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.
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)
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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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