The Copper-Silver Cell

Now consider a similar standard voltaic cell consisting of a strip of Cu immersed in 1 M CUSO4 solution and a strip of Ag immersed in 1 M AgN03 solution. A wire and a salt bridge complete the circuit. The following observations have been made. 

The mass of the copper electrode decreases. The Cu ion concentration increases in the solution around the copper electrode. 

The mass of the silver electrode increases. The Ag ion concentration decreases in the solution around the silver electrode. 

As before, ions from the salt bridge migrate to maintain electroneutrality. Some NO3 ions (from the cathode vessel) and some Cu ions (from the anode vessel) also migrate into the salt bridge to keep the overall charge balanced.Two NO3 ions migrate for each Cu ion. 

Recall that in the zinc-copper cell the copper electrode was the cathode-, now in the copper-silver cell the copper electrode has become the anode. 

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Given the half-cell potentials in Table 17.2, calculate the cell potential of (a) the Daniell cell, (b) the copper/silver cell. 

The Zinc-Copper Cell 21-10 The Copper-Silver Cell... 

Left) A spiral of copper wire was placed in a colorless solution of silver nitrate, AgN03. The silver has been displaced from solution and adheres to the wire. The resulting copper nitrate solution is blue. The same reaction occurs when the two half-reactions are separated in the copper-silver cell (see Figure 21-7). (Right) No reaction occurs when silver wire is placed in a blue copper sulfate solution. The reaction... 

The Zinc-Copper Cell 21-10 The Copper-Silver Cell Standard Electrode Potentials 21-11 The Standard Hydrogen Electrode 21-12 The Zinc-SHE Cell 21-13 The Copper-SHE Cell 21-14 Standard Electrode Potentials 21-15 Uses of Standard Electrode Potentials 21-16 Standard Electrode Potentials for Other Half-Reactions 21-17 Corrosion 21-18 Corrosion Protection... 

The same spontaneous (product-favored) reaction occurs when the two half-reactions are separated in the copper-silver cell (see Figure 21-7). 

Figure 21-7 The copper-silver voltaic cell utilizes the reaction...

The accuracy of the silver chloride reference electrode depends upon the amount of chloride ion that is present in the solution and the accuracy with which it is controlled. In practical applications two concentrations of chloride ion are popular. In the first the electrolyte surrounding the silver chloride element is seawater. The other type of reference electrode uses a saturated sodium or potassium chloride solution. Both silver chloride cells have large temperature coefficients but there is no hysteresis or other effects so that these variations can be calculated. These reference electrodes typically have a higher resistance than the copper sulfate cells and this resistance is a function of the thickness of the silver chloride layer. 

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. 

Electrodes. AH of the finished silver electrodes have certain common characteristics the grids or substrates used in the electrodes are exclusively made of silver, although in some particular cases silver-plated copper is used. Material can be in the form of expanded silver sheet, silver wire mesh, or perforated silver sheet. In any case, the intent is to provide electronic contact of the external circuit of the battery or cell and the active material of the positive plate. Silver is necessary to avoid any possible oxidation at this junction and the increased resistance that would result. 

Molybdenite [1309-56 ] M0S2, normally floats with the copper sulfides. Therefore, the copper concentrate from the cleaner cells frequently has to be separated from molybdenite in a separate flotation circuit before the copper concentrate goes to the smelter. Gold, silver, selenium, and tellurium are collected with the copper concentrate. 

New chemical specks are produced in each half of the cell. The copper rod is converted to copper ions (the rod loses weight) and the silver ions are changed to metal (the silver rod gains weight). The new species can be explained in terms of gain of electrons (by silver) and loss of electrons (by copper). 

Before examining the processes in a cell, we should name the parts of a cell and clear away some language matters. The electrons enter and leave the cell through electrical conductors—the copper rod and the silver rod in Figure 12-5— called electrodes. At one electrode, the copper electrode, electrons are released and oxidation occurs. The electrode where oxidation occurs is called the anode. At the other electrode, the silver electrode, electrons are gained and reduction occurs. The electrode where reduction occurs is called the cathode. 

AOTF w/c RMs bearing the silver, silver iodide and silver sulfide nanoparticles were depressurized slowly and the nanoparticles in the cell were collected and re-dispersed in ethanol. Finally, the sample grids for the TEM (FEl TECNAl G ) measurements were prepared by placing a drop of ethanolic dispersion of nanoparticles on the copper grid. The morphology and size distribution of the silver, silver iodide, and silver sulfide nanoparticles were determined by TEM at an operation voltage of 200kV. The crystallinity of the silver, silver iodide, and silver sulfide nanoparticles was studied by electron diffraction techniques. 

And finally, the same procedure was followed as above, but instead of obtaining an unknown concentration of silver ion, the student prepared a solution containing 2 drops of 1.00 M Cu(N03)2 in 10. mL of 6.00 M NH3. The student determined that it took 20. drops to equal 1 mL. This solution was then added to the cell containing the copper electrode. The voltage was read as 0.56 V. The cell can be represented as ... 

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. 

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