Silver Nitrate and penny reaction

A. Can't really help you about the second part of your question, but when you first put silver nitrate on your penny, that "black buildup" was actually elemental silver. Its simply on such a small scale and not in crystal form that it doesn't appear silver and shiny.
Watch youtube for a demonstration of copper wire in silver nitrate.

A. As Zach notes, the deposit is silver without the batteries applied, Tommy. What drives the reaction is that the copper in the penny and the silver in the silver nitrate actually form a battery that cause silver to plate out onto the copper.

But once there is an extremely thin coating of silver on the penny, no more copper is exposed, so there is no longer a battery to cause the plating to continue and the reaction stops. When you connect your external AAA batteries, however, that will cause the reaction to continue and you'll get a much thicker layer of silver. So, yes, the additional deposit is silver as well. But 4.5 V is way too much for a beaker test. Try 1 battery instead of three.

If you keep it up though, copper will dissolve from your copper wire anode will begin plating out onto the penny.

We have an FAQ, "Silver Plating at Home" that you might find interesting, and we have dozens of science project Q&A's about this reaction as topic 31790. Good luck.

Regards,

A. Hi Himshek. One possible answer is silver nitrate.

Regards,