How does aluminum foil clean silverware
Q. Dear Helper,
I am in year 10 at St Pius X College Chatswood. At present I have an assessment task for science which requires me to carry out a scientific investigation. I chose to research and report on a method of cleaning tarnished silverware. The method involves submerging silver items into a bowl lined with aluminum and filled with boiling water and a teaspoon of salt (dissolved). (no baking soda) I have found that the salt is only a catalyst, as the silver and aluminium combo works as well. I am writing this e-mail to ask you if you could explain the process that is occurring and provide me with an equation (words and symbols) Thank you for taking the time to read my posting.
I am sorry if this is inconvenient but I really need a reply.
Please help me.Patrick Robinson
- Sydney, NSW, Australia
A. The principle behind this is that most metals corrode with exposure to oxygen. For example, iron rusts with time because of its exposure to moisture in the air, oxygen. You may also have noticed that cars in the northeast rust a lot faster because of the salt used on the roads in winter. The whole process involves electrons moving between the metal and oxygen atoms. It happens spontaneously with most metals (gold being a notable exception). Silver does pretty much the same thing, only that tarnish is the combination of silver with sulfur and not oxygen. Silver is special with its more complex reactions, but the principle by which silver tarnishes is the same by which iron rusts.
Aluminum also does the same thing, only it happens more readily than silver...(see where this is going?)
So we need to move the electrons to and from the metals and we need a metal that will take the electrochemical abuse for the silver. The aluminum takes the hit for the silver, and the salt water allows the electrons to move between the silver and aluminum. I would explain more, but this is not a general chemistry article.
This of course raises the question of why airplanes (which have aluminum) don't dissolve in mid flight...Lisa Robbinson
- NSW, Australia
A. Explanation: Silver tarnishes because it undergoes a chemical reaction with sulfur-containing substances in the air. Silver combines with sulfur to form silver sulfide, which is black, and darkens the silver.The silver can be made shiny again by removing the silver sulfide coating from the surface.
Two ways to remove the silver sulfide are to: remove it from the surface, or reverse the chemical reaction and turn silver sulfide back into silver. The first method involves polishes that remove some of the silver during polishing. The above demo uses a chemical reaction (which is sped up by heating the water) to convert the silver sulfide back into silver, without removing any silver.
Aluminum has a lower ionization energy (energy required to remove electrons from an atom of the element) than silver. As a result, aluminum is oxidized (loses electrons and oxidation number increases), and silver is reduced (gains electrons and oxidation number is reduced). Depending on the amount of tarnish, the silver will be bright and the aluminum foil may be brown with tarnish (aluminum oxide), in a short while. The silver tarnish is "transferred" to the aluminum via reactions, which occur instantaneously, as follows:
3Ag2S(s) + 2Al(s)+ 3H2O(l) => 6Ag(s) + Al2O3(s) + 3H2S(aq)
silver sulfide + aluminum + water => silver + aluminum oxide + hydrogen sulfide
The baking soda (sodium bicarbonate) reacts with the (sulfur-smelling) H2S:
3 NaHCO3(aq) + 3 H2S(aq) => 3 NaHS(aq)+3 H2O(l)+ 3 CO2(g)
baking soda + hydrogen sulfide => sodium hydrosulfide + water + carbon dioxide. The CO2 gas can be observed escaping from the most tarnished parts of the silver.
The silver and aluminum must be in contact with each other because a small electric current flows between them during the reaction.This type of reaction, which involves an electric current (because atoms are charged), is called an electrochemical reaction, and is used in batteries to produce electricity.Tania R. Chase
- Topsham, Maine
May 1, 2012
Q. I can understand Tania from Maine's equation from my schoolboy chemistry,and it's exactly what I wanted to know.
What I don't understand are the letters in parentheses next to each compound.
powder soda? Does it convert the gas from hydrogen sulphide to carbon dioxide -- hydrogen sulphide is poisonous .
May 1, 2012
A. Hi, David.
Tania is apparently indicating whether the compounds are solids, liquids, gases, or ionized in an aqueous solution.
Baking soda merely supplies conductivity. Similar results can be had with washing soda, Spic 'n' Span, or other conductive salts. Although hydrogen sulphide is poisonous, Paracelsus reminded us that everything is poison; it's all in the dose. Eggs release hydrogen sulphide as well.
January 10, 2009
Q. Tania, I do believe you got the reaction correct. Very nice explanation! However, I don't think the silver needs to be in contact with the aluminum because the saltwater acts as an electrolyte.Susan Ammons
- Bowling Green, Kentucky
A. Hi. The silver does need to be in contact with the aluminum. For silver sulphide to be reduced to silver, electrons must flow to it from the aluminum, and there needs to be metal-to-metal contact so the electrons can flow. Ions flow through the liquid, electrons flow through metal.
Ted Mooney, P.E. RET
Brick, New Jersey
Should the aluminium foil be shiny side up or dull side up?
- Houston, Texas
December 2, 2008
Robert Franklin Kynor
The aluminum foil should be bright side up.
- Newburyport, Massachusetts
March 5, 2009
Q. It appears that foil with salt works, somewhat. Thanks for your help.
What do you suggest I do to bring a sparkle to serving trays? Some are larger than the sinks.
- Burnaby, BC, Canada
A. Hi, Rod. There is no end to the size of containers. Bathtubs or stoppered shower areas can accommodate rather large trays. But I have heard, without verifying, that scrubbing the tray with the aluminum foil wetted with the washing soda will work. Good luck.
Ted Mooney, P.E. RET
Brick, New Jersey
March 6, 2009
Can I use the above method for silver with freshwater pearls jewelry as well? Or, do I have to wrap the pearls separately with aluminium foil first before submerging the piece of jewelry in the solution?
Designer - Chicago, Illinois
Pearls should only be cleaned with a good quality pearl cleaner
- Los Angeles, California
August 7, 2010
Q. About the optimum Water, Salt, Soda, and Foil amounts. I would assume that both Water and Foil are bulk for the reaction, meaning that as long you have enough present, the amount doesn't matter (too much doesn't hurt)
Salt being the conductor (when dissolved) is dependent on the amount of water you use. More Water requires more Salt.
Soda deals with the Sulfur from the Silver so I would assume you only need so much, based on the amount of Silver (and the amount/years of tarnish on it)
I see so many "recipes" around that only have Salt to Soda ratios 1:1, and 1:2 is common, but there are others like 1:12 and 1:24~48 these don't relate to how much Water you have at all. A cup, a pan, and a bathtub worth of Water really do need different amounts of Salt.
Long ago when I first heard of this (pre-internet) it was to add Salt until it doesn't dissolve (a few crystals sit on the bottom and persist). This method adds Salt dependent on the amount of Water. I think it was 2 Tbsp of Soda for a Silver set (8 settings), this adds Soda, based on the Tarnish (Silver).
A Setting is commonly 1 knife, 1 fork, 1 spoon, 1 Salad fork, 1 soup spoon, and the set pieces 1/8 Butter Knife, 1/8 Serving fork, 1/8 Serving Spoon, 1/8 Pickle Fork. So 5-1/2 (~6) tableware pieces per-seat gives a ratio of
1 piece:1/8 tsp
So here is the question,
Is there a better Water:Salt Tarnish:Soda ratios that make sense?
- Ludington, Michigan USA
November 23, 2010
Q. Can the chemical reaction be sped up by adding additional electrical current (connect battery to the 'soup')?Mike Lowe
- San Diego, California, USA