rusty
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Perhaps someone will tidy this information up then repost it with the attached pdf file.
Copper's single potential toward solutions with normal metallic ion activity is +0.34 volts and silver's is +0.80 volts. Both are positive, but silver's is higher than copper's by 0.46 volts; therefore, the silver functions as the anode.
If the situation in the example above had been reversed, so that the copper was originally in solution as copper ions and a clean piece of silver had been dipped into the solution, the copper would remain in solution unchanged. In order to get a metal (in its metallic form) to exchange with the copper ions in solution, you would have to use a metal of a lower positive electrical potential—that is. a less noble metal—as the cathode, at which point the copper ions in solution
would act as the anode, and the copper would cement to the cathode. Iron would work well: its electrical potential is —0.44 volts.
Because zinc has one of the lowest electrical potentials among metallic elements (a single electrical potential of -0.76 volts), it is a very useful tool for many metallic precipitation operations. Zinc is very widely used to precipitate precious metal values from cyanide solutions in both primary and secondary extractive operations.
If you have only one or two types of metallic ions in solution, this system can be of advantage. By adding zinc to an acidic or basic (cyanide) solution you can precipitate the metallics. and then separate them from each other and from the undissolved zinc by selective digestion and precipitation. However, this system is slow at best.
If you have a sizeable number of different types of metallic ions in solution, your end product of cementation is going to be a complex of metals all mixed together, which you will have to part and refine individually anyway
SINGLE ELECTRICAL POTENTIAL
The accompanying table shows the approximate single electrical potential of metallic elements toward solutions with normal metallic ion concentration or activity, based on hydrogen as zero volts. Each metal will replace the ions of any metal in solution that is more noble (or more electrically positive) than itself. For example, zinc ions (at -0.76 volts) will replace cadmium ions (at -0.40 volts) because the cadmium ions are more positive than the zinc ions.
When an ion comes into contact with an ion that is more negative than itself (assuming that the solution is in equilibrium), it is neutralized and reconverts to metallic form.
This is the principle behind precipitating gold ions out of an aqua regia solution with ferrous sulphate. Iron has a single electrical potential of -0.44 volts, and gold a single electrical potential of +1.36 volts.
Copper's single potential toward solutions with normal metallic ion activity is +0.34 volts and silver's is +0.80 volts. Both are positive, but silver's is higher than copper's by 0.46 volts; therefore, the silver functions as the anode.
If the situation in the example above had been reversed, so that the copper was originally in solution as copper ions and a clean piece of silver had been dipped into the solution, the copper would remain in solution unchanged. In order to get a metal (in its metallic form) to exchange with the copper ions in solution, you would have to use a metal of a lower positive electrical potential—that is. a less noble metal—as the cathode, at which point the copper ions in solution
would act as the anode, and the copper would cement to the cathode. Iron would work well: its electrical potential is —0.44 volts.
Because zinc has one of the lowest electrical potentials among metallic elements (a single electrical potential of -0.76 volts), it is a very useful tool for many metallic precipitation operations. Zinc is very widely used to precipitate precious metal values from cyanide solutions in both primary and secondary extractive operations.
If you have only one or two types of metallic ions in solution, this system can be of advantage. By adding zinc to an acidic or basic (cyanide) solution you can precipitate the metallics. and then separate them from each other and from the undissolved zinc by selective digestion and precipitation. However, this system is slow at best.
If you have a sizeable number of different types of metallic ions in solution, your end product of cementation is going to be a complex of metals all mixed together, which you will have to part and refine individually anyway
SINGLE ELECTRICAL POTENTIAL
The accompanying table shows the approximate single electrical potential of metallic elements toward solutions with normal metallic ion concentration or activity, based on hydrogen as zero volts. Each metal will replace the ions of any metal in solution that is more noble (or more electrically positive) than itself. For example, zinc ions (at -0.76 volts) will replace cadmium ions (at -0.40 volts) because the cadmium ions are more positive than the zinc ions.
When an ion comes into contact with an ion that is more negative than itself (assuming that the solution is in equilibrium), it is neutralized and reconverts to metallic form.
This is the principle behind precipitating gold ions out of an aqua regia solution with ferrous sulphate. Iron has a single electrical potential of -0.44 volts, and gold a single electrical potential of +1.36 volts.
