Removing Tarnish from Silver by Electrochemistry 10 Report Paper

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Please write down the observation first and then answer all the questions

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Experiment 10: Removing Tarnish from Silver by Electrochemistry If you have any objects made from silver or plated with silver, you know that the bright, shiny surface of silver gradually darkens and becomes less shiny. When silver tarnishes, it combines with sulfur and forms silver sulfide Ag2S. 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, either 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 an electrochemical reaction to convert the silver sulfide back into silver. This does not remove any of the silver. Many metals, not just 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 ions are merely spectator ions, that is, they are observing the reaction between the silver ion in silver sulfide and the aluminum metal. The net result is to reform the silver metal and also form aluminum sulfide, Al2S3. Chemists represent this reaction with a chemical equation. 3 Ag2S silver sulfide + 2 Al aluminum --> 6 Ag silver + Al2S3 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 electrons must be transferred from one species to the other during the reaction. This type of reaction, which involves a transfer of electrons, is called a redox (oxidationreduction) reaction. Spontaneous reactions of this type are used in batteries to produce electricity. Materials: • a tarnished piece of silver • • • • • • a pan or dish large enough to completely immerse the silver in aluminum foil to cover the bottom of the pan enough water to fill the pan a vessel in which to heat the water hot pads or kitchen mitts with which to handle the heated water vessel baking soda, about 1 cup per gallon of water Procedure: Line the bottom of the pan with aluminum foil. Set the silver object on top of the aluminum foil. Make sure the silver touches the aluminum. Heat the water to boiling. Remove it from the heat and place it in a sink. To the hot water, add about one cup of baking soda for each gallon of water. (If you need only half a gallon of water, use half a cup of baking soda.) The mixture will froth a bit and may spill over; this is why you put it in the sink. Pour the hot baking soda and water mixture into the pan, and completely cover the silver. Almost immediately, the tarnish will begin to disappear. If the silver is only lightly tarnished, all of the tarnish will disappear within several minutes. If the silver is badly tarnished, you may need to reheat the baking soda and water mixture, and give the silver several treatments to remove all of the tarnish. When you have completed the experiment report observations your along with the answer to the questions below. Questions: 1. 2. 3. 4. 5. 6. 7. In silver sulfide, what is the charge on the silver ion? What must happen to the silver ion to convert it back to silver metal? Is this process an oxidation or a reduction? What is the charge on the aluminum ion when it forms aluminum sulfide? What must happen to the aluminum metal to convert it to the aluminum ion? Is this process an oxidation or a reduction? In the overall electrochemical reaction (see equation above) how many electrons are transferred? ...
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