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What's the easiest way to get pure Ag from AgNO3?

What is the easiest way to reduce silver nitrate crystals and obtain pure silver as the byproduct?

Electroplating is the best option. Pass an electric current through the silver nitrate solution. Silver will plate onto the negative electrode (the cathode). If you want pure silver, you'll need to use clean silver wire as the cathode (scour the oxide coating off with fine sandpaper). Use either pure silver or an inert metal (like a graphite rod, or a platinum wire) for the positive electrode (anode).

There are many experimental variables that must be controlled to get a very pure deposit.

  • The current should be low so that the silver plates slowly and evenly onto the cathode. If you're using a 0.5 M AgNO3 solution about a 3 V emf should be enough. Apply a current of about 0.02 amp per square centimeter of cathode surface.
  • Complex the silver so that it deposits more evenly. Add saturated KI solution to the silver nitrate solution until all of the AgI just dissappears (you've formed soluble AgI2-). The discoloration around the anode is the iodide ion being oxidized to elemental iodine. To prevent it from contaminating the silver plating on the cathode, put a porous ceramic cup around the anode.

Commercial silver platers convert the silver in solution into the soluble complex ion Ag(CN)2- to obtain high quality silver plate. But yes, that is cyanide ion complexed to the silver, which presents obvious safety and waste disposal problems. Don't try it. There is a safe procedure that uses ammonium acetate and no cyanide (R. J. Adams, W. J. Blaedel, Journal of Chemical Education, 36, 286 (1959).

You might browse through a jewelry supply catalog before trying to reinvent silver plating yourself. You might also check with your local astronomy club- plating silver onto mirrors using silver nitrate is an essential part of telescope making.

One warning. Silver nitrate is a strong oxidizing agent. It is easily reduced to silver by organic material. Paper, clothing and skin are very good for reducing silver nitrate to microscopic, jet-black particles of silver; in fact, silver nitrate was a component in some indelible inks. The black stains that result from careless handling of silver nitrate solutions usually can't be washed off, so wear gloves or wash your hands often during this experiment.

Author: Fred Senese senese@antoine.frostburg.edu

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