7. Bonus: The fraction extracted into solvent B is calculated by formula below t

Question

7. Bonus: The fraction extracted into solvent B is calculated by formula below the shown : fraction extracted into B - ( NY 1 + VB Van K where K is the distribution coefficient VA is the volume of the solvent A VB is the volume of the solvent B n is the number of extractions. If the distribution K compound X is 10, calculate and compare the fraction of compound X constant of extracted into solvent B from 30 mL solvent A with either (a) one single extraction with 30 mL solvent B or (b) three extractions with 10 ml solvent B each time Is it better to do several successive extractions with smaller volumes or a single extraction with larger volume?

Explanation / Answer

fraction extracted= 1/(1+VB/nVAK)n, K=10, VB= 30ml, VA= 30ml. n=1 for single extraction

fraction extracted= 1/{1+30/(30*1*30*10)}1= 0.91, if initial mass = 1 gm, extracted amount= 0.91 gm

when n=3, VB=10ml, VA=30ml, fraction extracted= 1/(1+10/(30*10*3)}3=0.967

extracted amount=0.967 gm

Hence it is better to extract thrice with the 1/3 of the volume of solvent than single solvent

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