Answer the following:
What are anode and cathode for Leclanche' dry cell? Write electrode reactions and overall cell reaction when it generates electricity.
Solution
1) The container of the cell is made of zinc which serves as anode (–) and an inert graphite rod in the centre of the cell immersed in the electrolyte paste (manganese dioxide (MnO2) and carbon black) serves as cathode (+).
2) Electrode reactions are as follows:
i) Oxidation at anode:
`"Zn"_("s") -> "Zn"_(("aq"))^(2+) + 2"e"^(-)`
ii) Reduction at cathode:
`2"NH"_(4("aq"))^+ + 2"MnO"_(2("s")) + 2"e"^(-) -> "Mn"_2"O"_(3("s")) + 2"NH"_(3("aq")) + "H"_2"O"_(("l"))`
iii) Overall cell reaction:
`"Zn"_("s") + 2"NH"_(4("aq"))^+ + 2"MnO"_(2("s")) -> "Zn"_(("aq"))^(2+) + "Mn"_2"O"_(3("s")) + 2"NH"_(3("aq")) + "H"_2"O"_(("l"))`
