Chapter 3, Problem 1Q

Interpretation Introduction

Interpretation:

The amount of caffeine present in each layer after mixing it with methylene chloride and water needs to be determined in which it has distribution coefficient of 4.6 and 52 mg of caffeine are added to 2 mL of water and 2 mL of methylene chloride.

Concept Introduction:

A polar covalent molecule will be soluble in water whereas a non-polar covalent compound will be insoluble in water based on the concept of "Like dissolves like". Some of the polar compounds also not soluble in water as they cannot form hydrogen bonding with water molecules.

The distribution coefficient can be defined as the ratio of the amount of the substance dissolve in one solvent to the amount of substance in the other solvent.

  $\text{distribution coefficient=}\frac{\text{Amount of substance in solvent x}}{\text{Amount of substance in solvent y}}$

Answer to Problem 1Q

The mass of caffeine in water and methylene chloride is 0.0427 g and 0.0093 g respectively.

Explanation of Solution

Distribution coefficientof caffeine = 4.6

Amount of caffeine = 52 mg = 0.052 g

Volume of water = 2 mL = 0.002 L

Volume of methylene chloride = 2 mL = 0.002 L

  $\text{distribution coefficient=}\frac{\text{Amount of substance in solvent x}}{\text{Amount of substance in solvent y}}$

Let's assume the amount of caffeine in methylene chloride = x

Thus,

  $\begin{array}{l}\text{distribution coefficient=}\frac{\text{Amount of substance in solvent x}}{\text{Amount of substance in solvent y}}\\ \text{ 4}\text{.6 =}\frac{\frac{\text{0}\text{.052 - }x\text{ g}}{0.002L}}{\frac{x\text{ g}}{0.002L}}\\ \text{4}\text{.6 =}\frac{(\text{0}\text{.052 - }x)0.002}{\text{0}\text{.002 }x\text{ g}}\\ \text{0}\text{.0092 }x\text{ = 0}\text{.000104 - 0}\text{.002 }x\\ \text{0}\text{.0092 }x\text{ + 0}\text{.002 }x\text{ = 0}\text{.000104}\\ \text{0}\text{.0112 }x=\text{0}\text{.000104}\\ x=\frac{\text{0}\text{.000104}}{\text{0}\text{.0112}}=0.0093\text{g in methylene chloride}\end{array}$

Thus,

  $\text{0}\text{.052 - 0}\text{.0093 = 0}\text{.0427 g in water}$

Conclusion

Thus, the mass of caffeine in water and methylene chloride is 0.0427 g and 0.0093 g respectively.