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Manganese dioxide is used as depolariser. The use of charcoal powder makes MnO, conduction and thus, decreases the internal resistance of the cell. Action. The electrolyte HN.Cl solution dissociates into NH4+ and Cl- ions. As zinc rod in dipping inside the NH Cl solution, some of the atoms go into the solution as Zn+ + ions. For each Zn+ + ion so produced, two electrons are left on the zinc rod and hence it becomes negative pole of the cell. The NH, ions are repelled by Zn+ + ions and they diffuse into the MnO, and charcoal mixture through the walls of the porus pot. Inside the glass vessel. Zn+ + ions combine with Cl- ions to form ZnCl2. On diffusing into porus pot, NH4+ ions extract electrons from the carbon rod making carbon rod as positively charged and producing ammonia and hydrogen gas. Whereas the ammonia gas escapes from the cell, hydrogen gas is neutralised by MnO, producing manganese trioxide (Mn203) and
water.
Secondary Cells A secondary cell is one in which chemical energy is converted into electrical energy but they do so when they are charged by passing current through them by some source. These are also called accumulators or storage cells. These are of two types: 1. Lead acid cell or lead accumulator, 2. Edison alkali cell Lead Accumulator It is a secondary cell and is the most common type of storage battery used in automobiles. It is known as lead acid cell. It was invented by French Physicist, Gaston Plante in the year 1859. Construction. It consists of a hard rubber, glass or celluloid container containing dilute sulphuric acid as the electrolyte. Each of the two electrodes consists of a set of alternate parallel mesh type perforated plates made of lead. The set of plates to be made the positive pole is filled with a paste of lead dioxide (PbO2), while the set of plates to be made the negative pole is filled with a paste of spongy lead (Pb.) The
positive and negative plates are kept separated and insulated from each TAH YEN 3411 - 09, 2004
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