Question

Suppose you have discovered a new organic molecule and it is somewhat soluble in water even though it is more soluble in dichloromethane or ether solvents. If you do a single extraction, you get only 60% of your material to transfer from the water to the organic layer. How many washes would it take to extract over 90% of your organic material from the water layer. Explain.

Answer 1

You need to perform 3 extraction to get 90 % of the organic molecule.

Extraction No. 1	Extracted = 60 %	Left in aqueous layer = 100-60 = 40 %	Total Extracted = 60 %
Extraction No. 2	Extracted is 60 % of the left in aqueous layer = 40 x 60/100 = 24 %	Left in aqueous layer = 40 - 24 = 16 %	Total extracted = 60 + 24 = 84 %
Extraction No. 3	Extracted is 60 % of the left in aqueous layer = 16 x 60/100 = 9.6 %	Left in aqueous layer = 16 - 9.6 = 6.4 %	Total extracted = 84 + 9.6 = 93.6 %
Extraction No. 4	Extracted is 60 % of the left in aqueous layer = 6.4 x 60/100 = 3.84 %	Left in aqueous layer = 6.4 - 3.84 = 2.56 %	Total extracted = 93.6 + 2.56 = 96.16 %