Redox Reactions

Redox Reactions
Oxidation And Reduction Oxidation Number

Redox Reactions

    A solution is a homogeneous mixture of gases, solids, or liquids in which the individual molecules of two or more substances are evenly dispersed throughout the medium (solution). For example, if one dissolves sucrose in water, the sugar granules will break down into individual molecules.

Oxidation And Reduction

   The earliest view of oxidation and reduction is that of adding oxygen to form an oxide (oxidation) or removing oxygen (reduction). They always occur together. For example, in the burning of hydrogen

2H2 + O2 -> 2H2O

the hydrogen is oxidized and the oxygen is reduced.

The combination of nitrogen and oxygen which occurs at high temperatures follows the same pattern.

N2 + O2 -> 2NO

This formation of nitric oxide oxidizes the nitrogen and reduces the oxygen. In some reactions, the oxidation is most prominent

When we take an iron metal nail and dip it into a blue solution of copper (II) sulfate, the nail becomes covered with a reddish substance. This reddish susbtance is metallic copper. The equation for this is:

Fe(s) + CuSO4(aq) -> FeSO4(aq) + Cu(s)

The net ionic equation, that is, the equation in which we have cancelled out the spectator ions (in this case the spectator ion is SO4).

Fe0(s) + Cu2+(aq) -> Fe2+(aq) + Cu0(s)



Oxidation Number

   he oxidation number is the charge an atom in a substance would have if the pairs of electrons in each bond belonged to the more electronegative atom. Now this means that in a compound made up of monatomic ions, like NaCl, in which the bonding pairs do belong to the more electronegative atom, the oxidation number equals the ionic charge. The sodium ion has an oxidation number of +1 while the chlorine ion has an oxidation number of -1.

Calculaton Of Oxidation Number

   The oxidation number of an atom in an elementary substance is 0. This means that the oxidation number of an O atom in O2 is 0.
  • The oxidation number of a Group IA atom in any compund is +1; The oxidation number of a Group IIA atom in any compund is +2.
  • The oxidation number of fluorine is -1 in all of its compounds.
  • The oxidation number of chlorine, bromine, and iodine is -1 in any compound containing only two elements.
  • The usual oxidation number of oxygen in a compound is -2. The major exceptions of this rule are peroxides, like H2O2, which have an oxidation number of -1.
  • The oxidation number of hydrogen in most compounds is +1.
  • The sum of the oxidation numbers in a compound is always zero.

For something that is an ion consisting of two atoms (a polyatomic ion), the oxidation numbers add up to the charge on the ion.  

For example, in the reaction

Mg + Cl2 -> Mg2+ + 2Cl-

the Mg is seen to increase in oxidation number from 0 to 2 (oxidation) while the chlorine atoms experience a decrease in oxidation number from 0 to -1 (reduction).

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