Question

Given below are two statements:
Statement I: Acid dyes are suitable for wool & silk
Statement II: Acid dyes form ionic bonds with the carboxylic groups found in silk & wool
In light of the above statements, choose the correct answer from the options given below:

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is correct but Statement II is false
• D. Statement I is incorrect but Statement II is true

Hint:

Acid Dye Mechanism: Anionic dye sulfonate group ($\text{Dye}-\text{SO}_3^-$) forms ionic salt bond with protonated amino groups ($-\text{NH}_3^+$) of wool/silk in acidic dyebath.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Dye chemistry of anionic acid dyes on amphoteric protein fibers (wool and silk).
Key Formula or Approach:
\[ \text{Dye}-\text{SO}_3^- + ^+\text{H}_3\text{N}-\text{Fibre} \xrightarrow{\text{Acidic pH}} \text{Dye}-\text{SO}_3^-\dots ^+\text{H}_3\text{N}-\text{Fibre} \quad \text{(Salt / Ionic Linkage)} \]

Step 2: Detailed Explanation:
1. Statement I: Acid Dyes (anionic dyes containing sodium sulfonates) are the classic dyes of choice for natural protein animal fibers (wool, silk, and specialty hairs) applied in an acidic dyebath ($pH \approx 3 - 5$). Hence, Statement I is correct.
2. Statement II: In an acidic medium, protein fibers become protonated at their basic amino groups ($-\text{NH}_3^+$). Anionic acid dye molecules form ionic salt linkages with these protonated amino groups ($-\text{NH}_3^+$), not with the negatively charged carboxylic ($-COO^-$) groups. Hence, Statement II is false.

Step 3: Final Answer:
Thus, Statement I is correct but Statement II is false, corresponding to option (C).