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Q113
(NDA-I/2023)
Science & Technology › Basic Science (Physics, Chemistry, Biology)
Official Key
Copper sulphate crystals available in the market are blue coloured crystals. By careful heating, they turn to white colour. Which one of the following is responsible for the blue colour ?
Result
Your answer:
—
·
Correct:
C
Explanation
The blue color of copper sulphate crystals is due to the presence of water of crystallization. The chemical formula for these crystals is CuSO4·5H2O (Hydrated Copper Sulphate), which contains five molecules of water per formula unit.
- Color Mechanism: In the hydrated form, the water molecules act as ligands surrounding the copper (II) ion. This interaction causes d-orbital splitting, allowing the compound to absorb specific wavelengths of light and reflect the blue color.
- Effect of Heating: Upon heating, the water of crystallization is evaporated. This process transforms the hydrated salt into anhydrous copper sulphate (CuSO4), which is a white, amorphous powder.
- Reversibility: The process is reversible; adding water to the white anhydrous powder restores the blue color as the hydration is re-established.
Thus, water is the substance responsible for the blue appearance of the crystals.
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