Question

Which of the following is a drying agent?
(A) $conc.\;{H_2}S{O_4}$
(B) ${P_2}{O_5}$
(C) Silica gel
(D) All of these

Answer 1

Hint: As we all know that a drying agent is a chemical compound which is used to remove the water from the organic compound during its preparation. Drying agents absorb water from the solution and the solution then becomes translucent.

Complete Step by step answer: We all know that drying agent is a chemical compound which is used to remove the water from the organic compound during its preparation. Drying agents absorb water from the solution and the solution then becomes translucent. They are basically anhydrous inorganic salts that absorb water of hydration when exposed to moist air or a wet solution. Commonly known drying agents include sodium sulphate and magnesium sulphate, they form larger cramps when they absorb water. Crystals are removed after a short period of time by filtration or decantation thereby making the solution free of water.
As we know that concentrated sulphuric acid ($conc.\;{H_2}S{O_4}$) has a very good and strong affinity for water and hence it is sometimes used to dehydrate (chemically remove water) many compounds like carbohydrates. It reacts with the sugars like sucrose and removes about eleven molecules of water from each molecule of sucrose and results in a brittle spongy mass of carbon and diluted sulphuric acid.
Next is Phosphorus pentoxide ${P_2}{O_5}$, it is also considered a good drying agent because its hydrolysis is so exothermic that releases so much energy which dehydrate the compounds and results in formation of anhydrides and phosphoric acid which further removes water molecules from the compound.
Lastly the Silica gel which is an amorphous and porous substance obtained from silicon dioxide. Like sulphuric acid, silica gel also has a strong affinity for water molecules and it remains hard when saturated with water.
Thus, from the above explanation we can say that all the three compounds are drying agents.

Hence the correct answer is (D).

Note: Some uses of drying agents:
-Silica gel is used in industrial compressed air systems to dry the air. It absorbs air from moisture when compressor discharge flows through silica beds.
-${P_2}{O_5}$is most commonly used in the conversion of primary amines into nitriles. It is a non-flammable substance but reacts vigorously with water.