Chapter 11, Problem 1Q

Interpretation Introduction

Interpretation:

The more effective drying agent should be identified among ${\text{CaCl}}_2$ or

  ${\text{CaCl}}_2.{\text{H}}_{\text{2}}\text{O}$ .

Concept introduction:

Drying agents are used to remove water from organic solvents. Mostly anhydrous drying agents are used that react with water to form insoluble hydrates in organic solvents and can be easily removed by filtration. Parameters that are considered to choose an effective drying agent are as follows:

• Capacity: The maximum number of moles of water molecules that can be trapped by a salt or drying agent defines its capacity.
• Efficiency: The amount of water left behind in the organic solvent after the drying process is called efficiency.
• Speed of removal of water: Time taken by the drying agent to form hydrate determines the speed of removal of water.
• Chemical inertness: Drying agents should be chemically inert that is it should not react with the organic solvent and the organic compounds dissolved in it.

Explanation of Solution

Among ${\text{CaCl}}_2$ and ${\text{CaCl}}_2.{\text{H}}_{\text{2}}\text{O}$, ${\text{CaCl}}_2$ is a more effective drying agent as it is anhydrous so it can react to more water molecules than ${\text{CaCl}}_2.{\text{H}}_{\text{2}}\text{O}$ that already have few water molecules attached to it. So drying capacity and efficiency of ${\text{CaCl}}_2$ to act as an effective drying agent will be greater than ${\text{CaCl}}_2.{\text{H}}_{\text{2}}\text{O}$ shown as follows:

  ${\text{CaCl}}_2+{\text{6H}}_{\text{2}}\text{O}\to {\text{CaCl}}_{\text{2}}{\text{.6H}}_{\text{2}}\text{O}$