Chemistry
A hydrocarbon contains 82.8% of carbon. Find it's molecular formula if it's vapour density is 29 [H = 1, C = 12]
Stoichiometry
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Answer
| Element | % composition | At. wt. | Relative no. of atoms | Simplest ratio |
|---|---|---|---|---|
| Carbon | 82.8 | 12 | = 6.9 | = 1 |
| Hydrogen | 100 - 82.8 = 17.2 | 1 | = 17.2 | = 2.5 |
C : H = 1 : 2.5 = 1 : = 2 : 5
Simplest ratio of whole numbers = 2 : 5
Hence, empirical formula is C2H5
Empirical formula weight = 2(12) + 5(1) = 24 + 5 = 29
Vapour density (V.D.) = 29
Molecular weight = 2 x V.D. = 2 x 29 = 58
Molecular formula = n[E.F.] = 2[C2H5] = C4H10
Hence, Molecular formula = C4H10
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