In this experiment, 0.070 g of caffeine is dissolved in 4.0mL of water. The caffeine is extracted from the aqueous solution three times with 2.0-mL portions of methylene chloride. Calculate the total amount of caffeine that can be extracted into the three portions of methylene chloride (see Technique12, Section12.2). Caffeine has a distribution coefcient of 4.6, between methylene chloride and water.

0.068 g

Explanation:

The equation that is used to determine the fraction q remaining in water of volume V₁ after n extractions of volume V₂ is:

qⁿ = (V₁ / (V₁ + KV₂)) ⁿ

Substituting in the values gives the fraction of caffeine left in the water phase:

q³ = (4.0mL / (4.0mL + 4.6 (2.0mL)) ³ = 0.0278

The fraction of caffeine extracted into the methylene chloride phase is:

1 - 0.0278 = 0.972

The amount of caffeine extracted into the methylene chloride is:

(0.070g) (0.972) = 0.068 g