Alkaline dry cell battery

Why does an alkaline dry cell battery typically last longer than a normal dry cell Write the chemical equation for the overall cell reaction in an alkaline dry cell. 

BATTERIES AND FUEL CELLS (SECTION 20.7) A battery is a self-contained electrochemical power source that contains one or more voltaic cells. Batteries are based on a variety of different redox reactions. Batteries that cannot be recharged are called primary cells, while those that can be recharged are called secondary cells. The common alkaline dry cell battery is an example of a primary cell battery. Lead-acid, nickel-cadmium, nickel-metal hydride, and lithium-ion batteries are examples of secondary cells. Fuel cells are voltaic cells that utilize redox reactions in which reactants such as H2 have to be continuously supphed to the cell to generate voltage. 

Mercury and lithium batteries are similar to alkaline dry-cell batteries. For example, a mercury battery has a zinc anode, but the cathode is steel in a mixture of HgO, KOH, and Zn (OH)2. The reduced product Hg is toxic and an environmental hazard. Mercury batteries come with warnings on the label and should be disposed of properly. 

Schematic diagram and examples of alkaline dry cells. These batteries provide electrical current for many portable devices.

Electrochemical processes occur all around us. We close this chapter by examining a few of these processes and relating them to the electrochemical principles previously introduced. Batteries are probably the most common example of electrochemical applications associated with everyday life. While batteries come in all sizes and shapes, all batteries contain the basic elements common to all electrochemical cells. What differentiates one battery from another are the materials used for cathode, anode, and electrolyte, and how these materials are arranged to make a battery. The standard dry cell battery or alkaline cell is shown in Figure 14.8. Batteries consist of... 

Another type of disposable battery, the more expensive alkaline battery, shown in Figure 11.10, avoids many of the problems of dry-cell batteries by operating in a strongly alkaline paste. In the presence of hydroxide ions, the zinc oxidizes to insoluble zinc oxide ... 

Alkaline batteries last a lot longer than dry-cell batteries and give a steadier voltage, but they are expensive. 

Closely related to the alkaline dry cell is the mercury battery, often used in watches, heart pacemakers, and other devices where a battery of small size is required (Figure 18.10). The anode of the mercury battery is zinc, as in the alkaline dry cell, but the cathode is steel in contact with mercury(II) oxide (HgO) in an alkaline medium of KOH and Zn(OH)2. Zinc is oxidized at the anode, and HgO is reduced at the cathode ... 

In the alkaline version of the dry cell battery the solid NH4C1 is replaced with KOH or NaOH. In this case the half-reactions can be approximated as follows ... 

Q Write chemical equations for the reactions utilized by (i) zinc chloride and (ii) alkaline manganese non-rechargable dry cell batteries. 

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 ... 

The Teclanche cell has the disadvantage that its concentrations change with time, and thus the voltage of the battery falls as it is used. In an alkaline dry cell, the ammonium chloride is replaced by potassium hydroxide, and the half-cell reactions become... 

A third primary dry cell is the zinc-mercuric oxide cell depicted in Figure 17.7. It is commonly given the shape of a small button and is used in automatic cameras, hearing aids, digital calculators, and quartz-electric watches. This battery has an anode that is a mixture of mercury and zinc and a steel cathode in contact with solid mercury(II) oxide (HgO). The electrolyte is a 45% KOH solution that saturates an absorbent material. The anode half-reaction is the same as that in an alkaline dry cell,... 

A more modem version of the dry cell battery is the alkaline version where the solid NH4CI is replaced by KOH and NaOH. Hereby the following half cell reaction takes place at the anode ... 

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. 

The only power sources feasible for all these portables are electrochemical batteries. Disposable batteries were the classical power source for flashlights, and still hold a very strong position (salt Leclanche later, alkaline dry cells of zinc-manganese dioxide type). Rechargeable batteries became ever more important first, nickel-cadmium, and more recently, nickel-hydride and lithium ion batteries. For convenient handling, a power source is usually placed somewhere inside the device, so it should respect certain limitations as to weight and volume. As a rule of thumb, a power source should not exceed 30-40% by mass and volume of the device powered by it. A similar upper limit 30-40% applies to the cost. 

Other primary cells are also used as batteries for certain applications. In some instances, the battery must be quite small. For a medical device, such as a heart pacemaker, a battery should not only be small, but long lasting. Mercury batteries have come to fill this role. In the mercury battery, shown in Figure 13.14, zinc is the anode as in the alkaline dry cell ... 

If alkaline batteries were not alkaline but rather acidic (as in the older dry cell batteries), what extra difficulties could you envision with corrosion, based on reactions that are part of the table of standard reduction potentials ... 

In the alkaline dry cell (alkaline battery), the acidic ammonium chloride of the regular dry cell is replaced by basic (alkaline) potassium hydroxide. With this chemical, corrosion of the zinc case is greatly reduced. 

Friedman M, McCauley CE (1947) The Ruben cell - a new alkaline primary dry cell battery. Trans Electrochem Soc 92 195-215... 

Nernst equation (20.7) zinc-carbon (Leclanche) dry cell (20.8) alkaline dry cell (20.8) lithium-iodine battery (20.8) lead storage cell (20.8) nickel-cadmium cell (20.8)... 

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