Question
Balance the following equation by oxidation number method:
Solution
(i) The skeleton equation along with oxidation number of each atom is
Total O.N. of Cr = +12
Total O.N of Cr = +6
(ii) Noting the change in O.N. of above atoms,
Increase Fe = +2 to +3 to i.e. 1
Decrease Cr = +12 to +6 i.e. 6
(iii) Equalise the increase/decrease in O.N. by multiplying Fe2+ by 6,
(iv) Balance Fe atoms by multiply Fe3+ by 6.
(v) Balance the hydrogen atoms
Net charge on LHS = +12 -2 + 1 = +11
Net charge on RHS = +18 + 6 = +24
So difference = 24 - 11 = 13
Therefore adding thirteen H+ LHS,
(vi) Balance O atoms and four more H2O molecules on RHS, the balanced equation is
