Combustion analysis (TBR Physics Section I Passage II)

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May 16, 2013
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The question presents a classic combustion experiment in which 4 unknown compounds are oxidized, and the initial and final masses of magnesium sulfate (which absorbs water) and sodium hydroxide (which absorbs carbon dioxide) in the side tubes are measured. The mass of all four of the unknown compounds were the same (~2g).

Question 11 asks "Which of the four unknown compounds is LEAST likely to contain oxygen"?

The explanation says "The greatest mass percent of carbon is found in the compound with the smallest number of oxygen atoms in its formula. Thus, the compound least likely to contain oxygen is the one that produces the most CO2 upon combustion."

I am wondering if my thought process is correct:
Out of the four compounds, I want to look for the compound that generated the most product in the sodium hydroxide tube. This tells me which compound generated the most carbon dioxide, and because the initial mass of the unknown compounds were all the same (2g), this tells me which compound has the greatest mass percent of carbon? And then, the greater the mass percent of carbon in the unknown compound, the less percent is left for oxygen atoms?

Thanks in advance :)

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