Sciencemadness Discussion Board

Crystallizing out 2 Compounds from Each other - How much Solvent to use?

LuckyWinner - 21-11-2020 at 07:40

The question, I want to separate these 2 compounds from each other
by using their high difference in water solubility.


You have :
------------------
Compound A : 10grams
Compound B : 70 grams


Solubility:
----------------
Compound A
Solubility in water:
10 g/100 cc @ 20 °C;
30 g/100 cc @ 100 °C;

Compound B
Solubility in water:
200 g/100 cc @ 20 °C;
300 g/100 cc @ 100 °C;

the calculation
-------------------
is 'solubility in water grams' is divided by compound grams you have ,
100cc of water is then divided by this number to get the min amount of water needed to dissolve your compound.


@ 100C water,
----------------------
when these 2 compounds are dissolved in 100ml of water at 100C.

Compound A : 10grams can be dissolved in 33ml of water.
Compound B : 70 grams can be dissolved in 23ml of water.

I need a min of 33+23ml of water = 56ml of water to dissolve both of these compounds in 100C water.


@ 25C water
-------------------
Compound A : 10grams can be dissolved in 100ml of water.
Compound B : 70 grams can be dissolved in 35ml of water.

I need a min of 100+35ml of water = 135ml of water to dissolve both of these compounds in 25C water.


Question:
-----------------
Now the question is, the correct amount of water to use to separate compund A from B.
Both can be dissolved in 56ml of 100C water.
if these 56ml of water are cooled down to 25C from 100C.
there are 135ml- 56ml = 79ml of water missing to dissolve both compounds.

how does compound B and A use this 56ml, what is the % of each compound
in these 56ml?

56ml of water could dissolve at 25C
Compound A =5.6 grams (4.6g will already be crashed out)
Compound B= 112 grams (70g fully dissolved)

but when I have
Compound A : 10grams
Compound B : 70 grams

how do these 2 share this amount of water?


Goal is the highest yield/purity of Compound B 70 grams.



[Edited on 21-11-2020 by LuckyWinner]

Maurice VD 37 - 21-11-2020 at 09:59

What would be known is how much A is soluble in a saturated solution of B, and how much B is soluble in saturated solution of A. And this is unknown. Or you have admitted that these two unknown but required values are equal to zero.

yobbo II - 22-11-2020 at 11:52


Look up a graph of mutual solubility of the two compounds and if you obtain one you can study the attached. It's quite a pain. You cannot simply seperate them unless one is very soluble and the other is insoluble.

Yob

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