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Recrystallisation and then measuring their melting points and comparing to a table of known melting points
Melting/Boiling points.
Reply 3
Is there no chemical test?
Reply 4
Doubt it, the only difference would be the aforementioned melting and boiling pts etc. They're a homologous series.
Nope. There's not enough difference between the two, and any composite of a "test" would react with both, as they have the same functional group, and the hydrocarbon part is fairly unreactive.
Reply 6
We had a question on this, methanoic acid if you draw it out has an aldehyde group as well as a carboxylic acid group so can be further oxidised

If you react it with KMnO4 (potassium permanganate) it will be oxidised and form a brown precipitate whereas ethanoic won't change and the solution will stay purple
Reply 7
Cassie218
We had a question on this, methanoic acid if you draw it out has an aldehyde group as well as a carboxylic acid group so can be further oxidised

If you react it with KMnO4 (potassium permanganate) it will be oxidised and form a brown precipitate whereas ethanoic won't change and the solution will stay purple


Thats superb thanks!
Reply 8
yh It does, my chem A-level coursework was on this

methanoic acid only has one central carbon which has a double bonded Oxygen, and an OH attached which makes up the COOH carboxylic acid group

but if you consider the second hydrogen attached and the double bonded Oxygen that's considered an aldehyde group and can be further oxidised
which means you can distinguish between it and ethanoic

EDIT: That was a reply to a post that someone has just deleted
Cassie218
yh It does, my chem A-level coursework was on this

methanoic acid only has one central carbon which has a double bonded Oxygen, and an OH attached which makes up the COOH carboxylic acid group

but if you consider the second hydrogen attached and the double bonded Oxygen that's considered an aldehyde group and can be further oxidised
which means you can distinguish between it and ethanoic

EDIT: That was a reply to a post that someone has just deleted

so would methanoic acid react with fehlings to give a red precipitate but if ethanoic acid is reacted with fehlings it will stay blue? is that one way one can distinguish between them?
Reply 10
I want to suggest putting it on your chips...but that would be a really bad plan.
Reply 11
Aeon Prince
so would methanoic acid react with fehlings to give a red precipitate but if ethanoic acid is reacted with fehlings it will stay blue? is that one way one can distinguish between them?


I'm not sure about that one, I know it reacts with potassium dichromate though as well so goes from orange - green whereas ethanoic won't
EasyTiger
How would you distinguish between methanoic acid and ethanoic acid?


If they are pure (rather than solutions) a few drops of conc sulphuric acid will produce bubbles of CO with methanoic acid and nothing with ethanoic acid.
charco
If they are pure (rather than solutions) a few drops of conc sulphuric acid will produce bubbles of CO with methanoic acid and nothing with ethanoic acid.

cant you just compare their finger print regions in a infared spectrometer?
Aeon Prince
cant you just compare their finger print regions in a infared spectrometer?


Or the molecular ion peak in a mass spectrometer?
vertigo.0012
Or the molecular ion peak in a mass spectrometer?



If you want instrumentation, 1H nmr will clearly show the difference...
charco
If you want instrumentation, 1H nmr will clearly show the difference...


So would 13C :eek: look at all these methods OP!
vertigo.0012
So would 13C :eek: look at all these methods OP!


For dilute acids titrate with NaOH and measure the pH at the half equivalence point...

methanoic acid = 3.75
ethanoic acid = 4.75
Also, if you use them regularly enough you can readily identify them by smell :wink:
Reply 19
Could you use methyl orange, as in it would go red with methanoic acid, and orange with ethanoic acid?