Thursday, June 24, 2010

Chemical Changes: Clean Your Silver

Line a non-metal container with aluminum foil.

Place tarnished silver in – make sure it touches the aluminum foil.

Boil water and add baking soda (1T per cup of water).
Pour this solution over the silver.

You'll quickly discover some shiny silver and may see a yellow haze on the aluminum foil.

I didn't fully submerge the lid, so you can see some of the tarnish at the top, and the "polished" part at the bottom.  It's not the best photograph, but it is nice and shiny (so much so that it reflects all kinds of other stuff and ruins my picture). 

Why:
The tarnish is silver sulfide, which forms from a reaction with sulfur in the air.   Sulfur has a greater affinity for aluminum than it does for silver.  So when you place the tarnished silver in the baking soda solution, the solution carries the sulfur to the aluminum.  The yellow haze on the foil is the sulfur that has been deposited there. 

The chemical equation:
Silver sulfide + Aluminum --> Silver + Aluminum Sulfide

Some Side Notes:
After hearing about this demonstration numerous times, I decided to give it a try (and get some pictures so I could share it with you).  It worked so well!  The yellow that's left on the foil isn't real apparent, although you could see an outline from where things had been sitting.  But, what was very apparent was the smell of sulfur, as soon as the solution was poured over the silver.  Wow!  I wasn't expecting that, but it certainly confirmed that the tarnish was composed of sulfur!  I'm now in search of a large enough vat to use to "polish" the teapot that goes with this lid! 

One more thing.... when researching the exact chemical equation I learned something else.... traditional silver polishes actually remove small amounts of silver along with the tarnish.  This method only removes the tarnish.  Seems like the way to go - no polishing and keeps the silver fully in tact!
*****
Presented at the 2003 New Jersey Science Convention.

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