All questions of Water for JAMB Exam

Efflorescence:
Efflorescence is a phenomenon that involves the loss of water of crystallization by a substance, resulting in the formation of a powdery deposit. This typically occurs when a hydrated salt is exposed to air and begins to lose its water molecules.

Causes:
- Hydrated salts contain water molecules within their crystal structure. When these salts are exposed to air, especially in dry conditions, the water molecules can evaporate, leaving behind a powdery residue.

Example:
- An example of efflorescence is the white powdery deposit that can form on the surface of concrete or brick walls. This occurs when the salts in the building materials react with moisture and lose their water content, leading to the formation of efflorescence.

Prevention:
- Efflorescence can be prevented by using proper construction materials, minimizing the exposure of materials to moisture, and ensuring proper ventilation to prevent the buildup of trapped moisture.
In conclusion, efflorescence is the phenomenon where a substance loses its water of crystallization, resulting in the formation of a powdery deposit. Understanding the causes and prevention methods can help in managing and preventing efflorescence in various materials.

Water of crystallization in compounds

Water of crystallization refers to water molecules that are bound within the crystal structure of certain compounds. These water molecules are often incorporated into the crystal lattice and are present in a specific ratio to the other components of the compound. The presence of water of crystallization can significantly affect the physical and chemical properties of the compound.

Identifying the compound

In this question, we are asked to identify the compound that exhibits water of crystallization. Let's analyze each option to determine which one fits the criteria.

a) Sodium carbonate (washing soda): Sodium carbonate does not exhibit water of crystallization. It exists as an anhydrous compound, meaning it does not contain water molecules within its crystal structure.

b) Calcium sulfate (gypsum): Calcium sulfate is the correct answer. It exhibits water of crystallization and forms crystals with a specific number of water molecules. The most common form of calcium sulfate with water of crystallization is gypsum, which has the chemical formula CaSO4·2H2O. In this compound, two water molecules are bound to each calcium sulfate molecule.

c) Iron(III) chloride (ferric chloride): Iron(III) chloride does not exhibit water of crystallization. It exists as an anhydrous compound or can form hydrates with a variable number of water molecules.

d) Potassium permanganate: Potassium permanganate does not exhibit water of crystallization. It exists as an anhydrous compound, meaning it does not contain water molecules within its crystal structure.

Conclusion

Among the given options, calcium sulfate (gypsum) is the compound that exhibits water of crystallization, forming crystals with a specific number of water molecules within its structure. This compound is commonly used in construction materials and as a fertilizer.