Does more oxygen in hydrocarbon = less CO2?

[chiddler]

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Comparing hydrocarbons, "...Thus, the compound is least likely to contain oxygen is one that produces the most CO2 upon combustion."

I'm testing this:
For butane:
2 C4H10 + 13 O2 = 8 CO2 + 10 H2O

For butanol:
C4H9OH + 6 O2 = 4 CO2 + 5 H2O

Both of these have a 1:4 ratio of Butan:CO2

I also tested this with methanol and decanol, and butanone. The ratios are the same when you compare oxygen containing compound vs simple hydrocarbon.

Am I missing something, or is this incorrect? Thanks very much.

 

[MedPR]

Comparing hydrocarbons, "...Thus, the compound is least likely to contain oxygen is one that produces the most CO2 upon combustion."

I'm testing this:
For butane:
2 C4H10 + 13 O2 = 8 CO2 + 10 H2O

For butanol:
C4H9OH + 6 O2 = 4 CO2 + 5 H2O

Both of these have a 1:4 ratio of Butan:CO2

I also tested this with methanol and decanol, and butanone. The ratios are the same when you compare oxygen containing compound vs simple hydrocarbon.

Am I missing something, or is this incorrect? Thanks very much.

The only thing I can think of is that compounds with oxygen are more likely to undergo other reactions, while hydrocarbons will typically undergo combustion and produce CO2.

 

[chiddler]

The only thing I can think of is that compounds with oxygen are more likely to undergo other reactions, while hydrocarbons will typically undergo combustion and produce CO2.

This reaction was specifically with the compound + oxygen. Good idea, but that's not the case. I'm thinking that this may be a book error.

 

[lunt]

Combustion reactions can be seen as a redox reaction, between a reduced hydrocarbon and oxidized O2, and forming oxidized CO2 and reduced water. So as long as you are adding alcohol groups (which are similar to -H), you don't change your yield in CO2. If you are adding a ketone or a carboxylic acid, on the other hands, things will get different.

I'm sure there's a better explanation that doesn't involve redox, but I can't think of it right now.

 

[theseeker4]

Comparing hydrocarbons, "...Thus, the compound is least likely to contain oxygen is one that produces the most CO2 upon combustion."

I'm testing this:
For butane:
2 C4H10 + 13 O2 = 8 CO2 + 10 H2O

For butanol:
C4H9OH + 6 O2 = 4 CO2 + 5 H2O

Both of these have a 1:4 ratio of Butan:CO2

I also tested this with methanol and decanol, and butanone. The ratios are the same when you compare oxygen containing compound vs simple hydrocarbon.

Am I missing something, or is this incorrect? Thanks very much.

For the part you quoted above, are they saying between two compounds with the same molecular mass, the one with the most O's produces the least CO2, or between two compounds with the same number of C's, the one with the most O's produces the least CO2? The former is correct, the latter doesn't seem to be correct.

 

[chiddler]

For the part you quoted above, are they saying between two compounds with the same molecular mass, the one with the most O's produces the least CO2, or between two compounds with the same number of C's, the one with the most O's produces the least CO2? The former is correct, the latter doesn't seem to be correct.

They are just two unknown compounds.

 

[theseeker4]

They are just two unknown compounds.

That tells us the statement made by the book is correct. If you don't know the number of carbons, or the molecular mass, all you have to go by is the actual mass of the compound. Since a compound that is free of oxygen has more of its mass tied up in C than the compound that has oxygen, the one without oxygen must produce more CO2. Some significant portion of the mass of the compound with oxygen in it is tied up in the oxygen, which can't react with O2 to form CO2 (obviously) so less CO2 is produced. The more oxygen in the compound, the less CO2 will be produced.

 

[MedPR]

They are just two unknown compounds.

Does the book give you any information about the identity of the unknowns? Molecular weight, empirical formula, anything? If not, then the above post (and quoted again below) is absolutely correct.

That tells us the statement made by the book is correct. If you don't know the number of carbons, or the molecular mass, all you have to go by is the actual mass of the compound. Since a compound that is free of oxygen has more of its mass tied up in C than the compound that has oxygen, the one without oxygen must produce more CO2. Some significant portion of the mass of the compound with oxygen in it is tied up in the oxygen, which can't react with O2 to form CO2 (obviously) so less CO2 is produced. The more oxygen in the compound, the less CO2 will be produced.

 

[chiddler]

That tells us the statement made by the book is correct. If you don't know the number of carbons, or the molecular mass, all you have to go by is the actual mass of the compound. Since a compound that is free of oxygen has more of its mass tied up in C than the compound that has oxygen, the one without oxygen must produce more CO2. Some significant portion of the mass of the compound with oxygen in it is tied up in the oxygen, which can't react with O2 to form CO2 (obviously) so less CO2 is produced. The more oxygen in the compound, the less CO2 will be produced.

OHH! that's right!

well put thanks a lot.