Question

From the given cells:
Lead storage cell, mercury cell, fuel cell and dry cell
Answer the following:
i. Which cell is used in hearing aids?
ii. Which cell was used in the Apollo space programme?
iii. Which cell is used in automobiles and inverters?
iv. Which cell does not have a long life?

Answer 1

Hint: A galvanic cell is a cell where the chemical energy of the redox reaction is converted into electrical energy. We know that more than one cell connected in series forms a battery. For the battery to be of practical use it must be compact and lightweight.

Step by step answer: we are given various cells, let us discuss each of them one by one and answer the questions asked. Firstly, a dry cell also known as a leclanche cell has a carbon rod as a cathode and zinc cup as anode. The space between anode and cathode is filled by the moist paste of ammonium chloride and zinc chloride. The cathode of graphite is surrounded by powdered manganese dioxide and carbon. The reaction occurs only once and after a period of time it can not be reused. Such cells are used in transistors and cells.
Mercury cell, suitable for low current devices like hearing aids, watches etc. consists of zinc and mercury amalgam as anode and a paste of HgO and carbon a cathode. The electrolyte is a paste of KOH and ZnO
Lead storage cell, is most important secondary cell used in automobiles and inverters. It consists of a lead anode and a grid of lead packed with lead dioxide as cathode. A 38% solution of sulfuric acid is used as an electrolyte. It can be reused again and again by charging and discharging cycles which leads to change in reactions.
Fuel cells are galvanic cells that are designed to convert the energy of combustion of fuels like hydrogen, methane, methanol etc. directly into electrical energy. It uses the reaction of hydrogen with oxygen to form water. It was used for providing electrical power in the Apollo space programme. In the cell hydrogen and oxygen are bubbled through porous carbon electrodes into concentrated aqueous sodium hydroxide solutions. The cell runs continuously as long as the reactants are supplied.
Hence the answer to above questions is-
(i)Mercury cell
(ii)Fuel cells
(iii)Lead storage cell
(iv)Dry cell

Note: Cell potential for mercury remains constant during its life as the overall reaction does not involve any ion in solution whose concentration can change during its lifetime.