1. Definition The Process Examples
Electrolysis
Definition
The Process
Examples

2. What is Electrolysis?
All oxidation and reduction reaction involve the transfer of electrons. Some of these reactions are spontaneous – they happen ‘naturally’ without any help from external forces. For example:
Sodium oxidises to sodium ions in water (Na → Na+ + e-)
Fluorine gas reduces to fluoride ions in water ( F2 + 2e- → 2F-)
But sometimes we want to get the reverse reaction to occur i.e. we want to make sodium and fluorine. This does not happen spontaneously so we have to force the electrons to travel in the opposite direction. To force electrons to move we use electricity. This is a process called electrolysis

3. The Process
Electrolysis is a very useful way of making elements from ionic compounds.
The process involves placing two electrodes into a dissolved or molten ionic compound. A current is passed through the liquid and the ions are attracted to the electrodes:
Cathode – this electrode attracts cations. It is negatively charged. It gives electrons to the cations, therefore reducing them
Anode – this electrode attracts anions. It is positively charged. It takes electrons from the anions, therefore oxidising them
As the ions get to each electrode the anions have their electrons removed and the cations have electrons added.
The ions end up losing their charges and are converted back to atoms

4. Examples of Electrolysis I
Electrolysis of water:
Because water contains ions it can be electrolysed. It breaks up into Hydrogen and Oxygen
The diagram to the right shows a Hoffman voltameter – an apparatus where to electrodes (at the bottom) are used to generate hydrogen and oxygen gas. The two graduated tubes can be used to measure the volume of gas being produced.
What are the volume ratios of hydrogen and oxygen?

5. Examples of Electrolysis II
The Extraction of Aluminium
Alumina (aluminium oxide) is poured into pot which contains a carbon cathode base
Carbon anodes are placed in and about amps of current is passed through the alumina.
The result is CO2 (from the production of O2 at the carbon anode) and molten aluminium which can be poured off
From:
See:

6. Exam Practice - 2008 Can’t see the exam paper below?
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Six
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7. Exam Practice - 2007 Can’t see the exam paper below?
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Seven
Eight
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8. Exam Practice - 2006 Can’t see the exam paper below?
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Four
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9. Exam Practice - 2005 Can’t see the exam paper below?
Have a go at Questions:
Three
Six
Can’t see the exam paper below?
Go to the NCEA website and search for 90311