Question

In this experiment, 0.170 g of caffeine is dissolved in 10.0 ml 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 the three portions of methylene chloride (see technique 12, section 12.2). caffeine has a distribution coefficient of 4.6 between methylene chloride and water.

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)=w*[(k_(Dx)v)/(k_(Dx)v+v)]^n\\</p><p>w_(3)=0.170[(4.6*10)/((4.6*10+5))]^3\\</p><p>=0.170[(46)/(46+5)]^3\\</p><p>=0.170[(46)/(51)]^3\\</p><p>=0.170[(97336)/(132651)]\\</p><p>=0.170*0.734=0.125gms`

amount of caffeine un extracted is 0.125gms

amount of caffeine extracted=0.170-0.125

=0.045 gms