Quick Revision: Redox Reactions | Chemistry Class 11 - NEET PDF Download

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REDOX REACTIONS
CONCEPT OF OXIDATION & REDUCTION
Oxidation Reduction 
(i) Loss of electron (i) Gain of electron 
(ii) Loss of hydrogen (ii) Gain of hydrogen 
(iii) Gain of oxygen (iii) Loss of oxygen 
(iv) Increase in oxidation number (iv) 
Decrease in oxidation number 
 
OXIDATION NUMBER
Oxidation number change is defined as the change (real or imaginary) which an atom appears to have undergone
when it is present in redox reaction. There are certain rules laid down in order to determine the oxidation number.
(a) Oxidation number of an atom in free elements is zero.
(b) Oxidation number of oxygen is –2, while in peroxides it is –1, in OF
2
 it is +2.
(c) Oxidation number of hydrogen is +1, while in metal hydrides it is –1.
(d) Oxidation number of an ion is equal to the electrical charge present on it.
(e) Oxidation number of group IA elements is +1 and that of group IIA elements is +2.
(f) For complex ions, the algebraic sum of oxidation numbers of all the atoms is equal to the net charge
on the ion.
(g) In case of neutral molecules the algebraic sum of the oxidation number of all the atoms present in the
molecules is zero.
(h) Oxidation number of an atom never be greater than its valence electron. e.g., valence electron for Cr is 6.
Increase in oxidation number of an element in a reaction is known as oxidation while decrease in oxidation
number of an element in a reaction is known as reduction.
Besides +ve and -ve values, fractional values of oxidation number (as average) are also possible.
Balancing of H
2
O can also be done as per the medium given