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Question
Find the empirical formula and the molecular formula of an organic compound from the data given below :
C = 75.92%, H = 6.32% and N = 17.76%
The vapour density of the compound is 39.5.
[C = 12, H = 1, N = 14]
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Solution
| Element | % | |
| C | 75.92 | `75.92/12 = 6.32/1.26 = 5` |
| H | 6.32 | `6.32/1 = 6.32/1.26 = 5` |
| N | 17.76 | `17.76/14 = 1.26/1.26 = 1` |
Empirical formula ; - C5H5N
Molecular weight = 2 × Vapour Density
= 2 × 39.5
= 79
Empirical formula weight = C × 5 + H × 5 + N × 1
= 12 × 5 + 1 × 5 + 14 × 1
= 60 + 5 + 14
= 79
`n = "Molecular weight"/("Empirical" "formula" "weight" )`
∴ Molecular formula = Empirical formula = C5H5N
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