Question

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

Short answer

(c) \( \mathrm{CaO} \) is suitable for drying ammonia.

Step-by-step solution

Identify Dehydrating Properties

Examine each dehydrating agent to determine its suitability for drying ammonia. Look for whether each agent can chemically combine or react with water effectively to remove moisture.

Evaluate Conc. \( \mathrm{H}_{2} \mathrm{SO}_{4} \)

Concentrated sulfuric acid is a strong dehydrating agent, but it reacts with ammonia to form ammonium sulfate. Thus, it cannot be used to dry ammonia.

Evaluate \( \mathrm{P}_{4} \mathrm{O}_{10} \)

\( \mathrm{P}_{4} \mathrm{O}_{10} \) is a strong dehydrating agent, but it also reacts with ammonia to form phosphoric acid or other products, making it unsuitable.

Evaluate \( \mathrm{CaO} \)

Calcium oxide (lime) is a good dehydrating agent and does not react with ammonia, thus it is suitable for drying ammonia.

Evaluate Anhydrous \( \mathrm{CaCl}_{2} \)

Anhydrous calcium chloride is another great drying agent. However, it tends to form a complex with ammonia which makes it unsuitable for drying purposes.

Key concepts

Chemical Reaction with Ammonia

Ammonia, a common chemical compound with the formula \( \text{NH}_3 \), is well-known in chemistry due to its extensive use and interesting properties. When considering how it interacts with other substances, it's necessary to understand its reactivity, particularly with dehydrating agents. Ammonia can undergo chemical reactions with these substances, potentially rendering them ineffective for drying purposes.

For example, concentrated sulfuric acid (\( \text{H}_2\text{SO}_4 \)) is a powerful dehydrating agent; however, it reacts with ammonia to produce ammonium sulfate, a salt. Similarly, \( \text{P}_4\text{O}_{10} \) can react with ammonia because it is such a strong dehydrating agent. This reaction potentially forms substances like phosphoric acid that are not conducive to drying ammonia.

Anhydrous calcium chloride (\( \text{CaCl}_2 \)) might seem suitable for drying due to its ability to absorb water. However, it forms a complex with ammonia, which also makes it an inadequate choice. This is why a deep understanding of how ammonia chemically interacts with other agents is crucial when deciding on the right dehydrating method.

Drying Methods in Chemistry

In the world of chemistry, drying substances is often crucial to various processes. Drying agents or desiccants are substances that can remove water from materials, which is especially important for gases such as ammonia. A good drying method will efficiently remove moisture without undergoing unwanted chemical reactions with the substance being dried.

Not all drying agents are alike in their effectiveness or compatibility with specific chemicals. For ammonia, using a dehydrating agent that doesn't react with the gas is paramount. Some common choices include:

• Calcium Oxide (\( \text{CaO} \)): Often used as a drying agent, also known as lime, it can absorb water without reacting with ammonia.
• Silica Gel: A widely used drying agent that doesn't react with many chemicals and is particularly effective for drying gases and liquids.

Each drying agent works under specific conditions and with particular substances, so it's essential to match the right method with the material being dried.

Properties of Calcium Oxide

Calcium oxide, commonly known as lime, is a compound that stands out for its utility in various applications, thanks to some key properties. It is a white, caustic, alkaline substance that absorbs moisture efficiently. This characteristic makes \( \text{CaO} \) an excellent choice for drying applications in the chemical industry.

One of the notable properties of calcium oxide is its ability to absorb water vigorously. This reaction forms calcium hydroxide (\( \text{Ca(OH)}_2 \)), a process that releases significant heat. This absorption does not alter other substances, such as ammonia, making \( \text{CaO} \) highly suitable for drying them.

Additionally, \( \text{CaO} \) is stable under normal conditions and does not decompose or react spontaneously with many chemicals. Its low reactivity with gases like ammonia, accompanied by its moisture-absorbing capacity, renders calcium oxide an invaluable tool for chemists seeking effective and safe drying solutions.