Loading....
Coupon Accepted Successfully!

 

Concept of Oxidation and Reduction


According to the early views, the process of oxidation involves the addition of oxygen or the removal of hydrogen atoms(s). The substance which supplies oxygen or absorbs hydrogen atoms(s) is known as oxidizing agent and the substance which absorbs oxygen or releases hydrogen atom is said to be oxidized. On the other hand, the process of reduction involves the removal of oxygen or the addition of hydrogen atoms (s). The substance that absorbs oxygen or releases hydrogen atom(s) is known as a reducing agent and the substance that releases oxygen or absorbs hydrogen atoms(s) is said to be reduced. In chemical reaction, if one substance releases oxygen (or absorbs hydrogen) atom, there must be present another substance which absorbs oxygen (or releases hydrogen) atom. Thus, a chemical reaction involves both oxidizing and reducing agents simultaneously and the processes of oxidation and reduction occur simultaneously in a chemical reaction. In other words, if a substance is oxidized (addition of oxygen or removal of hydrogen), there must be another substance that is simultaneously reduced (removal of oxygen of oxygen or addition of hydrogen). A few examples illustrating the above effects are displayed in the following reactions.
  1. For the reaction
    Mg + 
    We may state that Mg is oxidized to MgO in the forward reaction as it involves the addition of oxygen. In the backward reaction, we say the MgO is reduced to Mg as it involves the removal of oxygen.
  2. For the reaction

    We may state that hydrogen is oxidized to water (addition of oxygen) in the forward reaction or water is reduced to hydrogen (removal of oxygen) in the backward reaction. Alternatively, we may state that oxygen is reduced to water (addition of hydrogen) in the forward reaction or water is oxidized to oxygen (removal of hydrogen) in the backward reaction.
  3. The reaction involving KMnO4 and FeSO4 in an acidic medium may be visualized in terms of the earlier views on oxidation and reduction. We may write the reaction in two steps:
    2KMnO4 + 3H2SO4 K2SO4 + 2MnSO4 + 3H2O + 502
    [2FeSO4 + H2SO4 + O2 Fe2(SO4)3+ H2O] 5
    2KMnO4 + 10FeSO4 + 8H2SO4 K2SO4 + 2MnSO4 + 5Fe2(SO4)3+ 8H2O
    The first step involves the removal of oxygen atoms and the second step involves addition of oxygen atoms. So, we may state that
    1. The first step is the reduction reaction (removal of oxygen). A careful study of the reaction will reveal that the oxygen atoms have come form KMnO4 and thus KMnO4 is termed oxidizing agent (a substance which supplies oxygen).
    2. The second step is the oxidation reaction (addition of oxygen). A careful study of the reaction will reveal that oxygen atoms are absorbed by FeSO4, which is termed reducing agent (a substance which absorbs oxygen).
For the overall reaction, we say that the oxidizing agent KMnO4 has oxidized the reducing agent FeSO4. In this process of oxidation, the oxidizing agent KMnO4 has undergone reduction to MnSO4. Alternatively, we may say that the reducing agent FeSO4 has reduced the oxidizing agent KMnO4. In this process of reduction, the reducing agent FeSO4 has undergone oxidation to Fe2(SO4)3.

The above way of writing half-reactions is the outcome of the mental picture used to explain the process of oxidation or reduction. In actual practice, the reaction does not proceed the way it is shown, that is KMnO4 releases oxygen atoms and FeSO4 absorbs oxygen atoms. We will see shortly that the reaction actually involves the transfer of electron from one species to another.




Test Your Skills Now!
Take a Quiz now
Reviewer Name