ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY
Hydrated copper sulphate. Image 3 of 3. Copper sulphate crystals (CuSO4) have a blue colour due to the presence of water of crystallisation within the molecular structure of the crystals. Without this, they are white. Hydrated copper sulphate has the formula CuSO4.5H2O. Heating removes the five water molecules (H2O), leading to the colour being lost. The process is reversible, and addition of water to the anhydrous crystals restores their blue colour. For a sequence showing the addition of water to anhydrous crystals, see images A500/380-382.
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