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Metal atoms
Dissolved oxygen molecule adsorbed onto metal surface
Click to start corrosion
2. The electrons released by the atom must then be used
up and are used to reduce the adsorbed oxygen to water
1. Metal atom loses z electrons (here, z = 2) and becomes
z+ ion. This is the oxidation reaction:
M → M2+ + 2e−
M → M2+ + 2e−
Hydrogen ions from the solution are available to react.
Since hydrogen ions are being consumed, this region of the solution becomes less acidic
Since hydrogen ions are being consumed, this region of the solution becomes less acidic
Overall reaction:
2M + O2 + 4H+ → 2M2+ + 2H2O
2M + O2 + 4H+ → 2M2+ + 2H2O
The sites of oxidation and reduction need not be next
to each other. Provided there is electronic and electrolytic contact
between the two sites, they can be separated by large distances.