What Is the Molecular Formula of an Unknown Compound from Combustion Data?

[cp255]

Burning a 3.230 g sample of the unknown compound in an excess of oxygen produces 4.7341 g of CO2 (carbon dioxide). The carbon initially in the unknown compound is completely converted to carbon in the CO2.

If it is determined that the molecular weight of the unknown compound is 180.16 g/mol, what is the correct molecular formula?

I don't see how I can do this without know the mass of H2O.

 

[Borek]

Can you calculate mass of carbon in the compound sample?

Note: while you are missing something obvious, even after taking it into account it is still not possible to solve the problem, as it turns out compound contains more hydrogen than carbon (in terms of mass - so the molar ratio is even worse).

 

[cp255]

So there are 0.108 mols of C which is equal to 1.29g C. I still don't see how this helps since I do not know how much water was produced by this reaction.

 

[Borek]

OK, I probably misunderstood your question. Not that I am sure I understand it now.

My first idea was that if there was 3.230 g of the sample, and it contained 1.29 g of carbon, the remaining mass can be attributed to hydrogen - and then simply the answer is "no solution".

Chances are your comment about water really means "not knowing amount of water I can't calculate amount of oxygen in the original sample". Sadly, question is ambiguous, as it doesn't say anything about the composition - could be the compound contains any other elements as well. But let's assume it is just C_nH_kO_l only.

We can easily calculate number of moles of the substance, so at least n in C_n is obvious. Then we know how much mass can be attributed to other elements. Then (with a brute force) we can check that there exist a reasonable C_nH_kO_l formula that fits the data given - you just need such a pair of k, l that 16*l+k equals remaining part of the molar mass given.

I retract my earlier comment about lack of solution.

 

[DeeNos]

I would first like to clarify that the information provided in the content is not sufficient to accurately determine the molecular formula of the unknown compound. The combustion reaction only provides information about the amount of CO2 produced, but it does not give any information about the other products of the reaction, such as water (H2O) or any other possible byproducts.

To accurately determine the molecular formula of a compound, we need to know the masses of all the elements present in the compound, as well as the overall mass of the compound. In this case, we only have information about the mass of carbon, but we do not have any information about the mass of hydrogen or any other elements that may be present in the compound.

Additionally, the molecular weight of a compound is not enough to determine its molecular formula. For example, if we consider a compound with a molecular weight of 180.16 g/mol, it could have various molecular formulas such as C12H20O10, C6H10O5, C4H5O4, etc. Therefore, without knowing the masses of all the elements present in the compound, we cannot accurately determine its molecular formula.

In order to determine the correct molecular formula of the unknown compound, we would need to conduct further experiments and gather more information about the compound, such as its elemental composition and molecular weight, to accurately determine its molecular formula.