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Oxidation of methanol to methanoic acid

I've got a past paper question (WJEC CH2 Jan 2013) that asks the following:

Methanol can be converted to methanoic acid. Give the reagent(s) and condition(s) required for this reaction.


Would the reagent be dichromate ions (in sodium dichromate???)? What about the conditions? There's nothing in the WJEC revision booklet that even suggests we need to know them, so I'm totally stumped.
Reply 1
Avatar for Tappouni
Tappouni
8
Original post by O133
I've got a past paper question (WJEC CH2 Jan 2013) that asks the following:

Would the reagent be dichromate ions (in sodium dichromate???)? What about the conditions? There's nothing in the WJEC revision booklet that even suggests we need to know them, so I'm totally stumped.


For oxidising an alcohol to a carboxylic acid, you'd want acidified potassium dichromate, then for the conditions, heat under reflux.

I do OCR Salters Chemistry and you basically have to trawl through the book noting down reactants and conditions...no specific list as such :s-smilie:
Reply 2
Avatar for Pigster
Pigster
20
Wouldn't methanol oxidise to carbon dioxide? (if Cr2O72- is in XS)
Original post by Tappouni
For oxidising an alcohol to a carboxylic acid, you'd want acidified potassium dichromate, then for the conditions, heat under reflux.

I do OCR Salters Chemistry and you basically have to trawl through the book noting down reactants and conditions...no specific list as such :s-smilie:


Thanks! CH2 seems to be a lot of memorisation :frown: compared to CH1, which is a lot more mathsy.
Original post by Pigster
Wouldn't methanol oxidise to carbon dioxide? (if Cr2O72- is in XS)


Not according to the WJEC spec. Methanol -> Methanal -> Methanoic acid
Reply 5
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Tappouni
8
Original post by O133
Thanks! CH2 seems to be a lot of memorisation :frown: compared to CH1, which is a lot more mathsy.


Sounds like our Unit 2 (F332)...lengthy paper with plenty to remember. I'm actually retaking it - carries the most marks (UMS-wise) out of any of the AS or A2 units :s-smilie:
Original post by Tappouni
Sounds like our Unit 2 (F332)...lengthy paper with plenty to remember. I'm actually retaking it - carries the most marks (UMS-wise) out of any of the AS or A2 units :s-smilie:


I presume that's equivalent to our CH2 (which I guessis short for Chemistry Unit 2). Do your papers carry different weightings then? I think all of ours are the same.
Reply 7
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Tappouni
8
Original post by O133
I presume that's equivalent to our CH2 (which I guessis short for Chemistry Unit 2). Do your papers carry different weightings then? I think all of ours are the same.


Yeah it'll be the equivalent to your CH2. Yeah they carry different weights...F331 is 90 UMS, F332 is 150 UMS, F334 is 90 UMS and F335 is 120 UMS...so the shorter units are the same but the longer AS unit is worth more than the longer A2 unit, which isn't such a bad thing really, because A2 Chemistry isn't easy :frown: (not saying AS is necessarily easy...but comparatively it is)
Original post by Tappouni
Yeah it'll be the equivalent to your CH2. Yeah they carry different weights...F331 is 90 UMS, F332 is 150 UMS, F334 is 90 UMS and F335 is 120 UMS...so the shorter units are the same but the longer AS unit is worth more than the longer A2 unit, which isn't such a bad thing really, because A2 Chemistry isn't easy :frown: (not saying AS is necessarily easy...but comparatively it is)


WJEC AS ones are 120 and 120. I'm not sure about our A2 ones.

EDIT: The A2 ones (confusingly numbered CH4 and CH5 - 3 and 6 are practicals) are 120 each too.
(edited 9 years ago)
Original post by O133
I've got a past paper question (WJEC CH2 Jan 2013) that asks the following:



Would the reagent be dichromate ions (in sodium dichromate???)? What about the conditions? There's nothing in the WJEC revision booklet that even suggests we need to know them, so I'm totally stumped.


Crikey these new names are killing me... had to Google it to figure out that methanoic acid is FORMIC acid.

In any case... try an acidified dichromate of some sort (possibly kalium dichromate or natrium dichromate). This will turn methanol into formaldehyde. No idea how to change the aldehyde into an acid though.
Original post by honeywhite
Crikey these new names are killing me... had to Google it to figure out that methanoic acid is FORMIC acid.

In any case... try an acidified dichromate of some sort (possibly kalium dichromate or natrium dichromate). This will turn methanol into formaldehyde. No idea how to change the aldehyde into an acid though.


I don't think you'll need to know other names for the compounds - knowing methanoic acid is sufficient, they wouldn't expect you to know it's also called formic acid.

For going from an aldehyde to a carboxylic acid, it'd be the same again - use acidified potassium (or sodium) dichromate, and heat under reflux :smile: You can still oxidise the aldehyde in this way, as it has a hydrogen attached to the carbon.
Original post by Tappouni
I don't think you'll need to know other names for the compounds - knowing methanoic acid is sufficient, they wouldn't expect you to know it's also called formic acid.

For going from an aldehyde to a carboxylic acid, it'd be the same again - use acidified potassium (or sodium) dichromate, and heat under reflux :smile: You can still oxidise the aldehyde in this way, as it has a hydrogen attached to the carbon.


You didn't understand me---I didn't know what methanoic acid was... I knew it only and solely as formic acid. Same as I never really call hydrochloric acid by that name---it's either muriatic acid or spirits of salt.
Original post by honeywhite
You didn't understand me---I didn't know what methanoic acid was... I knew it only and solely as formic acid. Same as I never really call hydrochloric acid by that name---it's either muriatic acid or spirits of salt.


Oh sorry - I never really hear them called by their other names...I've always know them as e.g. methanoic acid or hydrochloric acid. Bit annoying having to basically relearn names of compounds I suppose :s-smilie:
Original post by Tappouni
Oh sorry - I never really hear them called by their other names...I've always know them as e.g. methanoic acid or hydrochloric acid. Bit annoying having to basically relearn names of compounds I suppose :s-smilie:


Trust me, you have no idea. I learned medicine with English weights... even now, a prescription for "200 mg of sulphate of morphia" throws me off, because I'm used to grains and ounces.

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