Primary cells or dry cells structure, chemical reaction and functions of the various of its components.
Answer Text: 1. Primary cells/dry cells:- Are of various types and an example is the Le’ clanche dry cell.The Le’ clanche dry celli) Structure- Consist of a Zinc can with carbon rod at the centre.- The central graphite/carbon rod is surrounded by powdered Manganese (IV) oxide and carbon; which are inturn surrounded by a paste of #NH_4Cl# (s) and Zinc Chloride.- The protruding portion of the carbon rod is covered with a brass cap; and the zinc can covered with a sealing material.Chemical reaction- The Zinc can is the negative terminal; while the carbon/graphite rod is the positive terminal;a) a the Zinc can/negative terminalb) positive terminal /brass capHydrogen gas#NH_3 (g) + 2^(e-) to 2NH_3 (g) + H_2 (g)#Note: These gases (#NH_3# (aq) and #H_2# (g) ) are NOT used immediately but are used in more complex reactions.- The ammonia gas forms a complex with the zinc chloride in the paste.- The hydrogen gas is oxidised to water by the Manganese (IV) oxide.Functions of the various components.a) Brass cap - Functions as the positive terminal where the reduction reaction occurs.b) Zinc can - Is the Negative terminal; where the oxidation reaction occurs.c) Carbon rod - It serves as the positive electrode.- Acts as the connecting wire between the positive and negative terminal through it electron flow form the Zinc can to the brass cap.d) Manganese (IV) Oxide - To oxidise the Hydrogen gas produced at the anode/positive terminal/brass cap to water.- A single dry cell can produce a potential of 1.5 VNote: Dry ammonium chloride does not conduct electric current. This explains why a paste, which is a conductor, is used.The dry cells cannot provide a continuous supply of electricity for an undulate period of time.Reason - The reactants (electrolytes) are used up and cannot be replaced.
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