A polystyrene, having formula Br3,C6H3,(C3H8)n was prepared by heating styrene with tribromobenzoyl
peroxide in the absence of air. If it was found to contain 10.46% bromine by weight, the value of n is
(A) 19
(B) 45
(C) 38
(D) 56
Answers
Answer:
b) 45
Explanation:
Constituency of bromine = 10.46%
Let the weight of polystyrene prepared = 100 g
Thus, the number of moles of Br in 100g of ploystyrene
= 10.46 / 79.9
= 0.1309
Formula of polystyrene - Br3,C6H3 - from the formula of polystyrene -
Number of moles of Br = 3 × number of moles of Br3C6H3(C8H8)n
= 0.1309 = 3 × Wt / molar weight
= 0.1309 = 3 × 100 / (314.7 + 44n)
= 0.1309 × ( 314.7 + 44n ) = 300
= 2291.825 = (314.7 + 44n)
= 44n = 2291.825 - 314.7
n = 1977.1/44
n = 44.93
n = 45 (approx)
Therefore value of n is 45.
100g polystyrene contains 10.46g Br
240g Br(1mole polystyrene )
By unitary method wecan find Molar mass of polystyrene
(100*240)/10.46=2294.45
MM=2294.45
MM-Mass of each component = 0
2294.45-(240+72+3+104n)=0
So n=19.03