The molecular formula of gypsum is

• (A). CaSO₄·H₂O
• (B). CaSO₄·2H₂O
• (C). 2CaSO₄·H₂O
• (D). CaSO₄·3H₂O

To determine the correct molecular formula of gypsum, let's break down the options provided. Gypsum is a naturally occurring mineral composed primarily of calcium sulfate and water. The key to identifying the right formula lies in understanding its composition.

Understanding Gypsum's Composition

Gypsum is chemically known as calcium sulfate dihydrate. This means that for every molecule of calcium sulfate (CaSO₄), there are two molecules of water (H₂O) associated with it. This dihydrate form is what makes gypsum unique and is crucial for its properties and uses.

Analyzing the Options

• (A) CaSO₄·H₂O: This formula represents calcium sulfate monohydrate, which is not gypsum.
• (B) CaSO₄·2H₂O: This is indeed the correct formula for gypsum, indicating that there are two water molecules for each calcium sulfate unit.
• (C) 2CaSO₄·H₂O: This suggests two calcium sulfate units with only one water molecule, which does not reflect gypsum's structure.
• (D) CaSO₄·3H₂O: This formula indicates a higher water content than gypsum actually has.

Conclusion on the Correct Answer

Given this analysis, the correct molecular formula for gypsum is (B) CaSO₄·2H₂O. This formula highlights the essential relationship between calcium sulfate and water in the mineral's structure, which is vital for its applications in construction, agriculture, and various industrial processes.

Real-World Applications

Gypsum is widely used in the construction industry, particularly in the production of drywall and plaster. Its ability to retain moisture makes it an excellent material for improving indoor air quality and regulating humidity levels. Understanding its chemical composition helps in appreciating its role in these applications.