1. Below 100°C: When heated below 100°C, copper (II) sulphate loses water molecules in a process called dehydration. The hydrate molecules in copper (II) sulphate pentahydrate (CuSO4·5H2O), the most common form, begin to evaporate as water vapor, leading to the formation of the mono- or anhydrous form (CuSO4). This can be seen as the blue crystals start to turn white and become powdery due to the loss of water.
2. Around 200°C: As the temperature is further increased, around 200°C, the anhydrous copper (II) sulphate undergoes decomposition. This process involves the breaking down of the copper-sulphate bonds and the release of various gases. The decomposition products include sulphur dioxide (SO2) gas, sulphur trioxide (SO3) gas, and oxygen (O2) gas.
3. Above 625°C: At temperatures above 625°C, copper (II) sulphate completely decomposes, leaving behind copper oxide (CuO) as a solid residue. Copper oxide is a black powder that can further decompose into copper metal and oxygen gas at very high temperatures.
The chemical reactions that occur during the heating of copper (II) sulphate can be summarized as follows:
CuSO4·5H2O (below 100°C) → CuSO4 + 5H2O (vapor)
CuSO4 (around 200°C) → CuO + SO2 + SO3 + O2
CuO (above 625°C) → Cu + O2
It is essential to note that the exact temperatures at which these reactions occur may vary slightly depending on the specific conditions, such as heating rate, pressure, and the presence of impurities. Heating copper (II) sulphate should be conducted in a well-ventilated area to avoid exposure to harmful gases released during decomposition.
