Urgent: Couple of questions (1 Viewer)

[Aerlinn]

Some quick urgent questions:
Oxidising CH3CH2OH to CH3COOH...
Cr2O7(2-)/MnO4- (these are meant to be above the arrow)
CH3CH2OH(aq) ----> CH3COOH(aq)
H+(aq)
Why does the oxidant, eg. acidified potassium dichromate, have to be acidified? , ie. the H+ ions?

Why do these reactions also all have to have H+ ions present?

H20(g?) (this is meant to be above the arrow)
1. CH2CH2(g) ----> CH3CH2OH(aq)
H+(aq) (this is meant to be below the arrow)

H+(aq) (this is meant to be above the arrow)
2. CH3COOH + CH3CH2OH <----> CH3COOCH2CH3 + H2O

With a reaction like... CH3COOH + CH3CH2OH ----> CH3COOCH2CH3 + H2O
to form an ester, are the states of CH3COOH, CH3CH2OH and CH3COOCH2CH3 liquid or aqueous? (and maybe, if you know, why that is? -- So i don't get mixed up again in future...)
Since this is a condensation reaction, what, exactly, is lost from the CH3COOH and CH3CH2OH? Is the OH given up the the CH3COOH or CH3CH2OH? 'Cause my sheet says one thing, and my teacher says another...

Some help before Monday would be great! :wave:

 

[victorheaven]

for the first question i think the answer is because H+ is a good oxidant
for the formation of ester. they are liquids
the OH is given up from the alconoic acid because the double bond C=0 is more reactive
hope this helps

 

[Aerlinn]

Okay, thanks

 

[xiao1985]

hmmm maybe abit late, but:

1) chromate and dichromate exist in an equilibrium:

2 CrO42− + 2 H3O+ <----> Cr2O72− + 3 H2O
http://en.wikipedia.org/wiki/Dichromate

i am suspecting Cr2O7 2- is the oxidizing agent, therefore, by adding H+, you effectively produce more oxidising species ...

2) most likely, they are all aqueous (meaning dissolved in water), not liquid (pure and molten)...
for them to be liquid:
CH3COOH: need to be above 16.5 C (MP of acetic acid, http://en.wikipedia.org/wiki/Acetic_acid)
CH3CH2OH: need to be above -114.3C (which is not all that hard to achieve, http://en.wikipedia.org/wiki/Ethanol)

however, their liquid form are quite a hazard to use and usually, you won't use them unless it is absolutely necessary...

in this case, i would say they are all aqueous...

3) victor heaven is correct, OH is given up from alconoic acid, reasons are more complicated however... an intermediate is formed, and finally kicks out the OH on alkanoic acid...

 

[Aerlinn]

1)

i am suspecting Cr2O7 2- is the oxidizing agent, therefore, by adding H+, you effectively produce more oxidising species ...

Hmm, for some reason, that doesn't strike me as logical, 'cause... I don't understand :'( *sniffs*
2) In some places they have states as liquid, in others, aqueous. I guess it probably varies with what you've got?
3) Interesting... what are these 'complicated reasons'? ^_^

 

[xiao1985]

1) look at it this way, eqlm:

CrO42− + 2 H3O+ <----> Cr2O72− + 3 H2O

Cr2O72− is the reactive species... therefore addition of H+ (or H3O+) give you more reactive species in the reaction, hence more reaction/faster reaction...

2) aq if the substance is dissolved in water, l if there's no water

3) lots of arrow drawing... will post some arrows when i get the chance....