....help!! (1 Viewer)

[saz]

I was doing one of thos online multiple choice tests on the BOS website and came across this q..... i dont know if im just stupid or we were never taught this but i have no idea how to do it!

Methanol (BP 64.7C) and propanoic acid (BP 140.8C) react under reflux to produce methyl propanoate (BP 79.9C) and water. Distillation of the reflux mixture produces four pure liquids and these are collected in separate beakers, labelled 1, 2, 3 and 4 in order of collection.
Which beaker will contain methyl propanoate?

A Beaker 1

B Beaker 2

C Beaker 3

D Beaker 4

The answer is b..... any explanations/ help would be appreciated! Thanks

 

[toknblackguy]

ok - one ican answer!
distillation works by boiling off liquids right?
now, when you're distillationing ( ) you're increasing temperature from like 25. therefore, first off, write down the temperatures in order of increasing boiling points.
1 - Methanol (BP 64.7C)
2 - methyl propanoate (BP 79.9C)
3 - water (100C)
4 - propanoic acid (BP 140.8C)

therefore, when you're boiling em off, the first one to reach boiling point is methanol, beaker 1, then metyl propoaate..

cheers

 

[Frigid]

Okay, realise that it will become four pure liquids, the liquids being the reagents, Methanol, Propanoic Acid and our products of esterification, Methyl Proponoate and Water. Assuming water boils at 100C, the stuff should be distillated by boiling point difference in the following order (from lowest to highest):

Methanol -> Methyl Propanoate -> Water -> Propanoic Acid.

Therefore, the ester, methyl propanoate, should be in Beaker 2 (Answer is B).

edit: dammit! pipped by tokenblack! why do i always offer these long long explanations...

 

[toknblackguy]

hey frigid...what's a reagent?

 

[Frigid]

"reagent n. - a substance which, on account of the reactions it causes, is used in chemical analysis."
- The Macquarie Dictionary

but basically to non-chemists, i often get reagents and reactants to mean the same thing.

 

[saz]

aha

Thanks guys! I knew i was missing something simple..... the complex ones i can deal with but its the ones that u need basic logic for i can never get!!!

 

[toknblackguy]

hahahaha
i'm sure that's not the case