posted by a Canadian on .
Explain why iron corrodes more quickly in seawater than in freshwater.
I'm getting conflicting answers from searching on Google; is it because the corrosion of iron is a redox reaction, which involves a transfer of electrons, and therefore this transfer of electrons would be quicker and happen more easily in salt water since salt water is an ionic compound and is a good conductor?
This seems to be what the majority of sources say (or at least along those lines).
I also found this:
"...in salt water the salt dissolves into the water creating ions of sodium Na +, and chlorine Cl -. This is called diffusion. These ions react with the water breaking it down or diffusing it into Oxygen and Hydrogen molecules. Thus there is more pure oxygen in salt water than fresh water.
As a result of increased oxygen, there is more Oxygen to react with the Iron thus causing faster rusting."
It's not a very reliable source, but it sort of seems right, but I don't think that diffusion is the proper label for that. And the part about water "breaking down" due to NaCl ions or "diffusing" into O2 and H2 molecules seems off to me... But it would make sense that rust occurs faster because of more oxygen. Since iron corrodes because of reactions with water and oxygen.
This looks like a good explanation. I would ignore the source that talks about diffusion and NaCl breaking down H2O into H2 and O2. That's hogwash.