Partition Coefficient? HELP!!?

[匿名]

2017-10-22 12:39 pm

1. Calculate the partition coefficient of caffeine in water/methylene chloride from the following data:
10.3 g/100 mL for methylene chloride and 2.04 g/100 mL for water.

2. In a very controlled experiment, a student is sure that 0.500 grams of caffeine is dissolved in 125 mL of water. The student extracts the caffeine using a single extraction of 21 mL of methylene chloride. How much caffeine is in the methylene chloride? How much remains in the
water? (use the partition coefficient calculated in #1

Can someone please explain to me the steps of how to solve these 2 questions? Thank you!

回答 (1)

不用客氣

2017-10-22 7:16 pm

1.
Partition coefficient of caffeine in water/methylene chloride
= (Concentration of caffeine in water) / (Concentration of caffeine in methylene chloride)
= (2.04/100 mL) / (10.3/100 mL)
= 2.04/10.3
= 0.198

2.
Let m g be the mass of caffeine in the methylene chloride.
Then, the mass of caffeine remained in the water = (0.500 - m) g

(Concentration of caffeine in water) / (Concentration of caffeine in methylene chloride) = 0.198
[(0.500 - m)/125] / (m/21) = 0.198
[(0.500 - m)/125] × (21/m) = 0.198
21 * (0.500 - m) = 125m * 0.198
10.5 - 21m = [125 * 0.198]m
(125 * 0.198)m + 21m = 10.5
m = 10.5 / [125 * 0.198 + 21]
m = 0.230

Mass of caffeine in the methylene chloride = 0.230 g
Mass of caffeine remained in the water = (0.500 - 0.230) g = 0.270 g

(The masses would be 0.229 g and 0.271 g instead if one takes the partition coefficient to be 20.4/10.3 instead 0.198.)

👍 2 👎 0