Basic knowledge of chemistry
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I have a question: dilute sulfuric acid is corrosive to carbon steel. If the sulfuric acid is neutralized by sodium hydroxide, and if the pH after neutralization is exactly 7, then sulfate ions must still be present in the solution. In this case, will these sulfate ions react with iron to form ferric sulfate or ferrous sulfate? In other words, under such conditions, do sulfate ions remain corrosive to carbon steel?
It are the hydrogen ions in sulfuric acid that cause corrosion; once the acid is neutralized, its corrosiveness **decreases**, and sulfate ions do not react with iron on their own.
But sulfate ions carry a charge. There should be no chemical corrosion, but there is electrochemical corrosion.
Electrochemical corrosion will occur because of the carbon
I believe the principle behind the corrosion of carbon steel by dilute sulfuric acid is that sulfate ions react with iron to form ferrous sulfate, while simultaneously displacing the hydrogen ions in sulfuric acid to produce hydrogen gas; it is not the hydrogen ions in sulfuric acid that react with iron and cause the corrosion of carbon steel. Therefore, I believe that the neutralized dilute sulfuric acid does not lose its corrosive effect on carbon steel, as the sulfate ions remain unchanged; is this understanding correct? I would appreciate some guidance from those with more experience. Thank you!
Go back upstairs; the view from the 5th floor is incorrect. The reason is that a sodium sulfate solution cannot react on its own with iron to produce ferric sulfate. Therefore, the presence of sulfate ions is not a sufficient condition for corroding carbon steel. Of course, if electrochemical factors are involved, it becomes complicated.
The theory that it’s on the fifth floor is supported by the fact that iron does not undergo a chemical reaction with salt; it reacts with acids, as iron reduces hydrogen ions. It gets complicated if an electrochemical reaction occurs.