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JEE Main 2019 · Chemistry · Biomolecules and Polymers · easy

A nylon-6,6 chain is formed from exactly 50 molecules of adipic acid (M=146) and 50 molecules of hexamethylenediamine (M=116), each chain being…

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A nylon-6,6 chain is formed from exactly 5050 molecules of adipic acid (M=146M=146) and 5050 molecules of hexamethylenediamine (M=116M=116), each chain being linear with one end amine and one end carboxylic acid group. The molar mass of this chain in g mol−1\mathrm{g\,mol^{-1}} is (H2O=18\mathrm{H_2O}=18)
  1. A. 1130011300
  2. B. 1310013100
  3. C. 1131811318
  4. D. 1133611336
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Answer: (C) 1131811318

The 100 monomer units sum to 50×146+50×116=7300+5800=1310050\times146+50\times116 = 7300+5800 = 13100. Joining 100 units into one linear chain forms 100−1=99100-1 = 99 amide links, each releasing one H2O\mathrm{H_2O}: mass lost =99×18=1782= 99\times18 = 1782. So M=13100−1782=11318 g mol−1M = 13100-1782 = 11318\ \mathrm{g\,mol^{-1}}. Subtracting 100 waters (1130011300) would be right only for a cyclic arrangement; 1133611336 adds an extra water.
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