reflux is not cool (1 Viewer)

[bellamy]

heya der... im doiing this work sheet and it asks the question..

why (in the process of reflux or esterification or whateva) is the purpose of adding one reagent in excess if they react in equimolar quantities...and why is it that you add the alkanol in excess?


ive looked in text books but the answers are all really vague and stuff....and i was sad... any help will help.

 

[Jumbo Cactuar]

I'll take a punt:

R-OH + R'-OOH <--H2SO4--> R-O-OR' + H2O

Excess R-OH drives reaction to the right.
Excess R-OH will (usually) lower the boiling point of the solution.
R-OH will solvate R'-OOH (usually).
R-OH is less dangerous (usually).
R-OH is cheaper or easier to produce (usually).
R-OH is less reactive and so more easily recoverable (usually).

It's not essential since most labs that are online don't bother. Likewise I can't find any info, but this is what I assume are the reasons.

 

[bellamy]

ok so yea thats what i thought as well... that you would add xtra alkanol to increase the yield cause the alkanoic acids would be more dangerous to ppl... that seems fully logical... and thats what my txt suggests

but...

i jst re read my prac sheet and it says to add extra acid?! so the two contradict one another...

then it mentions stuff about there densities as a clue to why to add extra acid (the acid is more dense)... man this is trippin me out...

 

[bellamy]

os so all those ppl out there that were worried...
It's okay....
i figured out the answer...ok so the two reactatnts react in equimolar quantities but the acid is of higher density and thus to get the same number of moles you have to add a greater quantity of the acetic acid...
txt bk was wrong... problem solved

 

[Jumbo Cactuar]

Well really it is because they have a different molar density (I don't know if this exists but you know what I mean). How silly of me.