What happens when Gypsum () is heated strictly above (e.g., at )? — s Block Elements Chemistry Question

💡 Solution & Explanation

When heated at exactly $393\text{ K}$ ($120^\circ\text{C}$), gypsum loses partial water to form Plaster of Paris ($CaSO_4 \cdot 0.5 H_2O$). However, if heated *above* $393\text{ K}$ (e.g., $200^\circ\text{C}$), it loses all water of crystallization to form anhydrous calcium sulphate ($CaSO_4$), which is called dead burnt plaster because it loses the property of setting with water.