Question
Balance the following,chemical equation by oxidation number method:
Solution
(i) The skeleton equation along with oxidation number of each atom is:
+2 -1 0 +3 -2 +4 -2
Fe S2 + O2
Fe2O3 + SO2
(O.N. of S in FeS2 is -1 and not - 2)
(ii) The oxidation number of iron, as well as sulphur, increases from +2 to +3 and -1 to +4 respectively. Since Fe and S must maintain their atomic ratio, the change in oxidation number will be considered together. But, the oxidation number of oxygen decreases from 0 to 2. Thus
O.N: increases 1 per Fe and 5 per S atom
(iii) Equalise the increase/decrease of O:N. multiply FeS2 by 4 and O2 by 11.
(iv) On counting and balancing the atoms on both sides, we get the balanced equation as,
+2 -1 0 +3 -2 +4 -2
Fe S2 + O2
Fe2O3 + SO2(O.N. of S in FeS2 is -1 and not - 2)
(ii) The oxidation number of iron, as well as sulphur, increases from +2 to +3 and -1 to +4 respectively. Since Fe and S must maintain their atomic ratio, the change in oxidation number will be considered together. But, the oxidation number of oxygen decreases from 0 to 2. Thus
O.N: increases 1 per Fe and 5 per S atom
(iii) Equalise the increase/decrease of O:N. multiply FeS2 by 4 and O2 by 11.
(iv) On counting and balancing the atoms on both sides, we get the balanced equation as,
