Cell reactions silver zinc

Other electrolytes, such as sodium sulfate or potassium nitrate, could be chosen for the salt bridge. Neither of these electrolytes interferes in the cell reaction. Silver nitrate, AgN03(aq), would be a poor choice for the salt bridge, however. Positive silver ions would migrate into the half-cell that contains the cathode. Zinc displaces both copper and silver from solution, so both copper(n) ions and silver ions would be reduced at the cathode. The copper produced would be contaminated with silver. 

The silver-zinc cell is a storage battery After discharge, it can be recharged by forcing through it an electric cnrrent in the reverse direction. In this process the two electrode reactions (19.3) and (19.4) as well as the overall reaction (19.2) go from right to left electrons flowing in the sense of arrow r in Fig. 19.1. 

One more example demonstrates how to use standard reduction potentials to determine the standard potential of a cell. Let s say you wanted to construct a cell using silver and zinc. This cell resembles the Daniell cell of the previous example except that a silver electrode is substituted for the copper electrode and a silver nitrate solution is used in place of copper sulfate. From Table 14.2, it is determined that when silver and copper interact silver is reduced and copper oxidized. The two relevant reactions are... 

The main features of zinc-silver oxide cells are similar to those of the zinc-mercuric oxide system, except for a higher OCV and significantly increased cost. The overall cell reaction is... 

The overall cell reaction is exactly similar to the zinc-silver oxide cell, with the final discharge products being silver and Fe(OH>2. The emf of the cell is only 1.34 V, but the cell has a superior cycle life and better reliability. Batteries up to 10 kWh have been built by Westinghouse for telecommunications and submersible vehicles. 

The silver oxide-zinc battery used in hearing aids delivers a voltage of 1.60 V. Calculate the free-energy change (in kilojoules) for the cell reaction... 

Silver oxide cells were developed in the 1960s. These cells use silver oxide mixed with carbon (to increase the electronic conductivity of the material) as cathode, amalgamated pellet zinc powder as anode, and a solution of potassium hydroxide or sodium hydroxide with dissolved zin-cates in water as electrolyte. Permion (a radiation graft of methacrylic acid onto a polyethylene membrane) is used as separator. The cell reactions are... 

Reaction Mechanisms. There is considerable difference of opinion concerning the specific cell reactions that occur in the silver—zinc battery. Equations that are readily acceptable are... 

Zinc/silver oxide button batteries are used in calculators and watches. Although the silver component makes them expensive, this is outweighed by their high performance. The battery uses KOH as the electrolyte, and the overall cell reaction is ... 

The overall electrochemical cell reactions for the sUver-zinc, sUver-cadmium, and silver-iron systems, all of which use aqueous solutions of potassium hydroxide (KOH) for electrolyte, can be summarized as follows ... 

The earliest cell to be widely used was the Daniell cell. The disadvantages of employing two electrolytes are obvious, and these are avoided in the Leclanche cell, on which are based the majority of dry cells (see dry cell). Other cells with special uses are the mercury cell (q.v.), the copper oxide cell (q.v.), the silver-zinc cell (q.v.), the zinc-air cell (q.v.) and the chloride cell (q.v.). These cells all vary in the cathode reaction but all have zinc anodes, although magnesium is a promising alternative. 

Because no solution species is involved in the cell reaction, the quantity of electrolyte is very small and the electrodes can be maintained very close together. The cell voltage is 1.8 V, and its storage capacity is six times greater than that of a lead-acid battery of the same size. These characteristics make batteries, such as the silver-zinc cell, useful in button batteries. These... 

By the half-cell potentials, we conclude the Zn-Zn+2 half-reaction has the greater tendency to release electrons. It will tend to transfer an electron to silver ion, forcing (54) in the reverse direction. Hence we obtain the net reaction by subtracting (54) from (52). But remember that this subtraction must be in the proportion that causes no net gain or loss of electrons. If two electrons are lost per atom of zinc oxidized in (52), then we must double half-reaction (54) so that two electrons will be consumed. 

The silver oxide and mercuric oxide button cells used in cameras and other devices requiring a miniature source of EMF consist of a zinc disk, which serves as the anode, and, on the other side of a porous separator, a paste of Ag20 or HgO. The reaction products are zinc hydroxide and metallic silver or mercury. Inert metal caps serve as the current collectors. 

Exactly 0.2 mol of electrons are passed through three electrolytic cells in series. One contains silver ion, the next zinc ion, and the last iron(III) ion. Assume that the only cathode reaction in each cell is the reduction of the ion to metal. How many grams of each metal will be deposited ... 

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