Nylon 6,6 has the repeat unit $- [NH (CH X_{2}) X_{6} NHCO (CH X_{2}) X_{4} CO] X^{-}$ (formula $C X_{12} H X_{22} N X_{2} O X_{2}$ , C 12, H 1, N 14, O 16). A chain of molar mass $22600 g mo l^{- 1}$ (end groups ignored) contains approximately how many amide linkages?

Answer: D

Repeat-unit mass

= 12 (12) + 22 + 2 (14) + 2 (16) = 226

. Number of repeat units

= 22600/226 = 100

. Each repeat unit has two amide bonds, so

200

in all.