To dry ammonia NH3 gas the drying agent used is:

(A) Conc. H2SO4

(B) P2O5

(C) soda lime

(D) anhydrous CaCl2

When it comes to drying ammonia (NH3) gas, the most effective drying agent among the options provided is anhydrous calcium chloride (CaCl2). Let's break down why this is the case and explore the properties of the other options as well.

Understanding Drying Agents

Drying agents are substances that absorb moisture from gases or liquids, effectively reducing the water content. The choice of drying agent depends on the specific properties of the substance being dried, including its reactivity and the presence of water vapor.

Analyzing the Options

• Concentrated H2SO4: While concentrated sulfuric acid is a powerful dehydrating agent, it is highly reactive and can react with ammonia to form ammonium sulfate. This reaction makes it unsuitable for drying ammonia gas.
• P2O5 (Phosphorus Pentoxide): This is another strong dehydrating agent that can effectively remove water. However, it can also react with ammonia, leading to the formation of phosphoric acid and other products, which complicates its use for drying ammonia.
• Soda Lime: This is a mixture of sodium hydroxide and calcium oxide, primarily used for absorbing carbon dioxide and moisture. It is not specifically effective for drying ammonia gas and can also react with it.
• Anhydrous CaCl2: This compound is highly effective at absorbing moisture without reacting with ammonia. It forms a hydrate when it absorbs water, making it an ideal choice for drying NH3 gas.

Why Anhydrous CaCl2 is the Best Choice

Anhydrous calcium chloride has a strong affinity for water, allowing it to effectively remove moisture from ammonia gas without undergoing any chemical reactions that would alter the ammonia itself. This property makes it particularly useful in laboratory and industrial settings where pure ammonia is required.

Practical Application

In practice, when drying ammonia gas, anhydrous CaCl2 can be placed in a drying tube through which the ammonia passes. As the gas flows over the CaCl2, any water vapor present is absorbed, resulting in dry ammonia gas exiting the other end of the tube.

Conclusion

In summary, when tasked with drying ammonia gas, anhydrous calcium chloride (CaCl2) is the most suitable drying agent due to its ability to absorb moisture without reacting with ammonia. This ensures that the ammonia remains pure and usable for various applications.