Question

Ammonia can be dried by (d) Anhydrous \(\mathrm{CaCl}_{2}\) (a) Conc. \(\mathrm{H}_{2} \mathrm{SO}_{4}\) (b) \(\mathrm{P}_{4} \mathrm{O}_{10}\) (c) \(\mathrm{CaO}\)

Short answer

Ammonia can be dried by anhydrous CaCl₂.

Step-by-step solution

Understanding Ammonia Properties

Ammonia is a polar molecule (NH₃) and forms hydrogen bonds with water, making it a gas that holds moisture. It is also a basic gas that reacts with acids and highly hygroscopic substances such as phosphorus pentoxide (P₄O₁₀) and concentrated sulfuric acid (H₂SO₄).

Evaluating Drying Agents

We need to assess ammonia's compatibility with each listed drying agent: (a) Concentrated H₂SO₄ is a strong acid and hygroscopic, making it unsuitable because it reacts with ammonia. (b) P₄O₁₀ is also acidic and is used to dehydrate or dissolve in the presence of moisture, thus reacting with ammonia. (c) CaO, a basic oxide, reacts mildly with water but does not react with ammonia directly, making it a viable option. (d) Anhydrous CaCl₂ is a neutral drying agent that absorbs moisture effectively without reacting with ammonia.

Selecting the Best Drying Agent

Considering ammonia's chemical properties and compatibility with the drying agents, anhydrous calcium chloride (CaCl₂) is identified as the best drying agent. It is neutral, does not react with ammonia, and absorbs moisture effectively.

Key concepts

Ammonia Properties

Ammonia, with the chemical formula \( NH_3 \), is a fascinating compound. It is a polar molecule, which means it has a positive and a negative side, much like how a magnet has two poles. This polarity allows ammonia to form strong hydrogen bonds with water molecules, making it capable of holding moisture quite effectively.
However, this ability to hold moisture also poses a challenge when trying to dry ammonia. Its strong affinity for water means typical drying processes need to be carefully considered. Additionally, ammonia is a basic gas, which means it can readily react with acidic compounds. When considering its drying, this reactivity needs to be taken into account.

Drying Agents

Selecting an appropriate drying agent is crucial for removing moisture from ammonia. The drying agent must effectively absorb moisture without reacting with ammonia itself.

• Concentrated sulfuric acid \( (\mathrm{H_2SO_4}) \): While a strong hygroscopic substance, it reacts with ammonia, making it unsuitable.
• Phosphorus pentoxide \( (\mathrm{P_4O_{10}}) \): Another hygroscopic compound that reacts with ammonia due to its acidic nature.
• Calcium oxide \( (\mathrm{CaO}) \): Does not react with ammonia, but is not as efficient in moisture absorption.
• Anhydrous calcium chloride \( (\mathrm{CaCl_2}) \): Effective in absorbing moisture without any reaction with ammonia, making it the ideal choice.

Choosing the right drying agent ensures that ammonia’s properties are not altered during the drying process.

Ammonia Compatibility

When drying ammonia, compatibility with other substances is key. Ammonia, being a basic substance, primarily reacts with acids. Therefore, drying agents that have acidic properties are typically unsuitable because they can form unwanted reactions.
Anhydrous calcium chloride stands out as the most compatible drying agent for ammonia. It remains neutral in chemical reactions, meaning it does not interact negatively with ammonia. This neutrality allows it to absorb moisture without compromising ammonia's integrity or properties. Choosing the correct drying agent helps maintain ammonia's desired properties for further use.

Chemical Properties

Understanding the chemical properties of ammonia is essential for successful application in various reactions or processes. Its capacity to form hydrogen bonds marks it as highly reactive, particularly with acid-forming agents. An essential part of working with ammonia is recognizing its basic nature and reactivity with acids.
Careful handling and choosing non-reactive materials for storage or treatment will preserve ammonia’s properties. This caution prevents any neutralization or unwanted by-products that might hinder the desired application. Thus, recognizing ammonia’s affinity for certain reactions is critical in many chemical processes.

Hydrogen Bonds

Hydrogen bonding allows ammonia to dissolve readily in water and maintain its moisture. These bonds occur when the highly electronegative nitrogen atom attracts hydrogen atoms from other molecules, forming a network of attractions.
This hydrogen bonding capability makes ammonia play a vital role in various industrial and laboratory settings, where controlled reactions with water are necessary. However, this same property also accounts for the challenge in drying ammonia, as the attraction between water and ammonia molecules must be broken without triggering a chemical reaction. It is these physical interactions that underscore ammonia’s unique behavior and influence in chemical reactions.