sulfur + oxygen ----+ sulfur dioxide • If this sulfur trioxide is added directly to water,
sulfuric acid is produced. Thi s reactio n , however,
S(, ) + 0 2(s) - S02(s) is very vio lent and a thick mist is produ ced.

• An y dust and impurities arc rem oved fr o m the sulfur triox ide + water ----> sulfuri c acid
S03 (g) + H 20 (!) - H2S0 4(1)
sulfor dioxide p rodu ced , as well as any unrcactcd
This acid mist is very difficult to deal with and
oxygen. These ' clean ' g ases arc heated to a so a different route to sulfuric acid is employed.
temperature of approximately 450 °C and tCd Instead , the sulfur trioxide is dissolved in
into a reactio n vessel , wh ere they arc passed over con centrated sulfuri c acid (9 8%) to g ive a
substan ce called oleum.
a catalyst o f vanadium(v ) oxid e (V20 5 ) . This
catalyses the reacti on between sulfur dioxide sulfuric acid + sulfur tri oxide ----> olcum
H2S0 4(,q ) + S0 3(g) - H 2S20 7(1)
and oxygen to prod uce sulfor trioxide (sulfur(VI )
oxid e, S03 ) . Th e olcum form ed is then added to the correct
am ount o f water to produce sulfuric acid o f the
sulfur + oxygen:;;::=: sulfur required con ce ntratio n.

d i o xid e tri o x id e o leum + water ----> sulfuric acid
H2S20 7(1) + H20 (!) - 2H 2S0 4(1)
2S0 2(g) + 0 2(g) ;= 2S0 3(g) 1'. H~ - 197 kJm oJ- 1
Questions
This reactio n is n:vcrsiblc and so the ideas o f
Le C hatdicr (C hapter 11 , p. 178 ) can be used 1 Produce a flow diagram to show the different processes
to increase the propo rtio n o f sulfu r trioxide in which occur during the production of sulfuric acid by
the equilibrium mixture . The fo rward reaction the Contact process. Write balanced chemical equations
is exothermic and so would be fu vourcd b y low showing the processes which occur at the different
temperatures . The temperature o f 450 °C u sed stages, giving the essential raw materials and conditions
is an o ptimum temperature whi ch produces used.
sufficient sulfur trio xide at an econo mical rate.
Since the reacti o n fr om left to right is also 2 Both the following reactions are reversible:
accompanied b y a decrease in the number
(i ) X2(g) + Oi(g) ----. 2XO(g)
{ii) 2XO(g) + Oi(g) -> 2X01(g)

Suggest a reason why an increase in pressure:
a does not favour reaction (i)
b increases the amount of X02 produced in reaction (ii).

Uses of sulfuric acid

Sulfuric acid has many u ses in industry. It is su ch an
important bulk chemical that th e am o unt o f sulfi.uic
acid whi ch a country u ses in o ne year can be seen as
a m easure o f that country's econo mic d evelo pment,
that is, h ow m o d ern or wealthy it is.

Sulfuric acid

Fo r example, concentrated sulforic acid is used: zinc granules
Figure 12.8 The laboratory preparation of hydrogen gas.
• for making detergents (Chapter 15, p. 239 )
• as a catalyst (Chapter 7, p. 109 and C hapter 14, The preparation of the acid salt with sodium hyd roxide
requires twice the volume of acid as that used in the
p. 224 ) preparatio n of the normal salt. Therefo re, if25 cm3 of
• as a dehydrating agent (sec p. 202 fo r the effect dilute sulfi.uic acid were required to form the normal
salt from a given volume of alkali of a particular
it has o n h ydrates such as coppcr(n) sulfatc concentratio n then 50 cm3 of the same acid solutio n
p e n t a h yd r a tc). would be required to produce the acid salt, sodium
hyd rogcnsulfatc, fro m the same volume of alkali.
H owever, the concentrated acid is often mixed with
water to fo rm dilute sulfori c acid. Th e diluted acid
is used:

• fo r making fertilisers (Chapter 11 , p. 180)
• for treating metals to remove ox idatio n

(' pickling') befo re painting
• in an odising aluminium (Chapter 5, p. 76 )
• as the acid in car batteries
• fo r making paints, dyes and fibres
• as a comm on laboratory reagent.

Properti es of sulfuri c ac id

Dil ut e sulfuric acid sodium + sulfuric so d i u m + water

Dilute sulforic acid is a typical strong dibasic acid. h yd r o x i d e acid hyd rogensulfute
A di basic acid is o ne with two replacea ble hyd rogen
ato ms which may produce two series of salts - NaOH(aq) + H 2S0 4(aq) ---,. NaHS04(aq) + H 20 (t)
normal and acid salts (Chapter 8 , pp. 122 and 126).
Su lfates
It will react with bases such as sodium hyd roxide
and coppcr(n) oxide to produ ce normal salts, called The salts of sulfuric acid, sulfates, can be identified
sulfates, and water. by a simple test -tu be reacti o n. To test fo r a sulfate,
add a few d rops of dilute hyd rochloric acid to your
• With sodium hyd roxide: unknown followed by a few d rops of barium chl oride.
If a sulfatc is present, a white precipitate of barium
sodium + sulforic ---> sodium + water sulfatc fo rms.

h yd roxide acid sulfatc barium io ns + sulfatc io ns ---> barium sulfatc
Ba2+(aq) + so/- (aq) ---> BaS0 4(s)
2N,OH(,q) + H,s o ,(,q) - N,,SO.(,q) + H, O (!)

• With coppcr(n) oxide:

coppcr(n) + sulforic ---> copper(n) + water Many sulfatcs have very impo rtant uses, as can be
seen from Table 12 . 1.
oxid e ac id sulfatc
Tab le 12.1 Uses of so m e m et a l sulfates.
CuO(s) + H2S0 4 (,q) - CuS0 4(,q) + H 20 (!)

It also reacts with carbonates to g ive normal Sa l t For mu la Use
salts, carbo n dioxide and water, and with reactive (NH4)iS04 Fertiliser
metals to give a normal salt and hyd rogen gas . Th e Ammonium
reaction between zinc and sulfuri c acid is often sulfate BaS04 'Bariummeal ' used indiagnostic
used to prepare hyd rogen gas in the laboratory medical X-ray studies
(Figure 12 .8 ). Barium
sulfate

zinc + sulfori c acid ---> zin c sulfatc + hyd rogen Calcium Ca504.1H20 'Plasterof Paris'usedtosetbones
Zn(s) + H2S0 4(,q) - ZnS0 4(,q) + H 2(g) sulfate MgS04 lnmedicineitisusedasalaxative

Magnesium
sulfate

12 SULFUR

Concentrated sulfuric acid Con centrated sulfuri c acid will also take water
fro m hydrated coppcr(n ) sulfatc crystals, leavin g
Concentrated sulfori c acid is a powerful dehydrating o nly anhyd rous copper(n ) sulfatc. If a few d rops of
agent - it will take water fro m a variety o f concentrated sulfuric acid arc added to some blue
substances . One such substance is cane su gar, o r h ydrated coppcr(n) sulfatc crystals, they slowly turn
sucrose (Figure 12.9 ). white as the water o f crystallisatio n is rem oved by tht:
acid. Eventually, o nly a white powd er - anhyd rous
su crose (sug ar) mnc tt,so. carbon + water coppcr( n ) sulfatc - remains.
C 12 H22 0 11 (s) ~ 12C(,) + IIH20 (1)

hydrated cone H,so. anhydro us + water

coppcr( n) sulfatc coppcr(n)

sulfutc

CuS0 4.5H20 (,) ~ CuSO.(,) + 5H20 (1)

Con centrated sulfuri c acid sh o uld be treated very
carefull y, becau se it will also rem ove water fro m
fl esh ! It is a very corrosive substance and sh o uld
always b e handled with care .

Diluting con centrated sulfuri c acid must be d on e
with great care because o f its affini ty fo r water. The
concentrated sulfuric acid sho uld always be add ed to
the water, not the other way around.

Many gases arc also dried by passin g th em
th rough concentrated sulfuric acid. One excepti on is
ammo nia. Amm o nia is alkaline so it cann o t be dried
in this way as it would react with the sulfuric acid.

Con centrated sulforic acid will also act as a
powerful oxidising agent. Fo r example, when
heated with m etal s su ch as copper it will oxidise
them to copper io n s and form coppcr(n ) sulfatc.

copper +concentr.i.ted ~ copper(n) + water + sulfur

sulfuric acid sulfate dio xid e

Cu(s) + 2H2S0 4(t) ---.... CuS0 4(aq) + 2H20 (t) + SOi(g)

This reactio n is o ften u sed as a m etho d o f making
sulfur dioxide in th e labo ratory.

An interesting property o f con centrated sulfuric
acid is that it can be u sed to make nitric acid and
h yd rochl oric acid (b o th these acids arc m ore volatile
than con centrated sulfuric acid ).

If concentrated sulfmic acid is added to a m etal
chl oride su ch as sodium chloride, hydrogen chloride
gas is produ ced.

sodium +concentrated---+ sodium + hyd rogen
chlo rid e sulfuric acid hyd rogcn sulfatc chlo ride
N,Cl(,)+ H2S04(l) - N, HS04(,) + HCl(g)

Figure 12.9 The concentrated sulfuric acid has removed the elements of If the hyd rogen chl o ride is dissolved in water, then
dilute hydrochlo ric acid is produced.
waterfromthesugar,leavingblac:kcarbon.

Checkfist

If concentrated sulfuric acid is heated with a m etal Quest ions
nitrate su ch as sodium nitrate, nitric acid vapo ur is
prod uced. 1 If you were given an unlabelled bottle which was
thought to be dilute sulfuric acid, how would you show
sodium + concentrated----+ sodium + nitric that the solution contained sulfate ions (So/-(aq)), how
nitrate sulfuric acid hydrogensulfate acid would you show that it was an acid and how would you
NaNOi s) + H 2S0 i1 ) ----+ NaHS0 4(s) + HN03(g) determine the concentration of the acid?

N eithe r o f these metho d s would be suitable for 2 Write balanced chemical equations for the reactions
making these acids o n a large scale . between dilute sulfuric acid and:
a zincoxide
b potassium carbonate
c aluminium.

3 Describe, with the aid of equations, how concentrated
sulfuricacid can react as:
a a dehydrating agent
b an oxidising agent.

Checklist • Oleum Very concentrated sulfuric acid (98%).
• Soapless det ergents Substances which are more
After studying Chapter 12 you should know and understand
the following terms. effective than soap at producing lathers, especially in hard
water areas. They are large organic molecules, produced
• Acid rain Rainwater with a pH in the range 3 to 4.8. usingsulfuricacid.
• Bulk chemica l A chemical produced in large quantities • Sulfate A salt of sulfuric acid formed by the reaction
of the acid with carbonates, bases and some metals. It is
by standard chemical reactions, for example ammoina and possible to test for the presence of a sulfate by the addition
sulfuricacid. of dilute hydrochloric acid and some barium chloride
• Contact p rocess The industrial manufacture of sulfuric solution. A white precipitate of barium sulfate is formed if a
acid using the raw materials sulfur and air. sulfate is present.
• Dehy dratin g agent A substance that will remove water
or the elements of water from another substance.
• Dibasic acid An acid which contains two replaceable
hydrogen atoms per molecule of the acid, for example
sulfuricacid, H2S04.

Q Sulfur

• Additional questions 4 Fossil fuels, such as oil, coal and natural gas, all
contain some su lfur. When these fuels arc burned
1 Sulfur has an atomic number of 16 and it is they produce many different gases. Concern has
represented as: grown in recent years about the effects of one of
these gases, sulfur dioxide. When sulfur dioxide
ns dissolves in rainwater it forms an acidic solution
which has become known as acid rain.
a How many electrons, protons and neutrons docs Money has been made available to solve the
a sulfor atom contain? problem of acid rain. Attempts arc being made to
clean gases being released from power stations and
b How many electrons will there be in the outer to look into ways in which the effects of acid rain
shell (energy level ) of this atom1 can be reversed. The table below and Figure 12.5
(p. 199 ) give some data about the emission of
c To which group of the Periodic Table docs sulfur dioxide.
sulfur belong?
USA Milliontonnesperyear
d Write down the names of two other elements Russia/Ukraine 26
found in the same group as sulfor. Germany 18
UK
e Write down the formula of the ion that sulfor Canada 30
will form in reactions with metals such as France
magnesium. Poland
Italy
f Sulfor will react with powdered calcium when Other countries
the mixture is heated. Write a word and a
balanced chemical equation for this reaction. :i Using the figures in the table, produce a bar
chart to show the amount ofsulfur dioxide
g Give two large-scale uses ofsulfur. produced by each of the countries listed.

2 Explain the following. b What percentage of th e world's sulfur dioxide is
a Chemical plants that produce sulfuric acid arc produced in:
often located on the coast. (i) France?
b Even though more sulfuric acid could be (ii) North America?
produced using high pressures, normal
atmospheric pressure is used. c Using the information above, explain why
c Natural rubber cannot be used to produce car countries such as the US, Russia and Germany
tyres but vulcanised rubber can. arc at the top of the list of sulfur dioxide
d Sulfur dioxide gas is regarded as a pollutant. producers.
e Coal-fired and oil -fired power stations produce
sulfur dioxide. Some ofthem arc being fitted d If the total amount ofsulfur dioxide produced
with flue gas dcsulfurisation ( FGD ) units. by Canada is 5 million tonnes per year, what
amount is produced by:
3 A type ofcoal contains 0.5% of sulfur by mass. (i) power stations/
:i Write an equation for the formation of sulfur (ii) domestic users?
dioxide gas when this coal is burned. (iii)industry?
b What mass of sulfur is contained in 1500 tonnes
of coal?
c What mass of sulfur dioxide gas would be
formed if 1500 tonnes of coal were burned?
d What volume would this mass of sulfur dioxide
gas occupy, measured at room temperature and
pressure (rtp )? (A.: 0 = 16; S = 32. One mole of
a gas occupies 24 dm3 at rtp. )

Additional questions

5 Study the following reaction scheme: 6 In a neutralisation experiment, 25 cm3 of dilute
sulfuric acid was required to react completely with
Sulfur oxygen/catalystG 40cm3 ofa solution of0.25moldm-3 potassium
hydroxide.
~ a Write a balanced chemical equation for the
reaction between dilute sulfuric acid and
/GasA\ Ga~ ;~,oc,at,at,d potassium hydroxide.
Oxygen gas ~furicacid b Calculate the number of moles of potassium
hydroxide solution used in the reaction.
rain/air Fumingsulfuric c How many moles of dilute sulfuric acid would
this number of moles of potassium hydroxide
Iacid (oleum) react with?
d Calculate the concentration of the dilute sulfuric
,,o, acid.
filings water e Which indicator could have been used to
Solution C - - - - Dilute sulfuric - - - - Concentrated determine when neutralisation had just
occurred?
acid sulfuricacid
7 Describe how you would prepare some crystals of
!'""~'GasD hydrated copper(n) sulfatc from coppcr(n ) oxide
Black solid E + Gas F and dilute sulforic acid. Draw a diagram of the
apparatus you would use and ,vritc a balanced
a Identify the substances A to F by giving their chemical equation for the reaction.
names and formub.c.
8 Sulfuric acid is manufactured by the Contact
b Write a balanced chemical equation for the process, in which a mixture of sulfur dioxide and
formation of gas B. excess air, preheated to 450 °C, is passed over a
catalyst.
c (i) Describe a chemical test, and give the a How is the sulfur dioxide made? Give an
positive result ofit, to identify gas D. equation for the reaction.
b Write the balanced chemical equation for the
( ii) Describe a chemical test, and give the reaction that takes place between sulfur dioxide
positive result ofit, to identify gas F. and air.
c Name a suitable catalyst for the reaction.
d How would you obtain solid C from the d Why is a catalyst necessary for this process?
solutionC? e The product of this reaction will react directly
with water. When it docs so, it forms sulfuric
e Which pathway shows the formation of acid rain? acid. However, the method is impractical
f In which way is the concentrated sulforic acid because the reaction is exothermic and an
acid mist forms. Describe the modern indirect
acting in its reaction with sucrosd method of changing the product of the reaction
g Where docs the oxygen gas come from to form between sulfur dioxide and air to form sulfuric
acid.
gas A? f Give two uses of concentrated sulfuric acid.

@ Inorganic carbon chemistry

Li mestone Carbon dioxide
Direct uses of limestone Uses of carbon dioxide
Indirect uses of limestone Laboratory preparation of carbon dioxide gas
Properties of carbon dioxide gas
Ca rbonates
Properties of carbonates Checklist

Additional questions

• Limestone As the newspaper artick on th e left says, limeston e
is fo und in th e Peak D istrict, an exam p le being this
Environmental Problems in gorge o n th e Ri ver Wyc in th t: UK (Figure 13 .l ). As
the Peak District National Park well as g iving rise to bcautifol and vari ed countrysid e,
lim esto ne is a very u seful raw material.
Local residen ts have been protesting against
p roposals to site a new limesto ne qu arry in the Limesto n e is com posed o f calcium car bon ate
beautiful D erbyshire Peak District in th e U K. (CaC03 ) in the form of the mineral calcite
H owever, limesto ne is such a u seful and soug ht- (Fig ure 13.2 ). Ch alk and marb le arc also made o f
after mineral th at dem and has encouraged mining calcite which is the second most abundant mineral in
in N atio n al Park areas . the Earth 's crust after the d iffere nt types o f silicates
(which include clay, g ranite and sandsto n e).

C h alk is m ade of the 'shel ls' o f marine algae (th at
is, plan ts) . It is a form o f limesto n e. Most other
lim esto nes arc fo rm ed fr o m the debris of animal
structures, fo r example brachiopod s and crino ids.

M arble is a m etam orphic rock mad e o f calcium
carbo nate. It is fo rm ed when limesto ne is subjected
to hig h pressures o r hig h temperatures, o r som etimes
b oth acting together, to create cr ystals o f calcium
carbo nate in the rock.

In a typical year, in excess o f 500 millio n to nnes
o flim csto nc arc qu arried worldwid e. Alth o ug h it is
cheap to qu arry, as it is fo und near the surface, there
arc som e en viro nmental costs in its extractio n .

Question

1 List the environmental issues which could arise through t he
quarrying of limestone.

Figure 13.1 ThisgorgeinthePeakDistrictNationalParkintheUKis
made from limestone.

Limestone

Fi gu re 13.2 Chalk, calcite and marble are all forms of calcium carbonate. construction
Industry
Direct uses of limest o ne
ca lcium oxide
Limesto ne has a variety of uses in , fo r exampk, the (ll me)manufacture
making of cement, road building, g lass making and
the ex tractio n of iron (Fig ure 13.3 ). manufacture

- - - - - - 1 sodium carbonate
manufacture

,~,

bulldlng

Fi g ure 13.3 Uses of limestone.

13 INORGANIC CARBON CHEMISTRY

Neutralisation of acid soil
Powd ered limesto ne is m ost o ft.en u sed to neutralise
acid soil (Fig ure 13.4) because it is cheaper than
any fo rm o fli1m: (calcium ox ide ), which has to be
produced by heating limesto ne (sec p. 209 ), and
becau se it is slow actin g and an excess d ocs n o t make
the soil alkalin e. The reactio n o flimc sto n c with acidic
soil can be shown by the fo llowing io nic equatio n.
carbonate ion + hyd rogen io n ----> carbo n + water

di o xid e

cem ent. lt contains a mixture o f calcium a.lumina.te
( Ca (AI 0 2)i ) and calcium silicate ( C aSi03 ) .
The dry product is ground to a powd er and then a
little calcium sulfate ( C aS04 ) is added to slow d own
the settin g rate o f the cem ent. W hen water is add ed
to the mixture, slow complex ch emical chan ges occur,
resultin g in th e fo rmatio n o f a hard interl ocking mass
o f crystals o f hydrated calcium aluminatc and silicate .

Con crete is a mixture o f cem ent with sto ne
chippings and sand , which help to give it body. After
the in gredien ts have been mixed with water they arc
po ured into wooden m o ulds and allowed to set hard.
Reinforced co ncrete is ma.de by allowing concrete to
set a.round steel rods or m esh to g ive it greater ten sile
streng th , which is required fo r the constructio n o f
large bridges ( Figure 13 .6 ) and ta.II buildings .

Figure 13.4 Spreadinglimestoneontosoil.

Manufacture of iron and steel Figure 13.6 This bridge in Brazil uses reinforced concrete.

In the bl ast furna ce, lim esto ne is u sed to rem ove
earthy and sandy materials fo und in th e iron ore.
A liquid slag is form ed , which is mainly calcium
silicate . M o re d etails o f th e extracti on o f iron and its
conversio n into steel a.re given in C hapter 10.

Manufacture of cement and concrete

Limeston e ( or chalk) is mixed with clay (or shale )
in a h eated rotary kiln , u sing coal or o il as the fuel
( Fig ure 13 .5 ). The material produ ced is called

Ind irect uses o f li mest one Limestone

Li me manufactu re 50%sand

\.Yhcn calcium carbonate is heated strongly it
thermally d issociates (breaks up reversibly) to fo rm
calcium ox id e (lime ) and carbon dio xide .

calcium carbonate ~ calcium oxide + carbon dioxide

CaCOis) C a O (s) CO ,(g)

This reaction can go in either directio n , d epending o n
the temperature and pressure u sed. This react ion is an
important indu strial process and takes place in a lime
kiln (Figure 13.7 ). In excess of 6 0 millio n to nnes of
calcium oxid e arc prod uced world wide every year.

C02and othe rgases

exit gases co oled 25% scrapglass
and limesto ne Fi gure 13.8 The composition of glass.
} (CaC03) heated

} ,eact;oo ,ooo gas desulforisatio n. It also has uses as a drying agent
in indu stry and in the manufacture o f mo uthwash.
:~:;oos Soda g lass is mad e by heating sand with soda (sodium
carbonate, Na2C 0 3 ) and lime ( Figure 13.8 ). Fo r
lime(CaO) forth cr discu ssio n o f glasses sec C hapter 3, p. 54.

} cooled and Large am ounts o f calcium oxid e arc also converted
air heated into calcium hyd roxide ( C a(OH )i) which is called
slaked lime.
lime(CaO) out
Figure 13.7 The calcium oxide produced from this process is known as Ma nu facture of ca lcium hyd roxide -
quicklime or lime and is used in large quantities in the manufacture of slaked lime
soda glass.
Ca lcium hyd rox id e is a ch eap indu strial a lkali
C alcium oxide (C a.O) is a base and is still used by ( Fi gure 13.9 ). It is u sed in large quantiti es to make
some farm ers to spread o n field s to neutralise soil bleachin g p owd er, by som e farm ers to redu ce
acidity and to improve drainage of water throug h soils soil acidity, fo r n eutralisin g acidic industrial wa ste
that contain large amounts o f clay. It is also u sed to p roducts, in th e manufacture o f whitewash , in g la ss
neutralise industrial waste p roducts, for example in flu e manufacture and in water purificatio n. C alcium
h yd roxide, in its white powd er form , is produ ced b y
addin g an equal amo unt o f water to calcium o xid e
in a care full y controlled reactio n. Th e control is
n eed ed becau se it is a very exothermi c reactio n.

13 INORGANIC CARBON CHEMISTRY

Thi s process can be shown on th e small scak in b The limewater turnscloudy.
the laborato ry by heating a lump of lim cstom: very
st rong ly to convert it to calcium oxide. Water can c If the C02 is bubbled for longer the white precipitate dissolves.
then be can:fully added d ropwisc to th e calcium Figure13 .1 0 Testingforcarbondioxide.
oxid e. An exo thermic reactio n takes place as th e
water and calcium o xid e react together in this slaking
p rocess to form calcium hydroxide.

calcium oxide + water -----,. calcium hydroxide

CaO(, ) + H2 0 (!) - Ca(OH ),(s)

A wea k solutio n o f calcium hyd roxide in water
is called limewater. It is used to test for carbo n
di oxid e g as, as a white solid o f calcium carbo nate
is fo rm ed if carbo n dioxide g as is mixed with it
(Figure 13.10):

calcium + carbon ----> calcium + water

hyd roxide dioxide carbo nate
Ca (OH ), (,q ) + C0 2(g) - CaC0 3( , ) + H20 (!)

This brin gs us full cycle fro m lim esto n e (calcium
carbonate, C aC 0 3 ) , throu gh calcium oxid e (C aO )
and back to calcium carbo nate (limesto n e). This is
kn o wn as the 'limesto ne cycle ' (Fi gure 13.11 ).

0

Ca rbonates

limestone
(calcium
carbonate,
CaC03'

heat
- C02

slaked lime quicklime
(calcium (calcium
hydroxide,
Ca(OH)2) oxide,CaO)

Figure 13.11 The limestone cycle. Figure 13 .12 Three naturally occurring carbonates -dolomite with
magnesiteinfrontOeft)andmalachite(rig ht).

If carbo n dioxid e is bubbled fo r a further leng th additio n to the calcium carbonate in limesto ne, chalk
of time th en th e white precipitate ofcalcium and m arble, m alachite is coppcr(11 ) carbon ate and
carbo nate dissolves and a solutio n o f calcium d o lo mite is m agn esium carbo nate (Fig ure 13 .1 2 ).
hyd rogcncarbon atc is produced:
Propert ies of carbonat es

calcium + carbon + water ca lcium • M ost metal carbo nates thermally d ecompose wh en
hyd rogen- heated to form th e m etal oxide and carbo n dioxide
carbo nate diox id e carbon ate gas (sec Chapter 10, p. 152 ). For example,
C,(H C03),(,q)
C, C03(s) + C02 (g) + H20 (!) - copper(11 ) copper(11 ) ca r b o n
carb o nat e
Calcium hyd roxide (slaked lime ) is mixed with sand CuC0 3( , ) oxid e di oxide
to give m ortar. When it is mixed with water and CuO (s)
allowed to set a stron gly b ond ed m aterial is fo rmed , + C0 2(g)
which is used to ho ld bricks together. The hard ening
o f m o rtar takes place as the fo llowing reactio n occu rs. Group I metal carbo nates, except fo r lithium
carbonate, d o no t dissociate o n heating. It is
calcium + carbo n ---+ calcium + water gen erally fo und th at the carbo nates o f the more
reactive metals arc mu ch m o re difficult to dissociate
hyd rox ide di o xid e carbon ate than , fo r example, coppcr(11 ) carbon ate . Fo r forth cr
discussion o f the effect o f heat o n carbonates sec
C,(O H ),(,q ) + C02(g) - C,C03(s) + H20 (!) C hapter 10, p. 152.
• Carbon ates arc generally insoluble in water except
Questions for those o f sodium , po tassium and ammo nium.
• Carbon ates react with acids to fo rm salts, carbon
1 Some suggested building alternatives to limestone are dioxide and water (C hapter 8, p. 12 3). For
sandstone and granite. What would be the benefits of cxampk, calcium carbo n ate reacts with dilute
using either of these two materials instead of limestone? hyd rochloric acid to fo rm calcium chlo rid e, carbo n
For further information, consult the Internet. dioxide and water.

2 Devise an experiment that you could carry out in the calciwn + hydrochloric -> calcium + carlxm + water
laboratory to establish whether or not powdered limestone
is better at curing soil acidity than calcium oxide.

3 Why is the metallic calcium oxide described as a 'base'?

carbonate acid chloride dioxide

CaCOJ(.) + 2H Cl(aq ) -> CaCl2(aq) + COi{g) + H20 (1)

• Carbonates • This reacti o n is used in th e laboratory preparatio n
o f carbon diox ide ( p. 21 4 ). It is also used as a
Carbonates fo rm an important range of compound s. test fo r a carbon ate because the reactio n p roduces
They arc all salts o f carbo nic acid (H 2C03 ) and carbo n dioxide which causes effervescen ce and if
contain the carbonate io n (CO/- ). Man y o f them
occur naturally in rock fo rm atio ns. Fo r example, in bubbled th roug h limcwatcr turns it ch alky white.

13 INORGANIC CARBON CHEMISTRY

Questions glucose + oxygen -+ carbon dioxide + water + energy
C6 H 120 daq) + 602(s) ---> 6C02(s) + 6H 20 (t)
1 Write word and balanced chemical equations to show the
Carbo n dioxid e is taken in by plants throug h their
effect of heat on cobalt carbonate (CoC03) and nickel leaves and used together with water, taken in
carbonate (NiC03). through their roots, to synthesise sug ars. This is the
2 Write word and balanced chemical equations for the process o f photosynthesis, and it takes place only
in sunlig ht and o nly in g reen leaves, as they contain
reaction of dilute hydrochloric acid with: chlorophyll (the g reen pig ment) which catalyses
a copper(n) carbonate b sodium carbonate. the process.

• Carbon dioxide carbon dioxide + water c~::.:~~.u» glucose + oxygen

C arbon form s two oxid es - carbo n m o noxide (CO ) 6COi(s) + 6H20 (1) ________. C6H u Oi><t) + 60i(s)
and carbo n diox ide (C0 2 ). C arbo n dioxide is the
m o re impo rtant o f the t wo, and in indu stry large The carbon cycle has continu ed in this m anner fo r
amo unts o f carbo n dioxidt: arc obtained fro m th e milli on s o f years. H owever, scientists have d etected
liqu efa ctio n of air. Air contains approximately 0.03% an imbalance in the carbo n cycle due to the increase
by volume of carbon di oxide. This value has remained in the amo unt o f carbon di oxid e p roduced throug h
alm ost con stant for a lo ng perio d o f time and is burning foss il fuel s and the d eforestatio n o fl arge
maintain ed via the carbon cycle ( Fig ure 13 .1 3). areas o f t ropical rain fo rest. Th e Earth 's climate is
H owever, scientists have recently d etected an increase affected by th e levels of carbon di oxid e (and water
in the am o unt o f carbo n di oxid e in th e atm osphere vapour) in the atm osphere. If th e am o unt o f carbon
to approximately 0.04%. dioxid e, in particular, builds up in th e air, it is
tho ught that th e average temperature of the Earth
~~( ;a,h,a;, \ SUN will rise. Thi s effect is known as the greenho u se
effect ( Figure 13.14 ).
:::;;;~:::~:"b~::~:·,~p\t;oo phot)osynthesis
Som e e nergy fr o m the Sun is absorbed b y
o"'CO' ~ ~ the Earth and its atmosphere. The remainde r
is refl ected back into space. The energy that is
~ absorbed helps to heat up the Earth. The Earth
'-... .·_p·l~~tsgiveoutoxyg~ radiates some heat ene rgy back into space but
th e 'greenh o u se gases', including carbo n di oxid e,
burned as fuels "-. - ·· \ prevent it fro m escaping . Thi s e ffect is similar
to th at o bser ved in a g ree nh o u se wh ere sunlig ht
p,orducingCr02 ldeatha~ecay decay (visible/ ultravio let radiati o n ) enters th rou gh
th e g la ss panes but heat (infrared radiati o n ) h as
- carbon compounds diffi cu lty escaping throu g h the g lass. Other gases
in oil,gas,coal also contribute to the g reenh o u se effect . One
and carbonates o f th ese is methan e, whi ch is p rodu ced fr o m
ag riculture and released fr o m landfill sites as well as
"""IEc,!,;0-"_"'.;:;, rice field s.

Figure 13.1 3 The carbon cycle. Th e lo n g -term effe ct o f the hig her temperatures
o f the greenho use effect and the subsequent global
C arbon dioxide is p roduced by burnin g fo ssil fod s. warming will be the continued gradu al melting o f
It is also produced by all living o rganism s throu gh ice caps and con sequent fl ooding in low-lying areas
aerobic respiration. Animals take in oxygen and o f th e Earth. Th ere will also be furth er changes in the
breathe o ut carbo n di oxid e. weather patterns which will furth er affect agriculture
worldwid e.

SUN Carbon dioxide
SUN
Uses of carbon dioxide

Carbo n dio xide has some important uses.

• Carbonated drinks. Large quantities arc used to
m ake soda and mineral waters. The carbon dioxide
gas is bubbled into the liquid und er pressure,
which increases its solubili ty.

• Fire extinguishers. It is used in exting uishers fo r
use o n electri cal fir es . C arbo n dioxide is d enser
than air and fo rm s a layer around th e burnin g
material. It covers the fire and starves it o f oxygen.
Carbon dioxide d ocs no t burn and so the fir e is put
o ut (Figure 13.15).

greenh o use

Figure 13.14 The greenhouse effect. a Any fire needs fuel, oxygen and heat. If any of these is removed, the
fire triangle is destroyed and the fi re will be extinguished.
These p roblem s have been recogni sed b y natio ns
worldwid e. Recent agreem ents und er the Kyoto
Protocol b etween nati ons m ean that there will be
som e reductio n in th e am o unt o f carbo n dioxide (and
o ther greenho use gases ) p rodu ced over the n ext few
years. H owever, th ere is still a lo ng way to go .

Questions

1 'Burning fossil fuel in an aircraft engine is significantly
worse than burning t he fuel at ground level.'
Discuss this statement in terms of the greenhouse effect
and global warming .

2 Use your research sk ills to find out abou t:
a the carbon trading scheme
b low-carbon homes
c the Kyoto Protocol.

3 Use your research skills to discover changes that are taking
place to t he ice caps and weather pa tterns worldwide.

b Carbon dioxide fire extinguishers starve the fire of oxygen. They are
usedmainly forelectricalfires.
Figure13.15

13 INORGANIC CARBON CHEMISTRY

• Refrigerants.So lid carbo n di oxid e (dry ice) is used Question
fo r rcfii gcrating ice cream, meat and soft fruit s. It
is u sed fo r this purpose because it is colder than 1 List the important uses of carbon dioxide and for each use you
ice and it sublimes (p. 5 ), and so it d ocs no t pass have given in your answer explain why carbon dioxide is used .
th roug h a potentially damag ing liquid stage.
Properties of carbon dioxide gas
• Special effects. Carbon dioxide is u sed to create
th e 'sm oke' effect you may sec at pop concerts and Physical properties
o n televisi o n. Dry ice is placed in boiling water and
it fo rm s thick clouds of white 'smoke' (Figure 1.9, Carbo n diox ide is:
p. 5 ). It stays close t o the floor du e to the fact that • a colo urless gas
carbon dioxide is d en ser than air. • sparingly soluble in water
• denser than air.
• Heat transfer agents. Carbon dioxide gas is used
fo r transferring heat in some nuclear power statio ns.

Laboratory preparation of carbon Chemical properties
dioxide gas
• When bubbled into wat er it dissolves slightly
In the laboratory th e gas is made by pouring dilute and som e o f the carbo n dioxid e reacts, fo rmin g
hyd rochloric acid on to marbk chips (CaC03) . a solutio n o f the weak acid carbo nic acid which
shows a pH o f 4 or 5.
calcium + hydrochloric ---> calcium + water + carbon

carbonate acid chloride dioxide water + carbon dioxide ~ carbonic acid

CaCOh) + 2HCl(aq) ---> CaCl2 (aq ) + H20 (1) + C02(g) H 20 (I) + C02 (g) ~ H ,co,(,q)

A suitable apparatus for preparing carbo n dioxide is • It will support the combustion o nly of stro ngly
sh own in Figure 13.16. burning substances such as magn esium. This
burning reactive m etal d ecomposes the carbo n
carbon dioxide to p rovide oxygen for its continu ed
d i oxide burning in th e gas . This reactio n is accompanied by
much crackling (Figure 13.1 7 ).

marble
ch ips

""If dry gas is required, then it is passed through conce ntrated
sulfuric acid (to dry it) and then collected as shown below

carbon•
d i oxide

concentrated Figure 13.17 When magnesium burns in carbon dioxide gas, magnesium
sulfuricacid oxide (white) and carbon {black) are produced.

Figure 13.16 Preparation and collection of carbon dioxide gas.

Checkfist

magn esium + carbo n magnesium + carbon Questions

di oxid e oxid e 1 Describe an experiment that you could carry out to show
that carbonic acid is a weak acid.
2Mg(, ) + C02(g) 2Mg0(, ) + C(s)
2 Why is it not possible to use dilute sulfuric acid to make
Thi s reaction is a good example o f a redox process carbon dioxide from limestone in the laboratory?
(C hapter 2, p. 14). Which o f these substances has
been oxidised and which has been redu ced ? Which 3 When carbon dioxide is 'poured' from a gas jar on to a
o f these substances is the oxidising agent and w hich burning candle the candle goes out. What properties of
is the reducing agent? carbon dioxide does this experiment show?
• When carbo n dioxide is bubbled throu gh limewatcr
(calcium hyd roxid e solution ), a white precipitate Checklist
is formed. This white solid is calcium carbonate
( CaC03 ) . This reactio n is used as a test t o show After studying Chapter 13 you should know and understand
that a gas is carbo n dioxide. the following terms.

carbon + calcium calcium + water • Aerobic respiration This is respira t ion that takes place
carbonate in air.
di oxide h yd r o xide
• Carbonate A salt of carbonic acid containing the
C02(g) + Ca(OH h(aq )
carbonate ion, coi-. for example CuC03.
If carbo n dioxide is bubbled throug h this solutio n
continuo u sly th en it w ill eventually become clear. • Carbon cycle The complex series of processes through
Thi s is because of th e formation o f soluble calcium which all of the carbon atoms in existence rotate.
hydrogencarbo nate solutio n.
• Chlorophyll The green substance in plants that acts as a
calcium + water + carbon calcium catalyst in photosynthesis.
h yd roge n -
carbonate di oxide ca rb o n a te • Global warming The increased average temperature on
Earth caused by the greenhouse effect.
• Carbon dioxide reacts with st rong alkalis, su ch as
sodium h ydroxid e, to form carbo nates. A soluti o n • Greenhouse effect The absorption of reflected infrared
o f sodium hyd roxid e can be u sed to absorb carbo n radiation from the Earth by gases in the atmosphere such as
dioxide fr om the air. If excess carbo n dioxide is carbon dioxide (a greenhouse gas) leading to atmospheric or
bubbled throug h a solutio n of an alkali then a global warming.
white precipitate may be o btain ed. Thi s is due
to th e formatio n and precipitation o f the sodium • Lime A white solid known chemically as calcium oxide
hydrogencarbo nate: (CaO). It is produced by heating limestone. It is used to
counteract soil acidity and to manufacture calcium hydroxide
sodium + water + carbon sodium (slaked lime). It is also used as a drying agent in industry.
hyd r o gen -
ca rb o n a te dioxide car bo nate • Photosynthesis The opposite of respiration. The process
by which plants synthesise sugars.

• Raw materia ls The basic materials from which a product
is made. For example, the raw materials for the Haber
process are nitrogen and hydrogen.

• Thermal decomposition The breakdown of a substance
under the influence of heat.

• Thermal dissociation The reversible breaking up of a
substance under the influence of heat.

Sodium h ydroge ncarbonate is quite a u seful
substance. Because it is thermally unstable (easily
decomposed by heat ) it is used as a ' raising agent'
in baking ( C hapte r 8, p. 126).

0

Q Inorganic carbon chemistry

• Additional questions e ( i ) What is the 'greenho u se effect '?
(ii ) Discuss the possible con sequences o f the
1 Thi s questio n is about the limesto ne cycle. g reenh ou se effect if no thing is d o ne to
counteract it.
heat
Limestone - - - - Compound A+ Carbo n dioxide 3 Limesto n e is an important raw material u sed in
many different indus tries.
Limewater - - - - - - - Compound B a One o f the p roperties o flim esto ne is that it
('slaked lime') reacts with acids.
(i) Why d o farm ers spread powd ered limesto ne
:i Name and g ive the fo rmula o f: on th eir field s?
(ii ) H ow can buildings made o flim esto ne be
(i) compound A (ii) compound B. affected by ' acid rain '?
( iii )Write an io nic equation which wo uld
b Write b alanced chemical equatio ns for the represent the react ion s taking place in b oth
( i ) and ( ii ).
fo rmatio n o f both compo unds A and B. b Limesto ne is u sed in the manufacture of iron
(Ch,ptc, 10 , p. 158 ).
c Name and g ive the symbol/formula fo r the io ns ( i ) Why is it add ed to the blast furnace alo ng
with coke and haematite?
present in limcwatcr. ( ii ) Write ch emical equatio n s fo r the reactio n s it
is involved in , in this process.
d Describe with the aid of a balanced chemical c ( i ) Nam e a bui lding material made by heatin g
a mixture of limeston e and clay in a
equatio n what happens ifcarbon dioxide is bubbled rotary kiln.
(ii ) What substance is t he dry produ ct produ ced
through limcwatcr until there is n o further change. in the rotary kiln added t o1
E xplain why this substance is add ed.
2 The diagram sh own below is a simplified versio n o f
th e carbon cycle.

4 dissolves in water

Carbo n dioxid e Acid A

b,bb1,,L o,gh~ + burning

ca lcium hydroxide magaosl~

,or a

a N am c the processes A, B , C and D. White precipitate D White solid B + carbon
b Write balanced chemical equatio ns to represent
I I
the processes taking place in A and B .
c There arc a number o f fuel s which could be further bubbling I
of carbon dioxide
placed in the ' fuel s' b ox. Name three su ch fuel s. Alkaline so lutio n C
d ' The air contains approximately 0.0 3% o f car bon I

dioxide and this amo unt is almost con stant.' Co lourless solution E
Explain why this is a trn e statem ent.
a N am e and g ive the fo rmulae o f substances A
to E.

Additional questions

b Write balanced ch emical equatio ns for the 6 a Give th e names and formula e o f the two maj o r
reactio ns in whi ch compo unds B, C and E were g reenhouse gases.
fo rmed.
b Name a natural source o f the gases you have
c Where would you ex pect to find acid N named in part a.
d Universal indi cator solutio n was add ed to
c Nam e a man -mad e source o f th e gases you have
solution C. What colo ur did it go? named in part a.
e Upon addition o f dilute hyd rochloric acid to
7 Use the words and fo rmulae belo w to complete th e
solution C , a neutralisatio n reactio n took place. foll owin g passage abo ut lim eston e and its uses .
(i) Write a balanced chemical equation fo r the
CaO build ing CaC03 acids
reactio n taking place. them1al C02 oxide acidity
(ii) Name the salt produ ced in this reactio n. quarries quicklime calcium

5 Th e fo llo wing qu estio n is abo ut carbon di oxide. Limeston e is a very comm on rock. The main

a Name and g ive the fo rmula o f each o f the chemical in limesto n e is carbonate
substances A, B and C .
(ch emical formula, _ _ _ ). Limesto ne is
b Identify by name the different pieces o f
apparatu s D , E , F and G. o btained fro m 1l1e uses o flim cston c

c Draw and label the apparatus that sho uld be arc many and varied. Fo r example, because it is
used if a dry sample o f carbo n dio xid e g as was
required. easy to cut into bl ocks it is uscfol as a _ __

d When a gas jar containing carbon diox ide is material. Also it will react with and
held over a burning wooden splint and the
cover rem oved , the flame goes o ut. State two so it is used in the powd er fo rm to reduce soil
properties o f carbo n dioxide illustrated by this
o bservatio n. _ _ _ . \¥ h en limesto ne is heated very

e Carbo n di oxid e is also prod uced when zinc st rong ly, it breaks d own into _ _ _ _ (ch emical
carbo nate is heated st ron gly.
( i) Write a balanced chemical equation fo r the name, calcium _ _ _ ) and carbo n dioxide
reactio n taking place.
( ii) Name the process which is taking place as (ch emical formula, _ _ _ ). This kind o f
the zinc carbonate is h eated.
(iii) Calculate the volume o f carbo n dioxide reactio n is known as _ _ _ decompositio n.
that would be produced (measured at room
temperature and pressure (rtp )) if 12.5 g o f 8 Lime (calcium oxid e) is produced in very large
zinc carbonate were heated stron gly. quantities in a lime kiln. The equatio n for the
(One m o le o f any gas occupies 24dm3 at rtp. reactio n is:

A,, c ~ 12; o~ 16; Zn~ 65) c , c O,(,) - C,O(,) + CO,(g)

a H ow mu ch limesto ne would be need ed to
produce 61.60 tonnes oflimd

(A" c ~ 12; o~ 16; c, ~ 40 )

b Why is the carbo n dioxide swept out o f the
lime kiln ?

c Give three uses o flim e .
d (i) What problems arc associated with th e

large-scale quarryin g o f limesto ne?
(ii) What steps have been taken to overcom e

or redu ce the problems you have outlined
in (i)?

@ Organic chemistry 1

A lkanes The chemica l behaviour of alkenes
Naming the alkanes Addition reactions
Structural isomerism
A special addition reaction of alkene molecules
The chemica l behavio u r of alkanes Other addition polymers
The ozone hole problem Thermosoftening and thermosetting plastics
Methane - another greenhouse gas! Disposal of plastics
Otherusesofalkanes
Check lis t
A lkenes
Naming the alkenes Addit ional questions
Where do we get alkenes from?

A lo t of th e com pound s th at arc present in • Alkanes
li ving thin gs h ave been fo und to be compo und s
containing carbo n (Fi gure 14. 1). These arc kn own M ost o f the hyd rocarbons in crud e oil belong to the
as o rg anic compo unds . All livin g things arc m ad e fa mily o f com pounds called alkanes . The mo lecu les
fro m o rganic compo und s b ased o n ch ain s o f ca rbo n within the alkan e family contain carbo n atom s
ato m s which an: n o t o nly cova lently b o nded to covalently bo nded to four other ato m s by single
each o ther but also covalently bonded to hyd rogen, bond s (Figure 14.2 ). Because these mo lecules possess
oxygen and/or oth er elements. The organic o nly sin gle bo nds they are said to be saturated , as
compo und s arc m an y and varied. Som e scientists n o furth er ato ms can be added . This can be seen in
su ggest that there are m o re than ten millio n kn own the bo nding sch eme fo r methane (Fi gure 14.3) . 1l1c
o rga ni c compo unds. physical properties o f the first six members o f the
alkan e fa mily arc shown in Table 14.1.

You will n o tice fro m Fig ure 14.2 and Tab le 14 .1
that th e compo unds have a similar structure and
similar nanu: endings. Th ey also beh ave ch emically in
a similar way. A family with th ese fa ctors in co mmo n
is called a homo logo us series .

Fi gure 14 .1 Living things contain organic compounds. All the m em hers o f a ho m o logous series can also be
represented by a gen eral fo rmula. ln th e case o f the
Yo u saw in C hapter 6 th at crud e o il is m ad e up o f alkanes the general fo rmula is:
a com plex mixture o f hydrocarbo n compo und s.
This mi xture is a very im portant raw material in the Cn H 2n +2
organic chemical industry. O ur world wo uld be a
very different place with o ut these substances. C m wh ere n is the number o f carbo n ato ms present.
you imagin e life with o ut th e substan ces fro m o il As you go up a ho m ologous seri es, in o rder o f
and natural gas? There would be n o o il-based fuel s,
such as pet rol and diesel, and the ch emical industry, increasing num ber o f carbo n ato m s, the physical
particularly the plastics industry, would also suftCr properties o f the compo unds g radually change .
since substances extracted fro m o il arc used as raw For example, the melting and boiling points o f the
m aterials fo r many plastics. alkanes sh own in Table 14 .l gradually increase. This
is due to an increase in the interm olecular forces
(van d er Waals' fo rces) as th e size and m ass o f the
m olecu le increases (Chapter 3 , p. 49 ).

Under norm al conditio ns m o lecules with up to
fo ur carbon ato m s are g ases, those with between fi ve
and 16 carbon ato m s are liquids, while th ose with
m o re than 16 carbo n ato m s are solids.

Alkanes

methane methane molecule (CH4)
Fi gu re 14.3 The covalent bonding scheme for methane.
i
Table 14.1 Some alkanes and their physical properties.
H -C- H
A lkane Fo rmul a Melting Bo ilin g Ph ys ica l st ate at
1 po in t / po int/ room t emperature
Methane CH,
ethan e Ethane C2H6 ·c ·c Gas
Propane C3He Gas
11 Butane C4H10 -182 -162 Gas
Pentane CsHu -89 Gas
H - C- C- H Hexane C6H14 -183 --42 Liquid
-188 Liquid
11 36
-138 69
propan e
-130
111
-95
H - C- C- C- H
Questions
111
1 Estimate the boiling points for the alkanes wi t h formulae :
butane a C7H16 b C8H 18 .
HHHH
2 Name the alkanes which have the following formula e:
IIII
a C7H16 b C10H22 .
H - C- C- C- C-H
Naming the alkanes
1111
All th e alkan es have names ending in -ane. The rest
pentane o f the n am e tells you the number o f carbo n ato m s
HHHH H present in the m olecule . Fo r example, the compo und
whose name begins with :
IIIII
• meth- has o ne carbo n ato m
H-c- c- c - c- c-H • et/J- has two carbo n ato ms
• prop- has three carbon ato m s
11111 • but- has fo ur carbon ato m s
• pent- has fi ve carbon ato m s
hexane
HHHHHH and so o n.

IIIIII

H-c- c- c- c- c- c-H

IIIIII

HHHHHH

Fi gure 14.2 The fullydisplayed(orstructural)formulae and
molecularmodelsofthefirstsixalkanes.

14 ORGANIC CHEMISTRY 1

Structura l isomer ism Gaseous alkan cs, su ch as m ethane, will burn in a
good supply o f air, fo rming carbo n dioxide and water
Sometimes it is possible to write m ore than o ne as wdl as plenty o f heat en ergy.
struch1ral formula to represent a molecular formula.
The structural fonnula of a compound sh ows how the m ethane + oxygen __., carbon + water + energy
ato ms an: jo ined together by the covalent bonds. For
example, there a.re two different compounds with the di oxid e
molecular fo rmula C4 H 10. The structural fo rmulae
o f these two su bstanccs alo ng with their names and CH 4(g) + 202(g) - C0 2(g) + 2H 20 (g)
physical properties arc sh own in Figure 14.4.
The gaseous alkancs arc som e o f the m ost u seful
IIII melting po int fuel s. 1\ kthan c, better kn own as natural gas, is u sed
-138"( fo r cooking as wd l as fo r h eating o ffi ces, sch ools and
H- C- C- C- C- H h om es (Figure 14.Sa ). Propan e and butane burn
boiling point with very ho t fl am es and they arc sold as li q uefi ed
IIII O"C petro leum gas ( LPG ). In rural areas where there
is no supply o f n atural gas, central h eating system s
HHHH can be run o n p ropane gas ( Fig ure 14.Sb ). Butane,
som etimes mixed with propan e, is u sed in po rtable
a butane bl owlamps and in gas li ghters.

H-,-C-,-HH H H melting point a Thisisburningmethane.
III - 159"(

HH bo iling point
-1 2°(
1

H- C- H

I
H

b 2-methylpropane

Figure 14.4 TheisomersofC4H10.

Compo und s su ch as those in Figure 14.4 arc
known as isomers. Isomers arc substances which
have the sam e mo lecular fo rmula but different
stru ctural fo rmulae. The different stru ctures o f the
compo unds shown in Fig ure 14.4 have different
meltin g and bo iling po ints. Mok culc b contains a
branched chain and has a lower melting p oint than
mo lecule a , which has no bran ched chain. All the
alkan c m o lecules with fo ur o r m o re carbon ato ms
possess isomers. Perhaps now you can sec why th ere
arc so many different o rganic com pounds!

Question b Central heating systems can be run on propane.
Figure 14.5
1 Draw the struct ural form ulae for the isomers of C5H12.
Ano ther u seful reactio n worth no ting is that
• The chemical behaviour between th e alkancs and the halogens. Fo r example,
of alkanes m ethan e and chlo rine react in the presen ce o f
sunlig ht (o r ultravio let lig ht). The ultravio let light
Alkancs arc rather unrcactivc com pounds. Fo r splits the chlo rine m o lecules into atom s. W hen this
example, they arc gen erally n o t affected b y alkalis, type o f reacti o n takes place, these ato m s arc call ed
acids o r many oth er su bstan ces . Their m ost important free rad icals and th ey arc very reactive.
property is that th ey burn easily.
chlo rine gas sunlight chl o rine ato m s
C l2 (g)
(free radicals)
2 C l(g)

The chemical behaviour of alkanes

The chlo rine ato m s then react furth er with m eth ane Early an aesth etics relied upon trichlorom cthanc,
C H C 13 , o r chloroform. Un fortunatdy, this
mo k cuks, and a hydrogen chl o ride mo lecule is anaesthetic had a severe p roblem since the leth al
d ose was only slig htly hi gh er tlun that required
prod uced alo n g with a m ethyl fr cc radi cal. to anaesth etise the patient. In 1956, halo tl1an c
was discovered by ch emists working at !C l. This
chlorine + m ethane ----+ methyl + hyd rogen is a compo und containin g chlo rine, b romine and
flu orin e. Its fo rmula is C F3C HBrC I. H owever, even
at o m radical chl oridc this is no t the perfect anacstl1etic since e,,idc ncc

Cl(g) + CH4(g) - CH3(g) + H Cl(g) su ggests tlut p rolo n ged exposure to this substan ce
may cau se liver d am age. The search continu es fo r
The mcthyl free radical reacts forth cr. even better anacstl1ctics.

m ethyl + chlorine ----+ chl orom ethane + chl o rinc A group o f com pounds were discovered in the
19 30s and were called the chl oroflu orocarbon s
radical gas atom (CFCs). Because o f their inertness they found
many u ses, especially as a propellant in aerosol can s.
CH3(g) + Cl2(g) - CH3Cl(g) + Cl(g) C F C - 12 or dichl orodifluorom eth ane, C F2 C l2 , was
o ne o f th e m ost p o pular C FCs in use in aerosols.
This chlo rine free radical , in turn , reacts furth cr and Scientists believe that C FCs released fr o m aerosols
thc proccss continues until all the chl o rine and the arc d est royin g the ozone layer and steps arc being
methan e have been used up. This typc o f process is taken to reduce this tlueat.
known as a chain reaction and it is very fa st. The
overall ch emical equatio n for this p rocess is: The ozone ho le prob lem

methan e + chlo rinc ----+ chlo rom ethan c + hydrogcn Our atmosphere protects u s fr om harmful ultravio let
radiati o n fr om the Sun. This d amag ing radiatio n is
chlo ride absorbed by the rdatively thin ozone layer fo und in
the stratosphere ( Fig ure 14.7) .
CH4(g) + Cl2(g) - CH 3Cl(g) + H Cl(g)
Large ho les have recently been di scovered in
We can sce that one hyd rogen atom o f the m ethane the ozone layer over Antarctica, Au stralasia and
m o lecule is substituted by a chlorine atom. This type Europe ( Figure 11.5, p. 17 3). Scientists think tlut
o freaction is known as a substin1tion reaction. these h o les have been prod uced by C FCs such as

Because we cannot contro l the chlorine free radicals
produced in this reactio n , we also o btain small
am ounts o f other ' substihited ' products - C H 2C l2
(dichloromethanc), C H C13 (trichlorom ethan c or
chloroform ) and CC14 ( tctrachlorom cthanc) - by
furthcr rcaction s such as those shown bdow.

chloromethane + chlorine ----+ chloromethyl + hydrogen

radical chl orid e thermosphera
80
+ Cl(g) - C H, Cl(g) + H Cl(g)
70
.'_ ~· ,,chloromethyl + chlorine ----+dichloromethane + chlorine Ionosphere

radi ca l gas i "60 ························ ·····r \

C H2Cl(g) + Cli(g) ----+ CH2Cl2(g) + Cl(g) I\

Many of these so -called halogenoalkanes arc used ; 40 stratosphe re I
as solvents. Fo r example, dichlorom ethane is u sed as
a solvent in paint stripper (Figurc 14.6) . ozone laye r

~ J..30 V
..............................

Cl !'\ .20
I
H- C- 10 ...........
I
H troposphe~ ~

CI

/ f /~1"1~, ,f,x~.._&

te mpe rature/°C

Figure 14.7 The ozone layer is between 25km and 50 km above
sea level.

Figure 14.6 Dic:hloromethane is used as a solvent in paint stripper.

14 ORGANIC CHEMISTRY 1

C FC -12 . C FCs escape into the atm osphere and , the iro n acts as a catalyst firstly rem oving carbo n
becaL1 sc o f their inertness, remain with o ut furth er fro m the methan e. W hen the surface of the iron
reactio n until they reach the stratosphere and the becom es saturated , nan otu bes begin to be fo rmed .
ozon e layer. In th e stratosphere the hi gh-en ergy lf H e or Ar is added to th e vacu um cham ber th en
ultravio let radiatio n causes a chlorine ato m to split ' m etallic' (electrical condu cting) nano tubcs arc mad e
off fr om the C FC mo lecule . This chlorine atom , or in the majority; this accounts fo r up to 91 % o f th e
free radical, then reacts with the o zo ne . n ano tubcs produ ced (Fig ure 14 .8) .

Cl(g) + O,(s) - OCl(g) + O,(s) Figure 14.8 Thesenanotubesarebeing used in electrical circuitry.

This is not the only problem with C FCs . They arc Other uses of alkanes
also sig nificant 'greenho use gases' (Ch apter 13,
p. 212 ). The ozone d epiction and g reenho u se Besides tl1eir major use as fuel s (p . 90), some o f
effects have become such serio us problem s that an the heavier alkancs arc u sed as waxes in candles, as
international ag reem ent known as the M ontreal lubricating o ils and in the manu fac ture o f ano ther
Protocol on Substances that Deplete the Ozone Layer fa mily o f hyd rocarbo n s - the alkcncs.
was agreed in 198 7.
Questions
Research is n ow going ahead , with som e su ccess,
to produce safer alternatives to C FCs. At present, 1 Write a balanced chemical equation to represent the
better alternatives called hyd rochloroflu orocarbon s combustion of propane.
( H C FCs) have been d evelo ped - th ese have lower
ozon e-depictio n effects and arc no t effective 2 In what mole proportions should chlorine and methane be
greenho use gases. It is beli eved that if the intended mixed to produce:
agreements arc adhered to then the ozon e layer will a mainly chloromet hane?
recover by 2050. b mainly tetrachloromethane?

Methane - another greenhouse gas! 3 Describe a method you would use to separate
chloromethane from the other possible reaction products
M ethan e, th e first m em ber o f th e alkancs, occurs when methane reacts with chlorine.
naturally. Cows produce it in huge qmntiti cs wh en
digesting their foo d. It is also fo rmed by growing 4 Explain why it is the C-CI bond and not the C-F bond in
ri ce. Like carbon diox ide, it is a greenho use gas CFCs tha t is disrupted in the stratosphere.
(Ch apter 13, p. 2 12) becau se it acts like the g lass in a
greenh o use - it will let in heat fro m th e Sun b ut will • Alkenes
n ot let all o f the heat back out again. It is th o ug ht
that the g reenhou se effect m ay contribute to climate Alkcn cs fo rm an o ther ho m o logou s seri es o f
change, which could have disast rou s effects fo r li fe o n hyd rocarbo ns o f the general fo rmula Cn H ln wh ere
this planet. n is the number o f carbo n atom s. The alkcnes arc
m o re reactive than the alkancs becau se they each
Question contain a d o uble covalent b o nd between the carbo n
atom s ( Figure 14.9). M o lecules that possess a d o uble
1 Use your resea rch skills to find out: covalent bo nd o f this kind arc said to be
a any other sources of met hane found in nature
b how climate change might affect your particular
environmen t.

Methane -the 21st century chemical

M ethan e is findin g an o ther u se, which sets it apart
fro m the rest o f th e alkancs, in the prod uctio n
o fnan o tu bcs fo r power gen eratio n and futuri stic
circuitry. A comm on way to grow nan o tubcs is fro m
a mixture o f methane gas and iron nan o particlcs.
Wh en h eated to around 700- 80 0°C in a vacu um

Alkenes

Figure 14.9 Thebondinginethene, thesimplestalkene. Where do we get alkenes from?

unsaturated, b ecause it is p ossible to break o n e o f Very few alkcn cs arc fo und in nature. Most o f the
the two bo nds to add extra atom s to the mo lecule. alkcncs used by th e pet roch emical ind ustry arc
o btain ed by breaking up larger, less useful al kanc
Th e chemi cal test to sh ow the differen ce between m olecules o btained fro m the fractio n al d istillatio n
saturated and unsaturated h ydrocarbo ns is discussed o f crude o il. This is usu ally d o ne by a process
on p. 225 . call ed catalytic cracking . In this process the alkan c
mo lecules to be 'crac ked ' (split up ) arc passed over a
Naming the alkenes mixture o f aluminium and chro mium oxid es heated
to about 500 °C.
All alkcncs have names ending in -ene. Alkcncs,
especially cthcnc, arc very important industrial d odccanc _______. d ccan c + cthcn c
chemicals. 1l1cy arc used extensively in the plastics C12 H26(B) _______. C10H22(s ) + C2 H4(g)
industry and in the productio n o f alco ho ls such as
ethano l an d propan ol. Sec Table 14.2 and Figure 14.10. (!oundinkerosene)

Ano ther possibility is:

Tabl e 14.2 Thefirstthreealkenesandtheirphysicalproperties. There is a furth er cracking process w hich is m o re
versatile, called thermal cracking. Thermal cracking
Alkene Fo rmula M elting Boiling Phy sical state at is carried o ut at a hig her tem perature than catalytic
point!°C pointr c room t emperature cracking, 8 0 0- 8 50 °C. This process is m ore expe nsive
owing to the high er tem perature used. H owever,
Ethene C2H4 -169 -104 Gas larger alkanc mo lecules can be m o re successfully
cracked using this p rocess than by the catalytic
Propene C1H6 -185 -47 Gas m etho d .

Butene C4Hs -184 -6 Gas N o te that in these reactions hyd rogen may also be
fo rmed during cracking. Th e am ount o f hyd rogen
eth ene I•-ll produ ced d epends o n the conditio ns used. Since
sm aller hyd rocarbo ns arc generally in greater d em and
pro pen e than th e larger o nes, crackin g is used to match
d em and (Table 14.3).
11 /
Tabl e 14.3 Percentages of the fractions in crude oil and the demand for
H-C-C= C them .
I \H
H Fraction Approx. % in crud e o il Approx. % demand
Refinery gas
butene Gasol ine 21 28
Kerosene 13
Diesel oil 17 25
Fuel oil and bitumen 47 34

Figure 14.10 Structure and sh ape of the first threealkenes. This m eans th at o il companies arc no t left with large
surpluses o f fractions containing the larger m o lecu les .

Figure 14.11 sh ows the simple apparatu s that
can be used to carry out cracking reactio ns in th e
laborato ry. Yo u will no tice that in th e laboratory we
may use a catalyst o f broken , un glazed pottery.

14 ORGANIC CHEMISTRY 1

paraffi n Addition reactions
soaked into
absorbent wool Hydrogenation

bro ken po rce lain This reactio n is called hydrogenation. Th e
or aluminium conditio ns necessary for this reactio n to take place
oxid e granules arc a temperature o f 200 °C in the presence o f a
nickel or platinum catalyst .
cold w ate r bath crystallising dish
Figure 14.11 Thecrackingofanalkaneinthelaboratory. cthcnc + hyd rogen _______. ethane
c, H. (g) + H , (g) ~ c, H,(g)
Questions
H yd rogenatio n reactio ns like the one shown with
1 Using the information in Table 14.2 (p. 223), make an cthcne arc used in the manufacture o f m arg arin es
estimate of the boiling point of pentene. fr om vegetable o ils. Vegetable o ils contain fatty
acids, such as lino lcic acid ( C 18H 320 2 ) . These arc
2 Write a balanced chemical equation to represent the unsaturated m o lecules, co ntaining several d o uble
process that takes place when decane is cracked. b o nds. Th ese d o uble b o nds m ake the m o lecule
less fl c.x iblc. H yd rogenati on can co nvert these
• The chemical behaviour m o lecules into m o re saturated o nes. N ow the
of alkenes m o lecules arc less rig id and can fl ex and twist m o re
easily, and h en ce pack m o re cl osely together. This
The d o uble bond m akes alkcncs mo re reactive in turn cau ses an in crease in the interm olecular
than alkancs in ch emical reacti o ns. Fo r example, fo rces and so raises the melting po int. Th e n ow
hyd rogen add s across the d ouble bo nd of cthcnc, so lid margarines can be spread on bread m o re easily
under suitable conditio ns, fo rming ethane than liquid o ils.
(Figure 14.12 ).
Th ere is an o ther sid e to this p rocess. Many
Figure 14.12 Theadditionofhydrogentoetheneu~ng molecular d octo rs n o w believe that un sa turated fats arc
models. h ealthie r th an saturated o n es . Becau se o f thi s,
m an y marg arin es arc le ft partially unsaturated.
Th ey d o n o t have all th e C = C take n o ut o f th e fat
m o lecules. H owever, the matter is far fr o m settled
and the debate continues.

Hydration

An o th er impor tant addition reaction is the o n e
u sed in th e manufacture o f ethan o l. Ethan o l has
impo rtant uses as a solvent and a fuel (p . 94 ). It is
fo rmed wh en wa ter ( as stea m ) is add ed across th e
d o u ble bo nd in e th ene . For this reacti o n to take
place, th e reactants have to be passe d over
a ca talyst o fph ospho ric(v ) acid ( ab sorbed o n
sili ca pellets) at a tempe rature o f 300 °C and
pressure of 60 atmosphe res ( 1 atmosphere =
l x 105 pasca ls) .

The chemical behaviour of alkenes

ethene + 300°C, 60 atm ethanol 4 Which of the following organic chemicals are
-------"-
alkanesora lkenes?
~
Propene, C3H6
p hos p h or ic{v) Butanol, C4HgOH
Octane, C8H18
acid catalys t Nonane, C9H20
Methanoic acid, HCOOH
+ HzO{g)
Butene, C4H8
HH ~~ State why you have chosen your answers.

'c---6 + H-O H H-C- C-H
II
/ '\ H OH
HH

This reactio n is reversible as is sh own by the
equilibrium (~ ) sign. The conditions have been
ch osen to ensure th e highest possible yield o f
ethan o l. In o ther word s, the conditio ns have been
ch osen so that they favour the for ward reactio n.

Fo r a further discussio n o f ethanol and alco h ols
generally sec p. 233.

Ha loge nati o n - a t est for un saturat ed
co mpo unds

The additio n reactio n between b romin e dissolved
in an o rganic solvent, o r water, and alkcn cs is used
as a chemical test for the presence o f a d o ubl e bo nd
between two carbo n atom s. When a few d rops o f this
bromine solution arc shaken with th e hydrocarbon,
ifit is an alkcn c, su ch as cthcnc, a reactio n takes
place in which b romine jo ins to the alkcne d o uble
bond. This results in the bromin e solutio n losing
its red/ b rown colo ur. If an alkanc, such as h exane,
is shake n with a b romin e solutio n o f this type, n o
colour change takes place (Fi gure 14 .13). Thi s is
becau se there arc no d ouble bonds between the
carbo n ato m s o f alkancs.

ethene + bromine dibromoetha ne

HH ~¥
'\ /
C=C + Br- Br H- C- C- H
/ '\ II
HH Br Br

Qu e stions

1 What is meant by the term 'addition react ion'?
2 Write a word and balanced chemical equat ion for the

reaction between ethene and hydrogen chloride.
3 Write the structural formula for pentene.

Figu re 14.1 3 The alkene decolourises bromine in 1, 1, I-trichloroethane.

14 ORGANIC CHEMISTRY 1

• A special addition
reaction of alkene
molecules

Po lyth en e is a plastic that was discovered by accid ent.
Thro ll g h the careful e xaminati o n of this subst ance,
w h en it was accid entall y discovered , the plastics
industry was b o rn. Po lythe ne is now prod LJccd in
million s o f t o nnes world wide ever y year. It is mad e by
heating cth cn c t o a relatively hig h te mpe rature und er
a high pressure in th e presen ce o f a cat alyst.

Figure 14.15 Thesecratesaremadefrompoly(ether.e).

w h ere n is a ver y large numbt:r. In po ly( cthc n c) th e O ther alkt:nt: molecules can also produce substances
cthc n c m olecules have jo ined t ogeth er to fo rm a ver y like poly(cthene); fo r nampl c, propcnt: prod uces
long hyd rocarbon chain (Figure 14.14). Th e cthcnc po ly(propcnt: ), which is used to make ropes and
m o lecu les a rc abk t o fo rm ch ains like this becau se p ackagin g .
they possess carbo n-carbo n d o uble b ond s.
When small molecules li ke cthcnt: jo in together
Figure 14.14 This model shows part of the poly{ethene) polymer chain. to form lo ng chains of atoms, called polymers, the
process is called po lymerisation. The small molecules,
Po ly(cthcnc ) is produced in three main fo rm s: like ctl1cnt:, which join togctl1t:r in this way arc calkd
• low density poly(cth cnc ) (LDPE ) monomers . A polymer chain , a very large molecule o r
• lin ear low density poly(ethcnc) (LLD PE ) a macrom olecule, often consists of man y tl1o usands
• high density poly(cth cnc) (HDPE ). of mo no mer units and in an y piece of plastic there
The world productio n of all types of po ly(cthcnc ) is will be many millio ns of polymer chains. Since in
in excess of 52 million to nnes per year. this po lymerisati on process th e mo nomer uni ts add
together to fo rm only o ne product, th e po lymer, tl1c
Po ly(cthcnc) has many useful properties: process is called additio n po lymerisatio n.
• it is easily mo ulded
• it is an excellent electrical insulator Other addition polymers
• it docs not corrode
• itis tough Many o ther addition polymers have been produced .
• it is not affected by tht: wt:atht:r Often the plastics art: produced with particular
• it is durable . properti es in mind , for exampk PVC (po lyvinyl
It can be fo und as a substitute fo r natural materials chl oride o r poly(chlo rocthcnc)) and PTFE
in plasti c bags, sandwich boxes, washing-up bo wls, (po ly( tctraflu oroc thcnc) ). Bo th of th ese plastics
wrapping film , milk-bo ttle crates and washing -up ha,'c mo nomer units similar to t:tl1cnc.
li quid bottles (Fig ure 14.15).
'H'c~c/ H FF

H/ Cl 'c~c/
'F/ F

PVC monomer PTFE monomer
(vinyl chloride or (tetrafl uoroethene)

chloroethene)

If wt: use chl o rocthent: (Fig ure 14. 16a ), the
polymer we make is slig htly stronger and harder
than po ly(etl1enc ) and is particularly good fo r
making pipes fo r plumbing (Figure 14.17).

(} -( ) (-~-~-) A special addition reaction of alkene molecules
H Cl H Cl n
polymer chain If wc start fro m tctraflu orocthcnc (Figure 14. 18a)
the polymer we make, PTFE, has some slightly
unusual properties :

• it will with stand very hig h temperatures, o f up to
260 °C

• it form s a very slippery surface
• it is hydropho bic (water repellen t )
• it is highly resistant to chemi cal attack.

These properties make PTFE an id eal ' n o n-stick'
coating for fr ying pans and sau cepans. Evt:ry year
m o re than 50 OOO to nnes o f PTFE arc made.

Fi gure 14.1 7 These pipes are made from PVC. "(>-<) (-H-)
FF n
PVC is th e m ost versatile plastic and is the second polymer chain
most widely used , after po ly(cthcnc) . Worldwid t:
mo re than 2 7 millio n tonnes arc prod LJ ccd annually. The p roperties o f som e additio n po lym ers alo n g with
their uses arc g iven in Table 14.4.

14 ORGANIC CHEMISTRY 1

Tabl e 14.4 Some addition polymers.

Plastic Monomer Properties Uses

Poly{ethene) CH2=CH1 Tough, Carrier
durable bags, bov.ls
buckets,

packaging

Poly{propene) CH3CH=CH2 Tough, Ropes,
durable pac kaging

PVC CH 2=CHCI Strong, Pipes,

hard(less electrical

flexible than insulation,

poly{ethene)) guttering

PTFE CF2=CF1 Non-stick Non-stic k
surface, frying pans,
v.it hstands soles of irons
high
temperatures

Polystyrene CH2=CHC6Hs Light,poor Insulat ion,
conductor of packaging
heat {especially as
foam)

"'""'' CH2=C(C02CH¥.H1 Transparent Used a s
a glass

substitute

Thermosoftening and thermosetting Figure 14.20 These objects are made from compression-moulded
plastics t hermosett ing pla stics.

Plastics can be put into o ne o f two categories . If Figure 14.21 shows the different mo lecular
they melt or soften when heated (like poly( cthcn c ), structures for therm osetting and thermosoftening
PVC and polystyrene) then they arc call ed plastics. 1l1ermosetting plastics have po lym er chains
thennopfostics or them10softening plastics. If which are linked or bonded to each other to g ive
they d o no t soften o n heating but o nly char and a cross -linked structure, and so the chain s are
decompose o n further heating, they are known as held firmly in place and no softening takes place
themiosetting plastics. o n heating. Therm osoftening plastics d o n ot have
po lym er chains jo ined in this way, so when th ey arc
Th ermopl astics are easily m o ulded or fanned subjected to heat their po lym er chains fl ow over o ne
into u seful articles. Once they are m o lten they another and the plastic soften s.
can be injected o r bl own into m o ulds, and a
variety of different-shaped item s can be produ ced
( Fig ure 14.19). Therm osetting plastics can
be heated and m o ulded o nly on ce, u sually by
compressio n m o ulding (Figure 14.20).

a In thermosetting plast ic t he b lnthermosofteningplasticthere
chains are cross-l in ked. is no cross-linking.

Figure14.21

Figure 14.19 These objects are made from thermosoftening pla stics.

A special addition reaction of alkene molecules

Disposal of plastics

In the last 30 to 4 0 years plastics have taken over as
replacem ent materials for metals, glass, paper and wood
as well as fo r natural fibres such as cotto n and wool.
This is not surprising since plastics are ligl1t, cheap,
rdativd y unrcactive, can be easily moulded and can be
dyed bright colours. H owever, plastics have contributed
significantly to tl1c ho useho ld waste problem, up to I 0%
in some countries, and it's getting worse (Figure 14 .22 )!

In the recent past, mu ch o f o ur pl astic waste has a This plastic bag is photodegradable.
been used to landfill disused quarries. H owever, all
over the world these sites are getting harder to find
and it is b ecomin g m ore and m o re exp ensive. Th e
alternatives to dumping plastic waste arc certainly
m o re econ o mical and m o re satisfa cto ry.

• Incineratio n schem es h ave been d eveloped to use tl1e b Thisplasticdissolves inwater.
heat generated fo r heating purposes (Fig ure 14.23). Figure14.24
H owever, probl em s witl1 the combu stio n process
(which can result in the productio n o f toxic gases)
mean that especially hig h temperatures have to be
employed during the incineratio n process .

• Recyclin g - large qmntitics o f black plastic bags
and sheeting arc produ ced for resale .

• Biodegradable plastics, as well as those po lym ers
tlut d egrade in sunlig ht (photodegradable,
Fig ure 14 .24 a), have b een d evelo ped . O ther
comm on categories of d egradable plastics include
synthetic bio d egradabl e plastics which arc b roken
d own by b acteria, as well as plastics which dissolve
in water (Fig ure 14.24b). The property that
allows plastic to di ssolve in water h as been used in
relatively new produ cts, including soluble capsules
containing liquid detergent. H owever, tl1c vast
majority o f po lym ers arc still no n-bi odegradable.

14 ORGANIC CHEMISTRY 1

Questions • Chain reaction A reaction which is self-sustaining owing
to the products of one step of the reaction assisting in
1 Write the general equation to represent the formation of promoting further reaction.
polystyrene from its monomer. Cross-linking The formation of side covalent bonds
linking different polymer chains and therefore increasing the
2 Give two advantages and two disadvantages of plastic rigidity of, say, a plastic. Thermosetting plastics are usually
waste (rubbish). heavily cross-linked.
Free radicals Atoms or groups of atoms with unpaired
3 Draw the structure of the repeating unit of the addition electrons and which are therefore highly reactive. They can
polymer formed from CH3----CH=CH2. be produced by high-energy radiation such as ultraviolet
light in photochemical reactions.
4 Draw the structure of the monomer from which the Halogenoalkanes Organic compounds in which one or
addition polymer below has been produced. more hydrogen atoms of an alkane have been substituted
by halogen atoms such as chlorine.
4 Hs H C.Hs H C.Hs H Homologous series A series of compounds in which
each member differs from the next by a specific number
-cI -cI -cI -cI -cI -cI - and kind of atom. These compounds have the same general
1I I I I I formula and similar properties.

HHHHHH • Isomers Compounds which have the same molecular
formula but different structural arrangements of the atoms.
Checklist
• Monomer A simple molecule, such as ethene, which can
After studying Chapter 14 you should know and understand be polymerised.
the following terms.
• Organic chemistry The branch of chemistry concerned
• Addition polymer A polymer formed by an addition with compounds of carbon found in living organisms.
reaction. For example, poly(ethene) is formed from ethene.
• Photodegradable plastics Plastics designed to degrade
• Addition reaction A reaction in which an atom or group under the influence of sunlight.
of atoms is added across a carbon-carbon double bond.
• Polymer A substance possessing very large molecules
• Alkanes A family of saturated hydrocarbons with the consisting of repeated units or monomers. Polymers
general formula CnH2,,,_1. The term 'saturated', in this therefore have a very large relative molecular mass.
context, is used to describe molecules that have only single
bonds. The alkanes can only undergo substitution reactions • Polymerisation The chemical reaction in which molecules
in which there is replacement of one atom in t he molecule (monomers) join together to form a polymer.
by another atom. Saturated hydrocarbon A type of hydrocarbon molecule
in which the molecule has the maximum possible number of
• Alkenes A family of unsaturated hydrocarbons with hydrogen atoms and so has no double bonds.
the general formula CnHln- The term 'unsaturated', in Substitution reaction A reaction in which an atom or
this context, is used to describe molecules which contain group of atoms is replaced by another atom or group of
one or more carbon-carbon double bonds. Unsaturated atoms.
compounds undergo addition reactions across the carbon-
carbon double bonds and so produce saturated compounds. • Test for unsaturation A few drops of bromine dissolved
The addition of hydrogen across the carbon-carbon double in an organic solvent are shaken with the hydrocarbon. If it
bonds is used to reduce the amount of unsaturation during is decolourised, the hydrocarbon is unsaturated.
the production of margarines.
• Thermal cracking The decomposition of higher alkanes
• Biodegradable plastics Plastics designed to degrade to alkenes of lower relative molecular mass at high
(decompose) under the influence of bacteria. temperatures, 80D-8S0°C.

• Catalytic cracking The decomposition of higher alkanes • Thermoplastics Plastics which soften when heated (for
into alkenes and alkanes of lower relative molecular mass. example poly(ethene), PVC).
The process involves passing the larger alkane molecules
over a catalyst of aluminium and chromium oxides, heated • Thermosetting plastics Plastics which do not soften on
to S00°C. heating but only char and decompose (for example, Bakelite
and melamine).
• CFC Abbreviation for chlorofluorocarbon, a type of
organic compound in which some or all of the hydrogen • Unsaturated hydrocarbon A hydrocarbon molecule
atoms of an alkane have been replaced by fluorine and which contains double or triple covalent bonds between
chlorine atoms. These substances are generally unreactive carbon atoms.
but they can diffuse into the stratosphere where they
break down under the influence of ultraviolet light. The
products of this photochemical process then react with
ozone (in the ozone layer). Because of this, their use
has been discouraged. They are now being replaced by
hydrochlorofluorocarbons (HCFCs).

Q Organic chemistry 1

• Additional questions b Alkancs can be converted into substances wh ich

1 Explain the following. arc used as solvents. To do this the alkanc is
a Ethcnc is called an unsaturated hydrocarbon. reacted with a halogen, such as chlorine, in the
b The cracking ofb.rgcr alkancs into simple alkancs presence of ultraviolet light.
and alkcncs is important to the petrochemical (i) Write a word and balanced chemical
industry.
c The conversion of cthcnc to ethanol is an equation for the reaction between methane
example of an addition reaction. and chlorine.
( ii ) Name the type of reaction taking place.
2 The following question is about some of the (iii ) H ighly reactive chlorine atoms arc produced
reactions of cthcnc. in the presence of ultraviolet light. When
atoms arc produced in this way, what arc
gas B they called?
(iv) Write a balanced chemical equation for the
" ' hyd,ogeo aod reaction which takes place between CHF3
~catalyst A and C l2 to produce a ch lorofluorocarbon
(CFC).
b7 J~~:;oETHENE --bu-rn i-n - gas C+ water (v) Why arc CFCs such a problem?

liq uid F 4 a Ethcnc, C 2H 4, is the starting material for making
plastic carrier bags.

"(H>=~() -------, (-H-)
HH HH n

liquid E

a Give the names and formulae for substances (i) Name the type ofchemical change taking
A to F. place in the diagram above.

b ( i) Write a word and balanced chemical ( ii ) Name the product formed by this reaction.
equation to represent the reaction in which ( iii )The alkcne, ethcne, is made by cracking
liquid Eis formed.
large alkane molecules. Describe a simple
( ii ) What reaction conditions arc required for chemical test to show that cthcnc is present.
the process to take place? b The majority ofcarrier bags arc difficult to
dispose of.
( iii )Hydrogcn is used in the production of (i) Explain why carrier bags shou ld not just be
margarine to remove unsaturation. Explain thrown away.
what you understand by this statement. ( ii ) Explain why the majority of plastic carrier
bags arc recycled.
c Name the homologous series that gas B belongs (iii )Givc one advantage that a plastic carrier bag
to. has over one made out of paper.
c A label like the one below is found on some
d Describe a chemical test which would allow you plastic carrier bags.
to identify gas C.
This plastic carrier bag is made from a substance
3 a Crude oil is a mixture of hydrocarbons which that is made from t he chemical elements carbon
belong to t he homologous series called t he alkanes. and hydrogen only. When t he carrier bag is
T his mixture can be separated into fractions by burned it produces carbon dioxide and water.
the process offractional distillation. Some of the These substances arc natural and will not harm the
fractions obtained arc used as fuels. Some of the environment.
other fractions arc subjected to catalytic cracking
in order to make alkenes.
Explain the meaning of the terms in italics.

14 ORGANIC CHEMISTRY 1

(i) W hat is the m eaning o f the term element? an answer. Yo u s hould also g ive a reason for your
(ii) W hat is the n am e given to the type o f answer in each case .
(i) W hich fractio n would contain the most
compound that contains the elem ents
carbo n and hyd rogen o nly? volatile substances?
( iii) W hcn the plastic bag burns, heat en ergy is ( ii ) W hich o f the fra ctio n s would collect at the
g iven out. W hat nam e is used to describe
reactio ns that g ive o ut heat en ergy? bottom o f the fractio nating column?
(iv) The plastic bag will probably give off a to xic (iii) W hich fractio n could be u sed as a fuel fo r
gas when it is burned . Why is this the case?
c a rs?
5 Alkan cs and alkcn cs arc h yd rocarbo n s. They arc (iv) W hich fractio n wo uld contain the largest
composed o f m o lecules which contain covalent
bonds. For each o f the m olecules below, use a d o t m olecules?
;md cross diagram to show the bo nding it contains. b Som e o f the fractio n s rn1dergo a furth er process
a Meth ane, C H 4 .
b Propcnc, C3 H 6 . called cracking to produ ce fur t her substan ces .
c Propan e, C 3H 8. (i ) E xplain what you understand by the term
d Ethcnc, C2 H4 .
'cracking' . W hat conditio n s arc employed
6 C rude o il is an impo rtant source o f o rganic when cracking occurs1
chemical fu els. It is refin ed by fractio nal distillatio n. ( ii ) Write a word and b alanced chemical
Use the in fo rmatio n in the tab le below to answer equatio n to sh ow how octane can be
th e qu estio n s which fo llow. p roduced by th e crackin g of C 15 H 32 .

Fracti on Boiling pointr c 7 a A hyd rocarbo n contain s 92 .3% by mass o f
A 40 carbo n. Work o ut the empirical fo rmula o f this
80 h ydrocar bon.
200
350 b The relative m o lecu lar mass o f this hyd rocarbon
above350 was fo und by m ass spect rometry to be 78 . Work
o ut its m o lecu lar fo rmula . (A,: H = 1, C = 12 )
a Fo r each o f the qu estio ns that fo ll ow, g ive the
letter o f the fra ction which is m ost appropriate as 8 :i W hich o f the fo llowing fo rmulae represent
alkanes, which represent alkcnes and which
represent neith cr1

CH 3, C6H 12, CsH1 2, C6H 6, c; H20, C12H 24,
C20H 42, C2 H 4, Cs H1 s, C3 H7

b Draw all the possible isom ers which have the
mo lecular fo rmula C 6 H 14.

@ Organic chemistry 2

Alcohols {R---OH) Condensation polymers
Combustion
Oxidation Some biopolymers
Cholesterol - a complex molecule that contains the -OH group Sta rch
Amino acids
Biotechnology DNA
Baking - an important use of biotechnology
New applications of biotechnology Pharmaceuticals
Drug abuse
Carboxylic acids
Othercarboxylicacids Checklist

Soaps and detergents Additional questions
Soapless detergents
Manufacture of soapless detergents

In C hapter 14 we discussed the organi c com pounds Tabl e 15.1 The functional groups present in some homologous series of
that arc obtained fro m o il, the alkan cs, and h ow they organic compounds.
arc converted into an o ther h om ologous seri es o f
hyd rocarbo ns called the alkcn cs . If you replace o ne Cla ss of compound Functional group
o f the hyd rogen atom s o n an alkan c m o lecule with Alcohols
a group su ch as - O H , the hyd roxyl group, then you Carboxytic acids R----OH
get a n ew ho m o logous seri es called the alcoh ols. If Esters R---COOH
you replace o ne o f the hyd rogen ato m s o n an alkan e Halogenoalkanes
m o lecule with a - COO H group (Figure 15 .1 ) then R---COOR
you get a h o m o logous series called the carboxylic R- X
acid s or alkano ic acids . Whi chever group you have {where X is a halogen atom such as
attach ed , it will brin g with it a new set o f physical Cl, Br. etc.)
and chemical p roperties. These groups arc kn own
as functional gro ups . Th e fun ction al group is th e e Alcohols (R-OH)
group o f ato m s respo nsible fo r the ch aracteristic
reactio ns o f th e organic compound . The alco ho ls (alkano ls) form an o ther h o m o logous
seri es with the general fo rmula C.,H 2.,+10H (or R-
Table 15 .l shows some examples of fun ctio nal O H , wh ere R represents an alkyl group ). All the
groups. ln the tab le, R represen ts an alkyl group or alco ho ls possess an - O H as th e fun ctio nal group.
a hyd rogen ato m . An alkyl group has the general Table 15.2 sh ows th e names and condensed fo rmulae
fo rmula based on the alkanes, i.e . C., H 2.,+ I · Wh en o f the first four m embers alo ng with their melting
n = 1, R= C H 3; wh en 11 = 2, R= C2 H 5 , and so on . and boilin g points.

Tabl e 15.2 Some members of the alcohol fam ily.

Alcohol Formula M elting point/ Boiling po int/

Methanol CH 30H ·c ·c
Ethanol CH3CH20H
Propanol CH3CH2CH20H -94 64
Butanol CH 3CH2CH 2CH20H
-117 78

-126 97

-89 117

Figure 15.1 ThisfruitjuicecontainsplentyofvitaminCorascorbicacid. Fig ure 15.2 shows the arrang ement o f the ato ms
which contains the functional group ....COOH. in the foll y displayed (structural ) fo rmulae o f these
m embers o f this famil y o r ho m o logous series .

The alco ho ls arc named by referen ce to the
correspo nding alkanc (sec C hapter 14, p. 2 19),
always ensuring that the h yd rocarbon ch ain is
numbered fro m the end that g ives the lowest

15 ORGANIC CHEMISTRY 2

methan o l

">(t Ii:

H/ H hyd ro g en
"'- bond

etha no l / (" "

H

Figure 15.3 Polar --OH groups in ethanol molecules lead to hydrogen
bonding and an attraction between neighbouring molecules.

propano l Because o f the presence o f the polar - OH groups,
there is a relatively strong po lar attractio n between
HHH alcoh o l m o lecules. This polar attraction between
the charges &t and 0- in neig h bourin g mo lecules
H- 1I- 1I- ,I- 0- H is called a hydrogen bond . This means that the
HHH m o lecules have a much stron ger attractio n fo r each
o ther th an m o lecules o f the corresponding alkanc
buta no l o f similar relative m olecular mass, M,. Fo r example,
ethano l has an M, valu e o f 4 6 and is a liquid at room
HHHH temperature with a boiling po int o f 78 °C, whilst
propan e (CH 3 CH 2 C H 3 ) has an M, o f 44 and is a gas
IIII at room temperature with a boilin g point o f - 42 °C.

H- C- C- C- C- 0 - H It is possible to think of alcoho l m olecules as water
m olecules in which an H atom has been replaced by an
IIII alkyl group, fo r cxam ple - C2H 5 in C2 H 50 H. This close
similarity between their mo lecules explains wh y water
HHHH and alco hols with small mo lecules, such as methan ol
and ethano l, arc miscible . They mi.x because o f the
Figure 15 .2 The molecule5 look like their corresponding models in the presence o f the polar - O H group in both mo lecules.
photographs.
Man y o ther m aterials, su ch as foo d flavourin gs, arc
num ber to the positio n of the - OH group . lfthc m ade fr o m eth ano l. fu ethano l is also a very good
- O H group is position ed at the end o f the alco h ol, solvent and evaporates easily, it is used extensively as
fo r example in CH 3CH 2CH 2CH 20H , then the a solvent for paints, g lu es, aftershave and many o ther
position o f this group is shown by num bering the everyd ay p rod ucts (Fig ure 15.4 ).
carbo n ato m it is attach ed to as ' l ' So this m o lecule
is called butan - 1-ol, o r butan o l fo r sh ort. This typt:
o f alco ho l is called a primary alco ho l.

Alcoh ols have hig h bo iling points and relatively low Figure 15 .4 Thisaftershavecontainsakohol.
volatility. Alco ho l m olecules arc like water m olecules
(H---OH ) in that they arc polar (sec C hapter 11 ,
p. 186 ).

Alcoh o l m o lecules arc p o lar because o f the presence
o f the - O H group, in which the h yd rogen attached
to oxygen creates (within this group ) a small
differen ce in charge (Fig ure 15 .3 ). O ther organic
m o lecul es that arc po lar arc carboxylic acids such as
cth an oic acid (p. 2 37).

Alcohols (R- OH)

Ethano l is by far the most important of the alcoho ls and Figure 15.5 Orange potassium dichromate(\11) slowly turns green as it
is o ften just called 'alcohol'. Ethano l can be prod uced oxidisesethanoltoethanoicacid.Potassiummanganate(w)turnsfrom
by fermentation (p. 236) as well as by the hyd ration of purple to colourless.
cthcnc (Chapter 14, p. 224). It is a neutral, colo urless,
volati le liquid which docs no t conduct electricity. Ch o lest erol - a complex mo lecule
The more concentrated form s of alcoholic drinks th at contains the -OH gro up
such as th e spirits whiskey and brandy contain hi gh
concentratio ns of ethano l. Th ese arc produced Cholesterol is a naturally occurring and essential
by d istill atio n after the fer mentatio n is complete chemical. It belongs to a fa mily of chemicals
(Chapter 2, p. 20 ). called steroid s and also contains an alcoho l group
(Figure 15.6 ). C holestero l is found in almost all of
Comb ustio n th e tissues in the body, including nerve cells. Levels
of cholesterol above normal (above 6 .5 mm oJ/1) arc
Ethano l burns q uite readily with a clean , ho t fl ame. associated with an increased risk of heart disease .
Cholesterol hardens and blocks off arteries by
ethanol + m.l'gen ---> carbon + water + energy buildin g up layers of solid material (ath croma)
inside the arteries (Fig ure 15.7, p. 2 36). Thi s is
dioxide particularly serio us if th e arteries that supply the
heart or brain arc blocked. Simpl e tests arc now
CH 3C H20H(1) + 30i{g) ---> 2COi{g) + 3H2 0 (g) + energy available to mo nitor cho lesterol levels and people
with high levels can be treated and can fo ll ow
As methylated spirit, it is used in spirit (camping ) special low-fa t and low-cho lesterol diets.
stoves. Methylated spirit is ethano l with small amo unts
of poisono us su bstances added to stop people drinking CH,
it. Some countries, like Brazil , alread y use ethanol
mixed with petrol as a fu el for cars (C hapter 6, p. 94 ) CH ,
and this use is increasing worldwide.
HO
Oxidati o n Figure 15.6 The structu re of cholesterol.

Ethano l can be oxidised to cthanoic acid (an
o rganic acid also called acetic acid) by powcrfol
oxidising agents, such as warm acidified potassium
dich romatc(VI ), or po tassium manganatc(VII ).
During the reaction the orange colo ur of potassium
dichromatc(VI ) changes to a d ark green (Figure 15.5 )
as the ethano l is oxidised to cthano ic acid.

ethanol + oxygen ~ ethanoic + water
C H JCH 20 H {t) (from acid

potassium
dichromate

(VI))

+ 2(0]

1;I 1;I H0

H-C - C - O -H + 2(0] --+ ' ,f + H2o
H-C - C
II
HI ' O - H
HH
L,---J

carboxylic acidgroup

Question

1 Write a word and balanced chemical equation for:
a the combustion of butanol
b the oxidation of butanol.

15 ORGANIC CHEMISTRY 2

a This artery is being blocked by atheroma, which may be related to
high levels of cholesterol in the blood.

Fi gure 15.8 Fermenting glucose and yeast to produce ethanol. The bag
isinflatedduringtheexperimentbyC02.

b Thisisahealthyartery. Bakin g - an impo rtant use of
Fi gu re 15.7 b iot echno logy

• Biotechnology To make bread, fresh yeast is mixed with warm
su gar solutio n and the mixture added to the fl our.
Bi otechno logy involves making u se o f mi cro - This d o u gh mixture is then put into a warm place
o rg anism s o r th eir compo nents, su ch as en zym es, to rise. The d o ug h ri ses due to the producti on
for the bcndit of humans to produce, for example, o f carbo n dioxide fr o m aerobic respiration
food s su ch as yoghurt and bread. One o f the o ldest ( respiration with oxygen ) by the yeast. The produ cts
bio techn ologies is that o ffennentatio n . It involves o f this style o f respiratio n arc different to those o f
a seri es o f bioch emical reactio ns b roug ht abo ut by an aero bic respiratio n.
mi cro -o rganism s o r en zym es.
sugar + oxygen ~ carbon + water + energy
Fermentation in the laborato ry can be carried out
using sugar solution. A micro-o rganism called yeast dioxide
is added to the solutio n. The yeast uses th e sugar for C6H 120 i oq ) + 60i(s) _____.. 6COi(s) + 6H2 0 (1) + energy
energy during anaerobic respiration (respiration
without o xygen ), and so the sugar is broken d own to After the d o ug h has 'risen ', it is baked and the heat
give carbon dioxide and ethano l. The best temperature kills the yeast and the bread sto ps rising .
for this process to be carried out is at 37 °C.
New applicatio ns of biot echn o logy
glucose ~ ethanol + carbon dioxide
C6H 12 0 6(aq) ---------.. 2C2H 50H(1 ) + 2C 0 2(g) A large number o f firm s throug h out the world
arc investing large sums o f mo n ey in the n ewer
Figure 15.8 sh ows a simple apparatus fo r o btaining biotechno logy appli catio n s n ow in use.
ethano l fr om glucose in th e laborato ry.
• En zym es can be isolated fro m micro -o rg ani sm s
lf a b o ttle o f wine is left exposed to the atmosphere and u sed to ca tal yse reactio n s in o ther p rocesses .
then further o xidation takes place and the ethano l is Fo r exampl e, proteases arc u sed in bio logical
oxidised to cthano ic acid. d etergents to digest protein stain s such as bl ood
and fo o d. Al so, catalasc is u sed in th e rubber
indu stry to h elp convert latex into fo am rubber.

• Our ability to manipulate an o rganism 's genes to
make it u scfol to u s is called gen etic engin eering.
This is being used , fo r example, to d evelo p n ovel
plan ts for agriculture as well as making important
human proteins su ch as the h orm o nes insulin and
growth hormone.

Carboxylic acids

H owever, a wo rd of cautio n is necessary. The n ew methanoicacid
biotechnologies may not be without dangers. For
example, new pathogens (organisms that CJ.use disease ) ethanoicacid
mig ht be created accidentally. Nso, new pathogens
may be created deliberately for use in warfare. As H
you can imag ine, there arc very strict guidelines
covering these new biotechnologies, especially in the Io
area o f research into gen etic eng ineering.
H- C- < 0-H
Question I

1 What do you understand by the term 'biotechnology'?
In your answer make reference to the making of bread.

H

• Carboxylic acids propanoicacid

The carboxylic acids form another ho m o logous HH o
series, this time with the general formula
CnH2 n+ 1COOH. All th e carboxylic acids possess II
- COOH as their fun ctional group. Table 15.3
shows the first four members of this ho m o logous I IH--C- C- <
series along with their melting and boiling po ints. 0- H
Figure 15 .9 shows the actual arrangement of the
atoms in these members o f this family. HH

Table 15.3 Some members of the carboxyl ic acid series. butanoicacid

Carboxylic Formu la Melt ing point/ Boili ng point/ HHH
acid H- L LLC°"0
·c ·c
HI HI HI ' OH

Methanoicacid HCOOH 101 Figure 15.9 The molecules look like the 30 models in the photographs.

Ethanoicacid CH3COOH 17 118 Ethano ic acid also undergoes o ther typical reactio ns
Propanoic acid CH 3CH 2 COOH -21 141 o f acids, in that it reacts with indicators, metals and
Butanoicacid CH3CH1 CH1 COOH 164 carbo nates in the usual way.
-6
Ethanoic acid will react with ethan o l, in th e
Methanoic acid is present in stin ging n ettles and presence o f a few drops o f concentrated sulfuric
ant stings . Ethanoic acid , h owever, is the m ost well acid, to produce ethyl cthanoate - an ester.
known as it is the main co nstituent o f vinegar. Like
o ther acids, cthanoic acid affects indicators and will ethanoic + ethano l ~ ethyl
react with metals such as magn esium. H owever,
wh ereas th e mineral acids such as hydrochloric acid acid tt,so, e thanoate
are called strong acids, cthano ic acid is a weak acid
(Chapter 8, p. 120). Even though it is a weak acid , it CHJCOO H(t) + CzH50 H(1) ~ CH!COOCzH5(og ) + H20(t)
will still react with bases to form salts. For example,
the salt sodium ethan oate is formed wh en cthano ic This reactio n is called esterific.,tion.
acid reacts with dilute sodium hydroxide.
Members o f the 'ester' family have stro ng and
pleasant sm ells. They have th e general formula

CnH ln+ICOOC)-12..,.. 1. Esters arc named after the
acid and alcohol fr om which they arc derived:

ethanoic + sodium ----> sodium + water • nam e - alcohol part first , acid part second ,
e.g. propyl ethanoatc
acid hydroxide cthanoatc
• formula - acid part first, alcohol part second ,
CH3COOH(aq) + NaOH(aq) ----> CH3COONa(aq) + HiO(t) e.g. CH 3COOC3H 7

15 ORGANIC CHEMISTRY 2

Este r Made from Structure 3D model
f-~~~~~~~---,
Ethylet hanoate
CH 3COOC2Hs Alcohol Carboxyli cacid

Ethanol Ethanoic acid H /
c,HsOH CH 3COOH C
I
H- C- HH

I \ 0 - ~- ~- H

H II

HH

Propyl methanoate Propanl-ol Methanoicacid
HCOOH
HCOOC3H 7 C3H,OH

Methylbutanoate Methanol Butanoicacid H- 1I- 1I- ,I- /0
C3H7CD0H c"o-
C3H7CD0CH 3 CH 30H JH- H

H HH I

H

Fi gure 15.10 The molecules of esters look like t he 30 models in the photographs.

Figure 15 . 10 sh ows the actual arrangem ent o f the 3 Which of the following organic chemicals are carboxylic
atom s in som e o f the m embers o f this family.
acids or alcohols?
Many esters occur naturally and arc resp onsible
fo r the fla vours in fruits and the smells o f fl o wers. Hexanoic acid, C6H13COOH
They arc used , th erefore, in so me food fla vourings Butanol, C4H90H
and in perfumes (Figure 15.11 ). Octane, C8H18
Nonane, C9H20
Methanoic acid, HCOOH

Pentene, C5H10
Hexanol, C6H 130H
State why you have chosen your answers.

Figure 15.11 Perfumes contain esters. Ot he r carboxylic acids

Fats and o ils arc naturally occurring esters which arc Asp irin
used as en ergy storage compounds by plants and
animals. They possess the sam e linkage as Tcryknc Aspirin (Figure 15. 12 ) is one o f the most frequently
but have different units (sec p. 241 ) . used painkillers in the world. It is also able to reduce
inflammation and fever and a low dose taken on a daily
Q u e st i o n s basis over the age o f 50 may prevent heart attacks. It is
derived from an otl,er acid, salicylic acid , which can be
1 Write the structural formula for propanoic acid. o btained from willow bark. Salicylic acid has the sam e
2 Write word and balanced chemical equations for the medicinal properties as aspirin and has been known
since 1829 . Salicylic acid, however, caused stomach
esterification of propanoic acid with ethanol. bleeding. The conversion of salicylic acid to aspirin
reduced these problems, but aspirin still has some
ad w rsc effects o n the stom ach if taken in excess.

Soaps and detergents

50"( r
asp.iri.n CH3
Figure 15.12 The structure of aspirin. IHooe "-..... _,,,...c "-..... _,,,... cooH
CH 2 CH2
Ascorbic acid (vitamin C) COOH
Vitamin C, also known as ascorbi c acid , is an
essential vitamin (Fi gure 15 .13). Vitamin C is citric acid
required by the body in very small am ounts and it is Figure 15.15 Thestructureofcitricacid.
o btained fr om food s.
• Soaps and detergents
ascorbic acid
Figure 15.13 Thestructureofascorbicacid (vitaminC). Milli ons o f to nnes o f soaps and soapl ess d etergents
arc manufactured worldwide every year. Soa p is
Vitamin C is impo rtant to all animals, including manufactured by heating natural fat s and o ils o f
humans, and is vital in the produ ction o f collagen. citl1cr plants o r animals with a st ron g alkali. These
Collagen is important in the fo rmatio n o f conn ective fats and o il s, called trig lyccridcs, arc complicated
tissues that g ive o ur bod y shape and help to support ester m olecules.
vital organs. Vitamin C prevents the disease scurvy.
It is found in citrus fruit s and brig htly coloured Fat is boiled with aqueous sodium hyd roxid e
vegetables, such as peppers and broccoli. Many to fo rm soap. Th e esters arc broken down in tlu:
people take vitamin C supplements, which arc presen ce of water -hydrolysed . This type o freactio n
readil y availabl e fro m supermarkets and pharmacies is called saponification. The equation givcn below is
(Figure 15 .14). Altho u gh vitamin C is destroyed by that fo r tlu: saponificatio n of glyccryl stcaratc (a fat ).
exp osure to air and heat, the average person usually
reaches tl1c recommended daily allowan ce o f 60 m g glyceryl + sodium ----+ sodium + glycerol
tluo ug h food. h ydroxide stearate (soap)

H 33C 11 - COOC H2 H O - CH2

II
H"C,,- COOCH +3NaOH (..i)-i-3C,,H,,;CX)O-Na+(1)+ H O - CH,

II
H 35C"- COOC H,(1) H O - CH,(1)

The cleanin g p roperties o f the soap depend on its
stru cture and bo nding. Sodium stcaratc consists
o f a lo ng hyd rocarbon ch ain whi ch is hyd ropho bic
(water hating) attached to an ionic ' h ead ' which is
h yd rophilic (water loving) (Fig ure 15.16).

hydro phili c
head

Figure15.14 ThesefruitsandsupplementsallcontainvitaminC. hydro ph obic chain (hydroc arbon)

Citric acid Figure 15.16 Simplified diagram of a soap molecule.
C itric acid is an example o f a tricarboxylic acid ,
o ne which contains three - C OOH groups Covalent compo unds arc generally insoluble in
(Figure 15 .15). It is an important acid and is fo und water but they arc m o re soluble in organic solvents.
in all citrus fruits, for example lemo ns and oran ges. Io nic compo unds arc gen erally water soluble but
tend to be insoluble in organic so lven ts. When a
soap is put into water which has a g reasy dish (o r
a g reasy cloth ) in it, the h yd ropho bic hyd rocarbo n
chain o n each soap m o lecule becomes attracted
to the g rease and becom es embedded in it
(Figure 15.1 7).