Obtaining & Using Metals

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Metal Ores

The majority of metals aren't found in lumps and need to be extracted from a compound, most metals are found in ores.

  • Unreactive metals don't normally form compounds with other elements. For example gold is an unreactive metal and is found uncombined so it just has to be dug up.
  • But most other metals do react with other elements and form compounds that are found naturally in the earths crust. If a compound holds enough of a metal to make it worth extracting then it's called a metal ore. There are limited numbers of metal ores because they're finite resources.
  • The more reactive a metal is, the harder it is to extract.

Metals offten have to be seperated from their oxides.

  • Many common metals react with oxygen and make oxides and this is called oxidation. These oxides are commonly the ores metals need extracting from.
  • A reaction that seperates a metal from it's oxide is called a reduction reaction.
  • The most common way to do this is to use carbon to seperate them.
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Methods Of Extraction

Methods of extraction are linked with the order of reactivity.

  • Metals that are less reactive than carbon are the only ones that can be extracted by a reduction reaction with carbon and this is done by heating the ore with carbon.
  • This is because more reactive metals form compunds more readily. Carbon is more reactive than iron so carbon takes oxygen from iron oxide. The same thing happens with zinc, tin & lead.
  • It basically means that carbon can only take oxygen away from metals that are less reactive than itself.
  • Really reactive metals form stable ores. (meaning they're difficult to remove from their compound)
  • Metals more reactive than carbon that come higher than it in the reactivity series are extracted using electrolysis. Electrolysis is a process that uses electricity to seperate the metal from the other elements in the compound.
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The Reactivity Series

Potassium - K

Sodium - Na

Calcium - Ca                                              Blue - Extracted using electrolysis

Magnesium - Mg

Aluminium - Al

CARBON - C 

Zinc - Zn

Iron - Fe                                                   Red - Extracted by heating with carbon.

Tin - Sn

Lead - Pb

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Electrolysis

Electrolysis is used to seperate metals higher in the reactivity series than carbon with their ores. 

  • The extraction method of electrolysis breakes down ores using electricity.

E.g. when taking aluminium form its ore...

  • The main ore of Aluminium is bauxite, that contains aluminium oxide. (Al2O3)
  • The alumimium oxide is melted and used as the electrolyte for aluminium extraction.
  • Electrolysis decomposes the aluminium oxide into the aluminium and oxygen atoms.
  • The aluminium atoms sink to the botom of the tank as molten aluminium metal.
  • Electrolysis is very expensive. It is only used if the metal can't be extracted using reduction with carbon.
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Properties of Metals

Metals are all the same but with slight differences. They have basic properties that are the same, however each has their own specific combination of properties, making them all good for different purpouses.

All metals have typical properties:

  • They are strong but can be hammered or bent into other shapes which makes them good for making into bridges and car bodies.
  • They're good at conducting heat which means they're good for saucepan bases.
  • Their Electrical conductivity means they can be used for electrical wires.

Exact properties determine how metals are used:

  • Aluminium is corrosion-resistant, has a low density and while pure alluminium isn't very strong, it does form hard alloys. This makes it a useful structural materialfor things like window frames, electricity cables and aircraft.
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Properties of Metals #2

Exact properties determine how metals are used:

  • Aluminium is corrosion-resistant, has a low density and while pure alluminium isn't very strong, it does form hard alloys. This makes it a useful structural material for things like window frames, electricity cables and aircraft.
  • Copper is very hard and strong with a high melting poin. It's a good conductor of electricity so is good for drawing out electricial wires. It can also be made into pipes and as it is below hydrogen in the reactivity series, doesn't react with water and so is good to use in plumbing.
  • Gold is shiny and easy to shape, it's used for jewellery and also in situations where metal that won't react with anything is needed like in tooth fillings or electric circuits.
  • Some metals corrode over time because the metal is being oxidised.
  • Metals that are high in the reactivity series are more likely to corrode because they react with oxygen.
  • When Iron rusts it's combining with oxygen and water to form hydrated iron oxide. (rust) Iron + oxygen + water → Hydrated iron oxide
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Making Metals More Useful

Pure Iron

  • 'Iron' extracted in a blast furnace using carbon monoxide is only 96% iron, the other 4% are impurities like carbon.
  • The impure iron is brittle, it is used for ornemental railings but doesn't have many other uses.
  • All the impurities are removed from most of the blast furnace iron and this pure iron has a regular arrangement of identical atoms that can slide over each other making it soft and easily shaped. This is far too bendy for most uses.

 

  • Most iron is converted into an alloy. (Steel) An alloy is a mix of 2 or more metals or a mix of a metal and a non metal.
  • Steels are made by adding small ammounts of carbon and sometimes other metals to iron.
  • The alloys made are stronger and more corrosion resistant.
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Making Metals More Useful #2

Alloys are harder than pure metals.

  • Different elements have different sized atoms. When an element like carbon is added to pure iron, the smaller carbon atom upsets the layers of pure iron atoms making it difficult for them to slide over each other. This is what makes alloys harder.
  • Becuase we understand the properties of metals, alloys can be designed for specific pourposes.
  • Some smart alloys "remember" their original shape. Nitinol (an alloy of nickel and titanium) is an example of this.
  • If a wire made of this smart alloy is bent, it returns to its original shape when  heated.
  • Scientists develop new materials like shampe memory alloys to fit new uses. For example Nitinol is good for things like glassed frames, so if they're bent or sat on can be easily reshaped. They are also used to make stents (tubes) for use in damaged blood vessels.
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Recycling

It is a chemists job to make sure we have the chemicals we need, but these chemicals come from the earth and we don't have an infinite supply. This is why it's important to recycle materials.

  • It uses less resources - there isn't an endless supply of metals in the earth. Recycling conserves these resources.
  • It uses less energy - mining and extracting metals uses a lot of energy that comes from using fossil fuels (that will run out and cause pollution)Recycling things like copper and alluminium takes a fraction of this energy.
  • It uses less money - Energy isn't cheap so recycling also saves money.
  • It makes less rubbish - Recycling cuts down on the ammount of rubbish that gets sent to landfill, which takes up space and pollutes surroundings.
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Recycling Bennefits

It's hard to work out the economic bennefits of recycling for these reasons...

  • Recycling isn't free, it costs to collect, transport, sort and process it all.
  • But if recourses like alluminium weren't recycled, more ores would need to be mined, 4 tonnes of ore for every 1 tonne of aluminium needed.
  • But mining makes a mess of the landscape and these mines can offten be in the rainforests. The ores then need transporting & aluminium needs extracting which needs electricity. The used aluminium also needs to be snet to landfill.

So it's difficult to say, but for every 1kg of aluminium cans recycled...

  • 95% of energy needed to mine and extrasct new aluminium is saved.
  • 4kg of aluminium is kept.
  • It stops a lot of waste.
  • Even though these differences are small it's still worth recycling and doing your bit for the environment.
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