Topics 9 & 19 : Redox process

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.

The importance of redox processes

Both the person that holds it and the smart phone itself are powered by redox reactions.

Much of the energy involved in life on Earth from photosynthesis, respiration, the burning of fossil fuels and even the energy to power students’ smart phones is all the result of redox reactions. Clearly this is an important topic  on its own for you to understand but it is also a topic which relates intimately to the whole of the rest of the core/AHL part of the chemistry programme.

Some examples of how it relates to the other ten topics are:

Topic 1 The use of half-equations and quantitative calculations from redox equations.

Topic 2

Electron arrangement to show oxidation is loss of electrons and reduction is gain of electrons.
Topic 3The trend from reducing agents to oxidizing agents across the elements of Period 3 and the variable oxidation states of transition metals.
Topic 4The redox reaction between sodium and chlorine to exemplify ionic bonding.
Topic 5Enthalpies of combustion as fossils fuels are oxidized by oxygen.
Topic 6The use of catalysts in redox reactions such as the decomposition of hydrogen peroxide or the formation of ammonia in the Haber process.
Topic 7The voltaic cell formed from two half-cells will have zero voltage once the redox reaction between the two half-cells has reached equilibrium.
Topic 8One of the characteristic reactions of an acid is the redox reaction between the acid and a reactive metal to produce hydrogen.
Topic 10     The products of the oxidation reactions of alcohols depend upon whether they are primary or secondary alcohols with tertiary alcohols resisting oxidation.
Topic 11Uncertainties when calculating results from redox titrations and when using apparatus such as a voltmeter.

Associated pages

9.1 Oxidation & reduction

After studying this topic you should be able to deduce the oxidation states of atoms in an ion or a compound and identify the oxidizing and reducing agents and the species that are oxidized and reduced in redox reactions...

9.2 Electrochemical cells

After studying this topic you should be able to construct and annotate both voltaic and electrolytic cells and distinguish between the flow of electrons and the flow of ions in both types of cells...

19.1 Electrochemical cells (AHL)

After studying this topic you should be able to calculate cell potentials using standard electrode potentials for half-cells and use E values to predict whether a reaction is spontaneous or non-spontaneous...

The Nature of Science

I received an e-mail from a student (not someone I teach) who asked me, "What is this nature of science business?” So what exactly does the IB mean by the Nature of Science? Essentially it covers five key points…

Topics 9 & 19

1. Aluminium production. The Hall-Hérault process for the production of aluminium by the electrolysis of alumina dissolved in molten cryolite was discovered independently in the 1880s by the American Charles...

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