Question

To the fiber add 85% formic acid at room temperature. Then the fiber dissolves. Identify the fiber.

• A. Acrylic
• B. Wool
• C. Silk
• D. Polyester

Hint:

Fiber identification often uses solubility: Silk → formic acid, Acrylic → DMF, Polyester → phenol, Wool → alkali.

Answer 1

The Correct Option is C

Step 1: Understanding fiber solubility tests.
Different fibers dissolve in specific solvents, and these chemical solubility tests are used to identify fiber types in textile laboratories.
Step 2: Reaction of silk.
Silk is a natural protein fiber made of fibroin. It is known to dissolve in concentrated formic acid (85%) at room temperature. This property is used as a quick identification method.
Step 3: Why not the others?
- Acrylic: Dissolves in dimethylformamide (DMF), not formic acid.
- Wool: Another protein fiber but resists formic acid; instead dissolves in chlorine bleach or strong alkali.
- Polyester: A synthetic thermoplastic fiber, insoluble in formic acid; dissolves in phenol or hot chlorinated solvents.
Step 4: Conclusion.
Thus, the fiber dissolving in 85% formic acid at room temperature is Silk.