Chemistry Labs

Problem 5

Only one product was obtained by the reaction of bromine with an unknown hydrocarbon. Its density was 5.207 times as great as that of the air. Determine the structural formula of the unknown hydrocarbon. Relative atomic masses: Ar(H)=1A_r(\text{H}) = 1; Ar(C)=12A_r(\text{C}) = 12; Ar(Br)=80A_r(\text{Br}) = 80.
Step 1 of 3: Molar mass of the product
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M(RBr)=29×5.207=151 g mol−1M(\text{RBr}) = 29 \times 5.207 = 151\ \text{g mol}^{-1}
Analysis

Air has an effective molar mass of 29 g mol−1^{-1}, so the vapour density ratio gives M=29×5.207=151M = 29 \times 5.207 = 151 g mol−1^{-1} for the brominated product.