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) \(\mathrm{NH}_{4} \mathrm{Cl}, \mathrm{CaO}\) (d) \(\mathrm{CaO}, \mathrm{Na}_{2} \mathrm{CO}_{3}\)

Step-by-Step Solution

Answer

The byproducts are \(\mathrm{NH}_4 \mathrm{Cl}\) and \(\mathrm{CaO}\) (option c).

Step 1: Understanding the Solvay Process

The Solvay process is an industrial method for producing sodium carbonate (\(\mathrm{Na}_{2} \mathrm{CO}_{3}\)) from sodium chloride (\(\mathrm{NaCl}\)) and calcium carbonate (\(\mathrm{CaCO}_{3}\)). It involves several key reactions, one of which leads to the formation of ammonium chloride (\(\mathrm{NH}_{4}\mathrm{Cl}\)) as a byproduct.

Step 2: Identifying Main Reactions

The Solvay process consists of the following main reactions: (1) Ammoniation of brine, where ammonia (\(\mathrm{NH}_3\)) is absorbed in brine to form ammonium bicarbonate, and (2) Reaction between ammonium bicarbonate and brine (\(\mathrm{NaCl}\)), leading to sodium bicarbonate precipitation. This bicarbonate decomposes upon heating, yielding sodium carbonate and carbon dioxide (\(\mathrm{CO}_2\)). Calcium oxide (\(\mathrm{CaO}\)) is used to regenerate ammonia.

Step 3: Determining the Byproducts

Byproducts are the materials that are produced alongside the desired product and are not reutilized in the manufacturing process. During the Solvay process, \(\mathrm{NH}_4\mathrm{Cl}\) results from the absorption of ammonia, and \(\mathrm{CaO}\) is used to recover ammonia from \(\mathrm{Ca(OH)}_2\), hence \(\mathrm{NH}_4\mathrm{Cl}\) and \(\mathrm{CaO}\) can be considered as byproducts.

Step 4: Selecting the Correct Option

Among the available options, those that accurately reflect the byproducts of the Solvay process are option (c) \(\mathrm{NH}_4\mathrm{Cl}, \mathrm{CaO}\). They are formed and not further used in creating the primary product, \(\mathrm{Na}_2 \mathrm{CO}_3\).

Key Concepts

Sodium Carbonate Production

The Solvay process is a widely used method for producing sodium carbonate, also known as soda ash, which is a key chemical in various industrial processes. This process began over a century ago and revolutionized sodium carbonate production by making it much more efficient and cost-effective than mining natural sodium carbonates.

Sodium carbonate plays a vital role in industries such as glass manufacturing, paper production, and as a water softener in laundry detergents. The process primarily uses sodium chloride (common salt) and calcium carbonate (limestone) to produce sodium carbonate, which is represented by the formula \(\mathrm{Na}_2 \mathrm{CO}_3\).

The Solvay process involves several chemical reactions. Initially, ammonia is absorbed in a brine solution to form ammonium bicarbonate. This compound then reacts with the sodium chloride in the brine, precipitating sodium bicarbonate. Upon heating, sodium bicarbonate decomposes into sodium carbonate, releasing carbon dioxide and water.

• Step 1: Ammoniation of brine.
• Step 2: Formation and precipitation of sodium bicarbonate.
• Step 3: Decomposition of sodium bicarbonate to yield sodium carbonate.

Ammonium Chloride Byproduct

In the Solvay process, while the primary goal is to produce sodium carbonate, the reactions also lead to the formation of byproducts, one of which is ammonium chloride. Ammonium chloride, \(\mathrm{NH}_4\mathrm{Cl}\), is a result of ammonia absorption in a brine solution that contains sodium chloride.

Ammonium chloride is not reused in the main process and thus considered a byproduct. However, it finds its own applications outside of this chemical manufacturing. Industries use ammonium chloride as a fertilizer, particularly for rice and wheat crops. In addition, it is used in metalwork, where it functions as a soldering flux, enhancing the adherence of solder to metals, and in some cases as a component in galvanizing.

• Ammonium chloride forms during the ammonia recovery phase.
• It is separated and often utilized externally as a valuable industrial chemical.

As a byproduct of the Solvay process, ammonia chloride's production exemplifies the interconnectedness of industrial reactions and their diverse applications.

Industrial Chemical Reactions

The Solvay process illustrates a fascinating series of industrial chemical reactions meticulously optimized to maximize efficiency and production yield. Key to this process is the precise handling and recycling of chemicals, which not only lowers costs but also minimizes waste.

Several reactions are critical within this system:

• Ammoniation of Brine: Ammonia is introduced to saltwater, creating ammonium bicarbonate.
• Sodium Bicarbonate Formation: Through interaction with sodium chloride, sodium bicarbonate is precipitated.
• Ammonia Recovery: Calcium oxide is used to reclaim ammonia from solutions of ammonium chloride.

These reactions happen in a cycle, highlighting the principle of reaction economy, where reactants are often recovered and reused.

Understanding these reactions not only helps in sodium carbonate production but also provides insights into efficient industrial strategies, balancing between maximal output and environmental considerations.