Redox Reactions | Oxidation and Reduction Reaction | Class 11 | Chemistry NCERT | CBSE Chemistry

Redox Reacitons | Oxidation and reduction reaction class 11 chemistry from NCERT and CBSE syllabus…..
At the same time, if a molecule gets oxidized and another gets reduced, such reactions are known as Oxidation Reduction Reactions. These are also called Redox Reactions. The word Redox is derived from the ‘Red’ in Reduction and ‘Ox’ in Oxidation.
Oxidation
Definition: Oxidation is the addition of oxygen/electronegative element to a substance or removal of hydrogen/ electropositive element from a substance.
2 Mg (s) + O2 (g) → 2 MgO (s)
In this reaction, Magnesium conjugates with oxygen and gets Oxidised.
S (s) + O2 (g) → SO2 (g)
In this reaction, Sulphur conjugates with oxygen and gets Oxidised.
Mg (s) + Cl2 (g) MgCl2 (s)
In this reaction, Magnesium conjugates with Chlorine, a electronegative substance and gets Oxidised.
In the above reactions, the elements Magnesium and Sulphur are oxidised on account of addition of Oxygen to them.
Reduction
Definition: Reduction is the removal of oxygen/electronegative element from a substance or addition of hydrogen/ electropositive element to a substance.
2 HgO s ∆→ 2 Hg (l) + O2 (g)
In this reaction, oxygen is removed from Mercury.
2 FeCl3 (aq) + H2 (g) 2 FeCl2 (aq) + 2 HCl(aq)
In this reaction, electronegative Chlorine is removed from Ferric Chloride.
CH2=CH2 (g) + H2 (g) H3C - CH3 (g)
In this reaction, Ethylene conjugates with hydrogen.
Effects on Oxidation in Daily life
Decay: Apples, Bananas and Potatoes etc contain Polyphenol Oxidase or Tyrosine enzymes. These enzymes react with oxygen. When fruits like apples are cut, the enzymes and chemicals in it react with the oxygen in air. This is why the top layer turns brown.
Rusting: When iron is left for a long time in an environment containing moisture, it turns brown. This is the rusting of iron. This reaction needs both oxygen and water. It is also an oxidation. However, when iron objects are placed in an environment without either oxygen or water, they do not rust. Galvanisation is the process by which a coat of zinc is applied on the surface of Iron to prevent it from rusting.
Damage to Silverware: Copper, Brass, Silver, Aluminium and Magnesium and other such metals maybe damaged by the formation of a thin layer of rust on them. Their external surfaces take part in this chemical reaction. Hydrogen Sulphide is essential to damage silver. Over time, this forms a tarnish with oxygen. In reality, this external tarnish protects the metal inside. This form is known as Patina.
Redox Reactions in terms of Electron Transfer Reactions
2 Na(s) + Cl2(g) by the loss and gain of two electrons form 2 Na+Cl- (s).
2 Na(s) + O2(g) by the loss and gain of two electrons form Na2+O2-(s).
2 Na(s) + S(s) by the loss and gain of two electrons form Na2+ S2- (s).
Electrons are gained in one phase and lost in another.
2 Na(s) → 2 Na+(g) + 2e-
Cl2(g) + 2e- → 2 Cl-(g)
Each of the above steps is called a half reaction. Sum of the half reactions gives the overall reaction.
2 Na(s) + Cl2 (g) → 2 Na+ Cl- (s) or 2 NaCl (s)
Half reactions that involve loss of electrons are called oxidation reactions. Similarly, the half reactions that involve gain of electrons are called reduction reactions.
Oxidising Agent: Acceptor of electrons is called the Oxidising agent.
Reducing Agent: Donor of electrons is called the Reducing agent.

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