Question

Which one of the following is dead burnt plaster? (a) Anhydrous \(\mathrm{CaSO}_{4}\) (b) \(\mathrm{CaSO}_{3}\) (c) \(\left(\mathrm{CaSO}_{4}\right)_{2} \cdot \mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}\)

Short answer

The dead burnt plaster is anhydrous \(\mathrm{CaSO}_{4}\) (Option a).

Step-by-step solution

Understand the Terms

Dead burnt plaster refers to **anhydrous plaster of Paris** commonly known as calcium sulfate that has been heated to a high temperature (above 200°C) to remove water content completely, forming anhydrous calcium sulfate.

Analyze Option A

Option (a) 'Anhydrous \(\mathrm{CaSO}_{4}\)' is calcium sulfate that has no water molecules attached, making it anhydrous. This matches the definition of dead burnt plaster.

Analyze Option B

Option (b) \(\mathrm{CaSO}_{3}\) refers to calcium sulfite, which is not related to plaster materials and therefore cannot be considered dead burnt plaster.

Analyze Option C

Option (c) '\((\mathrm{CaSO}_{4})_{2} \cdot \mathrm{H}_{2} \mathrm{O}\)' does not exist in common chemical forms particularly relevant to plaster industry. Therefore, not a candidate for dead burnt plaster.

Analyze Option D

Option (d) '\(\mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}\)' contains water molecules as part of its structure, making it the dihydrate form known as gypsum, which is not anhydrous.

Classify the Options

After analysis, only option (a) matches the anhydrous requirement for dead burnt plaster, confirming it as the correct choice.

Key concepts

Dead burnt plaster

Dead burnt plaster is a term used to describe anhydrous calcium sulfate, also known as anhydrous plaster of Paris. This material is created by heating gypsum, which is calcium sulfate dihydrate (\(\text{CaSO}_4 \, \cdot \, 2 \text{H}_2\text{O}\)) to temperatures above 200°C. This heating process removes the water content from gypsum, resulting in a form that is entirely devoid of water molecules, thus becoming "dead burnt".

• Dead burnt plaster is valued for its anhydrous nature, meaning it does not react with water or set until mixed with water again.
• This makes it a key component in construction and plastering due to its predictable setting behavior when rehydrated.

Understanding dead burnt plaster is crucial when studying how materials are processed in the plaster industry and the chemical transformations that occur during these processes.

Anhydrous compounds

Anhydrous compounds, such as anhydrous calcium sulfate (\(\text{CaSO}_4\)), are substances that possess no water molecules in their structure. These compounds play a vital role in the chemical industry, particularly in reactions where water could interfere or alter the desired outcome.

• Anhydrous calcium sulfate is essential in producing dead burnt plaster, showing how the absence of water transforms gypsum into something new.
• In institutions focusing on chemical education, understanding anhydrous compounds helps students grasp the significance of hydration and dehydration processes.

The uniformity and stability of anhydrous compounds make them ideal for applications where precise chemical compositions are required.

Plaster industry

The plaster industry relies heavily on the production of both hydrated and anhydrous forms of calcium sulfate. Plaster of Paris is widespread in construction, art, and orthopedics due to its ability to harden quickly when mixed with water.

• Plaster from gypsum creates surfaces that are smooth and easy to paint.
• The industry utilizes the dead burnt plaster for applications requiring stability, as it does not set until water is introduced.

Understanding how dead burnt plaster integrates into the larger framework of the plaster industry can help students appreciate the material's versatility and economic importance.

Chemical analysis in education

Chemical analysis in education equips students with the knowledge and skills to understand concepts like dead burnt plaster and anhydrous compounds.

• Lab experiments focusing on heating and dehydration reactions help students see the transition from gypsum to dead burnt plaster effectively.
• Such practical experiences solidify theoretical knowledge, making students better equipped to relate chemistry to real-world applications.

By engaging in chemical analysis, students get to witness firsthand how scientific principles apply beyond textbooks, fostering a deeper understanding of chemical processes.