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

• 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.

• It produces very pure tungsten.

• Hydrogen is a cheap reagent.

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

• 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.

• 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)

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

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

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

TiO_2(s)   +   2Cl_2(g)   +   2C_(s)   →   TiCl_4(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.

TiCl_4(g)   +   4Na_(l)   →   Ti_(s)   +   4NaCl_(l)

TiCl_4(g)   +   2Mg_(l)   →   Ti_(s)   +   2MgCl_(l)

• It produces very pure titanium.

• 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.

• 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!

CLICK HERE TO LEARN MORE ABOUT OUR AS/A-LEVEL CHEMISTRY COURSES

Drafted by Bonnie (Chemistry)