Estudiante

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EXPERIMENTS IN
ELECTROCHEMISTRY
by Giorgio Carboni, January 1998
Translated by G.L. Stuart
 
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CONTENTS
INTRODUCTION
CONDUCTORS
BATTERIES
THE LEMON BATTERY
DANIELL'S CELL
THE CONCENTRATION CELL
VOLTA'S PILE
MEASURING POTENTIALS OF REDUCTION
GALVANIC DEPOSITION
CONCLUSION
 
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INTRODUCTION [pic]In 1791 Luigi Galvani discovered electrical activity in the nerves of the frogs that he was dissecting. He thought that electricity was of animal origin and could be found only in living tissues. A few years later, in 1800 Alessandro Volta discovered that electricity could be produced through inorganic means. In fact, by using small sheets of copper and zinc and cloth spacers soaked in an acidsolution, he built a battery - the first apparatus capable of producing electricity. Naysayers were quick to predict that electricity would never serve a useful purpose. Obviously they were very wrong. Electricity has a central role in our lives and to this day Electrochemistry is a standard course of study.
While listening to lessons on Electrochemistry, many students may wonder why it was everinvented, if it was really ever necessary to invent it and if the world would be better off without it. With the small experiments that follow, we hope to make peace between these students and the study of Electrochemistry. These fun and simple experiments can teach the fundamental concepts of Electrochemistry without asking much of the student. As you will see, many of these demonstrations areeasily adapted to various configurations and each can be done independently or as part of the full curriculum.
POROUS VASE - An actual porous vase made for the purpose may be difficult to acquire. It is used to prevent the quick mixing of various solutions, while permitting the exchange of ions. For our purposes you can adapt a terracotta pot of the type used in gardening simply by plugging the holein the bottom with molten wax and allowing it to cool. Another even more economical answer lies in constructing a barrier of paper. As shown in figure 4, roll the paper to form a cylinder and glue it in place on the bottom of the main container using a silicone adhesive such that liquids cannot pass between the two areas defined by the paper. A barrier of just one sheet would be too permeable,therefore use at least three layers of paper when building this device.
DISTILLED WATER - Don't use de-ionized water in place of actual distilled water. Many times water sold for use in household irons is de-ionized rather than distilled water. Pharmacies sell actual distilled water. What is the difference? Many substances are soluble in water and a few of these substances separate into positive andnegative ions in water. Generally these are made up of molecules that have ionic bonds, while non-ionic molecules remain intact, just in solution. For example, sugar dissolves easily in water and the sugar molecules remain intact as sugar. De-ionized water can have any number of dissolved substances that do not result in ions, yet are present nonetheless. Apart from this, a poor quality sample ofde-ionized water can contain significant amounts of ions. On the other hand, distilled water is usually very pure - containing only actual water molecules.
WHERE TO OBTAIN THE MATERIALS - You can buy the chemicals in a store that sells chemicals and laboratory equipment. Often, this type of store is located near universities. Some grocery or hardware store are able to get you the chemicals neededfor these experiments. You can often purchase copper and zinc strips at a hobby retailer or hardware store. You can also ask a firm which works with sheets of these metals for some pieces, for example a gutter-pipe firm and a zinc galvanic treatments firm. For the first trials, you can also use a piece of copper and a zinc-galvanized nail or screw.
CATHODE AND ANODE - In the course of these...