Oxidation and reduction reactions (redox) are asked frequently in class 10 science. We shall discuss the definitions of redox reactions in this article.
Oxidation and reduction (redox) reactions form the basis of many life processes and life on earth would not be possible without these reactions. Oxidation and reduction reactions happen together and hence there are referred as redox reactions.
Oxidation can be defined in a number of ways. This can be defined on the basis of the transfer of oxygen, hydrogen or electrons between the reactants.
Redox reactions in terms of oxygen transfer.
In a reaction, when one reactant gains oxygen, it is said to be oxidised. Therefore, oxidation can be defined as a gain of oxygen. For this reactant to gain an oxygen atom, another reactant has to donate an oxygen atom. The donor is called an oxidising agent. And the donor reactant is in turn reduced. Therefore, loss of oxygen defines a reduction reaction.
Consider this example:
Fe2O3 + 3CO = 2Fe +3CO2
In this equation, iron loses its oxygen to carbon monoxide to produce carbon dioxide. Here, iron oxide is the oxidising agent. And since carbon monoxide removes an oxygen from iron oxide, it is called a reducing agent.
Redox reactions in terms of transfer of hydrogen atoms.
This definition is useful in organic chemistry. Let us consider this equation:
In organic chemistry, one will come across two terms- alcohol and aldehyde. Alcohols and aldehydes are inter-convertible. When alcohol loses hydrogen, it converts to an aldehyde and this process is called oxidation. Similarly when an aldehyde gains hydrogen, it forms alcohol. This process is called reduction. Equations in organic chemistry are complex, therefore we have simplified this reaction using ethanol and its corresponding aldehyde ethanaldehyde.
CH2CH3OH — ———–> CH3CHO
Loss of hydrogen
Redox reactions in terms of transfer of electrons.
This is the most useful and comprehensive definition of oxidation and reduction reactions. Based on the transfer of electrons, oxidation is defined as loss of electrons while reduction is defined as a gain of electrons. Consider this basic equation:
CuO + Mg + Cu + MgO
In the above equation, copper oxide loses oxygen to magnesium, therefore magnesium is getting oxidised and copper oxide is the oxidising agent. Now let us rewrite this equation as an ionic equation (copper oxide and magnesium oxide are both ionic, the metals aren?t).
Cu2+ + Mg = Cu + Mg2+
In this equation, the oxygen atom is simply a spectator. Thus if we look at this equation in terms of electron transfer, the copper gains 2 electrons from magnesium, hence it is being reduced and magnesium loses 2 electrons to copper, hence it is getting oxidised.
This can be more easily remembered as:
Oxidation= loss of electrons
Reduction= gain or electrons
Therefore, to summarise:
- Oxidation is loss of electrons.
- An oxidising agent oxidises another agent.
- Thus, an oxidising agent must gain electrons.
Similarly, a reducing agent reduces another substance, thus it must lose electrons (as the reduction is a gain of electrons).
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