Bleaching powder is produced by passing chlorine gas over dry slaked lime. Would the same reaction work with wet slaked lime or with calcium oxide? Justify your answer and write the balanced chemical equation for the preparation of bleaching powder.
Generated by claude-sonnet-4-6 · 2026-06-26 01:05 · grounding rag
Model Answer
No, the reaction does not work with wet slaked lime or with calcium oxide.
- Wet slaked lime contains moisture, and chlorine reacts with water to form hypochlorous acid and hydrochloric acid instead of forming bleaching powder. The product obtained is not bleaching powder.
- Calcium oxide (quicklime) reacts vigorously with water and heat; it does not react with chlorine in the same way to produce bleaching powder.
Only dry slaked lime [Ca(OH)₂] reacts with chlorine gas to give bleaching powder (calcium oxychloride):
$$\text{Ca(OH)}_2 + \text{Cl}_2 \rightarrow \text{CaOCl}_2 + \text{H}_2\text{O}$$
Source: Chapter 2, Acids, Bases and Salts
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Explanation
- Examiners expect: (1) clear rejection of both alternatives with reasons, (2) the correct balanced equation.
- The key point is that dry Ca(OH)₂ is required — moisture causes side reactions; CaO reacts with water first before it can react with Cl₂ meaningfully to form bleaching powder.
- Write the chemical name of bleaching powder (calcium oxychloride) or its formula (CaOCl₂) for full marks.
- The balanced equation shown is the standard one expected in board exams.