Question

Consider a 0.3 L aqueous solution that contains 2.6 g of caffeine. The solubility of caffeine in water is 2.2 g/100 mL and the solubility in methylene chloride is 10.2 g/100 mL.

a) How much caffeine can be extracted with 70 mL of methylene chloride?

b) How much caffeine will be extracted if the aqueous solution is extracted twice with 30 mL of methylene chloride?

c) Which is more effective a or b?

Answer 1

a)

c = solubilty in water

solubility in methelene chloride = 8 x solubility in water

methelene chloride = 8 c

300 ml aqueous solution contain -------------- 2.6 g of caffeine

70 ml aqueous solution ------------- ??

mass of caffine in 70 ml = 70 x 2.6 / 300

                                       = 0.606 g

mass of caffine extract with methelene chloride = 8 x 0.606

                                                          = 4.848 g

b)

c x 300 + 8 c x 30 = 2.6

c = 2.6 / 540 = 0.00481 g/mL = 1.44 g remaining in the 300 mL water.

2.extraction:

540 c = 1.44

c = 1.44 /540 = 0.0027 g/mL = 0.8 g caffeine remaining in the 300 mL water.

0.8 g caffeine remaining in the 300 mL water.