Iron Corrosion in water

[GuMing]

When iron corrodes in water, it loses electrons to oxygen and becomes iron ions. The oxygen retrieved the free electrons and along with water molecules formed hydroxide ions. Eventually, the iron ions and hydroxide ions react to form iron hydroxide. So based on this, would the iron loses mass when i weigh it, since iron hydroxide flakes off and would not stay on the surface of the iron? Am i right? Please correct me if i am incorrect! Thank you !:)

 

[Borek]

A lot depends on what is the real question - does it ask about a mass of the object, or mass of the iron?

Some of the corrosion products will flake off, some will stay on the surface. Hard to tell what would be the net effect, as it may change with time. In general I don't think it will flake off substantially, at least in the beginning, so the mass of the object (say nail) would go up.

 

[GuMing]

Thank you for answering my question!
One more thing, if the oxide film (which is the corrosion products)stay on the surface of iron, would it slows down the corrosion process?

 

[Borek]

To some extent it should.

This is a process called passivation, that can completely stop the oxidation reaction. That's why aluminum or stainless steel don't corrode. For passivation you need oxides to adhere very strongly to the metal surface, which is why it doesn't work for iron.

 

[chill_factor]

there is no surface pacification for iron because the iron oxide formed is porous.

 

[Borek]

there is no surface pacification for iron because the iron oxide formed is porous.

Agreed, I should be more clear. There is no passivation in the exact meaning of the word, but presence of oxides still slows the corrosion.