Balance the following redox reaction by oxidation number method: Zn + HNO3 --> Zn(NO3)2 + NO + H20
1. The zinc atoms are changing their oxidation number from 0 to +2, and some of the nitrogen atoms are changing from +5 to +2.
2. Determine the changes in oxidation number for the atoms oxidized and reduced.
Zn = 0 to +2; Net Change = +2
Some N = +5 to +2; Net Change = -3
3. We need three Zn atoms (net change of +6) for every 2 nitrogen atoms that change (net change of -6).
4. Because some of the nitrogen atoms are changing and some are not, place the 2 as coefficient in front of the NO (g) on the product side.
5. The 3 for the zinc atoms is placed in front of the Zn(s).
3Zn(s) + HNO3(aq) --> Zn(NO3)2(aq) + 2NO(g) + H2O(l)
6. Balance the rest of the atoms but keep the ratio of Zn to NO as 3:2.
3Zn(s) + 8HNO3(aq) --> 3Zn(NO3)2(aq) + 2NO(g) + 4H2O(l)