Problem 95 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following set of raw materials are used in the manufacture of \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) by Solvay process? (a) \(\mathrm{CaCl}_{2}, \mathrm{NH}_{3}, \mathrm{CO}_{2}\) (b) \(\mathrm{NaOH}, \mathrm{NH}_{3}, \mathrm{CO}_{2}\) (c) \(\mathrm{NaCl}, \mathrm{NH}_{3}, \mathrm{CO}_{2}\) (d) \(\mathrm{Ca}(\mathrm{OH})_{2}, \mathrm{NH}_{3}, \mathrm{CO}_{2}\)

Step-by-Step Solution

Answer

Option (c) \(\text{NaCl}, \text{NH}_3, \text{CO}_2\) is correct for the Solvay process.

Step 1: Identify the Key Reactants in the Solvay Process

The Solvay process is a method to produce sodium carbonate \(\text{Na}_2\text{CO}_3\). The key reactants involved in this process are sodium chloride \(\text{NaCl}\), ammonia \(\text{NH}_3\), and carbon dioxide \(\text{CO}_2\). Also, calcium carbonate \(\text{CaCO}_3\) is initially used to obtain carbon dioxide and lime \((\text{Ca(OH)}_2)\) in the recycling step. However, \(\text{NaCl}\) is the main source of sodium.

Step 2: Match the Raw Materials with Given Options

Examine the given options for the presence of \(\text{NaCl}\), \(\text{NH}_3\), and \(\text{CO}_2\). Option (c) \(\text{NaCl}, \text{NH}_3, \text{CO}_2\) contains all of the key reactants directly used in the Solvay process.

Step 3: Verify the Role of Each Component

Within the Solvay process, \(\text{NaCl}\) provides sodium for \(\text{Na}_2\text{CO}_3\), \(\text{NH}_3\) acts as a catalyst, and \(\text{CO}_2\) is used to precipitate \(\text{NaHCO}_3\), which then gets heated to form \(\text{Na}_2\text{CO}_3\). This confirms that the selection in Step 2 is correct.

Key Concepts

Sodium Carbonate Production

The production of sodium carbonate, also known as soda ash, is primarily carried out using the Solvay process. This process is a major industrial method and is favored due to its high efficiency and cost-effectiveness. The Solvay process revolves around the conversion of sodium chloride (\(\text{NaCl}\)), ammonia (\(\text{NH}_3\)), and carbon dioxide (\(\text{CO}_2\)) into sodium carbonate (\(\text{Na}_2\text{CO}_3\)). The process consists of the following main stages:

• Dissolving ammonia in a brine solution of sodium chloride.
• Bubbling carbon dioxide into this solution to form ammonium bicarbonate which reacts with sodium chloride to precipitate sodium bicarbonate (\(\text{NaHCO}_3\)).
• Heating the sodium bicarbonate to decompose it into sodium carbonate, water, and carbon dioxide.
• Recycling the ammonia using calcium hydroxide (\(\text{Ca(OH)}_2\)) obtained from the decomposition of limestone (\(\text{CaCO}_3\)).

The Solvay process is renowned for its minimal waste production, with most by-products being recycled within the plant.

Raw Materials

The Solvay process heavily relies on specific raw materials. These include sodium chloride (\(\text{NaCl}\)) sourced primarily from sea water or rock salt, ammonia (\(\text{NH}_3\)) which acts as a catalyst in the reaction, and carbon dioxide (\(\text{CO}_2\)). Additionally, calcium carbonate (\(\text{CaCO}_3\)), which is often derived from limestone, is vital as it provides the carbon dioxide necessary for the process and lime for ammonia recovery. These raw materials are abundant and easily accessible, which makes the Solvay process a preferable choice for industrial production.
The use of these raw materials in a typical Solvay plant is efficiently managed, with carbon dioxide and ammonia being involved in multiple cycles to ensure little wastage. This high efficiency in material usage is essential for maintaining low production costs and ensuring environmental sustainability.

Chemical Engineering Processes

In chemical engineering, the Solvay process is noteworthy for its ingenious use of multi-step reactions that are integrated into a continuous process cycle. This involves:

• An initial phase where all reactants are mixed in a solution.
• A reaction phase where specific chemical transformations occur under controlled conditions.
• A crystallization process to precipitate sodium bicarbonate.
• Final steps involving the heating of sodium bicarbonate to generate usable sodium carbonate.

This sequence of chemical reactions demonstrates a classic application of chemical engineering principles such as reaction kinetics, equilibrium, and thermodynamics. It provides insights into the design of reactors, heat exchangers, and crystallizers, equipment that plays key roles in the commercial production of chemicals.
By converting simple raw materials into a valuable product like sodium carbonate, the process illustrates the potency of chemical engineering in transforming naturally occurring resources into essential industrial commodities.

Industrial Chemistry

The Solvay process illustrates a pivotal development in industrial chemistry, providing a sustainable and efficient method to mass-produce sodium carbonate. Industrial chemistry involves the large-scale production of chemicals necessary for various applications, from consumer goods to metallurgy.
This process displays classic industrial chemistry strategies such as synthesis, separation, and recycling, all operating at a scale that meets global demand. The continuous cycle of ammonia usage and the recycling of calcium chloride by-products highlight the process's inherent ecological and economical advantage.
Understanding the Solvay process is crucial for students and professionals within industrial chemistry as it presents a model of integrating chemical reactions with environmental consideration. It remains a critical case study in optimizing resource usage and minimizing waste, embodying the principles of green chemistry and sustainability.