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Chapter 9: Manufactured Substances in IndustryUnderstand the
manufacture of sulphuric acid.Synthesize the manufacture of ammonia
and its salt.Understand alloys.Uses of synthetic polymers.Apply the
uses of glass and ceramics.Evaluate the uses of composite
materials.Appreciate various synthetic industrial
materials.SULPHURIC ACIDSulphuric acid is a highly corrosive strong
mineral acid with the molecular formula H2SO4.Sulphuric acid is a
diprotic acid.Sulphuric acid has a wide range of applications.
manufacturing fertilisermanufacturing detergentmanufacturing
pesticidemanufacturing synthetic fibreas electrolyte in lead-acid
accumulatorremoving metal oxidemanufacturing paint
Manufacture of Sulphuric acid in industrySulphuric acid, H2SO4
is manufactured in industry through Contact Process.The raw
materials used are sulphur, air and waterThe Contact process
consists of four stages.
Stage 1Molten sulphur is burnt in dry air to produce sulphur
dioxide.The gas produced is then purified and cooled.S+O2SO2Sulphur
dioxide can also be produced by burning metal sulphide such as
lead(II) sulphide or zinc sulphide in dry air.2PbS+3O22PbO+2SO2
Stage 2In a converter, sulphur dioxide and excess oxygen are
passed through vanadium(V) oxide.vanadium(V) oxide act as catalyst
to expedite the process.The optimum condition for maximum amount of
product are as follow:Temperature: 450 500 CPressure: 2 3 atmAbout
99.5% of the sulphur dioxide, SO2 is converted into sulphur
trioxide, SO3 through this reversible reaction.
Stage 3Sulphur trioxide is dissolved in concentrated sulphuric
acid to form oleum H2S2O7.SO3+H2SO4H2S2O7
Stage 4The oleum, H2S2O7 is then diluted with water to produce
concentrated sulphuric acid, H2SO4 in large
quantities.H2S2O7+H2O2H2SO4
Environmental and health issue.Sulphur dioxide, SO2 is one of
the by-products of the Contact Process. It is one of the source of
environmental pollution.
Acid RainSulphur dioxide (SO2) is the pollutant primarily
associated with acid rain.Acid rain occurs when pH of the rain is
between 2.4 and 5.0. This is due to the reaction of sulphur
dioxide, SO2 with rainwater.SO2+H2OH2SO3The negative effect of acid
rains include:corrosion of concrete building and metal
structure.corrosion of monuments and statues made from marblecauses
erosion of top soil.killing aquatic life.
Health EffectsSO2 is an irritant when it is inhaled and at high
concentrations may cause severe problems in asthmatics such as
narrowing of the airways, known as bronchoconstriction.Asthmatics
are considerably more sensitive to the effects of SO2 than other
individuals.
Sources of SO2The principal source of SO2 is from the combustion
of fossil fuels in domestic premises and more importantly,
non-nuclear power stations.Other industrial processes such as
manufacturing of sulphuric acid also contribute to the presence of
SO2 in the air.AMMONIAAmmonia is a compound of nitrogen and
hydrogen with the formula NH3.It is a colourless gas with a
characteristic pungent smell.Ammonia is a very important compound
in industry.Although in wide use, ammonia is both corrosive and
hazardous.
Uses of Ammonia
manufacturing nitrogenous fertilisersas cooling agent in
refrigeratorto prevent coagulation of latexas raw material to
manufacture nitric acid (Ostwald process)to make explosiveas
cleaning agent to remove grease
MANUFACTURING AMMONIA : Haber ProcessAmmonia is manufactured in
industries through Haber Process.In Haber process, nitrogen gas, N2
from the air is mixed with hydrogen gas, H2 derived mainly from
natural gas.The mixture is compressed to a high pressure of 200
atmosphere at a temperature of about 450C.Iron is used as catalyst
to speed up the rate of reaction.Chemical equation below shows the
reaction.N2 (g) + 3H2 (g) 2NH3 (g)About 98% of mixture are
converted into ammonia, NH3.The unreacted nitrogen gas, N2 and
hydrogen gas, H2 are recycled and passed back into the reactor
together with the new source of nitrogen gas, N2, and hydrogen gas,
H2.
Characteristics of ammoniaAmmonia gas can turn a moist red
litmus paper to blue.As an alkali, ammonia can react with acid to
form salt and water.Example:H2SO4(aq) + 2NH3(aq)
(NH4)2SO4(aq)HNO3(aq) + NH3(aq) NH4NO3(aq)H3PO4(aq) + 3NH3(aq)
(NH4)3PO4(aq)Ammonia dissolve into water to form ammonium and
hydroxide ion.NH3 + H2O NH4+ + OH-The hydroxide ion can react with
positive ions to form precipitate.Example:Mg2+ + 2OH- Mg(OH)2Fe2+ +
2OH- Fe(OH)2Al3+ + 3OH- Al(OH)2Test for AmmoniaAmmonia is the only
common alkaline gas, so it can be identified with moist red litmus
paper turning blue.Concentrated ammonia when reacts with
concentrated hydrochloric acid produces white fume.Ammonia gas +
Hydrogen chloride gas ammonium chlorideNH3 (g) + HCl (g)
NH4ClProperties of ammoniaColourlessPungent smellLess dense than
airVery soluble in waterAlkaline gasForm white fume with hydrogen
chloride.ALLOYAn alloy is a mixture of two or more metals mixed in
a certain percentage.Most pure metals are weak and soft. The
properties of pure metals can be improved by making them into
alloys.Alloys are made toincrease the hardness of
metals.Example:Magnalium is made from aluminium and magnesium to
improve the hardness of the pure metals but at the same time,
maintaining their lightness.prevent the corrosion of
metals.Stainless steel which can resist rusting is made by adding
carbon, chromium and nickel to iron.improve the beauty and lustre
of metals.Copper and antimony added to tin produces pewter, used to
make decorative items.
When force is applied, layers of atoms in pure metalslide. So,
metals areductile. There are empty space between the atoms. When it
is knocked, the shape of the metal changes.
So, metals aremalleable.
Pure metalWeak and soft.-contain atoms of same size regular and
orderly arrangement.
Examples of alloyExamples of copper base alloy
areCupro-nickelBronzeBrassMost copper base alloy has shiny
surface
Cupro-nickelComponent: Cu 75%, Ni 25%Applications: Coins
BronzeComponent: Cu 90%, Sn 10%Applications: Decorative items,
medals, artwork, pots and pans
BrassComponent: Cu 70%, Zn 30%Applications: Decorative items,
electrical appliances, musical instruments, bell, nails, screw,
pots
Examples of iron base alloy aresteelstainless steelmanganese
steelThe iron base alloys are usually very hard
Steel Component: Fe 99%, C 1%Applications: Vehicles, ships,
bridges, buildings
Stainless steelComponent: Fe73%, Cr 18%, Ni 8%, C
1%Applications: Kitchen appliances, watches, machine parts, knives,
forks, spoons
Manganese steelComponent: Fe 85%, Mn 13.8%, C 1.2%Applications:
Helmet, spring
Examples of aluminium base alloy areDuraluminMagnalium
Aluminium has low density, hence the density of aluminium base
alloy is also low.
DuraluminComponent: Al 95%, Cu 4%, Mg 1%Applications: Aeroplane
parts, electric cables, racing bicycles
MagnaliumComponent: Al 70%, Mg 30%Applications: Tyre rim of
racing cars, skeletal body of aeroplanes
Examples of tin base alloy arepewtersolderMost tin base alloy
has shiny surface and low melting point.
PewterComponent:Sn 91%, Sb 7%, Cu 2%Applications:Decorative
items, souvenirs
SolderComponent:Sn 50%, Pb 50%Applications:Welding and soldering
work
POLYMERS Polymer is a large molecule that is in the form of a
long chain with a high relative molecular mass (RMM).It is made up
of many smaller units called monomers -- joined together through a
process called polymerisation. Thus the monomer is actually the
repetitive unit of a long polymer chain.There are two types of
polymers:Natural polymersSynthetic polymers
Natural PolymersThese occur naturally in living things. Some
examples of natural polymers are:Natural rubberProtein in meat,
leather, silk, hair and furCarbohydrates in cellulose, starch and
sugarNatural polymers are made up of carbon, hydrogen, nitrogen and
oxygen.
Synthetic PolymersSynthetic polymer is a polymer that is
manufactured in industry from chemical substances through the
polymerisation process.Examples of synthetic polymers
are:plasticssynthetic fibreselastomers-- elastic polymer /
rubberThe two types of polymerisation are:polymerisation by
additionpolymerisation by condensation
Polymerisation By addition: Polymerisation by addition involves
monomers with >C = C< bonding, where the monomers join
together to make a long chain without losing any simple molecules
from it.
By condensation:Polymerisation by condensation involves the
elimination of small molecules like water, methanol, ammonia or
hydrogen chloride during the process. Examples of products of this
process are terylene and nylon-66.
Examples of synthetic polymer PlasticsPlastics are light, strong
and do not react with any chemical substances, like acids and
alkalis.They can be made into many shapes and sizes.They are also
good insulators of heat and electricity.
Examples of Plastics:1. Polythene (polyethylene)Structure
Monomer: EtheneProduced by polymerisation: Addition Uses:
Plastic bags containers and cupsAdvantages: light and strong
2. Polyvinyl chloride or PVC (polychloroethene)Structure
Monomer: ChloroetheneProduced by polymerisation: AdditionUses:
Raincoat, Pipes to insulate electric wiresAdvantages: can be
coloured; heat resistant
3. Polystyrene (polyphenylethene)Structure
Monomer: PhenyletheneProduced by polymerisation: AdditionUses:
Packaging materials, children toys, ball-point pens, as heat and
electric insulatorsAdvantages: light and strong
4. Perspex (polymethyl 2-methyl propenoate)Structure
Monomer: Methyl-2-methylpropenoateProduced by polymerisation:
AdditionUses: Aeroplane window panes, Lenses, car lamp
coversAdvantages: light, strong, translucent, stable towards
sunlight
5. PolypropeneStructure
Monomer: PropeneProduced by polymerisation: AdditionUses:
Plastics, Bottles, plastic tables and chairsAdvantages: strong and
light
6. Teflon (polytetrafluoroethene or PTFE)Structure
Monomer: TetrafluoroetheneProduced by polymerisation:
AdditionUses: To make non-sticky pots and pansAdvantages: hard, can
withstand high temperatures and corrosives chemicals
Synthetic RubberSynthetic rubber is an elastomer or polymer
which regains its size original shape after being pulled or
pressed. [Natural rubber is an elastomer too.]Examples of synthetic
rubber are neoprene and styrene-butadiene(SBR).
1. NeopreneStructure
Monomer: ChloropreneProduced by polymerisation: AdditionUses: to
make rubber gloves and to insulate electric wires.
2. Styrene-butadiene or SBRStructure
Monomer: Styrene and butan-1,3-dieneProduced by polymerisation:
AdditionUses: to make tyres, soles of shoes and mechanical
belts.
Synthetic FibreNylon and terylene are synthetic fibres which
undergo the condensation polymerisation process.These fibres
resemble natural fibres but more resistant to stress and chemicals,
and more long-lasting. In both cases, water is eliminated during
the polymerisation process.
1. NylonStructure
Monomer: Produced by polymerisation: CondensationUses: To make
umbrellas, carpets, comb, curtains, nylon string and rope, socks,
toothbrush and so on.
2. TeryleneStructure
Monomer: Produced by polymerisation: CondensationUses: To make
fishing nets, clothes (quick-dry, non-iron), cassette and video
tapes.
Issue in Using Synthetic PolymersSynthetic polymers have
multiple uses in daily life because of the following
properties:Light and strongRelatively cheapWithstand corrosion and
chemical reactionWithstand action of waterNon-flammableCan be
coloured easilyEasily mould to shapeSynthetic polymers are also
used to replace natural polymers such as cotton, silk and
rubber.
However, synthetic polymers cause environmental pollution.Most
polymers are not biodegradable .The open burning of plastics gives
rise to poisonous and acidic gases like carbon monoxide, hydrogen
chloride and hydrogen cyanide.These are harmful to the environment
as they cause acid rain.Burning of plastics can also produce carbon
dioxide--- too much of this gas in the atmosphere leads to the
`greenhouse effect'.
These problem can be overcome by the following ways:Recycling
polymers: Plastics can be decomposed by heating them without oxygen
at 700C. This process is called pyrolysis. The products of this
process are then recycled into new products.
Inventing biodegradable polymers: Such polymers should be mixed
with substances that can be decomposed by bacteria (to become
biodegradable) or light (to become photodegradable).
Glass and CeramicsReferred to as transparent, shiny
substance.The most important component of glass and ceramics is
silica ( silicon(IV) dioxide, SiO2).Both glass and ceramic have the
following properties:Hard and brittleDo not conduct heat
electricityInactive towards chemical reactionsWeak when pressure is
appliedCan be cleaned easily
GlassIt is a mixture of two or more types of metallic silicates
but the main component is silicon(IV) dioxide.
Glass has the following properties:
Transparent and not porousInactive chemicallyCan be cleaned
easilyGood insulators of heat and electricityHard but brittleCan
withstand compression but not pressure
Soda lime,glassComposition: SiO2 70%, Na2O 15%, CaO 10%, Others
4%
Properties:Low melting point (700C)Moldable into
shapesCheapBreakableCan withstand high heatUses: Glass containers,
Glass panes, Mirrors, Lamps and bulbs, Plates and bowls BottlesMade
by heating sand (silica) with lime stone and Na2CO3Lead glass
(crystal)Composition: SiO2 70%, Na2O 20%, PbO 10%
Properties:High density and refractive indexGlittering
surfaceSoftLow melting point (600C)Denser Uses: Containers for
drinks and fruit, Decorative glass and lamps, Crystal glassware,
Lenses for spectacles.Made by substituting lead oxide for calcium
oxide.
Borosilicate glass (Pyrex)Composition: SiO2 80%, B2O3 13%, Na2O
4%, AI203 2%
Properties:Resistant to high heat and chemical reactionDoes not
break easilyAllows infra-red rays but not ultra-violet raysUses:
Glass apparatus in laboratories, Cooking utensilsFused silicate
glassComposition: SiO2 99%, Other - 1%
Properties:High melting point (1700C)ExpensiveAllows ultraviolet
light to pass throughDifficult to melt or mould into shape
Uses: Scientific apparatus like lenses on, spectrometer, Optical
lenses, Laboratory apparatusCeramicsCeramic is a substance that is
made from clay and hardened by heat in a furnace maintained at a
high temperature.Clay is composed of aluminosilicate with sand and
iron(III) oxide as impurities.Examples of ceramics
includeTilesCementBricksporcelain
The differences between the properties of ceramics, metals and
non-metals are given
belowPropertyMetalsNon-metalsCeramicHardnessHard but malleable and
ductileSoft and brittleHard but brittleDensityHighLowAverageMelting
pointHighLowVery highResistance to heatHighLowVery highHeat
andElectrical
conductivityGoodconductorGoodinsulatorGoodinsulatorChemical
reactionsCorrodesCorrodesStable, does not corrodeComparing Glass
and Ceramic
New Uses of Glass and Ceramics
Photochromic Glass
Photochromic glass is very sensitive to light.It darkens in the
presence of bright light and lightens when the amount of sunlight
lessens.
Conductive Glass
Conducting glass is a type of glass which can conduct
electricity. It is obtained by coating a thin layer of a conducting
material around the glass, usually indium tin(IV) oxide.It is used
in the making of Liquid Crystal Display (LCD)Car Engine Block
When clay is heated with magnesium oxide, the ceramic that is
produced has a high resistance to heat.This material is used to
build the engine blocks in cars as they can withstand high
temperatures.
Superconductors
Superconductors are electrical conductors which have almost zero
(0) electrical resistance. Therefore, this conductor minimises the
loss of electrical energy through heat.Yttrium barium copper oxide
is a type of ceramic superconductorSuperconductors are used to make
magnets which are light but thousands of times stronger than the
normal magnet.
Composite MaterialsComposite materials are substances which
contain 2 or more materials that combine to produce new substances
with different physical properties from the original
substances.
Wood and bones are examples of natural composite materials. Wood
consists of strong and flexible cellulose fibres surrounded and
held together by stiffer material called lignin.Bone is made up of
living cells in a matrix of collagen fibres and calcium salts.
Reinforced ConcreteComponent: Concrete (cement, sand, stones),
steel
Ordinary concrete is strong but heavy. Concrete pillars must be
big to support the weight. They take up space and cannot withstand
stress for example from earthquakes.Steel pillars are too expensive
and can rust.Reinforced concrete, containing steel rods in the
concrete pillars, can make them stronger and able to support larger
loads. It also does not rust.
Optical FibreComponent: SiO2, Na2CO3, CaO
This is a fine transparent glass tube that is made of molten
glass.In telecommunications, light has replaced electrons as the
transmitter of signals. This light transmits signals through
optical fibre.Optical fibre is also used in the medical field as
laser to do operation , endoscope to examine the internal organs of
patients
Photochromic GlassComponent: glass, AgCl (or AgBr
Photochromic glass is very sensitive to light.It darkens in the
presence of bright light and lightens when the amount of sunlight
lessens.FibreglassComponent: Fibreglass and polyster resin
Fibre glass is obtained by adding a polyester resin to molten
glass. It cannot be compressed easily and is more tensile than the
original materials.Fibre glass is light, withstands corrosion, can
be cast into different shapes, is impervious to water, not very
flammable, not brittle and stronger than even steel.It is used to
make racquets, construction panels, electrical appliances, pipes,
and water tanks.
SuperconductorComponent: Yttrium oxide (Y2O3), BaCO3, CuO
Superconductors are electrical conductors which have almost zero
(0) electrical resistance. Therefore, this conductor minimises the
loss of electrical energy through heat.Yttrium barium copper oxide
is a type of ceramic superconductorSuperconductors are used to make
magnets which are light but thousands of times stronger than the
normal magnet and electrical generators.