Problem 11 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is a basic dye? (a) alizarin (b) indigo (c) aniline yellow (d) congo red

Step-by-Step Solution

Answer

Aniline Yellow (c) is a basic dye.

Step 1: Understanding Dye Types

There are three main types of dyes: basic, acid, and direct. Basic dyes are cationic and are used mainly for coloring acrylic fibers, while acid dyes are anionic and used for wool and silk. Direct dyes simply dye cotton directly without the aid of additional chemicals.

Step 2: Analyze the Options

Look at each option: (a) Alizarin is an acid dye often used for wool; (b) Indigo is a natural dye used for denim; (c) Aniline Yellow is known as a basic dye for acrylic fibers; (d) Congo Red is an azo dye used as a pH indicator, not typically basic.

Step 3: Identifying the Basic Dye

From the analysis, option (c) Aniline Yellow is identified as a basic dye. It is used for dyeing acrylic fibers because of its positive charge, making it the correct answer.

Step 4: Conclusion

Based on our analysis and knowledge of dyes, "Aniline Yellow" fits the description of a basic dye. Therefore, option (c) is the correct choice.

Key Concepts

Cationic Dyes

Cationic dyes are fascinating substances primarily characterized by their positively charged ions. This positive charge allows them to bind effectively with negatively charged groups in fibers, making them quite useful in the textile industry.

• **Use in Textiles:** Cationic dyes are extensively used for dyeing materials like acrylic fibers. Their ability to form strong ionic bonds with these fibers results in vibrant and colorfast hues.
• **Types and Variations:** These dyes often include various categories of synthetic dyes, and the term "basic dye" is commonly used interchangeably with cationic dye, due to their basic nature confirmed by their chemical structure.

To sum up, the unique properties of cationic dyes make them vital for creating bold and long-lasting colors on fabric surfaces.

Aniline Yellow

Aniline Yellow is a classic example of a basic dye and serves as an excellent representative of cationic dyes. This dye is particularly known for its application in coloring acrylic fibers, where its positive charge is a beneficial trait.

• **Chemical Properties:** It's derived from aniline, a simple aromatic amine, which contributes to its vivid yellow color. The molecular structure of aniline enables it to accept protons, thus exhibiting cationic behavior.
• **Application in Industry:** Beyond acrylic fibers, Aniline Yellow is occasionally used in tinting other materials, though its primary use remains in textile applications.

In essence, Aniline Yellow stands out as a basic dye due to its chemical properties and industrial applications, showcasing the effective use of cationic dyes in everyday products.

Dye Types

Dyes are classified into various types based on their chemical properties and uses. This classification helps industries choose the most suitable dyes for specific applications.

• **Basic Dyes:** These are cationic and are used for fibers like acrylic. They bond through ionic interactions and are known for their brightness and intensity.
• **Acid Dyes:** Unlike basic dyes, acid dyes are anionic and work well with proteins like wool and silk. They require an acidic environment for effective binding.
• **Direct Dyes:** These dyes are designed to dye materials such as cotton directly. They do not need auxiliary substances and are usually applied in a neutral environment.

Understanding these dye types allows for better decisions in dye selection and application, catering to specific needs of the textile and related industries.