Aluminium hydroxide is used in the dyeing industry as a

Analysis

The question asks for the specific function of aluminium hydroxide in the dyeing industry. To answer this, we need to understand how dyes interact with fabrics and the role of chemical additives in that process.

Concept Explanation

In the dyeing industry, some dyes do not have a natural affinity for certain types of fabrics (like cotton). If you simply dip the fabric in the dye, the color will wash out easily. To solve this, a substance called a mordant is used.

A mordant is a chemical substance that acts as a "bridge" or a fixing agent. It binds to both the fabric and the dye molecule, forming an insoluble complex (often called a "lake") within the fabric fibers. This ensures that the color becomes permanent and resistant to washing. Aluminium hydroxide is a classic example of a metallic hydroxide used for this purpose.

Step-by-Step Solution

1. Identify the role of the substance: Aluminium hydroxide is a gelatinous precipitate. When applied to fabric, it adheres to the fibers.
2. Examine the interaction: When the dye is added, the aluminium hydroxide reacts with the dye to form an insoluble compound that stays trapped in the fabric.
3. Match with terminology: The specific term for a substance that fixes a dye to a fabric is a mordant.
4. Evaluate the options: • A (Dye): Incorrect. Aluminium hydroxide provides the base for the color, but it is not the dye itself. • B (Dispersant): Incorrect. A dispersant is used to keep particles suspended in a liquid, not to fix color to fabric. • C (Salt): Incorrect. While aluminium compounds can be salts, "salt" is a broad chemical classification and does not describe its functional role in dyeing. • D (Mordant): Correct. This is the technical term for a dye-fixing agent.

Conclusion

Aluminium hydroxide is specifically utilized in the dyeing industry to fix dyes onto fabrics, making it a mordant.

Exam Tip: Remember the "M" in Mordant stands for "Make it stick." Whenever you see questions about fixing dyes to fabrics in Chemistry, think of mordants like aluminium hydroxide or alum.