Why does the treatment of cotton fabrics with dilute acids weaken the materials?

1. Analyze the question The question asks why dilute acids weaken cotton fabric. Cotton is almost pure cellulose, so we need to think about what acid does to cellulose.

2. Explain the concept Cellulose is a natural polymer (polysaccharide) made of many glucose units joined by glycosidic (β-1,4) linkages. Its strength comes from these long chains and the hydrogen bonding between them.

Dilute acids catalyse hydrolysis of the glycosidic linkages:

(C₆H₁₀O₅)ₙ + H₂O → shorter chains (and eventually glucose, C₆H₁₂O₆)

Under mild conditions (dilute acid, short contact time), hydrolysis is only partial. Some glycosidic bonds break, so the chains become shorter, but the fabric is not fully converted to glucose.

3. Solution, option by option

• A. Complete hydrolysis to glucose needs strong acid, heat and a long time. Dilute acid does not do this to a fabric. Wrong.
• B. Cellulose is insoluble in dilute acids. Wrong.
• C. Some glycosidic links are broken, so the chains are shorter and the fibre loses strength. The fabric is weakened but still present. Correct.
• D. Hydrolysis shortens chains; it does not lengthen them. Wrong.
• E. The threads are made of cellulose itself, and they are not completely destroyed. Wrong.

4. Answer C. The molecular chains are partially broken.

5. Exam tip Remember: acid + polymer (cellulose, starch, protein) → hydrolysis → shorter chains. For "weakens" think partial breakdown. For "completely converts" think strong, prolonged conditions. Words like "completely" in options are often a clue that the option is wrong.