Question

Which of the following reactions occurs at the cathode of a common dry cell?
A. \[{\rm{Mn}} \to {\rm{M}}{{\rm{n}}^{{\rm{2 + }}}} + 2{e^ - }\]
B. \[2{\rm{Mn}}{{\rm{O}}_{\rm{2}}} + {\rm{Z}}{{\rm{n}}^{{\rm{2 + }}}} + 2{e^ - } \to {\rm{ZnM}}{{\rm{n}}_{\rm{2}}}{{\rm{O}}_{\rm{4}}}\]
C. \[2{\rm{Zn}}{{\rm{O}}_{\rm{2}}} + {\rm{M}}{{\rm{n}}^{{\rm{2 + }}}} + 2{e^ - } \to {\rm{MnZ}}{{\rm{n}}_{\rm{2}}}{{\rm{O}}_{\rm{4}}}\]
D. \[{\rm{Zn}} \to {\rm{Z}}{{\rm{n}}^{{\rm{2 + }}}} + 2{e^ - }\]

Answer 1

Hint: The electrochemical cell defines the cell that produces electricity from the chemical reaction. A dryer is an electrochemical cell or we can say a battery used mostly in the portable electronic device and equipment of houses. The dry cell that is used in common is zinc-carbon dry cell.

Complete Step by Step Solution:
Let's understand the dry cell in detail. The electrolyte of a dry cell is present in the paste form of immobilised electrolytes of low moisture content. This restricts the flowing of the paste and the low moisture is enough for the flowing of current.

Let's discuss the Zinc carbon dry cell. In a Zinc -Carbon dry cell, a zinc container acts as an anode and carbon graphite behaves as a cathode. The space between both the electrodes is filled up with manganese dioxide and an electrolyte of low moisture content consists of zinc chloride and ammonium chloride.

At anode, the oxidation reaction of zinc takes place. After losing two electrons, the formation of cations of zinc occurs.
\[{\rm{Zn}} \to {\rm{Z}}{{\rm{n}}^{2 + }} + 2{e^ - }\]

At the cathode of graphite, the reduction reaction takes place.
\[2{\rm{Mn}}{{\rm{O}}_{\rm{2}}} + {\rm{Z}}{{\rm{n}}^{{\rm{2 + }}}} + 2{e^ - } \to {\rm{ZnM}}{{\rm{n}}_{\rm{2}}}{{\rm{O}}_4}\]
Hence, the correct answer is option B.

Note: The dry cells are of two types, primary and secondary. A primary dry cell is neither rechargeable nor reusable. For example, lithium cells, mercury cells. The recharge of a secondary cell is possible with the help of a battery. One example is, nickel-cadmium cell.