Problem 74 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is not correct? (a) a mixture of \(\mathrm{Ca}(\mathrm{CN})_{2}\) and \(\mathrm{C}\) is known as nitrolim (b) hydrolysis of \(\mathrm{NCl}_{3}\) gives \(\mathrm{NH}_{3}\) and \(\mathrm{HOCl}\) (c) a mixture of \(\mathrm{Ca}\left(\mathrm{H}_{2} \mathrm{PO}_{4}\right)_{2}\) and \(\mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}\) is known as super phosphate of lime (d) ammonia is used as refrigerant

Step-by-Step Solution

Answer

Option (c) is incorrect; super phosphate of lime is not a mixture of \( Ca(H_2PO_4)_2 \) and \( CaSO_4 \cdot 2H_2O \).

Step 1: Analyze Option (a)

Option (a) states that a mixture of \( Ca( ext{CN})_2 \) and \( C \) is known as nitrolim. This is correct because nitrolim is indeed the common name for the commercial mixture of calcium cyanamide and carbon.

Step 2: Analyze Option (b)

Option (b) states that the hydrolysis of \( NCl_3 \) gives \( NH_3 \) and \( HOCl \). This is correct, as nitrogen trichloride reacts with water to form ammonia and hypochlorous acid.

Step 3: Analyze Option (c)

Option (c) states that a mixture of \( Ca(H_2PO_4)_2 \) and \( CaSO_4 \cdot 2H_2O \) is known as super phosphate of lime. This is incorrect because superphosphate of lime is actually a common name for calcium dihydrogen phosphate, typically formed from treating phosphate rock with sulfuric acid.

Step 4: Analyze Option (d)

Option (d) states that ammonia is used as refrigerant. This is correct, as ammonia is commonly used in industrial refrigeration systems due to its efficient cooling properties and cost-effectiveness.

Key Concepts

Calcium Cyanamide

Calcium cyanamide, represented as \( \mathrm{Ca(CN)}_2 \), is a nitrogen-rich compound primarily used in agriculture as a fertilizer. When mixed with carbon, it forms a product commonly known as nitrolim. This mixture is significant in the context of farming because it acts as a slow-release nitrogen fertilizer, beneficial for continuous nutrient supply to plants.

Calcium cyanamide is synthesized from calcium carbide. This synthesis involves reacting calcium carbide with atmospheric nitrogen at high temperatures:

• \[ \text{CaC}_2 + \text{N}_2 \rightarrow \text{CaCN}_2 + \, C \]

Because of its properties, calcium cyanamide not only provides essential nitrogen but also has secondary benefits such as controlling certain soil-borne pests and diseases. These attributes make it highly valuable in sustainable agricultural practices.

Nitrogen Trichloride Hydrolysis

Nitrogen trichloride (\( \mathrm{NCl}_3 \)) is a chemical compound that, when hydrolyzed, forms ammonia (\( \mathrm{NH}_3 \)) and hypochlorous acid (\( \mathrm{HOCl} \)). The hydrolysis reaction can be represented as:

• \[ \text{NCl}_3 + 3 \, \text{H}_2\text{O} \rightarrow \text{NH}_3 + 3 \, \text{HOCl} \]

This reaction showcases how reactive nitrogen trichloride can be when exposed to water.The formation of hypochlorous acid is notable because \( \mathrm{HOCl} \) is a mild oxidizing agent, often used in sanitizing and disinfecting processes. Nitrogen trichloride itself is unstable and has to be handled carefully due to its explosive potential. Therefore, in the industry and laboratory settings, its hydrolysis is significant for neutralizing the compound's reactivity.

Superphosphate of Lime

Superphosphate of lime is a term commonly used to describe calcium dihydrogen phosphate, which results from treating phosphate rock with sulfuric acid. The reaction can be simplified as follows:

• \[ \text{Ca}_3(\text{PO}_4)_2 + 2 \, \text{H}_2\text{SO}_4 \rightarrow 2 \, \text{CaSO}_4 + \text{Ca(H}_2\text{PO}_4)_2 \]

This product provides plants with readily available phosphorus, an essential nutrient for their growth and development.Superphosphate is widely used in agriculture because it enhances root development and increases the yield of crops. The compound boosts photosynthesis efficiency and plays a key role in energy transfer within plants. Identifying superphosphate of lime correctly is crucial for choosing the right kind of fertilizer for agricultural activities.

Ammonia as Refrigerant

Ammonia (\( \mathrm{NH}_3 \)) is extensively used as a refrigerant in industrial applications. Its effectiveness stems from its excellent thermodynamic properties, including a high latent heat of vaporization and a low boiling point. This makes it an efficient and cost-effective choice for refrigeration systems.Some key attributes of ammonia as a refrigerant include:

• Environmentally friendly, as it does not contribute to ozone depletion.
• Highly efficient, leading to lower energy costs.
• Non-proprietary, which keeps costs down compared to other synthetic refrigerants.

It's important to note that while ammonia is advantageous, it is also toxic and corrosive. Thus, ammonia-based refrigeration systems must be handled with care, incorporating proper safety measures and maintenance protocols to ensure safe operation. Understanding these characteristics is vital for students learning about refrigerant technologies.