TBR Gen Chem Passage 2 Q 11

[howtomedicine]

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The question asks which of the four unknown compounds is least likely to contain oxygen.
A. Compound I
B. Compound II
C. Compound III
D. Compound IV

The answer is D, but I'm not sure about how to get to this answer. The explanation stated that the greatest mass % of carbon is found in the cmpd with the greatest # of carbon atoms and then smallest # of oxygen atoms. Thus the compound least likely to have oxygen is the one that produces the most CO2 upon complete combustion.

Couldn't oxygen in the original samples be used to make CO2 or H2O after the sample has been combusted?

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[aldol16]

Couldn't oxygen in the original samples be used to make CO2 or H2O after the sample has been combusted?

Where would the carbon and hydrogen atoms come from?

 

[howtomedicine]

The carbon and hydrogens come from the original sample


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[howtomedicine]

Let's say for example if I combusted ethanol, how would I know if the alcohol O was used in the CO2 collected afterwards? Wouldn't that somehow skew the mass of CO2 collected? Or should I assume that the CO2 collected only has C from the original sample and O2 from the O2 tank


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