CHAPTER 14 CHEMISTRY IN INDUSTRY AND TECHNOLOGY
(IB OPTION C) SUMMARY
Iron and steel
The principal ores of iron are Haematite (Fe2O3) and Magnetite (Fe3O4)
In the blast furnace the solid ore, coke (C) and limestone (CaCO3) are fed in at the top and air
blown in at the bottom. Starting at the bottom the reactions producing the iron are:
C + O2 Ò! CO2
C + CO2 Ò! 2 CO
FexOy + y CO Ò! x Fe + y CO2
The limestone is added is to react with sand (SiO2), inevitably a major impurity:
CaCO3 Ò! CaO + CO2
CaO + SiO2 Ò! CaSiO3
The iron produced in this way contains a great deal of dissolved carbon (~4%), as well as
other impurities, which make it very brittle. To remove these pure oxygen is blown through
the molten liquid to convert these to the oxides. The volatile ones (such as CO2) escape as
gases, the non-volatile ones (such as SiO2) react with the calcium oxide which is also added.
The properties of the steel may be modified either by adding other metals or non-metals to
form alloys with the iron, or by heat treating it, which affects the crystal structure of the iron.
Three common heat treatment processes are:
" Annealing, in which the metal is allowed to cool slowly to produce a soft malleable
steel
" Quenching, in which very hot metal is rapidly cooled so that the high-temperature
crystal structure is retained, giving a hard, brittle steel
" Tempering, in which the quenched steel is reheated to achieve a hardness
intermediate between that achieved by annealing and quenching.
Some common steels, along with their composition and uses are:
Aluminium
Aluminium is obtained from Bauxite impure, hydrated aluminium oxide. The aluminium
oxide is separated from Fe2O3, the main impurity, by dissolving the amphoteric Al2O3 in
concentrated sodium hydroxide, filtering off the Fe2O3, then acidifying the mixture to
precipitate out pure alumina, Al2O3.
Because it is too high in the reactivity series for chemical reduction, aluminium is obtained
from alumina by electrolysis:
" The Al2O3 is dissolved in molten cryolite (Na3AlF6) which reduces the melting point
and improves the conductivity, at about 900°C
" Aluminium is formed at the steel lining cathode and the molten metal sinks to the
bottom of the cell.
" Al3+(l) + 3 e Al(l)
" At the carbon anode, oxygen, from the oxidation of the oxide ions, reacts with the
carbon:
o 2 O2 (l) O2(g) + 4 e
o C(s) + O2 (g) CO2 (g)
" The carbon anodes therefore burn away and require periodic replacement.
© IBID Press 2007 1
CHAPTER 14 CHEMISTRY IN INDUSTRY AND TECHNOLOGY
(IB OPTION C) SUMMARY
Aluminium has a very low density and, owing to a thin impervious layer of its oxide, it is
corrosion resistant. Though quite soft it can be made harder by alloying with other metals such
as magnesium.
The production of both steel and aluminium consume large amounts of energy and use great
volumes of water. They both generate CO2, a greenhouse gas, and produce solid waste (slag
and Fe2O3 respectively) which requires disposal. In both cases recycling waste metal can
greatly reduce the environmental impact.
Petrochemicals
Currently about 90% of oil is used as a fuel and about 10% for petrochemicals. It is probably
easier and, because of the production of greenhouse gases, such as CO2, better for the
environment to search for new energy sources to conserve more oil for petrochemical
production.
Owing to the low reactivity of alkanes, cracking to form alkenes is an important first step in
petrochemical production. They all involve heating fractions from the fractional distillation of
oil, in the absence of air, for a brief period then rapidly cooling. There are three important
types of cracking:
" Thermal cracking; in which the gaseous alkane is heated to a very high temperature
giving ethene as the major product.
" Catalytic cracking; in which the alkane vapour is passed over a zeolite catalyst at a
lower temperature to give less ethene and more branch-chained hydrocarbons, which
are excellent fuels.
" Steam cracking; in which the alkane vapour is mixed with steam before cracking
which produces more aromatic hydrocarbons.
There are two distinct processes by which ethene polymerises to form polyethene, giving two
distinctly different products:
LDP (Low Density Polyethene) - carried out at high temperature and very high pressure
in the presence of a free-radical initiator (trace of O2 or peroxides). Produces branch
chain polymers which cannot form a regular lattice - hence lower density, weaker
intermolecular forces and lower melting point.
HDP (High Density Polyethene) - carried out at much lower P and T in presence of
complex catalysts (Al(C2H5)3 & TiCl4). Produces a polymer with very little branching
that can form a regular lattice - hence higher density, stronger intermolecular forces and
higher melting point.
Production of LDP involves a free radical mechanism:
Initiation R-H + O=O Ò! R" + HO-O"
Propagation R" + H2C=CH2 Ò! R-CH2-CH2-"
Termination 2 R-CH2-CH2-" Ò! R-CH2-CH2-CH2-CH2-R
The radicals (R" ) can however remove hydrogen atoms in the middle of a chain, giving rise to
branching of the chains:
R-CH2-CH2-CH2-CH2-R + R" Ò! R-CH2-CH" -CH2-CH2-R + R-H
Production of HDP involves the formation of a complex with the catalyst. Ethene molecules
then insert themselves into this very polar ( ionic , C´--Ti´+) bond resulting in polymer chains
without any branching. The following equation is an oversimplification of this:
TiCl4 + Al(C2H5)3 Ò! C2H5-TiCl3 + Cl-Al(C2H5)2
CH2=CH2 + C2H5-TiCl3 Ò! C2H5-CH2-CH2-TiCl3 etc.
© IBID Press 2007 2
CHAPTER 14 CHEMISTRY IN INDUSTRY AND TECHNOLOGY
(IB OPTION C) SUMMARY
When propene polymerises to form polypropene, there are again two distinct products:
Isotactic - the methyl groups are on alternate carbons and are on the same side of the
hydrocarbon chain. This allows a regular lattice structure, so stronger intermolecular
forces and a higher melting point.
Atactic - there is a random distribution of methyl groups and they are on different sides
of the hydrocarbon chain. This interferes with regular lattice structure, so weaker
intermolecular forces and a lower melting point.
Condensation polymers result from the joining of monomers that have two functional groups
on each monomer and a small molecule (often water) is formed for each bond between the
monomers. Usually two monomers are involved, each having two identical functional groups.
Common examples are give in the text.
The properties of polymers are very dependent on their structure and hence may be altered by
modifications to the structure. Some examples are:
" Because of the polar nature of chlorine, PVC has strong forces between the polymer
chains hence it is quite rigid. Adding plasticisers (smaller molecules that come
between the polymer chains) reduces the intermolecular forces giving a much more
flexible product.
" If volatile hydrocarbons are present when styrene (phenylethene) polymerises then
they vapourise to leave large gaps between the polymer chains. This produces a very
low density polymer (expanded polystyrene) with excellent thermal insulation
properties.
" If water is added during the polymerisation of polyurethane it reacts with the
isocyanate to produce carbon dioxide gas (-NCO + H2O Ò! -NH2 + CO2) which results
in a foam suitable for soft furnishings.
" Polyacetylene contains conjugated double bonds (that is alternate single and double
bonds), but in spite of the possible extensive delocalisation it is only a poor conductor
unless doped with iodine.
The structure of the polymer determines its properties, hence phenol-methanal polymers are
very rigid owing to the extensive cross-linking between the chains and in Kevlar, used for
bullet-proof vests, there is strong hydrogen bonding between the polymer chains.
Kevlar molecules (see structure above) has rigid rod-shaped molecules with strong
intermolecular hydrogen bonds between the chains. As a result it can give rise to a lyotropic
liquid crystal with a very strong, ordered structure.
If concentrated sulfuric acid is added to Kevlar, then the O and N atoms are protonated,
destroying the hydrogen bonded structure.
The feel of fibres made from some polyesters can be rather harsh and they are not easy to dye.
Blending with other fibres, either natural (like cotton) or synthetic (like polyamides) can
improve these properties.
Some specific examples of desirable properties are phenol-methanal polymers which are rigid
and are excellent electrical insulators making them ideal for power sockets etc. Polyurethane
foams have a low density and high elasticity making them excellent for use as padding in
mattresses and soft furnishings. PET has a high tensile strength and low gas permeability
making it ideal for fizzy drink bottles, plus it is easily recycled.
Homogeneous catalysts (such as an acid in esterification, or Fe2+ in the reaction of H2O2 & I-)
are in the same phase as the reactants. They react with one of the reactants to produce an
intermediate, which is consumed at a later stage to regenerate the catalyst. These stages have
lower activation energies than the uncatalysed process. Homogeneous catalysts can however
be difficult to separate from the final product.
© IBID Press 2007 3
CHAPTER 14 CHEMISTRY IN INDUSTRY AND TECHNOLOGY
(IB OPTION C) SUMMARY
Heterogeneous catalysts are in a different phase to the reactants and hence are easy to
separate. They provide an active surface on which the reaction can take place with a reduced
activation energy. It is important that the product does not bond to the surface so the surface is
freed for other reactants. As it is a surface phenomenon heterogeneous catalysts must have
high surface areas.
Most industrial processes involve catalysts because they speed up the reaction (greater
efficiency) and can also increase the yield of the desired product rather than by-products
(greater selectivity). Some disadvantages are the way conditions can reduce the activity of
catalysts (denaturing of enzymes, surfaces deactivated by poisons ) and the environmental
impact of the escape of toxic catalysts.
The highly exothermic reaction between hydrogen and oxygen can be harnessed to produce
electricity, and hence the production of hydrogen used to store energy, in a fuel cell:
Electrode Negative Positive
Alkaline conditions
2 H2(g) + 4 OH (aq) 4 H2O(l) + 4 e O2(g) + 2 H2O(l) + 4e 4 OH (aq)
Acidic conditions
2 H2(g) 4 H+(aq) + 4 e O2(g) + 4H+(aq) + 4e 2H2O(l)
Energy can also be stored through rechargeable batteries the reactions below are those that
take place when they are delivering a current:
Lead-acid cell Negative electrode Pb(s) + SO42-(aq) PbSO4 (s) + 2 e
(2.0 V) Positive PbO2(s) + 4H+ (aq) + SO42 (aq) + 2e PbSO4(s) + 2H2O(l)
NiCad cell Negative electrode Cd(s) + 2OH (aq) Cd(OH)2(s) + 2e
(1.4 V) Positive electrode NiO(OH)(s) + H2O(l) + e Ni(OH)2(s) + OH (aq)
Lithium ion Negative electrode LiC6 Li+ + 6C + e
(3.0 V) Positive electrode Li+ + e + MnO2 LiMnO2
Fuel cells and rechargeable batteries are both ways of converting the chemical energy of an
exothermic reaction into electrical energy. The major difference is that the reactions in
rechargeable batteries have to be reversible.
Liquid crystals are fluids that have anisotropic physical properties (electrical, optical and
elasticity), if the molecules of the fluid all have the same orientation. Many natural materials,
such as cellulose, DNA and spider silk display this.
There are two types of liquid crystal:
Thermotropic liquid-crystals - are pure substances, such as biphenyl nitriles, that show
liquid-crystal behaviour over a temperature range between the solid and liquid states.
Lyotropic liquid crystals - are solutions, such as soap and water, that show the liquid
crystal state at certain concentrations.
In the nematic phase rod-shaped molecules are distributed randomly but tend to align
themselves giving rise to anisotropic properties. If the temperature is raised, the increased
thermal agitation disrupts this directional order until it is lost at the temperature at which the
normal liquid phase is formed.
© IBID Press 2007 4
CHAPTER 14 CHEMISTRY IN INDUSTRY AND TECHNOLOGY
(IB OPTION C) SUMMARY
Liquid-crystal displays (LCDs) are used in digital watches, calculators and laptops In these the
orientation of the polar molecules can be controlled by the application of a small voltage
across a thin film of the material. The ordered areas of the display have anisotropic optical
properties, hence the light and dark areas can be controlled by the applied voltage to a grid of
electrodes.
In order to be useful, a liquid crystal must be stable, maintain the liquid crystal state over a
large temperature range, be polar so the orientation can be controlled by an electrical field and
be capable of rapidly changing orientation.
Biphenyl nitriles (R- - -CN)produce an effective liquid crystal state because the biphenyl
group makes the molecule more rigid and rod-shaped, whilst the nitrile group makes the
molecule polar, so that the intermolecular forces are strong enough to make the molecules
align.
Nanotechnology involves research and technology development at the 1 nm to 100 nm range.
It creates and uses structures that have novel properties because of their small size and builds
on the ability to control or manipulate at atomic scale.
Scanning probe microscopes are able to move individual atoms on a surface one atom at a
time, whereas chemical reactions allow atoms to be positioned at a particular site in a
molecule.
Nanotubes are cylinders made only from carbon hexagons (like a looped round graphite
sheet). The closed ends of the tube also involve pentagons to produce the curvature (as in
fullerenes). Nanotubes can be either single or multiple, comprising a series of concentric
single nanotubes.
Nanotubes have anisotropic properties with high tensile strength along their axes. As the
surface of nanotubes allows the flow of electrons (like graphite), the electrical conductivity of
nanotubes increases with their length.
The threat to health of nanoscale particles is largely unknown, hence there are people who
have significant concerns in this regard. It is an issue that requires industrial responsibility and
strong political leadership.
Silicon, a semiconductor, has four electrons in its valence shell, meaning that the lowest
electron band in the lattice structure is totally filled. It therefore cannot conduct except when
electrons gain enough energy to jump into the next unfilled band (hence conductivity increases
with temperature).
If traces of atoms with one more electron (e.g. As, Sb) are added to the structure (doping) then
the extra electrons have to go in the unfilled band, increasing conductivity (n-type
semiconductors). Similarly if traces of atoms with one less electron (e.g. Ga, In) are added to
the structure then this creates a space ( hole ) in the filled band, again increasing conductivity
(p-type semiconductors).
If p-type and n-type conductors are placed next to each other electrons flow from the surface
of the n-type conductor to the p-type conductor, producing an electric field. This allows a pn
flow, but not a np flow, because the extra electrons just inside the p-type repel other
electrons. If solar energy excites electrons in silicon into the conducting band then they can
move pn, but not the other way, hence the n-type semiconductor becomes the negative
terminal of as solar cell. Electrons can flow through the external circuit back to the p-type
(which acts as the positive terminal because it has lost electrons).
In a LCD display each pixel contains a liquid crystal sandwiched between two scratched glass
plates, which have a polarising film aligned with the direction of the scratches. The liquid
crystal molecules in contact with the glass line up with the scratches, and because the
scratches in the two plates are at 90o to each other, the molecules form a twisted arrangement
© IBID Press 2007 5
CHAPTER 14 CHEMISTRY IN INDUSTRY AND TECHNOLOGY
(IB OPTION C) SUMMARY
between the plates, stabilised by intermolecular forces between the chains. These molecules
rotate the plane of polarisation of plane-polarized light so that light will pass through the film
and the pixel will appear bright. If a voltage is applied across the film, the polar molecules will
align with the field, rather than the scratches, so the twisted structure is lost and the plane of
the plane-polarized light is no longer rotated. As a result, the crossed polarising films cause
the pixel to appear dark.
The electrolysis of brine (aqueous NaCl) produces chlorine, hydrogen and sodium hydroxide:
At cathode 2 H2O(l) + 2 e 2OH (aq) + H2(g)
At anode 2 Cl Cl2(aq) + 2e (but at low [Cl-]) 4 OH (aq) 2H2O(l) + O2(g) + 4 e )
As a result Na+ and OH- remain in the solution, hence sodium hydroxide.
It is important to keep the products apart, otherwise they react to form bleach:
Cl2(aq) + 2 OH (aq) 2 Cl (aq) + ClO (aq) + H2O(l)
In the membrane and diaphragm cells this is done by physically separating the two electrode
compartments with. In the diaphragm cell the flow from anode to cathode is ensured by a
pressure differential. In the membrane cell the compartments are separated by a membrane
that allows cations (Na+) to pass through, but not anions (Cl- and OH-), hence no OH- can
travel back to the anode compartment.
An alternative is the mercury-cell in which mercury is used as the cathode, which results in the
formation of a sodium amalgam rather than hydrogen. This amalgam is then pumped to a
separate vessel where it is allowed to react with water to give the sodium hydroxide:
Na+(aq) + e Na(Hg)
2 Na(Hg) + 2 H2O(l) 2 Na+(aq) + 2 OH (aq) + H2(g)
Though it produces purer products than the diaphragm cell, the mercury-cell is being phased
out in favour of the membrane cell because of concerns of brain damage that can result from
the escape of mercury and its concentration in the food chain.
Chlorine is used in the production of plastics (Polychloroethene - PVC), treating drinking
water to kill bacteria, bleaching paper, producing chlorinated solvents, antiseptics and
insecticides.
Sodium hydroxide is used in the production of wood pulp for paper, the purification of
bauxite, soap manufacture and as a general alkali in the chemical industry.
(Shaded areas indicate AHL material)
© IBID Press 2007 6
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