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The evaluation of formation constants of some complex ions of silver is described. The method utilizes a concentration cell and the Nernst equation to determine the equilibrium concentration of the aquated metal ion. Suitable for an honors or advanced placement laboratory at the secondary level or in an introductory college course, the required data can be collected in an abbreviated time period.
The experiment requires a voltmeter capable of recording millivolts (or a good pH meter) and inexpensive chemicals. It allows students to check the validity of the Nernst equation and compare their experimental Kform values to reported ones.
This method involves some approximations and assumptions, but gives quite acceptable results. It can be extended to include equilibria involving a host of metal-ligand complexes, as well as the determination of Ksp values for relatively insoluble salts.
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