The number of water molecules in gypsum, dead burnt plaster and plaster of Paris, respectively are :
Show Hint
Remember the sequence of heating gypsum:
Gypsum (CaSO\(_4\)\(\cdot\)2H\(_2\)O) \(\xrightarrow{\sim 120^\circ\text{C}}\) Plaster of Paris (CaSO\(_4\)\(\cdot\)\(\frac{1}{2}\)H\(_2\)O) \(\xrightarrow{>120^\circ\text{C}}\) Dead Burnt Plaster (CaSO\(_4\)). This helps to recall the number of water molecules in each.
Step 1: Understanding the Question:
We need to state the number of water molecules of crystallization for three related calcium sulfate compounds: gypsum, dead burnt plaster, and plaster of Paris. Step 2: Key Formula or Approach:
This is a factual question that requires knowing the chemical formulas for these common compounds. Step 3: Detailed Explanation:
Let's identify each compound and its formula:
1. Gypsum: This is the naturally occurring, fully hydrated form of calcium sulfate. Its chemical formula is CaSO\(_4\)\(\cdot\)2H\(_2\)O. It contains 2 molecules of water of crystallization.
2. Dead Burnt Plaster: This is formed when gypsum is heated strongly, above 393 K. It loses all of its water of crystallization and becomes anhydrous calcium sulfate. Its formula is CaSO\(_4\). It contains 0 molecules of water. It is called "dead burnt" because it loses the property of setting with water.
3. Plaster of Paris (POP): This is calcium sulfate hemihydrate. It is prepared by carefully heating gypsum to about 393 K (120°C), causing it to lose three-quarters of its water. Its formula is CaSO\(_4\)\(\cdot\)\(\frac{1}{2}\)H\(_2\)O. It contains 0.5 (or \(\frac{1}{2}\)) molecules of water per formula unit of CaSO\(_4\).
The question asks for the number of water molecules in the order: gypsum, dead burnt plaster, and plaster of Paris.
The corresponding numbers are 2, 0, and 0.5. Step 4: Final Answer:
The correct sequence of the number of water molecules is 2, 0, and 0.5. This matches option (D).
