Oxidation-Reduction in Aqueous Solutions

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INSTRUCTOR: In this demonstration, we will investigate the oxidation reduction properties of aqueous solution by taking a strip of copper metal and placing it into a solution of silver nitrate. What will happen when we take a piece of copper metal and drop it into a silver nitrate solution? So as we can see, the copper wire that we started with has definitely changed in physical properties after we put it into the silver nitrate solution. If we want to explain what happened in this particular reaction, we can look at the piece of copper metal that we started with. The copper metal is going to be oxidized in the copper 2+ ions in solution, and we can kind of see those ions in the solution as the solution is turning a faint blue color. The silver nitrate that we started out with goes from silver ions in solution and gets reduced to silver metal. We can visually see that with the silver plating onto the surface of the copper wire. So in order to predict whether a strip of metal will be oxidized by a particular salt solution, we must consult the activity series. The activity series arranges metals in order of decreasing ease of oxidation. Metals at the top of the table are easily oxidized, and those found at the bottom of the table are not easily oxidized and are very stable. This is why silver, gold, and platinum are used in jewelry. Generally, we say that any metal in the activity series can be oxidized by the ions of the elements below it. In the reaction we just witnessed, copper is above silver in the activity series. This means that copper metal is oxidized by silver ions, giving experimental evidence that a redox reaction is taking place. So now that we have this physical evidence of this chemical reaction that occurs, we need to now be able to express this to another chemist so they understand what's going on. So we have to put together a balanced chemical reaction for this. In this case, the copper solid is going to be oxidized to copper 2+. We cannot have oxidation without reduction. So for the balanced chemical equation, it will be copper solid plus silver plus ions in solution, and we need two of them to balance that chemical equation that will give copper 2+ ions in solution plus two equivalents of silver solid. We can perform similar experiments with any metal on the activity series. What will happen when I take a piece of silver metal and place it into a solution of copper nitrate? In this reaction, nothing happens. Because in this case, copper is less likely to be reduced, and this is why we place it above silver on the activity series.