# AAMC 7 Physics #46

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#### StilgarMD

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incase this is the wrong number, its the passage that involves rate laws of SO3 and H2O, and the water is labeled with O-18.

#46 asks which method produces radiolabeled SO4 the fastest, and the answer is bubbling SO3(g) through radiolabeled H2O. one of the other answer choices is bubbling radio labeled SO3(g) through normal H2O. are we suppose to rely purely on the fake that happens to be how its done in the passage and pick that choice, or is there some sort of other logic?

#### Saint Fu

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It's more than just that. Take a look at the problem again, and notice which molecules have the labeled O-18. The other choices already have SO3 with O-18, so you wouldn't get the compound asked for in the question stem, which asks for only 1 O-18 atom.

#### gtbROX

##### Full Member
It's more than just that. Take a look at the problem again, and notice which molecules have the labeled O-18. The other choices already have SO3 with O-18, so you wouldn't get the compound asked for in the question stem, which asks for only 1 O-18 atom.

This, but also to support what he's saying, the passage implied that an H2O would bind first and result in the SO3-OH2 formula (sorry if I'm writing it wrong) which leads to the assumption we have to make that a labeled water must attack a nonlabeled SO3.

#### SKation

##### Full Member
incase this is the wrong number, its the passage that involves rate laws of SO3 and H2O, and the water is labeled with O-18.

#46 asks which method produces radiolabeled SO4 the fastest, and the answer is bubbling SO3(g) through radiolabeled H2O. one of the other answer choices is bubbling radio labeled SO3(g) through normal H2O. are we suppose to rely purely on the fake that happens to be how its done in the passage and pick that choice, or is there some sort of other logic?
Hey,

Did you ever get a proper understanding of this im still confused.
Thanks!!

#### SN2ed

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