Generated by claude-sonnet-4-6 · 2026-06-17 12:36 · grounding rag
Model Answer
Plaster of Paris (CaSO₄·½H₂O) should be stored in a moisture-proof container because it readily reacts with water (moisture) present in air and gets converted back into gypsum (CaSO₄·2H₂O). This makes it set and harden prematurely, making it unfit for further use.
Source: Chapter 2 – Acids, Bases and Salts (Plaster of Paris section)
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Explanation
- The examiner expects you to state what happens when POP absorbs moisture (it converts to gypsum/sets hard) and why that is a problem (becomes useless).
- Two clear points = 2 marks: (1) reacts with moisture → forms gypsum, (2) hardens prematurely / cannot be used.
- Note: The source passages provided do not cover this topic — this answer is drawn from the standard NCERT Class 10 Science Chapter 2 content on Plaster of Paris, which is the correct textbook reference for this question.