Using Chemistry to Find that Silver Lining

Silver plate: before and after

I recently gave a public lecture on my campus in which (among other things) I discussed the chemistry of metallic copper, silver, and gold. During the talk I conducted a chemistry demonstration very similar to the Journal of Chemical Education’s Classroom Activity #25: Silver to Black – and Back.1 Through the process of conducting this experiment several times, I learned quite a bit about the chemistry of silver. The things I learned touch on several topics in chemistry that might be of interest to your students. If you’d like to skip my musings on this subject and simply watch videos of the demonstration, scroll down to the videos at the bottom of this post.

The main focus of JCE Classroom Activity #25 is the demonstration of the formation and removal of tarnish from items made of silver. Silver tarnish results from the formation of silver sulfide from the reaction between silver, oxygen, and hydrogen sulfide:2,3

2 Ag(s) + ½ O2(g) + H2S(g) --> Ag2S(s) + H2O(l).

Hydrogen sulfide is released into the atmosphere from sewers, factories, and farms. Hydrogen sulfide can also form from the reaction between carbonyl sulfide and water:

OCS(g) + H2O(l) --> H2S(g) + CO2(g)

Carbonyl sulfide is expelled into the atmosphere from volcanoes and the ocean. Both hydrogen sulfide and carbonyl sulfide are considered to be particularly effective in forming tarnish on silver.2,3

Fortunately, it is relatively easy to remove tarnish from silver, because several metals are more reactive than silver. It is easy to see the metals that are reactive than silver by inspecting the metal activity series (Figure 1). Any metal higher than silver on the series is more reactive, is more easily oxidized, and is more likely to react with sulfide ions than silver.  

Figure 1: Metal activity series. Because magnesium and aluminum are higher in the series than silver, both of these metals are more likely to bind with sulfide ions than silver.

Thus, by treating tarnished silver with aluminum foil, the chemical transfer of sulfide ions from the tarnished silver to the aluminum foil takes place:

3 Ag2S(s) + 2 Al(s) --> Al2S3(s) + 6 Ag(s)

Because I wanted to see this reaction take place for myself, I bought several tarnished silver items on eBay.4 As I experimented with the removal of tarnish using aluminum, I noted that some tarnish was particularly resistant to removal with aluminum. Seeing that magnesium is higher than aluminum on the activity series, I decided to try to use magnesium as a tarnish remover:

 Ag2S(s) + Mg(s) --> MgS(s) + 2 Ag(s)

Sure enough, because magnesium is more easily oxidized than aluminum, I found it to be particularly good at removing the tarnish from silver. I’m not the first one to have this idea. Apparently a product called “Maggie Pan”, which is no longer sold, used magnesium as a silver cleaner.5 

This experiment – the removal of tarnish with aluminum foil or magnesium – is quite easy to accomplish. While it does take a bit of time, the results are impressive and I think your students will enjoy seeing the process take place. Check it out in the video below:

Once you have chemically removed the tarnish from your silver item, you might want to conduct this experiment again for another group of students. However, the formation of tarnish on silver from gases in the atmosphere usually takes several years. In JCE Classroom Activity #25, it is suggested that egg yolk, mayonnaise, powdered sulfur, and mustard applied to silver will cause it to tarnish in about 24 hours.  While testing out these suggestions, I quite by accident discovered a way to form tarnish on a silver item in less than one hour.6 You can see this process of discovery unfold in the video below:

I find it interesting to note that in JCE Classroom Activity #25, it is claimed that the yolk of an egg in contact with a silver item will cause the silver to tarnish. Therefore, I was surprised to find that a hot egg white did the trick in less than an hour.7 I wish I had monitored the experiment more closely to try to observe how quickly the tarnish formed. Because I set the experiment aside and didn’t check on it until an hour later, I don’t know how long it took for the hot, hard-boiled egg white to tarnish the silver plate. Did it take less than 30 minutes? What about less than 10 minutes? I don’t know the answer to this question! If you get the chance, maybe you or your students could repeat this experiment and report back how quickly tarnish forms on a silver item through treatment with a hot, hard-boiled egg white.

NOTES:

1. JCE Editorial Staff; JCE Classroom Activity #25: Silver to Black – And Back. J. Chem. Educ. 2000, 77, 328A – 329A.  

2. J. Novakovic, J.;  Vassiliou, P.;  Georgiza, E.; Electrochemical Cleaning of Artificially Tarnished Silver. Int. J. Electrochem. Sci., 2013, 8, 7223 – 7232.

3. Salas, B. V.; Wiener, M. S.; Badilla, G. L.; Beltran, M. C.; Stoycheva, R. Z. M.; Diaz, J. D. O.; Osuna, L. V.; Gaynor, J. T.; H2S Pollution and Its Effect on Corrosion of Electronic Components.  

4. Surprisingly, I purchased all silver items for less than $10 each. It appears that people are quite willing to sell tarnished silver items for substantially less than untarnished silver.

5. Google “Maggie Pan silver cleaner” and you might find this vintage product on sale on Ebay or elsewhere online!

6. Do not attempt to add tarnish to your fine silver for these experiments. In some experiments I conducted I was not able to remove purposely added tarnish – even when using magnesium. This mostly occured when I used powdered sulfur to tarnish the silver items.

7. It makes sense to me that the egg white would form tarnish. Egg white is primarily made of protein, and the sulfur containing amino acids cysteine and methionine are found ubiquitously in proteins. 

Join the conversation.

Comments 5

Andres Tretiakov's picture
Andres Tretiakov | Fri, 03/04/2016 - 04:23

Hi Tom,

Fantastic videos as usual and great investigation. One question: were the silver items sterling or pure silver metal? I would also suggest (from what I have done in the past) cover the silver items (like a silver spoon) with lots of rubber bands (they are still made of natural rubber, latex and sulfur is added in the vulcanization process) in a zip-lock bag (it takes about 24 h and a bit less messy). In your video to accelerate the reaction you could have placed the whole tray/dish inside a sealable bag.

There is also something that bugs me. During the displacement reaction in the warm salt or sodium bicarbonate solution with aluminium metal you can smell a distinctive odour. Some is hydrogen sulfide (rotten egg smell) maybe from the hydrolyzation of aluminium sulfide but I'm not sure if that is all there is to it. Gas chromatography or even better GM-MS could easily identify the gaseous products being given off, alas I don't have that instrumentation.

Hope this helps,

Andres

 

Tom Kuntzleman's picture
Tom Kuntzleman | Fri, 03/04/2016 - 18:15

Hi Andres, good to hear from you again.

I don't know if the silver I used was sterling or not. I don't know how to tell the difference. Do you happen to know any way to test the difference between sterling silver and silver? Exploring the difference might make for a nice video and blog post. I was aware of using rubber bands, but did not try it for myself. Your suggestion to use rubber bands brings up an interesting idea. You might recall that I postulated that vulcanization of balloon rubber makes them resistant to popping when squirted with an orange peel. What if we tried placing balloons that do an do not pop when squirted with orange peel on my silver dish? We might be able to detect sulfur in pop resistant balloons. I think I'll get one of my students to test this out.

We do have a small Vernier GC. I wonder if we could capture the gases responsible for the odor in the tarnish removal experiment and run them through the Vernier GC. I'll have to get some students working on this, too!

Thank you for your comments, they are very stimulating as always.

Tom

Andres Tretiakov's picture
Andres Tretiakov | Sat, 03/05/2016 - 13:41

Hi Tom,

it's my understanding that sterling silver should have some kind of marking/engraving or punching with 925 which means it's 92.5 % Ag by weight. It may vary but as long as it has anything between 900-950 I think you can assume it's mostly silver. Plated silver usually (if old or from dubious ebay sellers) have some parts where the plating has come off due to wear and tear and you can see copper or brass/bronze below.

A nice simple test to perform if you find yourself in an antique store/ car boot sale or flea market is to light a safety match blow the flame and immediately place the burnt head on the item. The head of the match contains antimony trisulfide which can decompose to produce hydrogen sulfide especially in damp or wet weather. If the black smudge left by the burning match can be removed with your finger then it's probably plated but if the black spot remains then it's sterling. 

Sounds like a good and interesting idea to follow up your rubber balloons experiments and I hope you can manage to detect any other gases being given off with your Vernier GC.

I look forward to your results and findings. WATCH THIS SPACE!

All the best,

Andres

Linda Smith's picture
Linda Smith | Wed, 05/31/2017 - 10:46

Magnesium plates are still being manufactured and sold for the removal of tarnish by a company in Knoxville, TN.  

Silver Lion, P.O. Box 53012, Knoxville, TN 37950  (865) 691-6274

I have one of their plates that I bought at an antiques show. It does not say anywhere on it or in the instructions what type of metal is in their plate and I had assumed it was aluminum. But in one of their Youtube videos, their salesman says something about the magnesium capturing electrons from the silver sulfide which piqued my curiosity to know about that reaction; I already knew about aluminum. Google, the satisfier of all curiosity led me to your site. Thank you for explaining why my plate works better than aluminum foil.

Tom Kuntzleman's picture
Tom Kuntzleman | Thu, 06/01/2017 - 06:30

Hi Linda:  I'm glad you found my site informative. Thank you for alerting me to the Silver Lion company. I will be contacting them soon to purchase my own magnesium plate!

Tom