Write the preparation of following compounds with balanced chemical equation :
(i) Baking soda
(ii) Bleaching powder
(iii) Plaster of Paris
Generated by claude-sonnet-4-6 · 2026-06-15 06:42 · grounding rag
Model Answer
(i) Baking Soda (NaHCO₃):
Baking soda is prepared by passing excess CO₂ through a saturated solution of sodium chloride (brine) in the presence of ammonia:
$$\text{NaCl} + \text{H}_2\text{O} + \text{CO}_2 + \text{NH}_3 \rightarrow \text{NaHCO}_3 + \text{NH}_4\text{Cl}$$
(ii) Bleaching Powder (CaOCl₂):
Bleaching powder is prepared by passing chlorine gas over dry slaked lime [Ca(OH)₂]:
$$\text{Ca(OH)}_2 + \text{Cl}_2 \rightarrow \text{CaOCl}_2 + \text{H}_2\text{O}$$
(iii) Plaster of Paris (CaSO₄·½H₂O):
Plaster of Paris is prepared by heating gypsum (CaSO₄·2H₂O) at 373 K:
$$\text{CaSO}_4 \cdot 2\text{H}_2\text{O} \xrightarrow{373\text{ K}} \text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O} + \frac{3}{2}\text{H}_2\text{O}$$
Source: Acids, Bases and Salts, Chapter 2
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Explanation
- All three are standard CBSE questions from Chapter 2 (Acids, Bases and Salts). Each preparation must include the correct equation — examiners award marks for the balanced equation specifically.
- For baking soda, name the process (Solvay-type) and mention CO₂ + NH₃ + brine.
- For bleaching powder, remember it is Cl₂ over dry slaked lime.
- For Plaster of Paris, the temperature 373 K (100°C) is important — higher temperature gives anhydrite (dead burnt plaster), so mention it.
- Writing ½H₂O in the formula of Plaster of Paris is acceptable; some write it as CaSO₄·½H₂O.