anactualmess
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How is combustion oxidation? Why is being oxidised? Also same question for oxidation of alcohols to aldehydes or ketones, what is being oxidised and how exactly is it an oxidation reaction? And why can’t tertiary alcohols be oxidised? Please help thank you
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charco
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Oxidation number is an artificial construct designed to help us understand and keep track of electrons in redox equations. The oxidation number, or state, for each element follows simple rules.

The sum of the oxidation numbers of the elements in a species equals the charge on that species.
The most electronegative element takes a negative oxidation state.
Oxygen in compounds is -2 unless the compound is a peroxide (contains an O-O bond) in which case it's -1.
etc.

In hydrocarbons, such as methane the carbon atom takes a negative oxidation state of -4, as each H atom is +1

After combustion the carbon is in carbon dioxide and now has an oxidation state of +4

Hence its oxidation number has increased, it has been oxidised.
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anactualmess
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(Original post by charco)
Oxidation number is an artificial construct designed to help us understand and keep track of electrons in redox equations. The oxidation number, or state, for each element follows simple rules.

The sum of the oxidation numbers of the elements in a species equals the charge on that species.
The most electronegative element takes a negative oxidation state.
Oxygen in compounds is -2 unless the compound is a peroxide (contains an O-O bond) in which case it's -1.
etc.

In hydrocarbons, such as methane the carbon atom takes a negative oxidation state of -4, as each H atom is +1

After combustion the carbon is in carbon dioxide and now has an oxidation state of +4

Hence its oxidation number has increased, it has been oxidised.
Thank you so much. Could you also explain the reduction of nitriles to form amines and where the reduction is occurring?
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charco
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(Original post by anactualmess)
Thank you so much. Could you also explain the reduction of nitriles to form amines and where the reduction is occurring?
It's the same idea.

CH3CN
Nitrogen is the most electronegative and so takes a negative oxidation state = -3
Each hydrogen is +1, making the (average) of the two carbon atoms = 0

After reduction

CH3CH2NH2

Nitrogen remains -3
however, 2 x carbon now must balance out +7 from the hydrogen atoms, hence the (average) carbon = -3.5

So carbon has been reduced from (average) 0 to -3.5

The reason I write (average) is that some texts like to deal with the carbon atoms in different environments having different oxidation numbers. I find this both confusing and misleading.
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anactualmess
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Thank u
(Original post by charco)
It's the same idea.

CH3CN
Nitrogen is the most electronegative and so takes a negative oxidation state = -3
Each hydrogen is +1, making the (average) of the two carbon atoms = 0

After reduction

CH3CH2NH2

Nitrogen remains -3
however, 2 x carbon now must balance out +7 from the hydrogen atoms, hence the (average) carbon = -3.5

So carbon has been reduced from (average) 0 to -3.5

The reason I write (average) is that some texts like to deal with the carbon atoms in different environments having different oxidation numbers. I find this both confusing and misleading.
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