Oxidation and Reduction
Oxidation
- gain of oxygen
- loss of hydrogen
- loss of electron
- increase in oxidation number
Reduction
- loss of oxygen
- gain of hydrogen
- gain of electron
- decrease in oxidation number
Gain / loss of oxygen
In the example on the left, magnesium gains oxygen to become magnesium oxide. Since magnesium has gained oxygen, magnesium is oxidised to become magnesium oxide. In doing this, magnesium has caused copper(II) oxide to lose oxygen. Therefore, magnesium acts like a reducing agent.
Copper(II) oxide loses oxygen and is reduced to become copper. Since it causes magnesium to gain oxygen, it acts as an oxidising agent.
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Gain / loss of hydrogen
Ammonia loses hydrogen to become nitrogen. Since ammonia has lost hydrogen, ammonia is oxidised to become nitrogen gas. By losing hydrogen, ammonia has caused bromine to gain hydrogen. Therefore, ammonia acts as a reducing agent.
Bromine gains hydrogen and is reduced to hydrogen bromide. Since it causes ammonia to lose hydrogen, it acts as an oxidising agent.
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Gain / loss of electron
In the example, sodium loses an electron and each chlorine atome gains an electron. Sodium is oxidised while chlorine is reduced.
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Oxidation number
The method to determine the oxidation number of an element is different depending on whether its an element or a compound. Even then, there are some exceptions!
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Try the questions below to test your knowledge.
IUPAC nomenclature
The International Union of Pure and Applied Chemistry (IUPAC) introduced a uniform naming system for metals and oxoanions that have elements with multiple oxidation states. There are some rules in place to determine the IUPAC name of the compounds containing these elements.
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Iron(II) to iron(III)
Iron(II) can be oxidised to iron(III) by using the following oxidising agents:
- potassium manganate(VII)
- potassium dichromate(VI)
- bromine water
- concentrated nitric acid
- acidified hydrogen peroxide
Watch the video for the half equations and ionic equations for oxidation of iron(II) to iron(III).
Iron(III) to iron(II)
Iron(III) can be reduced to iron(II) by using the following reducing agents:
- potassium iodide
- sulphur dioxide
- hydrogen sulphide
- tin(II) chloride
- sodium sulphite
- magnesium
Watch the video for the half equations and ionic equations for reduction of iron(III) to iron(II).
Displacement of metal from its salt solution
The displacement of a metal from its compound (salt solution) depends on the position of the two metals in the reaction.
X + YCl → Y + XCl
If a metal (X) is more reactive than the metal (Y) in the salt solution (YCl), then it will be able to displace the metal.
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Displacement of halogen from its halide solution
Similar to displacement of metals, the displacement of a halogen from its compound (halide solution) depends on the position of the two halogens in Group 17 (Group VII).
X + YCl → Y + XCl
If a halogen (X) is more reactive than the halogen (Y) in the halide solution (YCl), then it will be able to displace the halogen.
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