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 ?
[amp_mcq option1=”Oxygen” option2=”Nitrogen” option3=”Water” option4=”Hydrogen” correct=”option3″]
This question was previously asked in
UPSC NDA-1 – 2023
Copper sulphate crystals available in the market are typically copper(II) sulphate pentahydrate (CuSO₄·5H₂O). The blue colour is due to the presence of water molecules coordinated to the copper ions in the crystal lattice. When heated, these crystals lose the water of crystallization, turning into anhydrous copper(II) sulphate (CuSO₄), which is white or off-white. The colour change is a classic demonstration of the role of water of crystallization.
The blue colour of hydrated copper sulphate is caused by the presence of water molecules bound within the crystal structure.