SCHA 312
1
Problem Set #1
A solute, S, has a partition coefficient between water and ether of 1.5. Calculate
the following if you start with the solute concentration of 50 mM of S in the
aqueous phase. (12)
a)
What is the fraction extracted into the organic phase by one 100.0 mL
portion of ether. 50.0 mL of the aqueous solution is extracted?
b)
The concentration (in M) of the solute in the organic phase for (a)?
c)
In a second experiment, what is the faction extracted into the organic
phase if one takes 50.0 mL of the aqueous solution and extracts it with one
500.0 mL portion of ether?
d)
What is the concentration of the solute in the organic phase for (c)?
e)
In a third experiment, what is the combined fraction extracted into the
organic phase(s) from 50.0 mL of aqueous solution by five extractions of
100.0 mL of ether each?
f)
The concentration of the solute in the organic phase when the five portions
of organic phase in (e) are combined?
2
Solute A has a partition coefficient of 2.00 between water and chloroform. What
volume of chloroform would be required to extract 95% of the solute from 50.0
mL of aqueous solution of A? (6)
3
For a system with a partition coefficient of 1.0, calculate the number of
extractions that would be needed to remove 99.99% of compound A from the
aqueous solution. Use a Vr of 1. (6)
4
You have two compounds in equal amounts in an aqueous solution that you will
extract with an organic solvent. Solute A has a distribution ratio of 6 and Solute
B has a distribution ratio of 3. (10)
a)
After one extraction with an equal volume of organic phase what will be
the purity of A in the organic phase?
b)
If you carry out a back extraction (keeping the Volume ratio the same) to
purify A, then what would be the purity of A in the organic phase?
5
c)
What yield would you have for A in part b?
d)
If you wanted to do just a single extraction of this system and you are
starting with 100 mL of aqueous solution then what would be the optimum
volume of organic solvent to use?
e)
What would the purity and yield of A in the organic phase in this case?
You have a 25 tube Craig counter current apparatus to separate compounds A and
B. The D value for A is 4.0 and for B it is 0.33. The Vr for this system is 1 and
you may assume equal moles of A and B to start. (4)
a)
How many transfers would be required to distribute A and B through the
entire 25 tubes?
b)
Which tube has the most A? (start numbering the tubes with zero)
6
This Craig system is cleaned out and restarted with the same compounds. The
system is taken through seven transfers. How many tubes contain some A and/or
B? (2)
b)
What is the purity and yield of A in the entire last tube containing both
phases of the system? (3)
c)
What would be the purity and yield of A in the entire next ot last and last
tubes containing both phases of the system? (3)
7)
What is the Dc at pH 6.00 for an organic acid if the partition coefficient is
20.0 and the pKa for the acid is 5.00? (4)