Experiment - Silver Tarnish Removal

Background:  Silver, Ag, is one of the metals commonly used in jewelry, coinage and flatware. Its use in the manufacture of these objects is based on the fact it is not very reactive with oxygen and other metals do not readily oxidize it. Silver tarnish is a black solid product, silver sulfide, Ag₂S formed by reaction of silver with small amounts of sulfur present in the atmosphere.  In this lab we will use a reduction-oxidation (Redox) reaction to remove tarnish from silver.  This silver-cleaning process uses all household products:  sodium chloride (table salt), sodium bicarbonate (baking soda), and aluminum foil. 

Materials: 

You will need to find a tarnished piece of silver and a Pyrex glass (or ceramic) bowl (or cup) in which it easily fits.  Good quality silver works best; if there are other metals present they may discolor.  A silver coin that is old enough to not contain the copper center works pretty well and it can be cleaned in a coffee mug.  As a last resort, use a copper-centered coin that is old enough to be tarnished.

You will also need: 1 piece of aluminum foil (large enough to line your glass container), baking soda, and table salt (see amounts required in table below).

Procedure:

1. Figure out what volume of water can easily fit into your glass/ceramic container.  Do this by filling the container most of the way.  Place your tarnished silver in the water to make sure it is possible to cover the object with water; if it does not cover the object, find another container or tarnished object.  Next, pour the water into your 50 mL graduated cylinder, large beaker, or a measuring cup to determine the volume needed.

2. Once you know what volume of water you will be using, use the table below to determine the amounts of baking soda and salt to use:

3. Once you have determined how much water, baking soda, and salt you will use, record these amounts on your report sheet.  You are now ready to proceed; you should begin with an empty glass/ceramic container.

4. Lightly crumple a square of aluminum foil.  Partially flatten it out, leaving some of the ridges.  Line the bottom of your glass/ceramic container with the aluminum foil.  The foil does not have to hold the water inside; it is preferable that water can leak and touch the container.

5. Place your glass/ceramic (with foil) container under the faucet and run hot water until it is as hot as it gets.  (This will warm the container gradually, so it won't break.)  When the water is fully hot, adjust the water level in the container to approximately the volume you estimated before. 

6. Add the predetermined amounts of sodium bicarbonate (NaHCO₃) and sodium chloride (NaCl) to the water in the beaker.  Stir, but it is not necessary to make it all dissolve before proceeding.

7. Place the tarnished silver in the foil-lined container.  Make sure the silver touches the foil.

8. Let the silver incubate in the hot water 15-30 minutes or until the water is cool.   Pour the solution down the drain.

9. Remove and examine your silver.  If the silver looks dull yellow (this is elemental sulfur) rub it lightly with a little sodium bicarbonate using your fingers.  If the silver still looks tarnished, you can repeat the process with more foil, hot water, baking soda, and salt.

Answer the questions on the report sheet.