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Difficulty: HardSynthetic Polymers, Carbohydrates, Amino Acids, and Proteins

Four organic substances—starch, nylon-6,6, polyethene, and natural rubber—were analyzed to compare their chemical structures, reaction behaviors, and environmental properties. Which of the following statements provides a correct scientific comparison among these materials?

  1. Starch consists of monomeric glucose units joined by glycosidic linkages that undergo acid hydrolysis, whereas nylon-6,6 contains recurring amide linkages formed via condensation polymerization.Answer
  2. B
    Polyethene is a synthetic addition polymer that undergoes rapid microbial degradation in soil in a manner similar to starch.
  3. C
    The charring of starch when exposed to concentrated H2SO4\text{H}_2\text{SO}_4 occurs via a reversible acid-base neutralization reaction rather than chemical dehydration.
  4. D
    Natural rubber is an addition polymer whose double bonds react with ammoniacal silver nitrate solution to form a characteristic silver precipitate.

Answer

Starch consists of monomeric glucose units joined by glycosidic linkages that undergo acid hydrolysis, whereas nylon-6,6 contains recurring amide linkages formed via condensation polymerization.
Starch is a carbohydrate (polysaccharide) composed of glucose units connected by glycosidic bonds that can be broken down by acid hydrolysis. Nylon-6,6 is a synthetic condensation polymer (polyamide) made from a dicarboxylic acid and a diamine, containing amide linkages.

Step-by-Step Solution

1
Analyze the structural classification and linkages of starch and nylon-6,6.
Starch is a naturally occurring polysaccharide composed of glucose monomer units linked via α\alpha-glycosidic bonds. Nylon-6,6 is a synthetic polyamide composed of hexanedioic acid and hexane-1,6-diamine monomers joined by amide (−CO−NH−-\text{CO}-\text{NH}-) linkages with the elimination of water.
Identifying monomer units and linkage types distinguishes condensation polymers and carbohydrates.
2
Evaluate the biodegradability of synthetic addition polymers like polyethene versus natural polymers like starch.
Starch is readily degraded by enzymatic action and micro-organisms. Polyethene is a synthetic addition polymer containing strong C−C\text{C}-\text{C} single bonds that resist microbial enzymatic attack, rendering it non-biodegradable.
Synthetic addition polymers lack functional linkages susceptible to hydrolysis.
3
Assess the chemical action of concentrated H2SO4\text{H}_2\text{SO}_4 on carbohydrates.
Concentrated H2SO4\text{H}_2\text{SO}_4 acts as a dehydrating agent, removing water elements from starch according to (C6H10O5)n→conc. H2SO46nC+5nH2O(\text{C}_6\text{H}_{10}\text{O}_5)_n \xrightarrow{\text{conc. H}_2\text{SO}_4} 6n\text{C} + 5n\text{H}_2\text{O}, turning the sample black.
This is a dehydration reaction, not an acid-base neutralization.
4
Analyze the chemical test reagents for unsaturation in rubber versus terminal alkynes.
Bromine water or acidified KMnO4\text{KMnO}_4 is used to test for unsaturation in alkenes and dienes like natural rubber. Ammoniacal silver nitrate selectively reacts with terminal alkynes to give a silver acetylide precipitate.
Different unsaturated functional groups require specific chemical reagents for qualitative identification.

Key Concept

Classification of polymers and biomolecules by linkage type (glycosidic vs amide), reaction mode (addition vs condensation), and chemical reactivity.
Estimated Time:2m 0s
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Topics

Synthetic Polymers, Carbohydrates, Amino Acids, and Proteins

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