Carbon-zinc dry cells

The electrolyte was a solution of ammonium chloride that bathed the electrodes. Like Plante s electrochemistry of the lead-acid battery, Leclanche s electrochemistry survives until now in the form of zinc-carbon dry cells and the use of gelled electrolyte.12 In their original wet form, the Leclanche electrochemistry was neither portable nor practicable to the extent that several modifications were needed to make it practicable. This was achieved by an innovation made by J. A. Thiebaut in 1881, who through encapsulating both zinc cathode and electrolyte in a sealed cup avoided the leakage of the liquid electrolyte. Modern plastics, however, have made Leclanche s chemistry not only usable but also invaluable in some applications. For example, Polaroid s Polar Pulse disposable batteries used in instant film packs use Leclanche chemistry, albeit in a plastic sandwich instead of soup bowls.1... 

Lithium batteries can be either primary or secondary, depending on which reduchon reachons are coupled to the oxidahon of hthium. For example, some hthium batteries use the same cathode reaction as zinc-carbon dry cells, the reduchon of manganese(IV) oxide (Mn02) to manganese(III) oxide (Mn203). These baheries produce electric current at about 3 V compared to 1.5 V for zinc-carbon cells. Lithium batteries last much longer than other kinds of batteries. As a result, they are often used in watches, computers, and cameras to maintain hme, date, memory, and personal sethngs—even when the device is turned off. 

What is reduced and what is oxidized in the ordinary zinc-carbon dry cell battery What features make the alkaline dry cell an improvement over the earlier type of dry cell battery ... 

What part of a zinc-carbon dry cell is the anode Describe the reaction that takes place there. (21.2)... 

Batteries vary in size and chemistry. Shown here are an automobile lead-storage battery, rechargeable nickel-cadmium cells, alkaline cells, and zinc-carbon dry cells. 

The cell components are hermetically sealed in a steel shell that is in contact with the zinc and acts as the negative terminal of the battery. A fresh zinc-carbon dry cell generates a potential difference of 1.5 V. 

Some of the spontaneous cell reactions you have been reading about provide the energy of the batteries that you use every day. A battery is one or more voltaic cells in a single package that generates electric current. From the time of its invention in the 1860s until recently, the most commonly used voltaic cell was the zinc-carbon dry cell, shown in Figure 20.8. 

Zinc-carbon dry cells A dry cell is an electrochemical cell in which the electrolyte is a moist paste. The paste in a zinc-carbon dry cell consists of zinc chloride, manganese(IV) oxide, ammonium chloride, and a small amount of water inside a zinc case. The zinc shell is the cells anode, where the oxidation of zinc metal occurs according to the following equation. 

Figure 20.8 The so-called dry cell contains a moist paste in which the cathode half-reaction takes place. In the zinc-carbon dry cell, the zinc case acts as the anode. 

In the zinc-carbon dry cell, a spacer made of a porous material and damp from the liquid in the paste separates the paste from the zinc anode. The spacer acts as a salt bridge to allow the transfer of ions, much like the model voltaic cell you studied in Section 20.1. The zinc-carbon dry cell produces a voltage of 1.5 V until the reduction product, ammonia, comes out of its aqueous solution as a gas. At that point, the voltage drops to a level that makes the battery useless. 

Alkaline batteries A more efficient alkaline dry cell, shown in Figure 20.9, is replacing the standard zinc-carbon dry cell in many applications. In the alkaline cell, the zinc is in a powdered form, which provides more surface area for reaction. The zinc is mixed in a paste with potassium hydroxide, a strong base, and the paste is contained in a steel case. The cathode mixture is manganese(IV) oxide, also mixed with potassium hydroxide. The anode half-cell reaction is as follows. 

Figure 20.9 Alkaline batteries are more efficient than zinc-carbon dry cells and are useful when smaller batteries are needed. Silver button batteries are even smaller, making them well suited to devices such as watches. 

Dry cell see Alkaline dry cell and Zinc-carbon dry cell. 

Batteries such as those used in flashlights are zinc-carbon dry cells. These cells consist of a zinc container, which serves as the anode, filled with a moist paste of Mn02, carbon black, NH Cl, and ZnCl2, as illustrated in Figure 2.3a. When the external circuit is closed, zinc atoms are oxidized at the negative electrode, or anode. 

The reduction half-reaction, the reaction at the cathode, is exactly the same as that for the zinc-carbon dry cell. 

CRITICAL THINKING Distinguish What is the difference between a zinc-carbon dry cell and an alkaline battery ... 

Why is it possible for alkaline batteries to be smaller than zinc-carbon dry cells ... 

The shelf life of this battery is rather poor, as shown in Fig. 9.8, because of the slow loss of water and because of side reactions due to impurities in the Mn02 ore commonly used. When specially purified Mn02 is used, the performance of the battery is greatly improved. The zinc-carbon dry cell is considered the workhorse of the battery industry It provides power at a very low cost. 

Zinc-Carbon Battery. The Leclanche or zinc-carbon dry cell battery has existed for over 100 years and had been the most widely used of all the dry cell batteries because of its low cost, relatively good performance, and ready availability. Cells and batteries of many sizes and characteristics have been manufactured to meet the requirements of a wide variety of applications. Significant improvements in capacity and shelf life were made with this battery system in the period between 1945 and 1965 through the use of new materials (such as beneficiated manganese dioxide and zinc chloride electrolyte) and cell designs (such as the paper-lined cell). The low cost of the Leclanchd battery is a major attraction, but it has lost considerable market share, except in the developing countries, because of the newer primary batteries with superior performance characteristics. 

Dry cells You are probably most familiar with the type of battery knows as the dry cell, which contains a moist paste in which the cathode half-reaction occurs. Three types of dry cells are the zinc-carbon dry cell, the alkaline cell, and the mercury cell. Zinc is oxidized in each of these dry cells. In the zinc-carbon dry cell, the zinc shell is the anode and a carbon rod is the cathode. The newer alkaline batteries are smaller than zinc-carbon dry cells. Mercury batteries are even smaller and are used in such devices as hearing aids and calculators. 

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