Question

You are in possession of an organic compound that is 0.40 M in a 200.0 mL aqueous sample. You are tasked with extracting this compound into 100 mL of hexane. Describe what you will do to maximize the extraction from aqueous to organic phase and provide example calculations for the final amount remaining the aqueous phase after your extraction.

Answer 1

for extraction we have formula w = W [( Kd x V) / ( KdV + v) ] ^ n

where Kd is extraction coefficient , V is volume of solution in which solute present

v = volume of extrating liquid ,

n = number of times extraction happening.

If we take W = 1g , Kd = 0.5 , V = 200 , v = 100 ml

substituting we get w = 0.5 indicating 0.5 g of mass unextracted

now if we take v = 10 ml , then we do extractions 10 times ( since 10 ml used 10 times is 100 ml)

we get w= 1 [( 0.5 x 200) / ( 0.5x 200) + 10 ) ] ^ 10

= ( 0.386)

Thus 0.386 g of mass left unextracted.

Thus we can see that multiple extractions using small amount of extracting liquid gives better results than using all liquid once.

Hence in our problem we use hexane 10 ml and extract 10 times rather than using 100 ml hexane once