The half-reaction of 3 Pb + 2 NO3 + 8 H-->3 Pb2+ + 2 NO + 4H2O
To balance this redox reaction, you need to follow a few steps:
1. Split the reaction into two separate half-reactions, one for oxidation and one for reduction. In this case, the oxidation half-reaction involves the Pb atoms losing electrons to form Pb2+ ions, and the reduction half-reaction involves the NO3- ions gaining electrons to form NO molecules.
Oxidation half-reaction: 3 Pb --> 3 Pb2+ + 6 e-
Reduction half-reaction: 2 NO3- + 6 e- + 8 H+ --> 2 NO + 4 H2O
2. Balance the non-hydrogen and non-oxygen elements first. In this case, the only element that requires balancing is lead (Pb) in the oxidation half-reaction. We have 3 Pb atoms on the left side, so we need 3 Pb2+ ions on the right side to balance the number of atoms.
Oxidation half-reaction: 3 Pb --> 3 Pb2+ + 6 e-
Reduction half-reaction: 2 NO3- + 6 e- + 8 H+ --> 2 NO + 4 H2O
3. Balance the oxygen atoms by adding water molecules (H2O) to the side that needs more oxygen. In this case, the reduction half-reaction has 3 oxygen atoms on the left side and 4 on the right side, so we need to add a water molecule on the left side.
Oxidation half-reaction: 3 Pb --> 3 Pb2+ + 6 e-
Reduction half-reaction: 2 NO3- + 6 e- + 8 H+ --> 2 NO + 4 H2O
4. Balance the hydrogen atoms by adding hydrogen ions (H+) to the side that needs more hydrogen. In this case, the oxidation half-reaction has 6 hydrogen ions on the left side and 8 on the right side, so we need to add 8 hydrogen ions on the left side.
Oxidation half-reaction: 3 Pb --> 3 Pb2+ + 6 e-
Reduction half-reaction: 2 NO3- + 6 e- + 8 H+ --> 2 NO + 4 H2O
5. Finally, balance the charges by adjusting the number of electrons (e-) transferred in each half-reaction. In this case, the oxidation half-reaction has 6 electrons on the left side and no electrons on the right side, so we need to add 6 electrons to the right side.
Oxidation half-reaction: 3 Pb --> 3 Pb2+ + 6 e-
Reduction half-reaction: 2 NO3- + 6 e- + 8 H+ --> 2 NO + 4 H2O
Now, the number of atoms, charges, and mass is balanced on both sides.