Question

Which of the following cell reactions would require the use of an inert electrode?

a.) Ba(s) + 2Ag+(aq) → Ba2+(aq) + 2Ag(s)

b.) 3Fe(s) + 2Au3+(aq) → 3Fe2+ + 2Au(s)

c.) 3Rb+(aq) + Al(s) → 3Rb(s) + Al3+(aq)

d.) Zn(s) + 2MnO2(s) + 2NH4+(aq) → Zn2+(aq) + Mn2O3(s) + 2NH3(aq) + H2O(l)

e.) Cu(s) + 2Ag+(aq) → 2Ag(s) + Cu2+(aq)

If you could also explain how you got your answer, it would be highly appreciated!

Answer 1

An inert electrode is required when any of the half cell involves substances which cannot form a solid electricity conducting electrode.

For the given cell reactions, except reaction d) all other reactions involve a solid metal component for each of the two half cells, that can be used as an electrode.

But in case of d) MnO2 involving half cell does not have any solid component which can conduct electricity. Only solid in this half cell is MnO2, which is a poor conductor of electricity(note: other half cell -anode half cell where Zn is oxidized, Zn anode is used). So an external inert material like Platinum, that itself does not take part in the cell reaction but only acts as a medium of transfer of electrons, is used as an electrode.

Hence answer is : d)Zn(s) + 2MnO2(s) + 2NH4+(aq) → Zn2+(aq) + Mn2O3(s) + 2NH3(aq) + H2O(l).

Comment in case of any doubt.