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Activity 2.9 — Water of Crystallization
NCERT Activity 2.9: Heat blue copper sulphate crystals (CuSO₄·5H₂O). They turn white as water of crystallisation is driven off. Add water back — they turn blue again. The reaction is reversible.
How To Perform
1
Add CuSO₄·5H₂O Crystals
Blue crystals in a dry boiling tube.
2
Heat Gently
Water of crystallisation is driven off as steam.
3
Observe
Blue → white (anhydrous CuSO₄); water droplets on cooler walls.
4
Add Water Back
White powder → blue again (rehydration).
5
Conclude
CuSO₄·5H₂O ⇌ CuSO₄ + 5H₂O — reversible decomposition.
⚠️ Safety Notes
- •Hold the tube at an angle and point the mouth AWAY from your face.
- •Heat GENTLY — strong heating can decompose the salt further (CuSO₄ → CuO + SO₃).
- •Copper salts are toxic — wash hands after handling.