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× Oxidation is loss of electrons, or an increase in oxidation number.
× Redox is gain of electrons or a decrease in oxidation number.
× In a redox reaction, bot reduction and oxidation takes place.
× The substance that is reduced is an oxidising agent ­ it takes electrons from the substance that is
× The substance that is oxidised ­ it gives electrons to the substance that is oxidised.
× Reduction must always be accompanied by oxidation.
Constructing redox equations using relevant halfequations
× Redox reactions take place when electrons are transferred. We can construct an overall equation for
a redox reaction if we know the oxidation and reduction half equations.
× In the oxidation halfreaction, electrons are lost.
× In the reduction halfequation, electrons are gained.
Constructing redox equations using oxidation numbers
× Oxidation and reduction can be described in terms of oxidation numbers.
× You can easily identify the oxidation and reduction processes using oxidation numbers. An oxidation
number is assigned to each atom in the redox reaction. You can then easily see any changes in
oxidation number. Oxidation numbers make it easy to account for electrons and are a great way of
balancing off complex redox equations.
Hints for completing the redox equations
× Sometimes you will find that you are short of `H' on one side. In general, you may have to add H , OH
, or H O.
× If the reaction gas been carried out in acid conditions, then simply add the number of H ions that you
× For alkaline conditions, you can add OH .
× If `H' and `O' need to be added think `H 0'.


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