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Thread: The baking soda/aluminum foil reaction, revealed

  1. #1
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    Default The baking soda/aluminum foil reaction, revealed

    Ok, I'm the curious sort, so I did some research on exactly what happens when you use the baking soda/aluminum foil method of removing silver tarnish, and here's what I found:


    "When silver tarnishes, it combines with sulfur and forms silver sulfide. Silver sulfide is black. When a thin coating of silver sulfide forms on the surface of silver, it darkens the silver. The silver can be returned to its former luster by removing the silver sulfide coating from the surface.

    There are two ways to remove the coating of silver sulfide. One way is to remove the silver sulfide from the surface. The other is to reverse the chemical reaction and turn silver sulfide back into silver. In the first method, some silver is removed in the process of polishing. In the second, the silver remains in place. Polishes that contain an abrasive shine the silver by rubbing off the silver sulfide and some of the silver along with it. Another kind of tarnish remover dissolves the silver sulfide in a liquid. These polishes are used by dipping the silver into the liquid, or by rubbing the liquid on with a cloth and washing it off. These polishes also remove some of the silver.

    The tarnish-removal method used in this experiment uses a chemical reaction to convert the silver sulfide back into silver. This does not remove any of the silver. Many metals in addition to silver form compounds with sulfur. Some of them have a greater affinity for sulfur than silver does. Aluminum is such a metal. In this experiment, the silver sulfide reacts with aluminum. In the reaction, sulfur atoms are transferred from silver to aluminum, freeing the silver metal and forming aluminum sulfide. Chemists represent this reaction with a chemical equation.

    3 Ag2S + 2 Al -----------> 6 Ag + Al2S3

    silver sulfide + aluminum -> silver + aluminum sulfide


    The reaction between silver sulfide and aluminum takes place when the two are in contact while they are immersed in a baking soda solution. The reaction is faster when the solution is warm. The solution carries the sulfur from the silver to the aluminum. The aluminum sulfide may adhere to the aluminum foil, or it may form tiny, pale yellow flakes in the bottom of the pan. 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, is called an electrochemical reaction. Reactions of this type are used in batteries to produce electricity."

    This is from http://scifun.chem.wisc.edu/homeexpts/TARNISH.html

    So, it does indeed chemically reverse the tarnishing reaction, leaving all the silver intact on the piece you are cleaning.

  2. #2
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    Reports are that a tsp of disolved salt speeds the conversion process by providing a chemical "transmission line" that allows the sulfides to more quickly move through the warm water and baking soda brine.
    Last edited by goldminer; 16th April 2009 at 16:20.

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    Quote Originally Posted by goldminer View Post
    Reports are that a tsp of disolved salt speeds the conversion process by providing a chemical "transmission line" that allows the sulfides to more quickly move through the warm water and baking powder brine.
    That completely makes sense since this is an electrochemical reaction. The sodium and chlorine ions conduct electricity very well.

    BTW its baking soda, not baking powder, they are 2 different things. Baking powder contains some baking soda, but also contains other things such as cream of tartar. So if you wanted to use baking powder, you'd have to use considerably more of it to get the same effect.

    http://chemistry.about.com/cs/foodch...f/blbaking.htm

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    Quote Originally Posted by goldminer View Post
    Reports are that a tsp of disolved salt speeds the conversion process by providing a chemical "transmission line" that allows the sulfides to more quickly move through the warm water and baking powder brine.
    I wish I could remember all the chemistry classes I took in college.

    Yes you have the right idea, NaCl does form a stronger electrolyte than baking soda, but what you don't want to form is AgCl.

    NaCl + Ag --> no reaction

    The silver is more stable than the sodium, so the reaction wont take place. However, the introduction of aluminum creates electrolysis in the solution. Which means there is a transfer of ions, or in essence a battery. If the current is strong enough it might start the reaction (Although I don't think it will). This is the point where I must not have been paying attention in class. I do know, you don't want to accidentally dissolve your silver. So any help would be appreciated.
    The US Government is no brighter that a 40 watt . I feel embarrassed and ashamed for what they represent.

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    Default rotten eggs

    I've tried the aluminum foil, silver and spit test. It does smell like rotten eggs. There is certainly a chemical reaction. They say it proves silver....any thoughts?

    Salt is a better electrolyte but baking soda works well also. I know it from hydrogen tests. Salt increases the conductivity (and produces dangerous chlorine gas in some reactions)
    Please delete duneyman and jr. from the database....problem solved!!!

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    On second thought having actually used this process to clean silver, I would leave out the salt. It works just fine without it, and I'm not a good enough chemist to predict what might happen. There's no point in fixing things that work.
    Last edited by Argyria; 16th April 2009 at 03:12.

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    I'm not saying it makes chlorine in this process....I can tell you....water, salt, steel plates and current makes chlorine gas among other things.
    Quote Originally Posted by Argyria View Post
    On second thought having actually used this process to clean silver, I would leave out the salt. It works just fine without it, and I'm not a good enough chemist to predict what might happen. There's no point in fixing things that work.
    Please delete duneyman and jr. from the database....problem solved!!!

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    thanks for posting!

    gonna try it!

  9. #9
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    "...On second thought having actually used this process to clean silver, I would leave out the salt. It works just fine without it, and I'm not a good enough chemist to predict what might happen. There's no point in fixing things that work."

    In my experience over the last 12 years: (1) salt helps to more effectively remove the sulfides. (2) does not reduce the silver content or harm the surface of the silver item in any way, and (3) does not produce any noticable odor or fume(s).

    A lot quicker method to use on a single or few 1-10 oz. items is a 10-secod dip in the inexpensive "Silver Jewelry Cleaner" (Connoisseurs - silver plastic screw=top canister with a lift-out basket) sold in the jewelry departments at Wally World and other stores. It works well too and does not do anything noticable to bullion/coin silver, except remove the tarnish.

    DYOD
    Last edited by goldminer; 16th April 2009 at 16:31.

  10. #10
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    "A lot quicker method to use on a single or few 1-10 oz. items is a 10-secod dip in the inexpensive "Silver Jewelry Cleaner" (Connoisseurs - silver plastic screw=top canister with a lift-out basket) sold in the jewelry departments at Wally World and other stores. It works well too and does not do anything noticable to bullion/coin silver, except remove the tarnish. "

    Ah, but the point of this method is it is cheap, available, and best of all, actually turns tarnish back into silver. As I mentioned in the OP, other methods result in simply removing the AgS, thus incurring loss of silver. Not really important on pieces of solid silver, admittedly, but very important when dealing with silver plate. Silver plated items routinely have to go back to a silversmith to be replated, because the silver plate is rubbed or dissolved off. So the baking soda/aluminum method would seem to be superior, overall. Next experiment: I'm going to see if my local coin dealer can detect a cleaned coin by this method. Perhaps since no rubbing is involved, and its not a straight dip that dissolves it off, the original luster will be preserved. Doubt it, but I'm gonna try it.

    I also have my suspicions that harsh chemical dips leave the surface more prone to future reactions. I've used muratic acid before to strip all dirt and oxidation from steel and copper surfaces before, and what happens is they re-oxidize in record time after treatment, as if the surface is now activated for reaction. A piece of steel will be pristine when taken out of the acid bath, but just hours later is covered with rust. Copper pennies would become green within a day.
    Last edited by Argyria; 17th April 2009 at 03:04.

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