pH affecting the rust of nails

[kiwi.at.heart]

We were told to do a experiment of a factor that affects rust. I choose to do pH and placed iron nails in solution of pH 3, 5, 7, 9, and 11. I used HCl to make up the acidic solutions and NaOH to make up the basic solutions. What little research I could find said that acidic solution should cause the greatest corrosion and basic solution should minimise corrosion. If only my results showed that...

Basically the nails in pH 3 solution hardly rusted at all and the nails in pH 11 solution rusted the most. If anyone has any explanation of why this happened or could lead me to any sources of why this happened it would be really appreciated. I know the results I got are probably not wrong because two other guys in my class also did pH and their results are very similar to mine.

Thanks to anyone that can help me, its just frustrating me because a prac that was supposed to be simple has become a whole lot more complicated.

[Drake Glau]

Without going and looking up some information I'd say it's because you used different reactants. Nail rust is a redox reaction. Different reactions would have different oxidation states so that could be a cause of it (topic 9 would have details for oxidation).

[dessskris]

Did you have the nails in contact with AIR (oxygen) and the ACID at the same time? Rusting needs both to take place, if I am not mistaken.

[kiwi.at.heart]

Did you have the nails in contact with AIR (oxygen) and the ACID at the same time? Rusting needs both to take place, if I am not mistaken.

Each nail was completely covered in each solution. I would think there would have been enough dissolved oxygen in the water to allow for oxidation to take place, unless NaOH allows for a greater dissolved water concentrations that I don't know about, it shouldn't be a factor.

[Drake Glau]

NaOH(s) + H2O(l) => Na+ + OH- + H20

HCl(g) + H2O(l) --> H3O+Cl-(aq) (H3O might as well be H+ for all purposes here)

Oxygen is a MUST for rust to occur since the corrosion comes from the iron giving e- to the O2, water helps with this and and acidic solution speeds it up considerably.

Anyway, all I'm thinking of is that the iron is really reacting with your OH- ions with the water so even though your acid solution has the extra speed its not reacting as well with the iron.