Aluminum hydroxide is used in the dyeing industry as a?

1. Analyze the question

The question asks for the specific industrial application of aluminum hydroxide ($Al(OH)_3$) in the context of the dyeing industry. We need to identify its role in helping dyes adhere to fabrics.

2. Explain the concept

In the dyeing industry, many dyes do not have a natural affinity for certain types of fabrics (like cotton). To make the dye "stick" to the fabric and become wash-fast, a substance called a mordant is used.

A mordant acts as a binding agent. It forms a coordination complex with the dye and the fabric, effectively "locking" the dye molecules onto the fibers. Aluminum hydroxide is a classic example of a metallic hydroxide used for this purpose because it is insoluble and can form stable complexes with both the fabric and the dye.

3. Show the solution

• Dye (Option A): This is the substance that provides the color itself, not the binding agent.
• Dispersant (Option B): This is a substance added to a suspension to improve the separation of particles and prevent settling. While important in some chemical processes, it is not the primary role of aluminum hydroxide in dyeing.
• Salt (Option C): While aluminum hydroxide is a compound, it is not classified as a "salt" in the context of its function in dyeing.
• Mordant (Option D): As explained above, a mordant is a substance used to set dyes on fabrics by forming a coordination compound with the dye. Aluminum hydroxide is widely recognized in chemistry as a mordant.

4. Identify the answer

5. Tip

Think of a mordant as a "chemical glue." If you ever see a question about substances used to fix dyes to fabrics (like alum or aluminum hydroxide), immediately look for the word "mordant."