AAMC 5 CBT Question

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Hey,

Can anyone explain why the answer is not C? The reactions they are referring to are:

Reaction 3: F3CCl → F3C· + Cl·
Reaction 4: Cl· + O3 → ClO· + O2
Reaction 5: ClO· + O → Cl· + O2

From reactions 3–5, what can be determined about the relative concentrations of CFCs and O2?
A. One equivalent of CFC is required to produce one equivalent of O2.

B. One equivalent of CFC is required to produce two equivalents of O2.

C. A catalytic amount of CFC can produce much O2.
A careful look at Reactions 3-5 will show that, after the initial step of breaking the bond in the chlorofluorocarbon CF3Cl, the Cl· and ClO· radicals are recycled. In other words, these two species act as catalysts: they react with the substrate (O3 or O) and are re-formed. The re-formed chlorine free radical can participate in another cycle of the reactions 4 and 5. Thus, a small amount of the CFC can produce much O2 by catalyzing the decomposition of ozone. Answer choice C is the best answer.

D.The CFC is produced by a catalytic amount of O2.

Thanks

 

[rotatedline]

Hey,

Can anyone explain why the answer is not C? The reactions they are referring to are:

Reaction 3: F3CCl → F3C· + Cl·
Reaction 4: Cl· + O3 → ClO· + O2
Reaction 5: ClO· + O → Cl· + O2

From reactions 3–5, what can be determined about the relative concentrations of CFCs and O2?
A. One equivalent of CFC is required to produce one equivalent of O2.

B. One equivalent of CFC is required to produce two equivalents of O2.

C. A catalytic amount of CFC can produce much O2.
A careful look at Reactions 3-5 will show that, after the initial step of breaking the bond in the chlorofluorocarbon CF3Cl, the Cl· and ClO· radicals are recycled. In other words, these two species act as catalysts: they react with the substrate (O3 or O) and are re-formed. The re-formed chlorine free radical can participate in another cycle of the reactions 4 and 5. Thus, a small amount of the CFC can produce much O2 by catalyzing the decomposition of ozone. Answer choice C is the best answer.

D.The CFC is produced by a catalytic amount of O2.

Thanks

The answer is not A because: One CFC produces (at least) 2 equivalents of 02 in the reaction scheme.

The answer is not B because: A chlorine radical is left at the end of reaction 3 which can further split O3 into 02 and ClO- (as shown in the second reaction). Therefore 1 equivalent of CFC is catalytic.

The answer is not D because: CFC is not produced.

I think that's what you were asking, right? Also, this should be moved to the AAMC 5R, CBT topic in Q&A so people who have not taken this test do not see the question.