Does Iron Lose Mass When Exposed to Water and Oxygen?

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Discussion Overview

The discussion revolves around whether iron loses mass when exposed to water and oxygen, particularly in the context of corrosion processes. Participants explore the implications of corrosion products and their effects on the mass of iron objects over time.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes the corrosion process of iron, suggesting that it loses mass due to the formation of iron ions and hydroxide ions, which may flake off.
  • Another participant questions the framing of the question, indicating that the net effect on mass may vary depending on whether the mass of the object or the mass of the iron itself is considered.
  • It is noted that while some corrosion products may flake off, initially, the mass of the object may actually increase due to the accumulation of corrosion products.
  • A later reply suggests that an oxide film could slow down the corrosion process, referencing a phenomenon known as passivation.
  • Another participant clarifies that while iron does not achieve true passivation due to the porous nature of iron oxide, the presence of oxides can still slow corrosion.

Areas of Agreement / Disagreement

Participants express differing views on the impact of corrosion products on mass, with some suggesting an increase in mass initially, while others focus on the potential loss of mass due to flaking. The discussion remains unresolved regarding the net effect of corrosion on the mass of iron.

Contextual Notes

Participants acknowledge that the effects of corrosion may change over time and that the definitions of mass being discussed could influence the conclusions drawn.

GuMing
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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 !:)
 
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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.
 
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?
 
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.
 
there is no surface pacification for iron because the iron oxide formed is porous.
 
chill_factor said:
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.
 

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