![]() ![]() When the cell is connected in an external electrical circuit, the excess electrons on the zinc anode flow through the circuit to the carbon rod, the movement of electrons forming an electric current. As the Zn 2+ ions move away from the anode, leaving their electrons on its surface, the anode becomes more negatively charged than the cathode. they give up both their valence electrons to become positively charged Zn 2+ ions. The chemical process which produces electricity in a Leclanché cell begins when zinc atoms on the surface of the anode oxidize, i.e. – anode (oxidation of Zn): Zn → Zn 2+ + 2e − | E 0 = 0.76 volts – cathode (reduction of Mn(IV)): 2 MnO 2 + 2NH 4 + + 2e − → 2 MnO(OH) + 2 NH 3 | E 0 = 1.23 volts The redox reaction in a Leclanché cell involves the two following half-reactions: Improved dry cell In 1888, a German physician, Carl Gassner, improved the jellification process and produced a more portable dry cell by mixing plaster and hydrophilic chemicals with the ammonium chloride electrolyte. Starch addition In 1876, Georges Leclanché added starch to the ammonium chloride electrolyte in an effort to better jellify it. It has a lower internal resistance than either of the above (porous and agglomerate). In addition, the zinc rod is replaced by a zinc cylinder to give a larger surface area. Sack cell In this cell the porous pot is replaced by a wrapping of canvas or sacking. These blocks were made by mixing the manganese dioxide with binding agents and pressing the mixture into moulds. Agglomerate block cell In 1871 Leclanché dispensed with the porous pot and replaced it with a pair of "agglomerate blocks", attached to the carbon plate by rubber bands. The liquid solution acts as the electrolyte, permeating through the porous pot to make contact with the cathode. The anode (oxidation reaction), which is a zinc rod, is then immersed along with the pot in a solution of ammonium chloride. Porous pot cell In Leclanché's original cell the depolarizer (in fact, the oxidizing agent in the cell), consisting of crushed manganese dioxide, is packed into a pot, and a carbon rod is inserted to act as the cathode (reduction reaction). ![]() Leclanché first, and Carl Gassner later, both strived to transform the original wet cell into a more portable and more efficient dry cell. These included the "Agglomerate block cell" and the "Sack cell". This gave it a relatively high internal resistance, and various modifications were made to reduce the resistance. The original form of the cell used a porous pot. These reactions reverse themselves when the battery is left idle, making it good for many short periods of use with idle time between them, but not long periods of use. This is because certain chemical reactions in the cell increase its internal resistance and, thus, lower its voltage. The Leclanché cell could not provide a sustained current for very long in lengthy conversations, the battery would run down, rendering the conversation inaudible. The dry cell form was used to power early telephones-usually from an adjacent wooden box affixed to the wall-before telephones could draw power from the telephone line itself. This cell achieved very quick success in telegraphy, signalling and electric bell work. The manganese dioxide cathode had a little carbon mixed into it as well, which improved conductivity and absorption. In 1866, Georges Leclanché invented a battery that consisted of a zinc anode and a manganese dioxide cathode wrapped in a porous material, dipped in a jar of ammonium chloride solution. The chemistry of this cell was later successfully adapted to manufacture a dry cell. The battery contained a conducting solution ( electrolyte) of ammonium chloride, a cathode (positive terminal) of carbon, a depolarizer of manganese dioxide (oxidizer), and an anode (negative terminal) of zinc (reductant). The Leclanché cell is a battery invented and patented by the French scientist Georges Leclanché in 1866. ![]()
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