I have recently done an experiment for my chemistry EEI (Year 12) where we are testing what factors effect the rate of corrosion. I used vinegar (acetic acid) as one of the acids and Hydrochloric acid as the other.

In the one with the HCl, the results were as expected – the area exposed to the acid will corrode, the unexposed part won't (in the time frame I did).

However, for the vinegar, the results were different. The part exposed to the vinegar didn't show any rust however the part of it that wasn't exposed had a brown coating. Now I understand that the vinegar reacts with the rust, hence the reason we cant see it on the iron nail, but my question is: What is the brown coating on the top of the nail, and what is it caused from? Was there some sort of gas from the vinegar that caused it? If so, what is this gas called and how does it cause corrosion?

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    $\begingroup$ It could be simply that the moisture in the air rusted the unexposed part ... Though to confirm it you'll probably need to do more experiments..... $\endgroup$ – Kartik May 16 '17 at 8:30
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    $\begingroup$ They were in a container with a lid. So i feel like this isn't the case. Especially since it didn't do it to any of the ones. (HCl, water, NaOH). I don't have time to do more tests because the final is due on Friday. hmmmm. Thanks anyway $\endgroup$ – Caitlynisdunwithyou May 16 '17 at 23:57
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    $\begingroup$ Do you have an images? A Visual aid could make identification easier. $\endgroup$ – Harry David May 21 '17 at 13:22

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