25-04-2012, 04:22 PM
Basic Chemical Production of Electricity
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INTRODUCTION:
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 acid solution, he built a battery - the first apparatus capable of producing electricity. Many were quick to predict that electricity would never serve a useful purpose. Some still do. However, electricity has a central role in our lives today.
THE LEMON BATTERY
Roll the lemon firmly with the palm of your hand on a tabletop or other hard surface in order to break up some of the small sacks of juice within the lemon. Insert the two metal strips deeply into the lemon, being careful that the strips not touch each other. Using the voltmeter, measure the voltage produced between the two strips (figure 3). It should show about one volt.
It would be nice to be able to illuminate a light bulb using your new lemon powered battery, but unfortunately it is not strong enough. If you were to try to light a bulb using this setup, the voltage across the strips would fall immediately to zero. Given this, if you want to demonstrate that the current produced by this battery is capable of powering something, try with a small device that uses an LCD display. A clock or a thermometer usually works well.
MEASURING POTENTIALS OF REDUCTION:
Another method of explaining the function of a battery lies in the oxidation reduction reactions at the electrodes. Oxidation reduction reactions involve the transfer of electrons from one chemical element to another. The tendency of an element to acquire or give up electrons is measured as electrical potential compared to that of a special hydrogen electrode, which is considered by convention to have zero electrical potential at 25°C. At this electrode, the following reaction occurs:
CONCLUSION:
In the course of these experiments, you have become familiar with various concepts such as the conductivity of solutions by way of dissolved ions. you have seen oxidation-reduction (redox) reactions at work, and that they can be reversed by running current through the circuit. You have learned to measure potentials of reduction of various materials and to predict the voltage generated by a battery when you know it's material components. You can build a working battery from various materials, including lemons, tomatoes, potatoes, almost any fruit or vegetable. Up until now, batteries may have seemed mysterious, but now we are among the few that have a working knowledge of how and why they work. You can amaze your friends by building a battery out of almost anything, but more importantly, now the study and mastery of both chemistry and electricity will be easier and more meaningful.