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Topic: Separation  (Read 7937 times)

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Offline technologist

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Separation
« on: June 30, 2006, 12:18:50 AM »
A & B are two completely Miscible Liquids where A is solute & B is solvent.
A has 10% solubility in another solvent C. B & C r completely Immiscible.

Now if I start on 100 Kg solution basis of A & B with 20% concentration of A in B.
100 Kg of solution will have 20 Kg A & 80 Kg B.
Now I add 200 Kg of C in the Solution & mix it thoroughly and then allow to separate out 2 phases.

Question is

What will be the amount of A in B & in C?

I know it depends on Partition Coeff. of A in B & C but that is unknown at this stage.

Next Question.

Suppose whole A i.e. 20 Kg comes in C & I separate B & C (They r Immiscible). Now if I add 20 Kg of B again in 220 Kg of C+A & mix it & separate it again.

Will whole of 20 Kg of A go to B? Bcoz A have very good solubility in B?

Any help & discussion...



Offline lemonoman

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Re: Separation
« Reply #1 on: June 30, 2006, 12:57:20 AM »
A & B are two completely Miscible Liquids where A is solute & B is solvent.
A has 10% solubility in another solvent C. B & C r completely Immiscible.

So what you're saying is...that A will dissolve 1/10 as much in C as in B. (Assuming A is 100% soluble in B - because otherwise, it wouldn't be the solute any more, would it?)

Now if I start on 100 Kg solution basis of A & B with 20% concentration of A in B.
100 Kg of solution will have 20 Kg A & 80 Kg B.

Agreed.

Now I add 200 Kg of C in the Solution & mix it thoroughly and then allow to separate out 2 phases.

So now you have 20 kg of A dissolve among 80 kg of B and 200 kg of C.

Question is

What will be the amount of A in B & in C?

C dissolves A one tenth as much as B does.  So you need 10 kg of C to dissolve as much A as 1 kg of B.  In effect, the 200 kg of C is going to act just like 20 kg of B (20 is one tenth of 200).

Now it's like you have 20 kg of A dissolved among two systems: one with 80 kg of B, one with 20 kg of B.  And the concentration of A is going to be the same in each of them...since they're both B (or at least, effectively).  So, 80/(80+20) of the A will be dissolved in the REAL B, and 20/(80+20) will be dissolved in the pseudo-B (which is really C).

Hope that helps...maybe it was too confusing...I think it's alright.

I know it depends on Partition Coeff. of A in B & C but that is unknown at this stage.

I think I used partition coefficients without knowing it :P

And the whole second question can be solved similarly to the first one....and sometimes using a variable like x really really helps I find.

Man I hope I'm right on this...
« Last Edit: June 30, 2006, 01:03:09 AM by lemonoman »

Offline technologist

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Re: Separation
« Reply #2 on: June 30, 2006, 01:50:03 AM »
Its logical.

But Assumption of 100% Solubiility of A in B is something I am not sure about. Bcoz 80% A + 20% B solution also exist. I mean any no beyond 50% A gives more than 100% Solubiility for A&B solution.

However, I am not clear if C is also there.

Offline Donaldson Tan

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Re: Separation
« Reply #3 on: July 20, 2006, 08:24:47 PM »
Is solvent C much more volatile than solvent B?
"Say you're in a [chemical] plant and there's a snake on the floor. What are you going to do? Call a consultant? Get a meeting together to talk about which color is the snake? Employees should do one thing: walk over there and you step on the friggin� snake." - Jean-Pierre Garnier, CEO of Glaxosmithkline, June 2006

Offline technologist

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Re: Separation
« Reply #4 on: July 20, 2006, 11:50:39 PM »
Solvent B is more volatile.

Offline Donaldson Tan

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Re: Separation
« Reply #5 on: July 21, 2006, 12:01:56 AM »
If solvent B is more volatile than solvent C, wouldn't it be less energy intensive to distill A from A & B compare to distill A from A & C
"Say you're in a [chemical] plant and there's a snake on the floor. What are you going to do? Call a consultant? Get a meeting together to talk about which color is the snake? Employees should do one thing: walk over there and you step on the friggin� snake." - Jean-Pierre Garnier, CEO of Glaxosmithkline, June 2006

Offline technologist

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Re: Separation
« Reply #6 on: July 22, 2006, 03:44:29 AM »
U r right. But my planning is different to recover it.
Anyway it seems that now I need hands on lab experience to establish the things.

Thanks to all.

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