Element Collection

Element Collection

Saturday, April 3, 2010

Experiment: Silver Tree

This is an experiment I've had since the very beginning of my home laboratory, but for some reason I never got around to doing it. This is a single replacement reaction that precipitates pure silver metal out of a solution of silver nitrate in the presence of solid copper metal. The silver grows on the copper in very fine, hairlike crystals. After a while, they become thick enough to look almost like clouds (see the photos below). The reaction goes fairly quickly at first then slows down - mine appeared to be done after about 30 minutes, but I left it to stew for a few hours to make sure I got all the silver out of solution.

The balanced chemical equation for this reaction is
Cu + 2AgNO3 -> 2Ag + Cu(NO3)2

I used a 0.1M silver nitrate solution, created by dissolving 1.4g (more precisely 1.36g) of silver nitrate into 80ml of water. To start the reaction, I bent some heavy gauge copper wire into a coil and placed it in the beaker. It went surprisingly quickly at first, but I left it to react for a few hours to make sure all the silver was displaced out of solution.

This reaction is pretty nice visually - you start with a piece of shiny copper metal and a clear solution, and end with metallic silver and a very blue solution. The blue color is caused by the Cu 2+ ions present in solution. Copper nitrate isn't something you can pour down the drain, so I'd like to find some use for it. I may try to evaporate the water and crystallize it out into a solid, and store it for later.

Preparing for the experiment.







 

 About 3 minutes after placing the copper in the solution.









 After 10 minutes









 After 15 minutes









 After 18 minutes









 After 32 minutes - the reaction was mostly done by now, but I left it in for a few more hours to ensure all the silver had been deposited.









After just under 3 hours, I stopped the experiment.









The crystals were extremely fragile, and knocked off easily. You can see the copper is almost as shiny as it was in the beginning.









I recovered 1.7g of silver metal. This was more than the 1.4g of silver nitrate I used, so I can only assume there is still some liquid trapped in it, since it was quite spongy. The theoretical maximum I could get is only about 0.9g, because there is 63.5% silver in silver nitrate by weight. Further investigation is necessary!

6 comments:

  1. Wow, this is amazing. Where did you get the Silver Nitrate?

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  2. Nice write-up, thank you! I did a smaller scale version today, putting a tiny piece of copper wire on a microscope cavity well slide and dropping on silver nitrate. It was great watching the silver crystals grow like ferns. The RSC mention that this is a good demonstration of gain and loss of electrons: "By seeing the crystals grow, students can imagine the Ag+ ions pulling electrons off the silver crystals, which in turn remove electrons from the lump of copper and produce copper ions, thus setting up a simple electrochemical circuit. For each copper ion that forms in solution, two silver ions will add to the silver crystal structure.

    This is important to demonstrate because students might hold the misconception that the reaction takes place by silver ions colliding with the copper, which is not the case.

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    1. Thank you! Your version sounds very interesting, and I bet it happens pretty quickly at that level. That's a great quote too. It never really clicked with me how it doesn't just form a plating and stop, but that makes a lot of sense. Glad it worked for you!

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  3. What I now need to work out is whether this means something different is going on in single displacement reactions where the displaced metal does just form a plating and stop, eg iron in copper (II) sulphate. Very much learning as I go here!

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  4. This works! so happy!!! My friends and I are doing this for the Science Exhibition in school. The rehearsals went on perfectly. This is amazing! Thank You

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