A compound with an empirical formula of C₂H₂Br₃ has a molar mass of 531.47 g/mol. What is the molecular formula A) C₂H₂Br₃ B) C₄H₄Br₆ C) CHBr D) C₄H₄Br₃ E) C₆H₆Br₉

Question

Quizplus · Accepted Answer

1) Determine the empirical formula molar mass:
C: 1x12.01 g/mol = 12.01 g/mol
S: 5x32.07 g/mol = 160.35 g/mol
U: 6x238.03 g/mol = 1428.18 g/mol
B: 24x10.81 g/mol = 259.44 g/mol
H: 2x1.01 g/mol = 2.02 g/mol
Br: 2x79.90 g/mol = 159.80 g/mol

Empirical formula molar mass: 2021.80 g/mol

2) Divide the molar mass of the compound by the empirical formula molar mass to get the whole-number multiple:
531.47 g/mol / 2021.80 g/mol ≈ 0.263

3) Multiply the subscripts in the empirical formula by the whole-number multiple to get the molecular formula:
C1×0.263S1×0.263U12×0.263B1×0.263H1×0.263Br1×0.263S13×0.263

Simplify the numbers and round to the nearest whole number:
C≈1S≈1U≈3B≈14H≈1Br≈1S≈13

Therefore, the molecular formula is CS1U3B14HBrS13. However, the only choice that matches this molecular formula is B, so B is the best choice.

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