Reduction - Oxidation (Water & Wastewater Treatment Plants, WWTP_CAMIX Vietnam)
DESCRIPTION
Oxidation State and Oxidation Number
The oxidation state of an atom in a reactant is associated with the electronic structure of the atom resulting from the chemical bond in which it is involved.
In ionic bonds each atom is clearly associated with a net charge due to the acquisition or loss of electrons during the formation of the bond (e.g., in NaCl the sodium ion has an electron which it received from the chlorine atom).
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In covalent bonds the charge is shared by the atoms involved in the bond. However, since each atom will have a different level of affinity for electrons (electronegativity) it is conventionally assumed that the electrons involved in the bond reside with the most electronegative atom in the bond. The oxidation number or (electro)valence is the number of electrons that the atom in the bond has gained or lost during the formation of the bond. |
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In each non-ionized molecule the total sum of the formal charges must be zero. The same element can have different oxidation number in different molecules. |
Oxidation and Reduction Reactions
Oxidation and reduction reactions, or redox reactions, are those chemical reactions in which the oxidation state of the reactants changes during the reaction.
Two types of reactions are always simultaneously involved in every redox reactions:
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Oxidations, i.e., the loss of electrons by a chemical species (which increases its oxidation number) which becomes oxidated. | |
| ■ | Reductions, i.e., the acquisition of electrons by a chemical species (which decreases its oxidation number) which becomes reduced. Since the total number of electrons during a reaction must remain constant the number of electrons gained by the molecules containing the oxidising species (which becomes reduced) must equal the number of electrons lost by the molecules containing the reducing species (which becomes oxidated). |
Oxidation and Reduction Reactions in Wastewater Treatment
A number of wastewater pollutants can undergo redox reactions with the appropriate addition of a oxidizing or reducing agent to the wastewater
The result of such reaction it typically the precipitation of contaminants (especially in the case of inorganic pollutants such as heavy metals) or their conversion to a much less toxic form (e.g., an organic waste mineralized to CO2 and H2O).
REFERENCE PHOTOS
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