Question

So I did a experiment on extraction of caffeine.

Here is the question, If your goal was to isolate as much caffeine from the aqueous layer as poassible, which of the two methods used in this lab would you use and why?

We had 2 methods, first method was using 60 mL of CH2Cl2 to extract

second method was using 20 mL of CH2Cl2 three times to extract (60 mL total).

Now I know that the second method is better, but could you tell me why using the partition coefficeint K.

Answer 1

Partition coefficient is generally the ratio of concentration of solute in immiscible layers namely aqueous and organic.

So, we have a formula for extraction efficiency which determines the fraction of left over solute remain in the aqueous phase after n extractions with V_org,

ie, qⁿ = ( V_aq / V_aq+ KV _org)ⁿ

^{Where V = volume}

^{n = numberof times extraction takes place}

^{K = distribution coefficient}

So, when you put the respective values in the equation, you will find fraction of left over solute remain in the aqueous or oraganic would be more lesser in multiple extraction than in single extraction.