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Question
A gaseous hydrocarbon contains 82.76% of carbon. Given that its vapor density is 29, find its molecular formula. [C = 12, H = 11]
Solution
Vapour density = 29
| Element | Percentage | At. mass | Gram atom | Ration | |
| Carbon | 82.76 | 12 | 82.76/12 = 6.9 | 6.9/6.9 = 1 | 2 |
| Hydrogen | 17.24 | 1 | 17.24/1 = 17.24 | 17.24/6.9 = 2.5 | 5 |
Empirical formula is C2H5
Molecular weight = 2 × Vapour density
Molecular weight = n × (Empirical formula weight)
58 = n × (12 × 2 + 1 × 5)
n = 2
So, molecular formula = C4H10
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