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Oxidation means addition of oxygen, removal of hydrogen, increase in oxidation number, addition of a electronegative element or removal of an electropositive element
The term oxidation was first used to describe chemical reactions in which oxygen was added to an element of a compound. Later on the term oxidation was extended to describe many more reactions which occurred without the use of even oxygen.
Addition of Oxygen: Oxidation is a chemical reaction in which oxygen is added to any chemical species (atom, ion or molecule). Example
2Mg + O2 → 2MgO
S + O2 → SO2
2CO + O2 → 2CO2
Na2SO3 + H2O2 → Na2SO4 + H2O
Removal of Hydrogen : Oxidation is a chemical reaction in which hydrogen is removed from any chemical species (atom, ion or molecule).
H2S + Cl2 → 2HCl + S
4HI + O2 → 2H2O + 2I2
4HI + MnO2 → MnCl2 + 2H2O + Cl2
Addition of an Electronegative Element: Oxidation is a chemical reaction in which an electronegative element is added into any chemical species (atom, ion or molecule).
Fe+ S → FeS (Oxidation of iron)
SnCl2 + Cl2→ SnCl4(Oxidation of stannous chloride)
2Fe + 3F2 → 2FeF3(Oxidation of iron)
Removal of an Electropositive Element: Oxidation is a chemical reaction in which an electropositive element is removed from any chemical species (atom, ion or molecule).
2KI + H2O2 → 2KOH + I2 (Oxidation of potassium iodide)
2K2MnO4 + Cl2 → 2KCl + 2KMnO4 (Oxidation of potassium manganate)
2KI + Cl2 → 2KCl + I2 (Oxidation of potassium iodide)
A substance which brings oxidation is known as oxidizing agentt
Reduction is addition of hydrogen, removal of oxygen, removal of an electronegative element or addition of an electropositive element.
2HgCl2 + SnCl2 → Hg2Cl2 + SnCl4 (Reduction of mercuric chloride)
2FeCl3 + H2 → 2FeCl2 + 2HCl (Reduction of ferric chloride)
2FeCl3 + H2S → 2FeCl2 + 2HCl + S (Reduction of ferric chloride)
Mg, S, Cu, Na2SO3, H2S, HI, H2, C, KI are reducing agents, while O2, Cl2, F2, H2O2, MnO2, FeCl3, CuCl2, Fe3O4, CuO, etc., are oxidizing agents in the above examples.
In above example iron undergoes reduction from +3 to +2.
Oxidation and reduction always occur simultaneously, hence, the word “redox” was coined for this class of chemical reactions. In the following redox reaction, identify the species undergoing oxidation and reduction:
In the above reaction oxygen is transferred from Fe3O4 to Al, so Fe3O4 is reduced while Al is oxidised.
As per definition of oxidation and reduction , loss of oxygen i.e reduction occurs in Fe3O4 and gain of oxygen i.e Oxidation occurs in Al.
The formation of sodium chloride involves two half reaction, which clearly show involvement of electrons.
Sum of the half reactions gives
In terms of electron-transfer change, name the oxidising agent(s) and reducing agent(s)
According to the modern concept, loss of electrons is oxidation whereas gain of electrons is reduction.Redox reaction involves two half reactions, one involving loss of electron or electrons (oxidation) and the other involving gain of electrons or electrons (reduction)
In the given reaction Sodium(Na) is loosing 2 electrons, thus it is the reducing agent. Chlorine(Cl) is gaining 2 electrons , thus it is oxidising agent.
On placing a strip of mettallic zinc in an aqueous solution of copper nitrate for about one hour, the copper nitrate solution turns green in colour and zinc strip turns darker.
Formula and Ionic equation for the reaction is as follows.
|Formula Equation:||Zn (s) + Cu(NO3)2 (aq) → Cu (s) + Zn(NO3)2 (aq)|
|Ionic Equation:||Zn (s) + Cu2+ (aq) → Zn2+ (aq) + Cu (s)|
As is seen in ionic equation Zn is loosing 2 electrons, thus oxidation occurs and Cu is gaining 2 electrons, thus reduction occurs. Since oxidation and reduction takes place simultaneously in this reaction, it is a redox reaction. Also since Zn is loosing electrons and becoming darker in colour, it is the reducing agent and Cu is gaining 2 electrons, it is the reducing agent. The resultant solution Zinc nitrate [Zn(NO3)2] is green in colour.
This is due to the formation of Cu2+ ions in the solution illustrated in following ionic reaction:
Here, Cu is oxidized to Cu2+ (means relasing of 2 electrons from Cu to Cu2+ ) and Ag+ is reduced to Ag(s) (means gaining of 2 electrons from 2Ag+ to 2Ag ) and thus, silver converted into solid state and deposited on copper rod.