Oxidation state of elements in reactant side are as follow, Zn = +2 S = -2 N = +5 O = -2 Oxidation state of elements in product side are as follow, Zn = +2 S = 0 N = +2 O = -2 So, In this reaction Nitrogen is Reduced while Sulfur is Oxidized.
Now Split the reaction into two half cell reactions,
Reduction Reaction, ZnS → S + 2e⁻ Oxidation Reaction, NO₃⁻ + 3e⁻ → NO
As the oxygen atoms are not balance, So, in acidic medium add H⁺ on the side having greater number of Oxygen atom and H₂O on the side having less number of Oxygen atoms, Hence, H⁺ + NO₃⁻ + 3e⁻ → NO + H₂O Now Balance the reaction,
4H⁺ + NO₃⁻ + 3e⁻ → NO + 2H₂O
So, write both half cell equations as,
ZnS → S + 2e⁻ --------- (1) 4H⁺ + NO₃⁻ + 3e⁻ → NO + 2H₂O -------(2)
Multiply eq. 1 with 3 and eq. 2 with 2 to equalize the electron. So, 3ZnS → 3S + 6e⁻
Below Mechanism shows the mechanism of formation of diazonium ion. Aniline is treated with Nitrosonium ion which is generated in situ by the reaction of Sodium nitrile and strong acid. The resulting <span>benzenediazonium ion on reaction with CuBr yields Bromobenzene and on treatment with CuCN gives Benzonitrile. Mechanism is as folow,</span>