Question

For all of the following experiments, under standard conditions, which species could be spontaneously produced?

Oxygen gas is bubbled through an acidified solution of Fe2+
H2O (yes/no)
Fe (yes/no)
Fe3+ (yes/no)

A lead wire is placed in a solution containing Cu2+
Pb2+ (yes/no)
No reaction (yes/no)
PbO2 (yes/no)

A silver wire is placed in a solution containing Cu2+
Ag+ (yes/no)
Cu (yes/no)
No reaction (yes/no)

Answer 1

1) H2O (yes)
Fe (/no)
Fe3+ (yes)

4Fe+2 & O2 & 4H+ --> 4Fe+3 & 2H2O

Eo = +1.23 & -0.77 = +0.46

2) Pb(s) + Cu^2+(aq) -------> ?

Pb(s) --------> Pb^2+(aq) + 2e- E = 0.13 V
Cu^2+ + 2e- -------> Cu E = 0.16 V
E reaction = 0.13 + 0.16 = 0.29
It is spontaneous reaction. Pb can reduce Cu^2+ but since the reverse reaction will not be spontaneous, Cu can reduce Pb^2+.

3) Now look at the last one

Ag(s) + Cu^2+(aq) -------> ?


Ag -------> Ag^+ + e- E = - 0.80 V
Cu^2+ + 2e- -------> Cu E = 0.16 V
E reaction = - 0.80 + 0.16 = - 0.64
It is non-spontaneous reaction. Ag cannot reduce the Cu^2+ but as we know the reverse reaction will be spontaneous, Cu can reduce Ag^+.