It has been my understanding that when nitric, perchloric, or sulfuric acids act as oxidizing agents, they must exist as whole $\ce{HNO_3}$ or $\ce{HClO_4}$ or $\ce{H_2SO_4}$ molecules that are still protonated. For example, putting copper in dilute sulfuric acid does nothing, but using concentrated sulfuric acid does cause a redox reaction. This agrees with the fact that only concentrated forms of these acids can oxidize; only concentrated forms have undissociated/whole molecules. A dilute solution would contain mostly hydronium and the conjugate base of the strong acid, thus not be able to oxidize. However, the "General Properties" section of this Wikipedia article flat out contradict that. It says,
However, even dilute nitric acid can oxidize copper to $\ce{Cu^{2+}}$ ions, with the nitrate ions acting as the effective oxidant. (Emphasis: nitrate ions).
Then below it says that concentration is a factor for sulfuric acid. Is something amiss here?
UPDATE: I now embrace what user @matt_black is saying, and by now I'm not even surprised that something like this could happen. Chemical guidelines are just guidelines. However, I'm now even more curious as to this departure from the trend. If he or someone else would like to give an explanation of the mechanism of reactions involving oxidation (of copper, for instance) by $\ce{HNO_3}$ and $\ce{H_2SO_4}$ that accounts for this anomaly, that would be great.
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