Unit Where there is oxidation, there is always reduction – Chemistry is essentially a study of redox systems. In reactions ( . ) and ( . ), the elements magnesium and sulphur are oxidised on account of addition of oxygen to them.
Similarly, methane is oxidised owing to the addition of oxygen to it. CH (g) + 2O (g) → CO (g) + 2H O (l) ( . ) A careful examination of reaction ( . ) in which hydrogen has been replaced by oxygen prompted chemists to reinterpret oxidation in terms of removal of hydrogen from it and, therefore, the scope of term oxidation was broadened to include the removal of hydrogen from a substance.
The following illustration is another reaction where removal of hydrogen can also be cited as an oxidation reaction. H S(g) + O (g) → S (s) + H O (l) ( . ) As knowledge of chemists grew, it was natural to extend the term oxidation for reactions similar to ( . to .
), which do not involve oxygen but other electronegative elements. The oxidation of magnesium with fluorine, chlorine and sulphur etc. occurs according to the following reactions : Mg (s) + F (g) → MgF (s) ( . ) Mg (s) + Cl (g) → MgCl (s) ( .
) Mg (s) + S (s) → MgS (s) ( . ) Incorporating the reactions ( . to . ) within the fold of oxidation reactions encouraged chemists to consider not only the removal of hydrogen as oxidation, but also the removal of electropositive elements as oxidation.
Thus the reaction : 2K [Fe(CN) ](aq) + H O (aq) → 2K [Fe(CN) ](aq) + KOH (aq) is interpreted as oxidation due to the removal of electropositive element potassium from potassium ferrocyanide before it changes to potassium ferricyanide. To summarise, the term “oxidation” is defined as the addition of oxygen/electronegative element to a substance or removal of hydrogen/ electropositive element from a substance. In the beginning, reduction was considered as removal of oxygen from a compound. However, the term reduction has