Common salt (NaCl) is not used as a raw material for preparation of which one of the following compounds?
Plaster of Paris
Understanding Raw Materials for Common Compounds
Let's analyze the raw materials needed to prepare each of the given compounds to determine which one does not use common salt (NaCl) as a raw material.
Preparation of Bleaching Powder (CaOCl₂)
Bleaching powder is prepared by passing chlorine gas over dry slaked lime (calcium hydroxide), Ca(OH)₂.
\(\text{Ca(OH)}_2\text{(s)} + \text{Cl}_2\text{(g)} \rightarrow \text{CaOCl}_2\text{(s)} + \text{H}_2\text{O(l)}\)
Chlorine gas (\(\text{Cl}_2\)) is commonly produced by the electrolysis of brine, which is an aqueous solution of common salt (NaCl).
\(\text{2NaCl(aq)} + \text{2H}_2\text{O(l)} \xrightarrow{\text{electrolysis}} \text{2NaOH(aq)} + \text{Cl}_2\text{(g)} + \text{H}_2\text{(g)}\)
Therefore, common salt (NaCl) is used indirectly as a raw material for the production of chlorine, which is essential for making bleaching powder.
Preparation of Baking Soda (NaHCO₃) and Washing Soda (Na₂CO₃)
Baking soda (sodium bicarbonate) and washing soda (sodium carbonate) are typically produced using the Solvay process (also known as the ammonia-soda process). The main raw materials for this process are:
- Brine (concentrated solution of common salt, NaCl)
- Limestone (calcium carbonate, CaCO₃)
- Ammonia (NH₃)
The overall reactions involve common salt. For example, a key step is:
\(\text{NaCl(aq)} + \text{NH}_3\text{(g)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)} \rightarrow \text{NaHCO}_3\text{(s)} + \text{NH}_4\text{Cl(aq)}\)
This reaction directly uses common salt (NaCl) to produce baking soda (NaHCO₃).
Washing soda (Na₂CO₃) is then obtained by heating baking soda:
\(\text{2NaHCO}_3\text{(s)} \xrightarrow{\text{heat}} \text{Na}_2\text{CO}_3\text{(s)} + \text{H}_2\text{O(g)} + \text{CO}_2\text{(g)}\)
And then recrystallizing the sodium carbonate with water:
\(\text{Na}_2\text{CO}_3\text{(s)} + \text{10H}_2\text{O(l)} \rightarrow \text{Na}_2\text{CO}_3\cdot\text{10H}_2\text{O(s)}\)
Since baking soda production relies on common salt (NaCl), washing soda production also indirectly uses common salt as a raw material.
Preparation of Plaster of Paris (CaSO₄·½H₂O)
Plaster of Paris is prepared by heating gypsum (calcium sulfate dihydrate, CaSO₄·2H₂O) to a temperature of about 373 K (100 °C). Heating gypsum causes it to lose some of its water molecules.
\(\text{CaSO}_4\cdot\text{2H}_2\text{O(s)} \xrightarrow{\text{373 K}} \text{CaSO}_4\cdot\frac{1}{2}\text{H}_2\text{O(s)} + 1\frac{1}{2}\text{H}_2\text{O(g)}\)
Gypsum (\(\text{CaSO}_4\cdot\text{2H}_2\text{O}\)) is a naturally occurring mineral. Its composition is calcium sulfate with two molecules of water of crystallization. Common salt (NaCl) is not involved in the formation of gypsum or in the process of heating gypsum to produce Plaster of Paris.
Summary of Raw Materials
Here's a quick look at the primary raw materials involved in the preparation of these compounds:
| Compound | Key Raw Material(s) | Does it use Common Salt (NaCl)? |
|---|---|---|
| Bleaching Powder | Ca(OH)₂, Cl₂ (from electrolysis of brine) | Yes (indirectly) |
| Baking Soda | NaCl, CaCO₃, NH₃, H₂O, CO₂ | Yes (directly) |
| Plaster of Paris | Gypsum (CaSO₄·2H₂O) | No |
| Washing Soda | NaHCO₃ (derived from NaCl) | Yes (indirectly) |
Conclusion
Based on the analysis of the preparation methods and raw materials, common salt (NaCl) is a necessary raw material (either directly or indirectly) for the production of bleaching powder, baking soda, and washing soda. Plaster of Paris, however, is produced by heating gypsum, which does not require common salt as a raw material.
Therefore, common salt (NaCl) is not used as a raw material for the preparation of Plaster of Paris.
Revision Table: Common Salt Applications
| Compound Prepared | Uses of the Compound |
|---|---|
| Bleaching Powder | Disinfecting drinking water, bleaching cotton and linen, oxidizing agent in chemical industries. |
| Baking Soda | Ingredient in baking (creates CO₂ gas), antacid, in fire extinguishers. |
| Plaster of Paris | Making casts for fractured bones, making statues and decorative items, fireproofing material. |
| Washing Soda | Cleaning agent for domestic purposes, softening hard water, used in glass, soap, and paper industries. |
Additional Information: The Solvay Process
The Solvay process is an important industrial method for producing sodium carbonate (washing soda). It efficiently utilizes readily available and inexpensive raw materials like common salt (NaCl), limestone (CaCO₃), and ammonia (NH₃). The process involves several steps, starting with dissolving ammonia in brine and then reacting this solution with carbon dioxide obtained from heating limestone. This leads to the precipitation of sodium bicarbonate (baking soda), which is then heated to yield sodium carbonate (washing soda). The ammonia is recovered and recycled, making the process relatively economical and environmentally friendly.
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Which one of the following is the chemical formula of Hypobromous acid?
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