what is electrolysis?

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What is electrolysis?

An ionic compound conducts electricity when it is molten or in solution. The current causes the ionic compound to split up and form new substances.

Electrolysis has many uses, including:

purifying copper

plating metals with silver and gold

extracting reactive metals, such as aluminium

making chlorine, hydrogen and sodium hydroxide.

This process is called electrolysis, a word which comes from Greek and means “splitting by electricity”.

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heat

What happens during electrolysis?

In electrolysis, the substance that the current passes through and splits up is called the electrolyte.

Positive ions move to the negative electrode

and gain electrons.

This is reduction.

Negative ions move to the positive electrode and lose electrons.

This is oxidation.

The electrolyte contains positive and negative ions.

What happens to these ions during electrolysis?

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Electrolysis of molten lead bromide

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What redox processes occur at the electrodes during the electrolysis of molten lead bromide (PbBr2)?

Electrolysis of molten PbBr2 – redox equations

What is the overall equation for the electrolysis of molten lead bromide ?

At the negative electrode:

Pb2+ + 2e- Pb (reduction)

lead bromide lead + bromine

PbBr2 (l) Pb (l) + Br2 (g)

At the positive electrode:

2Br- Br2 + 2e- (oxidation)

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Electrolysis of molten PbBr2 – summary

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Why and how is aluminium extracted?

Aluminium is one of the most useful metals in the world.

Aluminium ore (bauxite) has a very high melting point (2050 °C).

Electrolysis is used to extract aluminium from its ore. Why is it not possible to extract aluminium by heating its ore with carbon?

For electrolysis, the ore is dissolved in a compound called cryolite (Na3AlF6), which lowers the melting point to 700 °C. Why is this important economically?

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Extracting aluminium

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What redox processes occur at the electrodes during the electrolysis of aluminium oxide (Al2O3)?

Extracting aluminium – redox equations

What is the overall equation for the extraction of aluminium by electrolysis?

At the negative electrode:

Al3+ + 3e- Al (reduction)

aluminium oxide aluminium + oxygen

2 Al2O3 (l) 4 Al (l) + 3 O2 (g)

At the positive electrode:

2O2- O2 + 4e- (oxidation)

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Extracting aluminium – summary

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What are the products of electrolysis?