September 2023 | Advice Column
My students performed an experiment where they precipitated Ag from Cu and AgNO3. We collected the Ag, and I stored it with the hopes of dissolving it back into AgNO3 to repeat the lab next year. Can you suggest a lab procedure to accomplish this? Would I mix it with nitric acid? If it’s not possible with general high school equipment and chemicals, can you suggest some other purpose for the flakes of precipitated silver? Thanks!
Puzzled with Precipitates
Dear Puzzled with Precipitates,
I’m sure your students enjoyed this activity! My students have always been impressed with the results of this reaction. So, what do you do with your silver now?
First of all, it’s important to consider the quantity of silver you have and how much you will continue to generate. If the objective of this activity is to observe a single replacement reaction, then it would be appropriate to carry this out in microscale to ensure small amounts of silver as product. According to Flinn, such small amounts can simply be thrown away (disposal method 26a). You could also simply store it in your chemical storage for use later since it’s benign.
If you have larger quantities, perhaps because your students were calculating percent yield and determining limiting reactants, then I can understand why you would hesitate to toss all these beautiful crystals. To answer your question, the primary method for dissolving silver is with nitric acid. This would generate a solution of silver nitrate, and you could easily calculate the molarity of the solution you make assuming the silver you have is relatively pure. However, there are important safety concerns when carrying out this procedure. The reaction between silver and nitric acid can produce gaseous NO and/or NO2, which one does not want to breathe in. Therefore, the reaction needs to be carried out in a fume hood. In my experience, the copper in silver nitrate reaction does not produce a large mass of silver from the materials I provide to my students, so I would not expect to generate a large volume of silver nitrate by dissolving the silver product in nitric acid afterward.
As a last alternative (assuming you haven’t already decided to enter the scrap metal business), and if you have enough silver, you might be able to perform a quantitative analysis lab similar to “Analysis of Silver in an Alloy” found in Laboratory Experiments for Advanced Placement Chemistry by Vonderbrink. The purpose might be to evaluate the purity of the silver your students generated in their previous lab if you think it’s not 100%. Note that this lab procedure does include a section in which silver is added to nitric acid, so if you choose to regenerate AgNO3 with your silver as discussed above, you could follow this procedure in part.
Yours in chemistry,