Exp 4 - Lab Manual: Electrochemistry & Vitamin C 1...

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Lab Manual: Electrochemistry & Vitamin C 1 Electrochemistry & Vitamin C (I) Basics of Electrochemistry (II) Application of Electrochemistry – Ascorbic Acid in Vitamin C Tablet INTRODUCTION & THEORY Electrochemistry is in common use today. Techniques in this field are used to produce active metals like aluminum, to refine copper, and to plate chromium or silver on other materials. It is also the basis for the operation of batteries, for many analytical chemistry methods, and for fundamental studies in thermodynamics and kinetics. You experience electrochemistry in useful processes such as these, in destructive processes such as rusting and corrosion, and in painful moments such as biting on aluminum foil with a new dental filling. Understanding electrochemistry makes life more interesting. Electrochemistry involves the transfer of electrons from one species to another. The species in the reaction losing the electrons is undergoing oxidation and is called the reducing agent. The species gaining those electrons is undergoing reduction. Since it is causing the first material to be oxidized, it is known as the oxidizing agent. Oxidation does not occur without reduction elsewhere and vice-a-versa. Such oxidation/reduction or redox reactions, as written, do not always occur spontaneously. This will depend on the two species' relative stabilities in their respective oxidation states. An activity series indicating these relative stabilities can be used to determine whether a reaction will occur spontaneously or not. An activity series, by convention, lists reduction half reactions. Spontaneity can be determined by comparing the relative locations of the two species in question. In the first part of this lab, you will experimentally devise a simple qualitative activity series. The easiest species to be reduced (therefore, the best oxidizing agent) will appear at the top of the series. An additional consideration, involving the concentrations of the species, is also important for determining actual reactions. For Part I, we will use solutions of approximately the same concentrations so that the effects of this factor can be minimized. Later we will investigate the effects of concentrations. When concentrations are taken into consideration, a quantitative activity series can be made. In this, actual reduction potential values can be tabulated. These indicate relative ease of reduction under standard conditions (25 C and 1 molar solution concentrations). The potentials are measured relative to the reduction of H ion to H 2 (g), which is assigned a value of 0.00 volts. We will see later how to calculate new nonstandard potential values for other concentrations. Redox reactions can also be set up in electrochemical cells. In these, the oxidation process and the reduction process are physically separated. The resulting voltage and current, which originate in the electrons being transferred, are often used for productive purposes.
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This note was uploaded on 06/02/2011 for the course CHEM 100A taught by Professor Dai during the Winter '06 term at UCSD.

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Exp 4 - Lab Manual: Electrochemistry & Vitamin C 1...

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