Question

When 100 mL of an aqueous solution containing 1.0 g of caffeine is extracted with 10 mL of chloroform at room temperature, 0.5 g of caffeine is transferred to the chloroform layer. Calculate the distribution coefficient of caffeine between chloroform and water at room temperature.

Answer 1

Answer – We are given the 100 mL of an aqueous solution containing 1.0 g of caffeine and 10 mL of chloroform at room temperature, 0.5 g of caffeine is transferred to the chloroform layer

Means 0.5 g of caffeine in 10 mL chloroform and 0.5 g of caffeine in 100 mL aqueous solution.

We know the distribution coefficient is the ratio in the two solvent with solutes

We know the two solvents are aqueous and chloroform

So, it is

The ratio in the chloroform = 0.50 g /10 mL

The ratio in the aqueous = 0.50 g/100 mL

So, distribution coefficient = ratio in the chloroform / ratio in the aqueous

distribution coefficient = 0.50 g* (10 mL)^-1 / 0.50 g *(100 mL)^-1

So                                = 0.50 g* (10 mL)^-1 *100 mL / 0.50 g

                                     = 5.0 g / 0.50 g

                                      = 10

So ,distribution coefficient of caffeine between chloroform and water at room temperature is 10:1