In basic inorganic chemistry, which drying agent is suitable for drying ammonia gas without reacting with it?

Introduction / Context:
This question tests knowledge of laboratory drying agents used in inorganic chemistry. When gases are prepared in the laboratory, they are often moist and need to be dried before further use or collection. The correct drying agent must remove water but should not react with the gas being dried. Ammonia is a basic gas, so its interaction with different drying agents is an important consideration in practical chemistry questions.

Given Data / Assumptions:

• The gas to be dried is ammonia (NH3).
• We have several possible drying agents: sulphuric acid, calcium oxide, phosphorus pentoxide, calcium chloride, and concentrated nitric acid.
• We must choose an agent that absorbs moisture but does not react with ammonia.

Concept / Approach:
Ammonia is a basic gas and is very soluble in water. Strong acidic drying agents, or drying agents that chemically react with bases, are not suitable for drying ammonia. Calcium oxide (quicklime) is a basic oxide that can absorb water to form calcium hydroxide and does not react with ammonia in a problematic way. Therefore, it is commonly used in the laboratory for drying ammonia gas. Other strong dehydrating agents like concentrated sulphuric acid or phosphorus pentoxide can react with ammonia and are not appropriate.

Step-by-Step Solution:

Verification / Alternative check:
Standard laboratory manuals and inorganic chemistry textbooks list quicklime (calcium oxide) as the recommended drying agent for ammonia. They also include cautionary notes that concentrated sulphuric acid, although good for many other gases, reacts with ammonia and should not be used. Practical laboratory setups often show a drying tower packed with quicklime placed after the apparatus that generates ammonia. This consistent recommendation across sources confirms that calcium oxide is the correct drying agent.

Why Other Options Are Wrong:

• Sulphuric acid: Reacts with ammonia to form ammonium sulfate, so it is not inert.
• Phosphorus pentoxide: Very strong dehydrating agent that can chemically interact with ammonia.
• Calcium chloride: Can absorb ammonia and form complexes, which interferes with the purity and yield of the gas.
• Concentrated nitric acid: Strong oxidizing acid that would react vigorously with ammonia and is dangerous in this context.

Common Pitfalls:
Students sometimes think that any strong dehydrating agent is suitable as a universal drying agent. However, compatibility with the gas is crucial. Another common error is to choose calcium chloride simply because it is a familiar drying agent, forgetting its tendency to interact with ammonia. The key lesson is to select a drying agent that both removes water and remains chemically inert toward the gas being treated.

Final Answer:
The suitable drying agent for ammonia gas is Calcium oxide.