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Oxidation of ethanol
At college in chemistry we carried out an experiment of the oxidation of ethanol. In apiece of homework relating to it, a question ask how might the outcome of your experiement have been different if you missed out the reflux step? (we refluxed it then distilled it to get ethanoic acid - a carboxyllic acid).
Is it that it would have produced an aldehyde - ethanal? Or am I wrong?
Thanks
Dan
Is it that it would have produced an aldehyde - ethanal? Or am I wrong?
Thanks
Dan
Yeah you're right, you would get ethanal
You're right, if you didn't use reflux conditions you could distil and collect ethanal as its boiling point is below that of ethanol.
Thank you! Another question is:
Why did the reaction mixture change colour when you refluxed it?
Am I right in thinking this is because a redox reaction is going on and so the reaction mixture is being reduced? I think this is sort of right and if it is could you elaborate a bit more on why it changes colour as I'm not 100% sure why it being reduced makes it change colour.
Thanks
Dan
Why did the reaction mixture change colour when you refluxed it?
Am I right in thinking this is because a redox reaction is going on and so the reaction mixture is being reduced? I think this is sort of right and if it is could you elaborate a bit more on why it changes colour as I'm not 100% sure why it being reduced makes it change colour.
Thanks
Dan
what were you using as the oxidising agent?
danhirons
acidified sodium dichromate
eek. Then it went from orange to green? It's because the chromate ion Cr2O72- was being reduced to Cr3+ as the alcohol became oxidised.
Yes it went from orange to green! Thank you very much for your help. Can I just ask - it's not for my homework, I'm just curious: why in the experiment I did, did we add sulphuric acid to the sodium dichromate to begin with?
And why do you need to sodium dichromate in order for the ethanol to be oxidised?
And finally (definitely is the final question) what is the mixture created from the reflux part of the experiment - Is that just the ethanoic acid along with the reduced chromate ions that just needs to be separated by distillation?
And why do you need to sodium dichromate in order for the ethanol to be oxidised?
And finally (definitely is the final question) what is the mixture created from the reflux part of the experiment - Is that just the ethanoic acid along with the reduced chromate ions that just needs to be separated by distillation?
danhirons
Yes it went from orange to green! Thank you very much for your help. Can I just ask - it's not for my homework, I'm just curious: why in the experiment I did, did we add sulphuric acid to the sodium dichromate to begin with?
You need acid to form the active species for the oxidation: H2SO4 + Na2Cr2O7 ---> Na2SO4 + H2O + 2H2CrO4 (this bit)
And why do you need to sodium dichromate in order for the ethanol to be oxidised?
You can use other oxidising agents.
And finally (definitely is the final question) what is the mixture created from the reflux part of the experiment - Is that just the ethanoic acid along with the reduced chromate ions that just needs to be separated by distillation?
Yeah, it's called the crude mixture, it'll be a mixture of inorganics for the oxidising agent, solvent, side products, and what you want. Distillation is used to purify your product.
Sorry I just realised one other thing I am unsure of if you are willing to help - why if the chromate ion is being reduced does it form Cr3+ - don't things being reduced gains electrons?
It is gaining electrons it goes from +6 to +3 (i.e. more negative)
danhirons
Ah ok thanks again - you are so useful! Rep is on your way!
Can I just ask what the oxidising agent actually does? Is it involved with the redox reaction?
Can I just ask what the oxidising agent actually does? Is it involved with the redox reaction?
The oxidisng agent increases the oxidation level of the carbon connected to the OH group in ethanol. You are literally putting on more oxygen molecules going from an alcohol to a carboxylic acid.
In all redox reactions is something gets oxidised then something else must be reduced - alcohol is oxidised, oxidising agent is reduced.
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