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Worksheet 14.2 Chapter 14: Chemistry in industry and technology – fast facts C.1 Iron, steel and aluminium • Iron is extracted from its ores hematite (Fe2O3) and magnetite (Fe3O4) in a blast furnace. • Iron ore, coke and limestone (CaCO3) are added and hot air is blown in from the bottom. • The coke burns to form carbon dioxide: C(s) + O2(g) → CO2. • The heat produced in this reaction makes the calcium carbonate decompose to calcium oxide:

CaCO3(s) → CaO(s) + CO2(g). • The carbon monoxide reduces the iron(III) oxide as it rises up the furnace:

Fe2O3(s) + 3CO(g) →2Fe(l) + 3CO2(g). • The calcium oxide produced from the thermal decomposition of limestone reacts with silicon

dioxide and aluminium oxide’s impurities to form liquid slag of calcium silicate, CaSiO3, and calcium aluminate, Ca(AlO2)2.

• CaO(s) + SiO2(s) → CaSiO3(l) CaO(s) + Al2O3(s) → Ca(AlO2)2(l) • The iron produced by the blast furnace contains about 4% of carbon, which makes it brittle. It is

converted into steel by the basic oxygen process (BOC): • Oxygen is blown throw the molten iron, and small quantities of alloying elements such as

nickel and chromium are added. • The oxygen combines with the unwanted non-metal impurities to form oxides which either

escape as gases: C(s) + O2(g) → CO2 (g) S(s) + O2(g)→ SO2 (g), or combine with the lime (CaO) (added to the converter) to form a slag of calcium phosphate, Ca3(PO4)2, and calcium silicate, CaSiO3. 4P + 5O2 → P4O10 Si + O2 → SiO2

• An alloy is a homogenous mixture containing at least one metal formed when liquid metals are added together and allowed to form a solid of uniform composition.

The presence of other elements makes it more difficult for atoms to slip over each other and makes the metal harder.

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• The properties of steel may be also be modified by three heat treatment processes:

• 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.

• Aluminium is found in the mineral bauxite.. Its extraction of aluminium involves three stages:

• The mineral is treated with aqueous sodium hydroxide. The amphoteric nature of the aluminium oxide allows it to be separated from other metal oxides as it dissolves.

Al2O3(s) + 2OH–(aq) + 3H2O(l) → 2Al(OH)4– (aq)

• The purified aluminium oxide is dissolved in molten cryolite. This reduces the melting point and so reduces the energy requirements of the process.

• The molten mixture is electrolysed.

• Reactions at anode: 2 O2–(l) → O2(g) + 4e– C(s) + O2(g)→ CO2(g)

• Reactions at cathode Al3+(l) + 3e– → Al(l)

• Aluminium has a high thermal and electrical conductivity, and a lower density than steel.

• It can be made stronger by alloying with other metals such as copper and magnesium.

• The production of both steel and aluminium consumes large amounts of energy, uses large amounts of water and produces a large amount of solid waste and the greenhouse gas CO2.

• Recycling can greatly reduce the environmental impact.

C.2 The oil industry • Crude oil, a mixture of hydrocarbons, is one of the most important raw materials in the world

today.

• It is a source of fuels and an important chemical feedstock for the production of polymers, pharmaceuticals, dyes and solvents.

• Petrol is a highly concentrated and convenient energy source for use in transport.

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• The burning of hydrocarbons produces environmental side effects such as smog and global warming.

• Crude oil will last longer if we conserve energy and recycle materials such as plastics.

• It is the most convenient and economical option at the moment but alternative energy sources and feedstocks may be developed.

• There are three important types of cracking:

• Thermal cracking; in which the very long chain alkanes are 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. The feedstock of ethane, butane and alkanes with eight carbon atoms is preheated, vaporized and mixed with steam at 1250–1400 °C.

C.3 Addition polymers • Polymers, with different chemical compositions can be formed by changing the monomer.

• Ethene can polymerize in two distinct processes.

• LDP (Low Density Polyethene) is produced at high temperature and very high pressure in the presence of a free-radical initiator (small amounts of O2 or peroxides). It is a branched-chain polymer with an irregular lattice. It has a lower density and lower melting point than HDP.

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• HDP (High Density Polyethene) is produced at lower pressure and temperature in the presence of Zeigler catalysts (Al(C2H5)3 and TiCl4). It has very little branching and forms a regular lattice. It has higher density and a higher melting point than LDP.

• The isotactic form has methyl groups arranged on one side.

• It is used to make car bumpers and plastic toys, and can be drawn into fibres to make clothes and carpets.

• The atactic form has methyl groups which are randomly orientated. It is softer and more flexible and used as a sealant and in other waterproof coatings.

• Pure PVC is quite rigid as it has strong intermolecular forces between its polar chains.

• Plasticiser molecules fit in between and separate the polymer chains. The resulting plastic is softer and more flexible.

• Expanded polystyrene is made by expansion moulding. A volatile hydrocarbon, such as pentane, is placed in a mould and heated when styrene (phenylethene) polymerizes.

• It has a low density, is white, opaque and an excellent thermal insulator.

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Advantages of polymer use: • Plastics are relative cheap.

• They are relatively unreactive and have low densities.

• They are good electrical and thermal insulators.

• They are flexible and can be easily coloured and moulded.

Disadvantages of polymer use: • Addition polymers are all currently produced

from crude oil – a limited resource.

• Many polymers are not biodegradable and so are difficult to dispose of.

C.4 Catalysts • Catalysts increase the rate of some reactions but they do not change the position of equilibrium.

• A catalyst can’t make more of a product than would eventually be produced without it. It can however act selectively when two or more competing reactions are possible with the same starting materials, to produce more of the desired product by catalyzing only that reaction.

• Heterogeneous catalysts are in different states to the reactants.

• They are generally preferred in industrial processes as they can be easily removed by filtration from the reaction mixture.

• They are only effective on the surface.

• Homogeneous catalysts are in the same state of matter as the reactants.

• All the catalyst is exposed to the reactants.

• Many catalysts are either transition metals or their compounds. Transition metals show two properties which make them particularly effective.

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• They have variable oxidation states and are particularly effective catalysts in redox reactions.

• They adsorb small molecules onto their surface and so provide a surface for the reactant molecules to come together with the correct orientation.

• The following factors should be considered when choosing a catalyst:

• Selectivity (produce only the desired product);

• Efficiency;

• Ability to work under mild/severe conditions;

• Environmental impact;

• Problems caused by catalysts becoming poisoned by impurities.

C.5 Fuel cells and rechargeable batteries • The hydrogen oxygen fuel cell operates with either an acidic or alkaline electrolyte..

With an alkaline electrolyte:

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With an acid electrolyte:

• The overall reaction is the sum of the oxidation and reduction half-reactions: 2H2(g) + O2(g) → 2H2O(l).

• The lead acid battery is used for heavy power applications as it can deliver a high current for short periods of time.

• It relies on the ability of lead to exist in two oxidation states: +2 and +4, and the insolubility of lead(II) sulphate: PbSO4.

Discharging a lead acid battery

The overall reaction is: Pb(s) + 2H2SO4(aq) + PbO2(s)→ 2PbSO4(s) + 2H2O(l)

Charging a lead acid battery

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Charging a nickel cadmium battery

Discharging a lithium ion battery

• Fuel cells and rechargeable batteries are both ways of converting the chemical energy of an exothermic reaction into electrical energy.

• The main difference is that the reactions in rechargeable batteries have to be reversible.

C.6, C.11 Liquid crystals • Liquid crystals are fluids that have physical properties (electrical, optical and elasticity) that are

dependent on molecular orientation relative to some fixed axis in the material.

• Examples include graphite, cellulose and the solution extruded by a spider to form silk and DNA.

• Liquid crystal materials may not always be in a liquid crystal phase.

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• Thermotropic liquid crystal materials are pure substances that show liquid crystal behaviour over a temperature range between the solid and liquid states. The biphenyl nitriles are common examples.

• Lyotropic liquid crystals are solutions that show the liquid crystal state at certain concentrations. Examples include soap and water.

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• Soaps and detergents form lyotropic liquid crystals when they combine with water.

• Liquid crystal displays (LCDs) are used in digital watches, calculators and laptops.

• The orientation of the polar molecules can be controlled by the application of a small voltage across a thin film of the material. Light and dark areas can be controlled by the applied voltage to a grid of electrodes.

• Pentylcyanophenyl is used in liquid crystal display devices as it has the following properties:

• It is chemically stable.

• The liquid-crystal phase is stable over a suitable range of temperatures.

• It is polar so can change its orientation when an electric field is applied.

• It responds to changes of voltage quickly; it has a fast switching speed.

• The biphenyl nitriles have nematic liquid crystal properties. The nitrile group makes the molecules polar, which ensures that the intermolecular forces are strong enough to align in a common direction.

• The biphenyl groups make the molecules more rigid and rod-shaped.

• The long alkane chain ensures that the molecules cannot pack together so closely and so maintains the liquid crystal state.

• It is used in electronic devices as:

• It is chemically stable.

• It has a liquid crystal phase stable over a suitable range of temperatures.

• It is polar, making it able to change its orientation when an electric field is applied.

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• It responds to changes of voltage quickly; it has a fast switching speed.

• The workings of a twisted nematic liquid crystal:

• Each pixel contains a liquid crystal sandwiched between two glass plates. The plates have scratches at 90° to each other.

• The molecules in contact with the glass line up with the scratches and form a twisted arrangement between the plates due to intermolecular bonds.

• In the ‘off’ state, the light passes through the second polarizing filter as the plane of polarization rotates with the molecular orientation as the light passes through the cell.

• When a small threshold voltage is applied across the cell (the ‘on’ state) the polar liquid crystal molecules now align with the field and the twisted structure is lost.

• The plane-polarized light is no longer rotated, and so no light is transmitted and the cell appears dark.

• When the electric field is turned off, the molecules relax back to their twisted state and the cell becomes light again. Each cell represents one dot or pixel of the final image.

• Kevlar® consists of a long chains lined up parallel to one another by hydrogen bonds between the NH2 groups from one chain and the C = O groups from another.

• Kevlar® has rigid rod-shaped molecules that can result in lyotropic behaviour.

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• It dissolves in concentrated H2SO4 as the hydrogen bonds break when the O and N atoms are protonated.

C.7 Nanotechnology • 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.

• Physical techniques allow atoms to be manipulated and positioned to specific requirements.

• Chemical techniques position atoms in molecules using chemical reactions.

• Nanotubes are made from carbon hexagons (like a rolled round graphite sheet) with pentagons needed to close the structure at the ends.

• Single- or multiple-walled tubes, made from concentric nanotubes, can be formed.

• Bundles of the tubes have high tensile strength as strong covalent bonding extends along the nanotube.

• As the behaviour of electrons depends on the length of the tube, some forms are conductors and some are semiconductors. This is a typical nanoscale (quantum) effect.

• The differences between the bulk properties and the size-dependent properties on the nanoscale should be noted.

• Concerns over the use of nanotechnology include:

• Large-scale manufacture can carry the same risk of explosion as materials have small particle size and large surface area.

• Toxicity regulations are difficult as properties depend on the size of the particle.

• There are unknown health effects, because new materials have new health risks.

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• Concern that the human immune system will be defenceless against particles on nanoscale.

• Responsibilities of the industries.

• Political issues, such as need for public education for informed debate and for public involvement in policy discussions.