Question

Which of the following is correct? (1) Gypsum is \(\mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}\) (2) Anhydrite is \(\mathrm{CaSO}_{4}\) (3) Naturally occurring fine powder of calcium sulphate is known as alabaster (4) All are correct

Short answer

All options (1), (2), and (3) are correct; therefore, option (4) is correct.

Step-by-step solution

Analyze the given options

Read through each option carefully to understand the chemical composition and terminology.

Verify option (1)

Option (1) states that Gypsum is \(\text{CaSO}_{4} \cdot 2 \text{H}_{2}\text{O}\). Gypsum is indeed a hydrated form of calcium sulfate, so this statement is correct.

Verify option (2)

Option (2) states that Anhydrite is \(\text{CaSO}_{4}\). Anhydrite is the anhydrous form of calcium sulfate. This statement is correct.

Verify option (3)

Option (3) states that a naturally occurring fine powder of calcium sulfate is known as alabaster. Alabaster is indeed a fine-grained form of gypsum and calcium sulfate, and thus this statement is correct.

Conclusion

Since all the individual statements (option 1, 2, and 3) are correct, the correct answer is option (4), which states that all are correct.

Key concepts

Gypsum

Gypsum is a widely used mineral composed of calcium sulfate dihydrate, with the chemical formula \(\text{CaSO}_{4} \cdot 2 \text{H}_{2} \text{O}\). It naturally forms in sedimentary conditions and is often found in thick beds associated with sedimentary rocks. One of its key characteristics is its ability to add hydration (water molecules) to its structure, making it softer than other minerals. This property makes gypsum useful in construction, for example, as drywall or plaster. Other common uses include fertilizer and soil conditioner due to its calcium and sulfur content. Gypsum's hydration property also means it can be cast into various shapes and used in making sculptures and molds. It’s always important to recognize its hydrated chemical structure when identifying gypsum.

Anhydrite

Anhydrite is the anhydrous form of calcium sulfate with the chemical formula \( \text{CaSO}_{4} \). It does not contain the water molecules found in gypsum. This gives anhydrite different physical properties. For instance, while gypsum is soft and can be scratched easily, anhydrite is harder and more brittle. Anhydrite typically forms in evaporative environments where oceans and lakes dry up, leaving behind calcium sulfate. Due to its anhydrous nature, anhydrite is used in situations where it’s advantageous not to have moisture, like in certain construction materials and as a drying agent (desiccant). Understanding the absence of water in anhydrite's structure is crucial to distinguishing it from gypsum.

Alabaster

Alabaster refers to a fine-grained form of gypsum. Its smoothness and translucency make it a favored material in sculpture and ornamental carving. Historically, alabaster has been used by various cultures for artistic pieces, ranging from ancient Egyptian artifacts to classical art. Unlike typical gypsum or anhydrite, alabaster is particularly valued for its ability to take a good polish, resulting in a smooth and lustrous surface. This unique quality is due to its fine grain, making it ideal for detailed work. It is important to remember that although alabaster is essentially composed of the same basic material as gypsum, its physical form and aesthetic appeal set it apart.

Chemical Composition Verification

When verifying chemical compositions, it’s crucial to refer to the proper chemical formulas and understand their context. For gypsum, the formula \( \text{CaSO}_{4} \cdot 2 \text{H}_{2}\text{O} \) indicates it includes two water molecules, which affect its physical and chemical properties. In contrast, anhydrite's formula \( \text{CaSO}_{4} \) shows it is devoid of water, changing its usability and where it might be found in nature. Alabaster, despite being gypsum-based, can be identified distinctly due to its texture and appearance. To systematically verify the chemical compositions, one should:

• Cross-check the given chemical formula with known scientific sources.
• Consider the physical context in which the minerals are found or used.
• Note any additional properties, like water content, that can alter the material's behavior and use.

Ensuring accurate verification helps in correctly identifying materials and their best use cases.