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AS/A-level Chemistry - Extraction of Metals (2)

Extraction of Metals (Using Hydrogen/Electrolysis/Scrap Iron)

· Ores,metal extraction,electrolysis,as level chemistry,A-level Chemistry

Apart from reduction with carbon/carbon Monoxide, there are other extraction methods in AS/A-level Chemistry.

Extraction of Tungsten (Using Hydrogen)

  • Tungsten can be extracted from its oxide with carbon, but that can leave impurities which make the metal more brittle.
  • If pure tungsten is needed, the ore is reduced using hydrogen instead.

WO3(s)   +   3H2(g)   →   W(s)   +   3H2O(g)

  • This happens in a furnace at temperatures above 700°C.
  • Tungsten is the only metal reduced on a large scale using hydrogen.
  • Hydrogen is more expensive but it is worth the extra cost to get pure tungsten, which is much easier to work with.
  • Hydrogen is highly explosive when mixed with air, which is a hazard.

Advantages of Reduction with Hydrogen

  • It produces very pure tungsten.

  • Hydrogen is a cheap reagent.

Disadvantages of Reduction with Hydrogen

  • The energy costs are high.
  • Using a flammable gas such as hydrogen at high temperatures is very dangerous.

Extraction of Aluminium (By Electrolysis)

  • Aluminium is too reactive to extract using reduction by carbon.
  • A very high temperature is needed, so extracting aluminium by reduction is too expensive to make it worthwhile.
  • Aluminium’s ore is called bauxite – it is aluminium oxide, Al2O3, with various impurities.
  • First, all of these impurities are removed.
  • Then it is dissolved in molten cryolite (sodium aluminium fluoride, Na3AlF6), which lowers its melting point from 2050°C to 970°C. This reduces operating costs.
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  • Aluminium is produced at the cathode and collects as the molten liquid at the bottom of the cell.

Al3+   +   3e-   →   Al

  • Oxygen is produced at the anode.

2O2-   →   O2   +   4e-

  • The current used in electrolysis is high (200,000 A), so the process is carried out where cheap electricity is available, often near hydroelectric power stations.
  • The overall cell reaction is:

2Al2O3   →   4Al(l)   +   3O2(g)

Advantages of Electrolysis

  • It is a continuous process, so is efficient
  • It makes the metal in a pure form

Disadvantages of Electrolysis

  • The cost of melting the aluminium and supplying the energy for electrolysis is very high.
  • It only works for ionic oxides.

Extraction of Titanium (A batch process with several stages)

  • The ore is converted to titanium(IV) chloride by heating it to about 900°C with carbon in a stream of chlorine gas.

TiO2(s)   +   2Cl2(g)   +   2C(s)   →   TiCl4(g)   +   2CO(g)

  • The titanium chloride is purified by fractional distillation under an inert atmosphere of argon or nitrogen.
  • Then the chloride gets reduced in a furnace at almost 1000°C.
  • It i heated with a more reactive metal such as sodium or magnesium.
  • An inert atmosphere is used to prevent side reactions.
  • Na and Mg are reducing agents.

TiCl4(g)   +   4Na(l)   →   Ti(s)   +   4NaCl(l)

TiCl4(g)   +   2Mg(l)   →   Ti(s)   +   2MgCl(l)

Advantages of Titanium Extraction

  • It produces very pure titanium.

Disadvantages of Titanium Extraction

  • It is a batch process, which means the titanium is not produced continuously. This adds to the cost of the process.

  • The sodium and magnesium are expensive.

  • The energy costs are very high.

Extraction of Copper (Using Scrap Iron)

  • Scrap iron can be used to extract copper from solution.
  • This method is mainly used with low grade ore – ore that only contains a small percentage of copper.
  • Acidified water dissolves the copper compounds in the ore.
  • The solution is collected and scrap iron is then added.
  • The iron dissolves and reduces the copper(II) ions.
  • The copper precipitates out of the solution.

Cu2+(aq)   +   Fe(s)   →   Cu(s)   +   Fe2+(aq)

  • This produces copper more slowly than carbon reduction and has a lower yield, which is why it is not used with ores that have a high copper content.
  • It is cheaper than carbon reduction because it does not need high temperatures.
  • It is better for the environment because no CO2 is produced.

That's the end of the topic!

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Drafted by Bonnie (Chemistry)

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