JEE Main 2017 · Chemistry · Biomolecules and Polymers · medium

A polyamide chain is formed from 50 molecules of hexane-1,6-diamine (M=116) and 50 molecules of hexanedioic acid (M=146), the chain having an amino…

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A polyamide chain is formed from

50

molecules of hexane-1,6-diamine (

M=116

) and

50

molecules of hexanedioic acid (

M=146

), the chain having an amino group at one end and a carboxyl group at the other. The number of amide linkages in the chain and the molar mass of the chain (taking water

=18

) are respectively

A. $99$ and $13100$
B. $99$ and $11318$
C. $100$ and $11318$
D. $100$ and $13100$

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Answer: (B) $99$ and $11318$

Joining

100

monomer units into one linear chain forms

100-1=99

amide bonds, each releasing one

\mathrm{H_2O}

. Mass

=50(116)+50(146)-99(18)=5800+7300-1782=11318

. The ends are

\mathrm{NH_2}

and

\mathrm{COOH}

, consistent with equal numbers of the two monomers.

100

linkages would apply to a ring (cyclic polymer), and

13100

ignores the water lost.

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