Question

4. A 300-ml aqueous solution containing 40 g compound A is to be extracted with ether. The solubility of compound A in either at room temperature is 20 g per 100 ml and in water is 13.3 g per 100 ml. calculate the weight of the compound that would be recovered by extraction with (a) two 150 ml portions of ether and (b) one 300-ml portion of ether.

Answer 1

First, determine K.
K_o/a = 20/13.3


Then K = (org layer)/(aq layer)
For part b.
Let x = grams in org layer; then 40-x = grams in aq layer. Then
(organic layer) = x/300
(aqueous layer) = (40-x)/300

K = (x/300)/(40-x)/300
Solve for x and 40-x.

For part a use the same set up but go through the equation twice with 150 mL each. Two extractions with half the amount will ALWAYS extract more.