Problem 27 - A Complete Resource Book in Chemistry for JEE Main

Question

In Solvay process of manufacture of \(\mathrm{Na}_{2} \mathrm{CO}_{3}\), the by products are (a) \(\mathrm{CaCl}_{2}, \mathrm{CO}_{2}, \mathrm{NH}_{3}\) (b) \(\mathrm{Na}_{2} \mathrm{CO}_{3}, \mathrm{CO}_{2}\) (c) \(\mathrm{NH}_{4} \mathrm{Cl}, \mathrm{CaO}^{2}\) (d) \(\mathrm{CaO}, \mathrm{Na}_{2} \mathrm{CO}_{3}\)

Step-by-Step Solution

Answer

The by-products in the Solvay process are \(\mathrm{NH}_{4} \mathrm{Cl}\). Hence, the best answer is (c), despite \(\mathrm{CaO}\) not being a final by-product.

Step 1: Understanding the Solvay Process

The Solvay process is an industrial method used to manufacture sodium carbonate (\(\mathrm{Na}_{2}\mathrm{CO}_{3}\)) from sodium chloride (\(\mathrm{NaCl}\)) and limestone (\(\mathrm{CaCO}_{3}\)). It involves several chemical reactions.

Step 2: Chemical Reactions in the Solvay Process

The key reactions are: 1. \(\mathrm{CaCO}_{3} \rightarrow \mathrm{CaO} + \mathrm{CO}_{2}\)2. \(\mathrm{CO}_{2} + 2\mathrm{NH}_{3} + \mathrm{H}_{2}\mathrm{O} \rightarrow \mathrm{NH}_{4} \mathrm{HCO}_{3}\)3. \(\mathrm{NH}_{4} \mathrm{HCO}_{3} + \mathrm{NaCl} \rightarrow \mathrm{NaHCO}_{3} + \mathrm{NH}_{4} \mathrm{Cl}\)4. \(2\mathrm{NaHCO}_{3} \xrightarrow{heat} \mathrm{Na}_{2}\mathrm{CO}_{3} + \mathrm{CO}_{2} + \mathrm{H}_{2}\mathrm{O}\)

Step 3: Identifying By-products

Identify by-products from the equations above:1. From Reaction 3, \(\mathrm{NH}_{4} \mathrm{Cl}\) is a by-product.2. From Reaction 4, \(\mathrm{CO}_{2}\) is released again but not really a new by-product since it's reused.3. From Reaction 1, \(\mathrm{CaO}\) is initially generated, but it isn't considered a by-product in the final stages.Hence, \(\mathrm{NH}_{4} \mathrm{Cl}\) is the main by-product.

Step 4: Choosing the Correct Option

Based on the identified by-products (specifically \(\mathrm{NH}_{4} \mathrm{Cl}\)), option (c) listing \(\mathrm{NH}_{4} \mathrm{Cl}, \mathrm{CaO}\) aligns partially, even though \(\mathrm{CaO}\) isn't a by-product after full process iteration.

Key Concepts

Sodium Carbonate

Sodium carbonate, often referred to as soda ash or washing soda, is a key chemical used in various industrial processes and household applications. It's a white, odorless powder that dissolves in water to form a mildly alkaline solution. This compound is essential in manufacturing glass, soaps, and detergents.
In the Solvay process, sodium carbonate is produced through a series of chemical reactions starting with sodium chloride and limestone. This process is advantageous due to its cost-effectiveness and efficiency. It mainly provides sodium carbonate without any direct environmental pollutants if managed well.
The final product, sodium carbonate, has many uses:

• It's a vital ingredient in the glass-making industry, as it helps lower the melting point of silica.
• In detergents, it acts as a water softener by binding to calcium and magnesium ions found in water.
• It serves in the chemical industry, acting as a buffering agent to maintain pH levels.

By-products in Industrial Processes

Industrial processes often involve by-products, materials that result during the production of a main product. Efficient management and utilization of these by-products can greatly reduce environmental impact and increase economic benefits.
In the Solvay process specifically, understanding by-products is crucial to optimize the procedure and minimize waste. The main chemical reactions yield not only sodium carbonate but also by-products, notably ammonium chloride ( NH_4Cl). By-products are managed through a variety of methods:

• Recycling within the process, often common when by-products can be reused to continue production.
• Conversion into commercially viable products, which can then be sold, adding economic value.
• Safe disposal procedures to prevent environmental harm, ensuring that chemical by-products do not lead to pollution.

Managing these by-products through reuse or conversion can transform a potential waste issue into a positive economic advantage for industries.

Chemical Reactions in Solvay Process

The Solvay process is a series of chemical reactions designed to manufacture sodium carbonate. Understanding these reactions deeply is essential to grasp how sodium carbonate is successfully produced.
The process begins with limestone ( CaCO_3) being calcined to produce calcium oxide ( CaO) and carbon dioxide ( CO_2). Then, CO_2 reacts with ammonia ( NH_3) and water to form ammonium bicarbonate ( NH_4HCO_3). This bicarbonate then reacts with sodium chloride ( NaCl) to produce sodium bicarbonate ( NaHCO_3) and ammonium chloride ( NH_4Cl).
Finally, heating sodium bicarbonate results in sodium carbonate, water, and a release of CO_2:

• CaCO_3 ightarrow CaO + CO_2
• CO_2 + 2NH_3 + H_2O ightarrow NH_4HCO_3
• NH_4HCO_3 + NaCl ightarrow NaHCO_3 + NH_4Cl
• 2NaHCO_3 ightarrow Na_2CO_3 + CO_2 + H_2O

The cumulative effect of these reactions in the Solvay process shows how each step is interconnected, with the clever recycling of materials enhancing the sustainability and economics of this industrial method.