TBR chemistry, section 1 question 11

[anbuitachi]

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I'm kind of confused by the explanation

Basically the question asked which unknown has least oxygen. The explanation was that the greatest mass percent of carbon is found in the coumpound with smallest number of oxygen atoms in its formula. So the compound w/ least oxygen produces the most CO2 upon combustion. Pure carbon when oxidized yeilds 7.33 g Co2.

Can someone explain this? I'm kind of confused to what it means. And How much pure carbon oxidize to 7.33g???

 

[BerkReviewTeach]

I'm kind of confused by the explanation

Basically the question asked which unknown has least oxygen. The explanation was that the greatest mass percent of carbon is found in the coumpound with smallest number of oxygen atoms in its formula. So the compound w/ least oxygen produces the most CO2 upon combustion. Pure carbon when oxidized yeilds 7.33 g Co2.

Can someone explain this? I'm kind of confused to what it means. And How much pure carbon oxidize to 7.33g???

In the procedure, they are burning 2.0 grams of different hydrocarbon or carbohydrate unknowns in excess oxygen, ensuring a complete reaction where all of the unknown is converted to CO2 and H2O. The greater the mass percent of C in the unknown, the greater the amount of CO2 that forms. The greater the mass percent of H in the unknown, the greater the amount of H2O that forms.

For reference purposes, they tell you that if you burned 2.0 g of pure carbon, you'd generate 7.33 g CO2. Because a 2.0-g sample of 100% carbon generates 7.33 g CO2, Compound IV must have a very high mass percent of carbon, given that it generates 6.53 g CO2 (almost the maximum possible).