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What happens to the water of crystallisation if the compound is heated to a high temperature?

  1. It forms a stronger bond with the crystal.

  2. It evaporates, leading to changes in the crystal structure.

  3. It remains unchanged within the structure.

  4. It increases the compound's reactivity.

The correct answer is: It evaporates, leading to changes in the crystal structure.

When a compound with water of crystallisation is heated to a high temperature, the water molecules that are integral to the crystal lattice can gain enough energy to break their bonds and escape as vapor. This process results in the evaporation of the water, which leads to significant alterations in the crystal structure of the compound. The removal of water can cause the crystal to collapse or transform into a different phase, which often has different physical and chemical properties compared to the hydrated form. This is an essential concept in understanding hydration states and the behavior of compounds under thermal conditions.