What are Oxidation Reduction reactions
What are Oxidation Reduction reactions
The corrosion of a metal (that is, the chemical transformation that is
recognized as destructive to the metal) is the oxidation step of the overall
oxidation-reduction process.
Oxidation is the process of losing electrons The metal atoms release electrons
(are oxidized) and become positive ions.
The site at which this occurs is known
as the anode.
Typical oxidation half-reactions include the following.
(1) Zn ----> Zn2+
+ 2e-
(2) Al ----> Al3+
+ 3e-
(3) Fe ----> Fe2+
+ 2e-
The cations (positive ions) may then go into solution, or they may
combine with any available anions (negative ions) or water to form ionic
compounds.
The exact fate of the cations is important to subsequent processes,
but the primary effect is that atoms leave the metallic state, and the metal
deteriorates.
An oxidation process cannot take place without a simultaneous
reduction (gain of electrons) process.
The nature of the reduction step in corrosion sometimes varies with the metal and the environment to which it is exposed.
For most metals in an aqueous environment, the important reduction
half-reaction is the reduction of hydronium ions (a hydronium ion is simply a
hydrogen ion attached to a water molecule).
(4) H3O+ + e-
----> H + H2O
Small concentration variations
within a solution in contact with the metal may also affect the rate and nature
of corrosion reactions. Therefore, it is often impossible to predict the exact
nature of corrosion reactions.
It is generally found, however, that for most
metals exposed to an aqueous environment the half-reactions involved in
corrosion are the reduction reaction of Equation (4) and an oxidation
half-reaction of the type shown in Equations (1) through (3).
this article is taken from: DOE FUNDAMENTALS HANDBOOK CHEMISTRY
Volume 1 of 2 - DOE-HDBK-1015/1-93 JANUARY 1993
see also:
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