Extraction and uses of metals
- Metals are found in ores containing minerals mixed with rock
- The mineral is a compound of the metal and needs to be purified
- Aluminium is extracted from the ore bauxite
- The aluminium oxide in the bauxite needs to be purified, and it is melted so that electrolysis can be carried out.
- The anode is made from carbon
- The cathode is the steel-lined case.
- Aluminium forms at the cathode
- Oxygen forms at the anode
- The oxygen formed reacts with the carbon anode to form CO2, and this causes the anode to be worn down
- This process requires large amounts of electricity
- Copper is obtained by heating the ore malachite with carbon
- All metals below carbon in the reactivity series can be obtained this way
- Iron is produced on a large scale by this process in a blast furnace:
- Iron ore (source of iron), coke (source of carbon) and limestone are added at the top of the blast furnace
- Hot air is blasted from the bottom of the furnace to the top
- Oxygen in the air reacts with coke to form CO2, which in turn reacts with the coke again to from carbon monoxide
- Carbon monoxide is a reducing agent and thus turns iron oxide into iron.
- Molten iron runs to the bottom of the furnace and is run off
- The limestone is broken down by heat into calcium oxide, which in turn reacts with impurities to form slag
· Zinc can be extracted from zinc blende:
1. Zinc sulphide is turned into zinc oxide by heating
2. Zinc oxide is either reduced by carbon monoxide or
3. it is dissolved in sulphuric acid and then electrolysed
- Uses of metals:
Strong + malleable
Car bodies, cutlery
Low melting point
Strong and non-corrosive
Stainless steel production
Good electrical conductor
Natural Gas and Oil
- Crude oil is a mixture of hydrocarbons
- Separate parts, or fractions, of crude oil can be separated using fractional distillation.
- The crude oil is heated in a furnace and passed into the bottom fo the fractionating column
- The mixture evaporates and the different fractions condense at different levels.
- The fractions are:
- Fractional distillation produces more long-chain hydrocarbons than required, and these are turned into short-chain hydrocarbons by cracking
- When hydrocarbons are burnt (combusted) they release CO2, and if they do not combust completely, they release CO (carbon monoxide)
- Carbon monoxide molecules bind with haemoglobin in the blood more strongly than oxygen, and thus are dangerous
- Hydrocarbons are damaging to the environment because when burnt they release CO2 which is a greenhouse gas
- If crude oil is spilled, it can destroy habitats and kill animals.
- Polymers are large molecules made up of many small molecules called monomers
- Polymers can be made in tow ways: addition and condensation
- Addition polymerisation consists of alkenes reacting with each other to form long chains
- Condensation polymerisation consists of joining two different monomers, and when they react they expel a small molecule, often water
- Ethene is used to make polyethene through addition polymerisation
- Nylon is manufactured using condensation polymerisation, and its starting monomers are: hexanedioic acid and 1,6-diaminohexane
The Manufacture of some Important Chemicals
- Ammonia is produced in the Haber Process from nitrogen (from the air) and hydrogen (from natural gas)
- The Haber Process involves an iron catalyst, a temperature of 450°C and 200 atmospheres
- Any unused hydrogen and nitrogen is recycled.
- Ammonia is used for the manufacture of nitric acid and fertilisers
- Sulphuric acid is manufactured in the contact process
- The raw materials needed are sulphur and air
- The conditions are as follows: 450°C, 2 atmospheres and a vanadium oxide catalyst.
- Four steps in process:
Sulphur+ Oxygen -> Dioxide Sulphur
- Sulphur Dioxide + Oxygen ->
trioxide Sulphur Trioxide + Sulphuric Acid -> Oleum Sulphur
- Oleum + Water -> Sulphuric Acid
· Sulphuric acid is used in the manufacture of chemicals
· Acid rain kills plants and animals and depletes the soil of minerals
· Sodium hydroxide is manufactured through the electrolysis of brine (sodium chloride solution)
· At the cathode, hydrogen ions are turned into atoms, and at the anode, chloride ions are turned into atoms.
· What is left is sodium hydroxide solution.
· Sodium hydroxide is used for the manufacture of soap.
· Chlorine is used in the manufacture of bleach.