Question

0.170g of caffeine is dissolved in 10.0mL of water. The caffeine is extracted from the aqueous solution three times with 5.0-mL portions of methylene chloride. Calculate the total amount of caffeine that can be extracted into three portions of methylene chloride. Caffeine has a distribution coefficient of 4.6 between methylene chloride and water.

Please explain throughoutly. This is my first time working with extraction question

Answer 1

Weight of caffeine is W = 0.170 gm.

Volume of water is V= 10 ml

Volume of methylene chloride which extracted caffeine is v= 5ml

No of portions n=3

Distribution co-efficient= 4.6

TOTAL AMOUNT OF CAFFEINE THAT CAN BE UNEXTRACTED IS GIVEN BY

                     w_n= WX[K_DxV/(K_DxV+v)]ⁿ

                                  w₃= 0.170[ (4.6x10)/(4.6X10+5)]³

                            = 0.170[46/46+5]³

                            = 0.170[46/51]³

                           =0.170[97336/132651

   = 0.170X0.734

                            =0.125 gms

. AMOUNT OF CAFFEINE UN EXTRACTED IS 0.125 gms.

AMOUNT OF CAFFEINE EXTRACTED = 0.170-0.125

                                                        =0.045 gms