Flashlight cells

Note that the case is actually one of the electrodes it s being used up in the reaction. If there s a thin spot in the case, a hole could form, and the cell could leak the corrosive contents. In addition, the ammonium chloride tends to corrode the metal case, again allowing for the possibility of leakage. 

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. 

Moist paste of ZnCl2 and NH4CI Mn02 and carbon black paste Graphite rod (cathode) 

Another cell with the same basic construction is the small mercury battery commonly used in watches, pacemakers, and so on. With this battery, the anode is zinc, as in the regular dry cell, but the cathode is steel. MercuryOO oxide (HgO) and some alkaline paste form the electrolyte. You should dispose of this type of battery carefully, to keep the mercury from being released into the environment. 

All these galvanic cells produce electricity until they run out of a reactant. Then they must be discarded. However, there are cells (batteries) that can be recharged, as the redox reaction can be reversed to regenerate the original reactants. Nickel-cadmium (Ni-Cad) and lithium batteries fall into this category. The most familiar type of rechargeable battery is probably the automobile battery. 

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The common flashlight cell (see Figure 9-2), a dry cell (it s not in a solution like a Daniell cell), is contained in a zinc housing that acts as the anode. The other electrode, the cathode, is a graphite rod in the middle of the cell. A layer of manganese oxide and carbon black (one of the many forms of carbon) surrounds the graphite rod, and a thick paste of anunonium chloride and zinc chloride serves is the electrol5rte. The cell reactions are... 

We use batteries as portable sources of electrical energy in many ways—in flashlights cell phones, notebook computersi calculators, automobiles etc. A battery Is a voltaic cell (or a set of voltaic cells coupled together) that has been designed for practical use. 

A battery is a device that stores chemical energy for later release as electricity. Some batteries consist of a single voltaic cell with two electrodes and the appropriate electrolyte(s) an example is a flashlight cell. Other batteries consist of two or more voltaic cells joined in series fashion—plus to minus—to increase the total voltage an example is an automobile battery. In this section, we will consider three types of voltaic cells and the batteries based on them. 

All flashlight batteries, button batteries, compact rechargeable batteries and vehicle storage batteries operate under the same basic principles. An electrochemical cell is constructed of two chemicals with different electron-attracting capabilities. Called an electrochemical couple, these two chemicals, itntncrscd in an electrolyte (material that carries the flow of energy between electrodes), are connected to each other through an external circuit. 

Electrochemical cells are familiar—a flashlight operates on current drawn from electrochemical cells called dry cells, and automobiles are started with the aid of a battery, a set of electrochemical cells in tandem. The last time you changed the dry cells in a flashlight because the old ones were dead, did you wonder what had happened inside those cells Why does electric current flow from a new dry cell but not from one that has been used many hours We shall see that this is an important question in chemistry. By studying the chemical reactions that occur in an electrochemical cell we discover a basis for predicting whether equilibrium in a chemical reaction fa-... 

A dry cell is the primary cell used in most common applications, such as portable CD players, remote controls, and flashlights (Fig. 12.21). Its familiar... 

C19-0125. The first battery to find widespread commercial use was the carbon-zinc dry cell, in which the cathode reaction is 2 Mn02( ) + q)+2e -> ZnMn2 04( ) In a flashlight, one of these batteries... 

The Leclanche cell (also known as the dry cell) is frequently used to power flashlights, watches, calculators, and a number of other portable devices. Despite the name dry cell, this battery does contain an electrolyte solution but only in the form of dense paste. There are two versions of this cell, the acid version and the alkaline version. 

Crystalline chemical and electrochemical manganese dioxides are employed in billions of cells of Leclanche type which remain today probably the most popular and inexpensive power sources for wrist watches, cameras, flashlights, portable electronic products, etc. Worldwide annual output of power sources is estimated at 40 bln. pieces more than 70% of them are those operating with Mn02 chemistry as a cathode active material or a... 

Fuel cells are also inherently flexible. Like batteries in a flashlight, the cells can be stacked to produce voltage levels that match specific power needs from a few watts for certain appliances to multiple megawatt power stations that can light a community. 

The Daniell cell is fairly large and full of liquid. Realistically, you could not use this type of cell to power a wristwatch, a remote control, or a flashlight. Galvanic cells have been modified, however, to make them more useful. 

Modern dry cells are closely modelled on the Leclanche cell, and also contain electrolyte pastes. You have probably used dry cells in all kinds of applications, such as lighting a flashlight, powering a remote control, or ringing a doorbell. Dry cells are inexpensive. The cheapest AAA-, AA-, C-, and D-size 1.5-V batteries are dry cells. 

A D-size dry cell flashlight battery is much bigger than a AAA-size dry cell calculator battery. However, both have cell potentials of 1.5 V. Do they supply the same quantity of electricity Explain your answer. 

Meanwhile, scientists studied the electrical activity of neurons. They discovered that the messages neurons pass to one another consist of brief electrical impulses known as action potentials. Neurons (and most other cells) have a small electrical potential of about 60 millivolts between their interior and exterior—this voltage, which is only about 4 percent as strong as a typical flashlight battery, exists across the cell s membrane. 

The ordinary dry cell (Leclanche cell) is a primary cell that is used in flashlights. In this cell, oxidation occurs at a zinc anode, and reduction at an inert carbon +" cathode (graphite). The space between the cell is filled with a moist paste of Mn02, ZnCl2 and NH CI. The half-reaction at the anode is as follows ... 

Manganese occurs in concentrated form as pyrolusite (Mn02) and man-ganite [MnO(OH)] deposits, and as manganese nodules on the ocean floor. The metal is used in alloys with iron, while MnC>2 is used in dry cells (flashlight batteries ) and as an oxidant in the chemical industry. 

The Leclanche cell, the inexpensive disposable flashlight-type cell, has been on the market for over 100 years, yet its chemistry is not completely understood. The cell consists of an outer zinc shell that acts as the anode (seen by the external circuit as the source of electrons and hence the negative terminal) and oxidizes away during operation of the cell, a carbon rod or disk that serves as the cathodic current collector (positive terminal), and a moist paste of manganese dioxide, ammonium chloride, and zinc chloride that fills the cell and acts as both the electrolyte and the source of the cathodic reaction (reduction of MnIV). Usually, graphite in the form of carbon black is added to the paste to increase the electrical conductivity. The basic reactions are... 

Electrolytic Cell. A combination of a liquid or semi-liquid electrolyte (soln of a salt, acid or base) and two solids serving as electrodes. The cell generates an electric current when the electrodes are connected by an external wire. Flashlight batteries (dry cells), storage batteries and fuel ceils (qv). 

Fig. 3.5 Intermilteirt discharge curve of a C-size Leclanche cell through load using a HIF (heavy industrial flashlight) lest schedule 4 min discharge every 15 min over an 8 hour period, repeated daily...

The cross-sections of two typical cylindrical cells are shown in Fig. 3.9. In Fig. 3.9(a) a D-size unit used for flashlights and similar applications is shown a large capacity alarm cell is shown in Fig. 3.9(b). The electrolyte or paste separator in Fig. 3.9(a) is a relatively thin layer of electrolyte solution immobilized in a gel or microporous separator. Different manufacturers favour different forms of separator. These range from gelled... 

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