Metals and their uses

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Extracting metals

  • Metals are found in Erths crust. We find most of them combined chemically with other chemical elements, often with oxygen. This meanit has to be seperated before you can use it.
  • If there id enough of the product in a rock then we extract it. It is called an ore. Some need to be concentrated before the matal is extracted and purified. For example, copper ores are ground up and then they are mixed with water and a chemical that makes it repel water. Then it bubbles and the copper compound floats on top.
  • Whether it's worth having a particualr metal depends on: How easy it is to extract and how much metal the ore contains.
  • These can change over time; there might be a new way of extracting or we might need the 'low grade' ores more.
  • A few metals are so unreactive that they are found as themselves, we say they exist in their 'native state'. Sometimes it can just be picked up.
  • the way we extract metals depend son it's reactivity series. A more reactive metal will displace a less reactive metal from it's compounds. Carbon will also displace less reactive metals even though it is a non-metal.
  • We find many metals as compound with  oxygen (metal oxides). We can use carbon to displace these.
  • Heat the metal oxide with carbon. It removes the oxygen from the oxide and makes carbon dioxide. Metal oxide + carbon = Metal + Carbon dioxide.
  • Metals that are more reactive than carbon are extracted using electrolosis.
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Iron and steels

  • Iron ore is iron oxide. This means it has iron and oxygen combined. We extract it in a blast furnace using the technique on the previous card.
  • Straight from the blast furnace it doesn't have many uses. It has a lot of impurities and it's very brittle, it can't be compressed. When molten you can make shapes out of it, it's called cast iron.
  • However we can treat it to remove all the carbon and get pure iron. It's soft and easily shaped but sometimes too soft. if we want to make it useful we have to ombine it with other elements such as nickel and chromium.
  • We call a metal mixed with other elements an alloy.
  • Steel is an alloy of iron and there are lot of different types of it.
  • The most simple steel is a carbon steel. We remove most of the carbon from cast iron but leave a tiny quantitiy. They are the most used and cheapest steels to make. Things like machinery, ships and knives are made of it.
  • Alloy steels are more expensive than carbon steels because they contain other metals too. Low-alloy contain between 1 and 5% of other metals but high alloy steels, such as stainless steel contain a much higher percentage. They have chromium and nickel in them and this make them hard and strong, and resistant to corrosion (they don't rust).
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Aluminum and titanium

  • Although they are very strong, manty metals are also quite dense. This means we can't use them if we need something strong and light . Aluminum and titanium are light and strong so we can use them.
  • Aluminum is a silver, shiny metal that doesn't corrode because it's top layer of atoms has reacted with the oxygen in the air to make a aluminum oxide coating on the top. It is an excellent conductor and we can shape it easily. We use it for drinks cans and bikes.
  • Because it is reactive we can't use carbon to displace it. Instead we use electrolosis (passing an electric current throught the molten aluminum at high temperatures). Unfortunatly, we have to remove the impurities first and then melt it and then pass the current through, so it can end up being very expensive and there are environmental issues too with using that much energy.
  • Titanium is silvery white, strong and resistant to corrosion because it forms a layer of oxide on its surface, same as aluminum, it has a high melting point so we can use it at high temperatures, such as in aircraft . It is also used in replacement hip joints because it's lighter than other metals.
  • It's not that reactive, so we could produce it by displacing it with carbon. Unfortunatly it rects with the metal and that makes it very brittle so, we have to use metals that are more reactive, like sodium and magnesium. This is a problem because we have to produce those too and it's expensive. Also, before it can be produced, we must seperate the oxide and convert it to a chloride to be distilled.
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Extracting copper

  • We extract most of our copper from copper rich ores. However these are limited and are in danger of running out. The two main methods are:
  • Using sulfuric acid to make copper sulphate and then extracting the copper from that.
  • Smelting- We heat it very strongly in a furnace to produce Crude copper.
  • For example, copper can be found in an ore called chalcolite. This contains copper sulfide, which decomposes on heating: copper(1) sulfide + oxygen = copper + sulfur dioxide. We have to make sure sulfur dioxide dosn't escape because it produces acid rain.
  • We use the impure copper as the positive electrode in electrolosis cells to make pure copper. Metal ions are positive and therefore gather at the negative electrode in electrolosis (called a cell). Electrolosis on mass means that there are thousands of cells working at once, to purify the impure copper made by smelting. 
  • The copper can also be extracted in a displacement reaction with iron: iron + copper sulfide = iron sulfate + copper
  • However, there are also low grade ores that we have to use more of now that the high-grade ones are running out. There are two ways to deal with these:
  • Bioleching- Using bacteria which feed on an ore and leave a solution of copper ions we can treat and make into copper metal. It is a very slow process.
  • Phytomining- Plants absorb copper ions, from **** heaps as they grow, and are then burned and the metals are extracted from the ash.
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Useful metals

  • In the centre of the periodic table there is a large block of metals called the transition metals. They are good conductors and are strong but malleable.You will find them in buildings, cars, trains, etc- they can be used for many different things.
  • Copper is a very useful metal; it can be bent but is still strong and doesn't react with water. It is ideal for pipes that carry water, or wires to conduct electricity.
  • Bronze is made by mixing copper with tin. We use it for ships propellors because it's tough and doesn't corrode
  • Brass is made by mixing copper with zinc. We use it for musical instruments because it's tough but workable.
  • Aluminum has a low density and there are 300 different alloys with different properties.
  • We can make gold and aluminum harder by alloying them. In jewellery, it's usually alloyed with copper because it wears away when pure. 
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Metallic issues

  • We would find it very diffucult to live without metals, but using them leaves a huge scar on the environment. Open cast mining is usually used to get metals out of the ground and this makes huge pits, creates dust and destroys habitats. They also leave large heaps of waste rock. The water in an area becomes more acidic from running through these holes . When they are smelted, the sulpuric gas that comes off causes acid rain.
  • When plants grow, they absorb ions through the roots. Some are better than others but we use this for phytomining. We can extract the metals fro their ashes- we dissolve them in sulfuric acid and this solution is electrolysed to get the copper. Or scrap iron can be added alternatively.
  • Each person uses around 8kg of aluminum per year, this is why we have to recycle- it uses 5% of the otherwise energy to recycle than get more aluminum. We also recycle steel and iron. Copper can be recycled but it is usually alloyed so it's hard to extract first. 
  • Steel is the most commonly used metal. For example, skyscrapers have steel girders, suspension bridges use thick steel cables, concrete bridges are reinforced with steel. However it isn't all good, the iron in it starts to rust. Stainless steel could be used but it is a lot more expensive to produce. 
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