IGCSE Double Award Extended Coordinated Science
Chemistry 7.2 - Redox Reactions
Redox Reactions
You need to know what redox reactions are - in terms of electron exchange.
Redox stands for reduction and oxidation - which we saw already in Unit C5 - with electrolysis. Electrolysis.
If an atom is reduced, the atom gains electron. Conversely, if an atom is oxidised, the atom loses electrons.
- Remember it with the acronym OILRIG - Oxidation Is Loss, Reduction Is Gain
Redox reactions are reactions where both reduction and oxidation occurs.
iron oxide + carbon monoxide -> iron + carbon dioxide
In this reaction, we analyse the charges on each element or ion, (not full compounds - they are always 0).
- The respective charges can also be thought in terms of oxidation number
If we ignored the stoichiometric ratios and focused on the oxidation numbers, we can see that:
Fe(+3)2O(-2)3 + C(+2)O(-2) --> Fe(0) + C( +4)O(-2)2
If we now see the changes in oxidation numbers we can see which chemicals were reduced and oxidised.
Carbon (C) goes from oxidation number of +2 to +4. The number increased.
- Increase in the charge (more positive), meaning there was a loss of electrons.
- Loss of electrons means oxidation (OIL)
- You can also see that the molecule gained oxygen atoms - this is also how oxidation is defined.
- Oxidation is also the gain of oxygen atoms.
Iron (Fe) goes from oxidation number of +3 to 0. The number decreased.
- Decrease in the charge (more negative), meaning there was a gain of electrons.
- Gain of electrons means reduction (RIG)
- Or simply, if the oxidation number is reduced (decreased), the chemical is reduced.
- You can also see that the molecule lost o
xygen atoms - this is also how reduction is defined.
- Reduction is also the loss of oxygen atoms.
The syllabus says you should be able to, (SO check if you can):
- Define oxidation and reduction in terms of oxygen loss /gain, and identify such reactions from given information.
- Define redox in terms of electron transfer, and identify such reactions from given information.
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