Introduction to Topic 9 and Topic 19

The core part of this topic involves the definitions of oxidation and reduction and introduces you to the concept of oxidation states and oxidation numbers. It includes simple half-equations and oxidizing and reducing agents together with some idea about an activity series. Simple examples are given of spontaneous reactions to produce electricity (voltaic cells) and non-spontaneous reactions where electricity is used to bring about reactions (electrolysis involving molten electrolytes). Coverage of the Winkler method to determine the amount of dissolved oxygen in water adds an environmental aspect to the topic. A more quantitative approach is included in the Additional Higher Level material where prominence is given to the electrochemical series, more complex redox reactions and the electrolysis of aqueous solutions (including the factors affecting the discharge of products). The importance of spontaneous and non-spontaneous as applied to redox reactions is stressed and the relationship between the Gibbs free energy and the electromotive force of the cell, ΔG^⦵ = − nFE^⦵ is covered.

This topic also provides many excellent links to the Nature of Science and Theory of Knowledge.  These include the ‘phlogiston theory’, the use of language when naming compounds, the validity of assumptions when devising the rules of oxidation states and the questioning of definitions of redox in terms of electron transfer.