Fractional Distillation : separation of mixtures

[jmarjorie]

Dear All,

 

This goes out to those expert in fractional distillation : A mixture contains 2 organic liquids (completely miscible with each other), one with a boiling point of 80 deg C and the other with a boiling point of 35 deg C.

 

Can the two liquids be completely seperated by fractional distillation using a very long column or will they behave as a binary azeotropic mixture at constant pressure (constant boiling point mixture) and the distillate still contain proportions of both mixtures ?

 

I'am asking as I have not fully understood the concept; some say the mixtures are not seperable while others say the mixtures are completely seperable; am confused.

[Forensicmad]

From what my GCSE chemistry course has taught me, they will seperate. They use the Fractional distillation method for crude oil, so they can seperate out the petrol from diesel and other hydrocarbons. This is only done by the different boiling points.

As it gets cooler towards the top of the column, the vapours (compounds) with the lowest boiling boint will eventually run off. Whereas at the bottom where it is extremely hot, those compounds with the highest boiling points will condense and run off. This essentially seperates them all out and runs them off into different containers; just because of their differing boiling points.

So in reply to your question, I believe the answer is yes. The 2 organic liquids would seperate out in a fractioning column. The 80 deg C liquid would condense lower down the column than the 35 deg C.

 

However, this is just from my GCSE course. I will need somebody to back me up or contradict me on this. I suppose this helps me revise for my exams.

[chuinhen]

1st , u need to know the mixture produced is deviate positively or negatively from Raoult;s Law !!!

 

A positive deviate mixture

 

forms when 2 mixture yields a product which has lower intramollecular bond

 

in distillation

Distiilate : azeotropic mixture residue : Pure liquid (higher boiling pt)

 

 

 

A negatively deviate mixture

forms when 2 mixture yields a product which has stronger intramollecular bonds !!!

 

 

in distillation

 

Distillate: Pure liquid ( lower boiling pt) Residue : azeotrpic mixture

[Forensicmad]

Okay.....

I would go with #2

 

It appears my knowledge on the subject is well, very inferior. Oh well. Thats what you get at GCSE higher. Or maybe its just my terrible school.

[chuinhen]

Im not in GCSE !!

but in STPM (K-12 education in Malaysia )

Heard of it ???

[RyanJ]

Im not in GCSE !!

but in STPM (K-12 education in Malaysia )

Heard of it ???

 

Thats what you get at GCSE higher[/b']. Or maybe its just my terrible school.

 

I believe Forensicmad was trying to say knowledge above the GCSE level

 

Cheers,

 

Ryan Jones

[KFC]

If you fractional distill a 3% solution of hydrogen peroxide or will the hydrogen peroxide decompose?

[RyanJ]

If you fractional distill a 3% solution of hydrogen peroxide or will the hydrogen peroxide decompose?

 

Hydrogen peroxide decomposes easily, just about anything can make it decompose... heating it will make this go faster so I'd say it probably would, yes.

 

Cheers,

 

Ryan Jones

[woelen]

KFC, with careful heating, you can concentrate a solution of H2O2 to a higher concentration. The loss, however, will be considerable.

 

If you want to make higher concentration H2O2, then use a freezer. Freeze some of the 3% solution and let appr. 50% of the liquid freeze. The ice can be thrown away, it is mainly water. The remaining liquid contains almost 6% of H2O2. Repeating this procedure with that 6% liquid will bring you to over 10% of H2O2.

 

In this way, it is said that you could even reach 30%, but I've never tried that. Reaching 10%, however, can be done quite well, with acceptable losses (due to presence of some H2O2 in the ice).

[KFC]

Thanks,

Woelen and RyanJ