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Oxidation of ethanol

Write a half-equation for the overall oxidation of ethanol into ethanoic acid.

This was the answer:
CH3CH2OH + H2O = CH3COOH + 4H+ + 4e–

But, i dont know how they got it. Can anyone explain?
Reply 1
Avatar for alow
alow
19
What's the product when you oxidise an alcohol?
Original post by 123chem
Write a half-equation for the overall oxidation of ethanol into ethanoic acid.

This was the answer:
CH3CH2OH + H2O = CH3COOH + 4H+ + 4e–

But, i dont know how they got it. Can anyone explain?


The oxygen of water (boldt print) reacts with ethanol.

CH3CH2OH + H2O = CH3COOH + 4H+ + 4e–

At the same time, the hydrogen atoms of water and the hydrogen atoms of the methylene group (CH2) in ethanol are ionized (in bold print above). That is why 4 H+ ions and 4e- come into being.

CH3CH2OH + H2O = CH3COOH + 4H+ + 4e–
Reply 3
Avatar for 123chem
123chem
OP
17
Original post by Kallisto
The oxygen of water (boldt print) reacts with ethanol.

CH3CH2OH + H2O = CH3COOH + 4H+ + 4e–

At the same time, the hydrogen atoms of water and the hydrogen atoms of the methylene group (CH2) in ethanol are ionized (in bold print above). That is why 4 H+ ions and 4e- come into being.

CH3CH2OH + H2O = CH3COOH + 4H+ + 4e–


That does help quite a lot! I've always thought of it in terms of oxidation number, and i couldnt work out these oxidation numbers for them!
Reply 4
Avatar for 123chem
123chem
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17
Original post by alow
What's the product when you oxidise an alcohol?


aldehyde or an acid?
Original post by 123chem
That does help quite a lot! I've always thought of it in terms of oxidation number, and i couldnt work out these oxidation numbers for them!


Sometimes it is better to have a closer look at the atoms and functional groups to understand it. :wink: to be honest, oxidation numbers are too complicated.

Original post by 123chem
aldehyde or an acid?


Aldehyde! whenever alcohol dehydrated, it leads to aldehyde. Here is a mnenomic for you: -dehyde in the name stands for dehydrated.
Reply 6
Avatar for 123chem
123chem
OP
17
Original post by Kallisto
Sometimes it is better to have a closer look at the atoms and functional groups to understand it. :wink: to be honest, oxidation numbers are too complicated.



Aldehyde! whenever alcohol dehydrated, it leads to aldehyde. Here is a mnenomic for you: -dehyde in the name stands for dehydrated.


But if its under reflux, its an acid, right?
Reply 7
Avatar for 123chem
123chem
OP
17
Original post by 123chem
But if its under reflux, its an acid, right?


And how did you know there was water molecule on left side?
Original post by 123chem
But if its under reflux, its an acid, right?


An acid comes into being when an aldehyde oxidises. Example:

CH3CHO (Ethanal) + O -> CH3COOH (ethanoic acid)

So, there are three steps of oxidation in total:

alcohol -> aldehyde -> acid
Original post by 123chem
And how did you know there was water molecule on left side?


So start off with

CH3CH2OH→CH3COOHCH_3CH_2OH \rightarrow CH_3COOH

This is not balanced, there are too many oxygens on the right hand side. So we add water to the left hand side to fix this

CH3CH2OH+H2O→CH3COOHCH_3CH_2OH+H_2O \rightarrow CH_3COOH

Now we need to balance the hydrogens on the right hand side so we add the 4 missing hydrogens in the form of H+

CH3CH2OH+H2O→CH3COOH+4H+CH_3CH_2OH+H_2O \rightarrow CH_3COOH+4H^+

The charge needs to be balanced too so add 4 electrons

CH3CH2OH+H2O→CH3COOH+4H++4e−CH_3CH_2OH+H_2O \rightarrow CH_3COOH+4H^+ + 4e^-

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