Chapter 10, Problem 1E

Interpretation Introduction

Interpretation:

Phosphorouspentoxide is a heck of a drying agent but it is unsuitable for drying many liquids or solutions present in organic chemistry laboratory is to be explained.

Concept Introduction:

A drying agent is a chemical used to remove water from an organic compound that is in solution. Phosphorous pentoxide, magnesium sulfate, or potassium chloride etc., are used as drying agent.

Drying agentsare usually certain anhydrous salts that combine with water in the product and hold it as water of crystallization.

Answer to Problem 1E

Due to its exothermic nature and difficult to handle, it is unsuitable for drying many solutions present in organic chemistry laboratory.

Explanation of Solution

The molecular formula of Phosphorous pentoxide is ${\text{P}}_{\text{2}}{\text{O}}_{\text{5}}$ or ${\text{P}}_{\text{4}}{\text{O}}_{\text{10}}$. It is used as drying agent. It is sealed in enclosure; it removes all the moisture present in the surrounding.

It is quicker and effective than sodium sulfate and magnesium sulfate in absorbing moisture because if dried an organic liquid with anhydrous sodium sulfate or magnesium sulfate alone, it leaves water in the organic liquid, even if it looks dry (not cloudy).

Though ${\text{P}}_{\text{2}}{\text{O}}_{\text{5}}$ or ${\text{P}}_{\text{4}}{\text{O}}_{\text{10}}$ is very prompt, effective and efficient as drying agent, but it is difficult to handle. It is only used for partially dried organic substance. It can dehydrate the sulfuric acid to sulfur trioxide gas.

Sulfuric acid and phosphorous pentoxide are both acidic drying agents that are mainly used in desiccators and not in direct contact with the solution since they are very aggressive reagents. Both have a very high capacity. Sulfuric acid forms hydrates while phosphorous pentoxide is ultimately converted into phosphoric acid.

When ${\text{P}}_{\text{2}}{\text{O}}_{\text{5}}$ reacts with water molecule in organic solution, it forms phosphoric acid $\left({\text{H}}_{\text{3}}{\text{PO}}_{\text{4}}\right)$.

This reaction is exothermic in nature as shown below:

${\text{P}}_{\text{4}}{\text{H}}_{\text{10}}{\text{+6H}}_{\text{2}}\text{O}\to {\text{4H}}_{\text{3}}{\text{PO}}_{\text{4}}+\text{heat}$

Hence, due to its exothermic nature and difficult to handle, it is unsuitable for drying many solutions present in lab.