Question

The distribution coefficient, $K_D$ for an organic compound between water and methylene chloride is 3.40. An aqueous solution of the organic compound contains 0.500 g per 100 mL and is extracted with 50.0 mL of methylene chloride. What percentage of the organic compound originally in water is extracted?

• A. 31.5%
• B. 63.0%
• C. 72.0%
• D. 92.6%

Answer 1

The correct option is B 63.0%

Let x g of organic compound are extracted into methylene chloride.
$0.500-x$ g of organic compound will remain in water.
$K_d=\frac{xg}{50.0mL}\times \frac{100mL}{(0.500-x)g}=3.40$
$\frac{2x}{(0.500-x)}=3.40$
$x=1.70(0.500-x)$
$x=0.85-1.70x$
$2.70x=0.85$
$x=0.315$
The percentage of the organic compound originally in water is extracted is
$=\frac{x}{0.500}\times 100$
$=\frac{0.315}{0.500}\times 100$
$=63.0$ %
Hence, the option (B) is correct answer.