Question

In Solvay's process, the products that are recycled arc (1) ${\mathrm{CO}}_2,{\mathrm{NH}}_4\mathrm{Cl}$ (2) $\mathrm{NaCl},\mathrm{CaO}$ (3) ${\mathrm{CO}}_2,{\mathrm{NH}}_3$ (4) ${\mathrm{CaCl}}_2,\mathrm{CaO}$

Short answer

The recycled products in the Solvay process are ${\mathrm{CO}}_2,{\mathrm{NH}}_3$ (Option 3).

Step-by-step solution

- Understand the Solvay Process

The Solvay process is an industrial method used to produce sodium carbonate (Na2CO3) from sodium chloride (NaCl) and limestone (CaCO3). Key intermediate compounds in this process are ammonia (NH3) and carbon dioxide (CO2). These intermediates are recycled within the process for efficiency and cost-effectiveness.

- Identify Recycled Compounds

In the Solvay process, ammonia (NH3) and carbon dioxide (CO2) are critical intermediates. They are recycled back into the process after being used, to continuously react with sodium chloride and produce sodium carbonate.

- Eliminate Incorrect Options

Option 1 lists ${\mathrm{CO}}_2,{\mathrm{NH}}_4\mathrm{Cl}$, but ammonium chloride (NH4Cl) is a by-product, not recycled. Option 2 lists $\mathrm{NaCl},\mathrm{CaO}$, but calcium oxide (CaO) and sodium chloride (NaCl) are not recycled like NH3 and CO2. Option 4 lists ${\mathrm{CaCl}}_2,\mathrm{CaO}$, both of which are either discarded or utilized differently.

- Confirm Correct Answer

Option 3 lists ${\mathrm{CO}}_2,{\mathrm{NH}}_3$. Both carbon dioxide and ammonia are recycled in the Solvay process, making this the correct choice.

Key concepts

Industrial Method

The Solvay process is a highly efficient industrial method used for producing sodium carbonate (Na2CO3). This compound is commonly known as soda ash and is widely used in manufacturing glass, detergents, and other products. Developed in the 1860s by Ernest Solvay, this method revolutionized chemical production due to its cost-effectiveness and the ability to recycle key intermediates. The Solvay process primarily involves several chemical reactions that convert sodium chloride (NaCl) and limestone (CaCO3) into sodium carbonate using ammonia (NH3) and carbon dioxide (CO2). The recycling of intermediates within the process itself makes it a standout industrial process.

Sodium Carbonate Production

Producing sodium carbonate via the Solvay process involves several steps. Initially, sodium chloride (NaCl) is mixed with ammonia (NH3) and water (H2O). This mixture then reacts with carbon dioxide (CO2) gas to form ammonium bicarbonate (NH4HCO3) and sodium bicarbonate (NaHCO3). The reaction can be represented as:
$$\text{NaCl}+{\text{NH}}_3+{\text{CO}}_2+{\text{H}}_2\text{O}\to {\text{NaHCO}}_3+{\text{NH}}_4\text{Cl}$$
Next, the precipitated sodium bicarbonate is heated to release carbon dioxide and water, leaving behind sodium carbonate:
$$2{\text{NaHCO}}_3\to {\text{Na}}_2{\text{CO}}_3+{\text{H}}_2\text{O}+{\text{CO}}_2$$
The released CO2 is then recycled back into the process, making it efficient and cost-effective. The final product, sodium carbonate, is collected and used in various industrial applications.

Recycling Intermediates

One of the most crucial aspects of the Solvay process is the recycling of intermediates, specifically ammonia (NH3) and carbon dioxide (CO2). These compounds are involved at various stages of the process and are continuously cycled back into the system to minimize waste and cost. After reacting with NaCl and CO2, ammonia is released as a byproduct with ammonium chloride (NH4Cl). The ammonium chloride is then treated with calcium hydroxide (Ca(OH)2) to regenerate ammonia and produce calcium chloride (CaCl2):
$${\text{2 NH}}_4\text{Cl}+{\text{Ca(OH)}}_2\to {\text{CaCl}}_2+{\text{2 NH}}_3+{\text{2 H}}_2\text{O}$$
The regenerated ammonia is recycled back into the initial stages of the process to react again with sodium chloride and water. Similarly, the carbon dioxide released during the heating of sodium bicarbonate is fed back into the process. This closed-loop recycling significantly enhances the efficiency and environmental friendliness of the Solvay process.

Chemical Reactions

The Solvay process involves several key chemical reactions, each crucial for the successful production of sodium carbonate. The process starts with the absorption of carbon dioxide (CO2) into an ammoniated brine solution, forming ammonium bicarbonate (NH4HCO3) and sodium bicarbonate (NaHCO3):
$${\text{NH}}_3+{\text{H}}_2\text{O}+{\text{CO}}_2\to {\text{NH}}_4{\text{HCO}}_3$$ $$\text{NaCl}+{\text{NH}}_4{\text{HCO}}_3\to {\text{NaHCO}}_3+{\text{NH}}_4\text{Cl}$$
Sodium bicarbonate (NaHCO3) precipitates out and is then separated and heated to form sodium carbonate (Na2CO3), releasing CO2 and water:
$$2{\text{NaHCO}}_3\to {\text{Na}}_2{\text{CO}}_3+{\text{CO}}_2+{\text{H}}_2\text{O}$$
The carbon dioxide (CO2) produced is captured and recycled back into the initial stages of the process. Another significant reaction is the treatment of ammonium chloride with calcium hydroxide:
$${\text{2 NH}}_4\text{Cl}+{\text{Ca(OH)}}_2\to {\text{CaCl}}_2+{\text{2 NH}}_3+{\text{2 H}}_2\text{O}$$
This regenerates ammonia (NH3), which is also fed back into the process, thus closing the loop. These reactions highlight the process's efficiency and the importance of recycling intermediates.