The method used to extract metals depends on their position in the reactivity series. The least reactive metals (gold, silver, platinum) are found in their natural forms and therefore can simply be extracted. Anything less reactive than carbon can be displaced from its ore by carbon, but those at the top of the reactivity series (magnesium, aluminium etc.) must be extracted by electrolysis.
Aluminium is extracted from purified aluminium oxide, using electrolysis.
|See illustration above|
Bauxite is purified into aluminium oxide, which is dissolved into cryolite. Molten cryolite to bring down the boiling point, as it is much lower than that of aluminium and therefore reduces the energy needed for extraction. The walls of the tank make up the cathode, where aluminium is collected.
It sinks to to the bottom and is tapped off.
Oxygen is formed at the positive electrode, which reacts with the graphite anode to from carbon dioxide. This means that the anode has to be replaced regularly.
At the anode, two oxygen ions lose four electrons: 2O2- → O2 + 4e- At the cathode, each aluminium ion gains three electrons: Al3+ + 3e- →Al
|Iron extration inside a blast furnace|
Extraction of iron takes place inside a blast furnace.
Aluminium and iron have many different uses industrially.
Crude oil is made up of a mixture of hydrocarbons of different chain lengths.
Industrially, crude oil is separated using fractional distillation. Crude oil is heated until it boils, and rises up the fractionating column. As it rises, the temperature decreases and the longer chained hydrocarbons re-condense into liquids. At this point, they are collected to be used.
Refinery Gases – bottled gas
Gasoline – Fuel for cars and other vehicles
Naphtha – used to make chemicals
Kerosene – aircraft fuel
Diesel – Fuel for cars and other larger vehicles
Fuel Oil – fuel for ships, power stations
Bitumen – used to make roads and roofs
As the chain length gets longer, the boiling point gets higher, so bitumen is found as a liquid/solid, whereas refinery gases are found as gases. The fractions also get less viscous as the chain length decreases.
Incomplete combustion of hydrocarbon fuels may result in the production of carbon monoxide, which is poisonous, because it reacts with haemoglobin, the red pigment in the blood that carries oxygen, more readily than O2 and reduces the capacity of the blood to carry oxygen.
In car engines, the temperatures get very high from the combustion of fuel, which results in nitrogen and oxygen from the air reacting, which forms nitrous oxides.
Nitrogen oxides and sulphur dioxides are pollutant gases, which contribute to acid rain. Sulphur dioxide causes acidic ‘water’ that mixes with rain clouds and nitrous oxides to form acid rain. This can lead to minerals leaching out of the soil, which results in infertile soil, and also kills aquatic animals.
Fractional distillation of crude oil produces more long-chain hydrocarbons than short chain hydrocarbons. Short chain hydrocarbons are much more useful than long chain hydrocarbons, which means that the process of cracking – breaking long chain hydrocarbons into shorter chain hydrocarbons – is necessary.
Long-chain alkanes are converted into shorter-chain alkanes and alkenes by the process of catalytic cracking. Silica or alumina are used a catalyst, and a temperature of around 600-700˚C is used.
Addition polymers are formed by joining together many small molecules, which are called monomers.
You can deduce the structure of a monomer from the repeat unit of an addition polymer. For example, with poly (ethene) the monomer that it is made from is ethene. The arms, which form the link between the polymers, come from a double bond in the monomer.
Different polymers have different uses: Poly (ethene)
Addition polymers can be hard to dispose of, because their inertness means that they do not easily biodegrade.
Some polymers, such as nylon 6-6, do not form by addition, but by a process called condensation polymerisation.
Condensation polymerisation produces a small molecule, such as water, which drops out of the chain, as well as the polymer.
Ammonia is industrially manufactured in the Haber process. It takes hydrogen from natural gas, such as ethane, and nitrogen from the air.
In the Haber process, there are certain essential conditions used to give a good yield:
Ammonia has a much higher melting point than nitrogen or hydrogen and so the system is cooled enough for the ammonium to liquefy and be pumped off whilst the hydrogen and nitrogen are re-circulated back into the system so they can react again. This shifts the equilibrium to the side of the products.
Ammonia is used in the manufacture of fertilisers and nitric acid. Fertilisers contain high levels of nitrates, whilst nitric acid is made by adding oxygen to ammonia: 4NH3 + 8O2 → 4HNO3 + 4H2O
Sulphuric acid is manufactured in a reversible reaction known as the contact process. The raw materials are sulphur and oxygen that are reacted together to give sulphur dioxide. The sulphur dioxide is then reacted with more oxygen (in excess air.) S (s) + O2 (g) → SO2 (g) 2SO2 (g) + O2 (g) → 2SO3 (g)
In the contact process, the conditions are engineered to give a good reaction speed and a good yield:
Reacting sulphur trioxide with water produces a mist of concentrated sulphuric acid, and so sulphur trioxide is absorbed into concentrated sulphuric acid to give oleum (or oleic acid.)
|Manufacturing sulphuric acid (H2SO4)|
H2SO4 (l) + SO3 (g) → H2S2O7 (l) H2S2O7 (l) + H2O (l) → 2H2SO4
Sulphuric acid has many practical uses, such as in detergents, fertilisers and paints. Sulphuric acid is used in extracting white pigment, titanium dioxide, from titanium ores.
The electrolysis of brine (NaCl) produces many useful products: sodium hydroxide, chlorine and hydrogen. This takes place in a diaphragm cell. Water provides OH- and H+ ions, whilst the ionic sodium chloride salt provides Na+ and Cl- ions.
The equation at the anode is: 2Cl- → Cl2 + 2e- The equation at the cathode is 2H+ + 2e- → H2
Sodium Hydroxide has many important uses:
Chlorine also has many uses, which are important to human life: