Question

Distinguish between drying agent and dehydrating agent.

Answer 1

Hint: Dehydrating agents mainly remove the water of crystallisation from the compound which is chemically bonded whereas the drying agent is used to remove the extra water present in the reaction mixture to get a dry product.

Complete solution
We know that drying agents can be defined as the substances which are used to dry a compound from the excess of water that is present with it. Also the dehydrating agents can be defined as the substances which are used to absorb water molecules which are present inside the lattice structure of a compound. Those water molecules are popularly known as the water of crystallisation.
The differences between drying agent the dehydrating agents are represented in the tabular form-

Drying agents	Dehydrating agents
The substances which are used to dry a compound from the excess of water that is present with it.	The substances which are used to absorb water molecules which are present inside the lattice structure of a compound.
They don't form any kind of bond with the compound.	They form chemical bonds to remove the water of crystallisation.
They are used in the reactions where the presence of water can affect the yield of reaction drastically. For e.g. in the reactions of Grignard reagent.	They are used in the reaction where the compounds are to be used in anhydrous form than in the hydrated form. For e.g. in the calculation of heat capacity of anhydrous copper sulphate, calorimetrically.
Examples of drying agents are silica gel, anhydrous calcium carbonate ($CaC{O}_3$ ), calcium hydride ( $Ca{H}_2$ ), etc.	Examples of dehydrating agents are concentrated $H_{3}P{O}_4$ (phosphoric acid), conc. $H_{2}S{O}_4$ (sulphuric acid), $A{l}_2{O}_3$ (aluminium oxide), etc.

Note: To remove the water of crystallisation from the compound copper sulphate pentahydrate $(CuS{O}_4.5H_{2}O)$, in the chemistry laboratories during calorimetry, heating of the compound in a hot ceramic is done. Thus the blue colour of hydrated compound after dehydration changes to colourless in anhydrous compound.