C1.3:Metals and Their Uses

METAL ORES - A rock which contains enough metal for it to be worth extracting from 

Chemical methods of extraction:

• Reduction - a reaction where electrons are gained
• Electrolysis - the process of breaking down a substance using electricity
• Displacement reaction - a reaction where a more reactive element replaces less reactive element in a compound 

REACTIVITY SERIES - A list of elements arranged in order of their reactivity. The most reactive elements are at the top and the least reactive elements at the bottom

REDUCTION:

• Metals that are below carbon in the reactivity series are less reactive than it. This means they can be extracted from their oxides by reduction where oxygen is removed using carbon.

ELECTROLYSIS:

• Metals that are higher than carbon in the reactivity series are more reactive than carbon. They have to be extracted from their oxides using electrolysis which is expensive.

Copper extraction by reduction with carbon - ore is heated in a furnace (smelting) producing impure copper.

Copper purification by electrolysis - electrolysis (breaking down of a substance using heat) requires an electrolyte (liquid used to conduct electricity).

Electrolytes are often metal salt solutions made from the ore or molten metal oxides and have free ions which conduct electricity.

How copper is purified using electrolysis?

• electrons are pulled off copper atoms at the positive electrode (made of impure copper) causing them to go into solution as Cu2+ ions
• Cu2+ ions move towards the negative electrode, gain electrons and turn back into copper atoms
• impurites are dropped at the positive electrode as a sludge, whilst pure copper atoms bond to the negative electrode

BIOLEACHING - The process by which copper is seperated from copper sulfide using bacteria

• seperates copper from copper sulfide using rock-eating bacteria
• bacteria gets energy from bond between copper and sulfur
• seperates copper from ore in process
• solution contains copper (extracted by filtering etc)

PHYTOMINING - The planting of vegetation that will selectively concentrate specific metals from the soil into their tissues

• plants grown on soil containing low-grade ores
• plants absorb copper from soil into leaves
• plants are burned, harvested or dried in a furnace
• copper collected from ash in furnace

PROS - cheap, requires less energy so less climate change etc., carbon neutral

CONS - slow (e.g. takes a long time for plants to grow and take up copper in phytomining)

SMELTING - The extraction of a metal from its ore by a process involving heating and melting

• copper ore is mined from earth 
• copper ore is heated in furnace with carbon (smelting) 
• produces impure copper
• purified by electrolysis
• pure copper produced

DISPLACEMENT - A reaction where a more reactive element replaces a less reactive element in a compound

• copper oxide comes into contact with a more reactive element – carbon    
• forms carbon dioxide  
• leaves pure copper

The more reactive metal bonds more strongly to the non-metal bit of the compound and pushes out the less reactive metal.

PROS:

• useful products can be made
• provides local people with jobs
• brings money to the area improve local services (e.g. transport and health)

CONS:

• noise pollution
• increased levels of traffic due to lorries visiting the mines
• bad for the environment as it destroys habitats and landscapes
• mining takes lots of energy which comes from burning fossil fuels causing acid rain etc.

Why is it important to recycle metals?

• requires less energy
• saves limited metal resources
• reduces the amount of waste going to landfill
• saves fossil fuels so less acid rain, climate change etc.

PROPERTIES and USES of metals:

• strong (hard to break) - bridges
• good conductor of heat - saucepan bases
• good conductor of electricity - electrical wires
• malleable (can be bent and hammered into shapes) - car bodies

Copper - good conductor of electricity, hard, strong, can be bent, doesn't react with water

e.g. electrical wires - good conductor of electricity, can be drawn out into wires (ductile)

Aluminium - corrosion-resistant, low density, lightweight, forms hard, strong alloys

e.g. aeroplane - strong, bent into shape, lightweight

Titanium - low density, very strong, corrosion-resistant 

e.g. replacement hip - corrosion-resistant, light, not bendy

ALLOY - A metal that is a mixture of two or more metals, or a mixture involving metals and non-metals

Alloys are made by melting the main metal and then dissolving the other substances in it. Alloys of iron are called steel. Steel is formed by adding small amounts of carbon to it

Iron - The regular pattern allows the layers of metal atoms to slip over each other easily. This makes pure iron soft and easy to shape.

Steel  - The pattern of iron atoms is disrupted by the impurities. This stops the layers sliding over each other making it harder and stronger.

Low-carbon steel (0.1% carbon) - easily shaped - car bodies

High-carbon steel (1.5% carbon) - very hard, inflexible - blades, bridges

Stainless steel (chromium and nickel) - corriosion-resistant - cutlery, sinks

Alloys are harder than pure metals because they are made from atoms of different elements which have different sized atoms. Smaller atoms will upset the layers of normal sized atoms, making it more difficult for them to slide over each other.

Common alloys:

Bronze (copper and tin) - harder than copper - medals, statues

Cupronickel (copper and nickel) - hard, corrosion-resistant - 'silver' coins

Gold (zinc, copper, nickel etc.) - harder than pure gold - jewellery

Aluminium (small amounts of other metals) - low density, stong, aircraft