METALS AND THEIR USES

EXTRACTING METALS

metals are found in the earth's crust- find most metals combined chemically with other chemical elements (oxygen), so must be chemically separated from its compounds before use
where there is enough of a metal compound or metal in a rock to make it worth extraction, the rock is a metal ore
ores are mined from the ground and some need to be concentrated before the metal is extracted and purified (copper ores are ground into powder), they are then mixed with water and a chemical that makes the copper compound repel water, air is then bubbled through the mixture and the copper compound floats on top as a froth (rocky bits sink), then scraped off the top ready for copper extraction
whether it is worth extracting a metal depends on how easy it is to extract it from its ore and how much metal the ore contains, these 2 factors change over time- an ore that was once thought of as low grade could become and economic source of a metal due to new cheaper methods being discovered
some metals are so unreactive that they are found in the Earth as the metals themselves (gold and silver). Occur in a native state.
gold flakes can be physically separated from sand and rocks by panning
the way we extract a metal depends on its place in the reactivity series- a more reactive metal will displace a less reactive metal from its compounds, carbon (a non-metal) will also displace less reactive metals from their oxides (this is used in industry)
find many metals combined with oxygen- metal oxides. carbon is more reactive than copper, lead, iron and zinc so can be used to extract the metals from their oxides- heat the metal oxide with carbon, carbon removes oxygen to form CO2 and metal is formed as an element- removal of oxygen = reduction
metals more reactive than carbon are extracted using electrolysis not reduction

IRON AND STEELS

Iron ore is displaced with carbon in a blast furnace, iron straight from the blast furnace has limited uses- contains 96% iron and some impurities, mainly carbon- makes it brittle, although it is very hard and can't be easily compressed- when molten can be run into moulds and cast into different shapes. This cast iron is used to make wood-burning stoves, man-hole covers on roads and engines
Can treat the iron to remove some of the carbon- giving us pure iron which is soft and easily shaped- to make more useful combine with tiny amounts of other elements = alloy
steel is an alloy of iron- by adding elements in carefully controlled amounts, we can change the properties of steel- lots of diff types of steel.- lots of different types of steel- all are alloys of iron with carbon and/or other elements- simplest steels are carbon steels (made by removing most of the carbon from cast iron, leaving small amounts (cheapest steel))- used in bodies of cars and machinery- high carbon steel is strong but brittle- low carbon steel is soft and easily shaped (type is mild steel)
low-alloy steels are more expensive because they contain between 1-5% of other metals
high-alloy steels even more expensive- higher percentage of other metals- chromium nickel steel = stainless steels (cutlery)- resistant to corrosion

ALUMINIUM AND TITANIUM

strong and have a low density (light)- also don't corrode
ALUMINIUM- silvery, shiny, light, low density, excellent conductor of energy and electricity, malleable- reactive but doesn't corrode easily due to thin layer of aluminium oxide that stops further corrosion taking place- forms alloys that are stronger, used in cooking foil and saucepans
extracting aluminium- electrolysis (al oxide must be melted before electrolysis)- electrolysis is expensive (high temps to melt and extract), and not good for the environment
TITANIUM- silvery, strong, very resistant to corrosion, has an oxide layer that protects it, denser than aluminium but less dense than other metals, high melting point, used for high performance aircraft and racing bikes, parts of jet engines, nuclear reactors, replacement hip joints
extracting titanium- could with carbon as less reactive than aluminium, however carbon reacts with it and turns it brittle, so use more reactive metals like sodium or magnesium (which have to be extracted through electrolysis)- takes a lot of steps to extract, takes time and costs money

EXTRACTING COPPER

most extracted from copper-rich ores (limited resource running out)- two methods- using sulfuric acid to produce copper sulfate solution before extracting and smelting (heating in a furnace)
ex. copper sulfide + oxygen - copper + sulfur dioxide
must avoid letting sulfur dioxide into the air
then use impure copper as the positive electrode in electrolysis cells to make pure copper
however 80% still done by smelting
smelting and purifying copper ore uses huge amounts of heat and electricity- costs a lot of money and has a huge impact on the environment
most copper is extracted by smelting copper-rich ores, copper can also be extracted from copper sulphate solutions by electrolysis or by displacement using scrap iron. Electrolysis is also used to purify impure copper (from smelting)
scientists developing new ways to get copper from low-grade ores, use bacteria (bioleaching) and plants (phytomining)
PHYTOMINING- plants absorb copper compounds from low-grade copper ore as they grow (could be from slag heaps of copper rich), plants are then burned and metals extracted from the ash (then leach using sulfuric acid then displacement with scrap iron)
BIOLEACHING- bacteria feed on low-grade metal ores, by a combination of biological and chemical processes get a solution of copper ions (then scrap iron and electrolysis)

USEFUL METALS

Transition metals, similar properties- strong, malleable, good conductors of electricity and energy- lots of uses
copper is a transition metal- water pipes, wires
copper alloys = bronze (copper and tin, resistant to corrosion), brass (copper and zinc, hard, used for musical instruments)
Aluminium alloys- over 300 available
gold and copper- doesnt wear away as quickly, durable, less expensive, vary proportions for different shades

METALLIC ISSUES

Cast mining for iron, copper and aluminium scar the landscape, creating noise and dust and destroying the habitats of plants and animals, also leave large heaps of waste rock
heating strongly and extraction - acid rain
groundwter acidity as a result of water draining through exposed ores and slag heaps of waste
electrolysis OR scrap iron
recycling- saves money of extraction- conserves earth's reserves of metal ores
steel most commonly used metal- steel girders suspension bridges, however rusts- affects strength (stainless too expensive)

	Criado por georgie.proctor mais de 10 anos atrás

Notas sobre GCSE core chemistry revision 1, criado por georgie.proctor em 07-06-2014.