A Buna-S sample has 3 butadiene units (-[CH2-CH=CH-CH2]-) for every 1 styrene unit (-[CH2-CH(C6H5)]-) in the chain. Taking C = 12, H = 1, the mass percent of styrene in the copolymer is

JEE Advanced levelSingle correct optionDifficulty 3 of 3pl035

A Buna-S sample has 3 butadiene units ( $- [CH X_{2} - CH = CH - CH X_{2}] X^{-}$ ) for every 1 styrene unit ( $- [CH X_{2} - CH (C X_{6} H X_{5})] X^{-}$ ) in the chain. Taking C = 12, H = 1, the mass percent of styrene in the copolymer is

Each unit has the same formula as its monomer: butadiene

C X_{4} H X_{6}

= 54, styrene

C X_{8} H X_{8}

= 104. Mass of styrene

= 104

out of

3 \times 54 + 104 = 266

, giving 39.1 percent. The 25.0 is the mole percent.