The distribution coefficient for iodine between CCl4 and H2O is 85. ?

Question

Calculate the concentration of I2 remaining in the aqueous layer after extraction of 50.0 mL of 1.00 x 10-3 F I2 with the following quantities of CCl4. 

Update:

(a) two 25.0 mL portions. 

(b) five 25.0 mL portions. 

Answer 1

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There is a real handy equation for doing this calculation:

(Qaq)n=[Vaq/(DVorg+Vaq)]^n

where Qaq = the fraction remaining in the aqueous solvent

Vaq and Vorg are the volumes of the aqueous and organic solvent used in each extraction

D = distribution coefficient

n = number of identical extractions

(a) Qaq = [50/85(25) + 50]^2 = 5.28X10^-4

So, the remaining concentration in the aqueous layer is (5.28X10^-4 X 1.00X10^-3) = 5.28X10^-7 

(b) Qaq = [50/85(25) + 50]^5 = 2.03X10^-16

remaining concentration = 2.03X10^-16 X 1.00X10^-3 = 2.03X10^-19