What is the significance of water of crystallisation in salts?

Water of crystallisation in salts is significant as it contributes to the formation, stability, and physical properties of the crystal structure.

Water of crystallisation refers to the water molecules that are chemically bonded into a crystal structure of a salt. These water molecules are not just physically trapped in the crystal lattice, but are an integral part of the crystal structure. They play a crucial role in the formation and stability of the crystal. Without these water molecules, the crystal structure would not form or would be significantly different.

The number of water molecules incorporated into the crystal structure varies depending on the type of salt. For instance, copper sulphate crystals (CuSO4.5H2O) contain five water molecules for each unit of copper sulphate, while magnesium sulphate crystals (MgSO4.7H2O) contain seven water molecules for each unit of magnesium sulphate. This is indicated by the dot and the number following it in the chemical formula of the salt.

The water of crystallisation also significantly affects the physical properties of the salt, including its colour, shape, and density. For example, hydrated copper sulphate crystals are bright blue due to the presence of water of crystallisation. If the water is removed by heating, the crystals turn into a white powder, which is anhydrous copper sulphate.

Furthermore, the water of crystallisation is important in chemical reactions involving salts. The water molecules can participate in the reaction, affecting the overall reaction process and the products formed. Therefore, understanding the role and significance of water of crystallisation is crucial in the study of salts and their reactions in chemistry.