Specification Point 2.23C (Paper 2C Only):
Explain how the method of extraction of a metal is related to its position in the reactivity series, illustrated by Carbon extraction for Iron and Electrolysis of Aluminium

Reactivity Series

Methods of Metal Extraction, Edexcel IGCSE Chemistry

Carbon Extraction (for elements below Carbon)

Carbon extraction of iron, CIE IGCSE Chemistry

The Carbon Extraction of Iron

Raw Materials: Iron Ore (Haematite), Coke, Limestone and Air

Explanation:

Iron Ore, Coke and Limestone are mixed together and fed into the top of the blast furnace. Hot air is blasted into the bottom of the blast furnace.

Coke is used as the starting material. It is an impure carbon and it burns in the hot air blast to form carbon dioxide. This is strongly exothermic reaction:

C (s)    +    O2 (g)    →    CO2 (g)

At the high temperatures in the furnace, carbon dioxide reacts with coke to form carbon monoxide:

CO2 (g)    +    C (s)    →    2CO (g)

Carbon Monoxide (the reducing agent) reduces the Iron (III) Oxide in the Iron Ore to form Iron, which will melt and collect at the bottom of the furnace, where it is tapped off:

Fe2O3 (s)    +    3CO (g)    →    2Fe (l)    +    3CO2 (g)

Limestone is added to the furnace to remove impurities in the ore. The Calcium Carbonate in the limestone decomposes to form calcium Oxide:

CaCO3 (s)    →    CaO (s)    +    CO2 (g)

The Calcium Oxide reacts with the Silicon Dioxide, which is an impurity in the Iron Ore, to form Calcium Silicate which melts and collects as a molten slag floating on top of the molten Iron and is tapped off separately:

CaO (s)    →    SiO2 (s)    +    CaSiO3 (l)

Electrolysis Extraction (for elements above Carbon)

Extraction-aluminium

The Extraction of Aluminium by Electrolysis

Raw Materials: Aluminium Ore (Bauxite)

Explanation:

The Bauxite is first purified to produce Aluminium Oxide Al2O3

Aluminium Oxide has a very high melting point so is dissolved in molten Cryolite to make the electrolyte with a lower melting point, as well as a better conductor of electricity than molten aluminium oxide. This reduces expense.

The electrolyte is a solution of aluminium oxide in molten cryolite at a temperature of about 1000 °C. The molten aluminium is siphoned off from time to time and fresh aluminium oxide is added to the cell. The cell operates at 5-6 volts and with current 100,000 amps. The heat generated by the huge current keeps the electrolyte molten.

A lot of electricity is required for this process of extraction, this is a major expense.

Reaction at the Negative Electrode:

The Aluminium melts and collects at the bottom of the cell and is then tapped off:

Al3+    +    3e    →    Al

Reaction at the Positive Electrode:

2O2-    –    4e    →    O2

Some of the Oxygen Produced at the positive electrode then reacts with the Graphite (Carbon) electrode to produce Carbon Dioxide Gas:

C (s)    +    O2 (g)    →    CO2 (g)

*This causes the carbon anodes to burn away, so they must be replaced regularly.

Specification Point 2.24C (Paper 2C Only):
Be able to comment on a Metal extraction process, given appropriate information

Carbon Extraction

Carbon Extraction:

Used to extract metals below carbon in the reactivity series.

Extracted by heating with a reducing agent such as carbon or carbon monoxide in a
blast furnace.

Carbon extraction of iron, CIE IGCSE Chemistry

The Carbon Extraction of Iron

Electrolysis Extraction

Electrolysis Extraction:

Used to extract metals above carbon in the reactivity series. Reactive metals are hard to reduce so need a powerful method of extraction, which is electrolysis.

Extracted by electrolysis of the molten chloride or molten oxide

Extraction-aluminium

The Extraction of Aluminium by Electrolysis

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Author: Jamie

Jamie got a First class degree in Chemistry from Oxford University before going on to teach chemistry full time as a professional tutor. He’s put together these handy revision notes to match the Edexcel IGCSE Chemistry specification so you can learn exactly what you need to know for your exams.