Question

Decide whether or not each metal dissolves in 1 molL−1 HNO3. Standard Electrode Potentials at 25 ∘C Reduction Half-Reaction E∘(V)

NO3−(aq)+4H+(aq)+3e− →NO(g)+2H2O 0.96

Cu2+(aq)+2e− →Cu(s) 0.34

Au3+(aq)+3e− →Au(s) 1.50

Pb2+(s)+2e− →Pb(s) -0.13

Write a balanced redox reaction showing what happens when Pb dissolves.

Answer 1

A solution with a higher (more positive) reduction potential than the new species will have a tendency to gain electrons from the new species (i.e. to be reduced by oxidizing the new species) and a solution with a lower (more negative) reduction potential will have a tendency to lose electrons to the new species (i.e. to be oxidized by reducing the new species). Hence, those metals whose reduction potential is less than that of Nitric acid will get dissolved or oxidised by Nitric acid solution.

As we already have the half reactions for Pb and NO3- we need to reverse the reaction (reduction rxn) for Pb as it is getting oxidised and multiply Pb reaction by 3 and Nitric acid rxn by 2 to make the number of electrons same on both the sides.

Hence, our reaction will be as follows:

3Pb(s) + 2NO3-(aq) + 8H+(aq)----> 3Pb2+(aq) + 2NO(g) + 4H2O