I was solving a chemical formula which includes a carbon, oxygen, and hydrogen compound. And it turned out to be something like this:


when $n$ is a natural number. So that, at least ostensibly, can be one of these:

$$\ce{CH4O, C2H8O, C3H12O, C4H16O, ...}$$

But a solution attached to it said

The only compound which has $\ce{C_nH_{4n}O}$ as the empirical formula is $\ce{CH4O}$

so the molecular formula is confirmed as above. So simply my question is this: why is that the only one which makes sense in this situation?

  • 1
    $\begingroup$ This is the only one which makes sense because the others do not make sense. Try to compose a structural formula for any of them and see what happens. $\endgroup$ Aug 4 '17 at 12:26
  • $\begingroup$ Well, technically there is ethane hydrate clathrate for $\ce{C2H8O}$, stable above $\pu{0.1 GPa}$ (Ceppatelli, M.; Bini, R.; Schettino, V. Phys. Chem. Chem. Phys. 2011, 13 (4), 1264–1275. DOI 10.1039/c0cp01318h). $\endgroup$
    – andselisk
    Aug 4 '17 at 12:49

I would look at it like recursive problem. Starting with the simplest situation:

Carbon has 4 electrons available to form covalent chemical bonds (so 4 simple bonds for example). Hydrogen has one electron - 1 bond.

If you add one more carbon to the situation, you have to bond it somewhere - you need to use the first carbon. Now with this new carbon you added 3 more possible places to add 3 more elements (like hydrogens) but you canceled one hydrogen place on the first carbon. So every time you add another carbon, you can go up only for 2 hydrogen. It is actually called homologous addition or something like that. (Sorry for my english as well)

I ignored the oxygen whole time, cos as far as he is 2 bonded, he never adds anything he either substracts two hydrogen places, or you can instert it between a carbon and a hydrogen.


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