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Unformatted text preview: 4-1Experiment 4PASCO Sensors and Chemical ReactionsI. Learning Objectives To learn the use of common sensors (transducers) that will be used in the laboratory.To investigate some types of reactions which occur in aqueous solutions. II. Background Information Much of the research carried out in the modern laboratory involves electronic instrumentation. This is as true in chemistry as it is in high-energy physics. Many of these instruments are expensive, sophisticated, extremely accurate, and require a Ph.D. and a team of dedicated technicians to operate. The advent of microelectronics, lasers, and computers has revolutionized the applications possible for analytical instrumentation in the laboratory. Unfortunately, many of these developments have made the link between the scientific principles of the experiment and the output from the instrument less clear for the undergraduate science student. For the well-experienced scientist or engineer, this is generally not a problem. For a student who is just getting started in science, however, instruments can become intimidating "black boxes," spewing forth a mass of meaningless output signals. In an attempt to circumvent some of these problems, the laboratories in this general chemistry course adopt a different approach in their use of instrumentation. The general idea is to work with small, simple versions of the more expensive, commercially available instrumentation. It is important at this point to note that simple and small does not mean trivial. With careful preparation, results are possible that are quite precise and accurate. Many students in the general chemistry curriculum will encounter the more sophisticated versions of some of the instruments in these experiments later in their academic/scientific careers. The basic principle of most scientific instruments is embodied in a sensor capable of probing/monitoring a physical condition of the system under investigation connected to a 4-2measuring device of some type. A simple, classical example is the instrument that has been used for many centuries to measure the thermal energy of a system i.e., the thermometer (measures hotness or coldness). The sensor in this instrument is a liquid (typically mercury or alcohol) that expands or contracts as it is heated or cooled by the environment. The key to the function of this sensor is the standardization of the liquid expansion to a useable measuring scale. Unfortunately, throughout the more than three hundred years of development, many different scales have been attached to many different designs of the thermometer. Even today, there are at least four or five scales commonly used throughout the world. It is proving an extraordinary difficult task to choose one as a standardized system (hence, the temperature conversion questions common on freshman chemistry tests!). It is worth emphasizing that if one particular scale were chosen, the choice would be arbitrary. Of course, every manufactured thermometer must somehow be...
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- Spring '08