On heating gypsum at what temperature does it lose water molecules and become calcium sulfate hemihydrate?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 373 K
At approximately 373 K (100°C), gypsum undergoes dehydration, losing water molecules to form calcium sulfate hemihydrate, commonly known as plaster of Paris. This temperature range is critical as it drives off the water of crystallization from gypsum, leaving behind a solid that can rehydrate to form a hardened material useful in various applications such as construction, art, and medicine. The process involves a chemical change where gypsum's structure transforms from hydrated calcium sulfate to the semi-hydrated form.