Assign oxidation numbers, find reductant and oxidant atoms and tie them before and after, then balance each molecular redox equation by the oxidation number method: HCIO2 + _NH3 - HСІ + N20 + H2O H2S +_NO2 + H2O →_SO2 + SO2 +_NH3 NO + _C6H6 + _H2O - _NH3 + _CO2
We follow the below rules to assign oxidation number to any atom in an element, molecule or ion
Rule-1:
Oxidation number(ON) of an atom in its standard state is 0. e.g oxidation number of Fe in Fe(s) is 0, O in O2(g) is 0 etc.
Rule-2:
Oxidaiton number of O is -2 in oxides, -1 in peroxides, and -1/2 in superoxides.
Rule-3:
Oxidation number of H is +1 in a molecule except in metal hydrides where it is -1.
Rule-4:
Oxidation number of group-1 elements is always +1 and that of group-2 element is +2 in their compounds.
Rule-5:
The sum of oxidation number of all the atoms in a neutral molecule is 0.
e.g In HClO2, (ON of H) + (ON of Cl) + 2*(ON of O) = 0
Rule-6:
The sum of oxidation number of all the atoms in a polyatomic ion is equal to its charge.
e.g in NO3-, (ON of N) + 3*(ON of O) = -1
Rule-7:
The oxidation number of a monoatomic ion is equal to its charge.
e.g Oxidation number of Fe in Fe3+ is 3.
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