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A hydrocarbon is burnt completely in excess oxygen to produce 0.04 mol of carbon dioxide and 0.72 g of water. What is the molecular formula of the hydrocarbon?

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closed as off-topic by Gaurang Tandon, Klaus-Dieter Warzecha, MaxW, aventurin, Loong Mar 24 '18 at 13:55

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  • $\begingroup$ Hi Cheong! welcome to Chem.SE! We require you to show your efforts on this problem. What formulae/steps did you try? Please add this to your question. Thanks! $\endgroup$ – MollyCooL Mar 24 '18 at 7:25
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There isn't enough information to solve the problem exactly, but it is still possible to get the empiric formula which shows the relation of the atoms.

We have 0.4 mol carbondioxide, there is only one carbon in carbondioxide so we know 0.4 mol carbon reacted with oxygen

We have 0.72 g of Water ( M = 18), we need the number of moles so we can just divide it through the molar mass. The result is 0.4, but we have to take into account that water contains 2 hydrogen, thus the amount of hydrogen that reacted with water is 0.8 mol.

The formula is: $C_nH_{2n}$

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  • $\begingroup$ good work but we usually don’t provide complete answers on homework questions with no work, maybe a hint instead. We aren’t a homework site, nor do we like the reputation of a homework site. $\endgroup$ – JavaScriptCoder Mar 24 '18 at 11:16

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