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Unformatted text preview: 7 Experiment 2 Measuring Mass and Volume Expt 2 Measurement.wpd INTENT The purpose of this experiment is to introduce some fundamental aspects of the measurement making process as well as to introduce some of the basic laboratory equipment used by chemists for measuring mass and volume. DISCUSSION The Importance of Measurements. Measurements are the means by which scientists gather quantitative information. Thus, in science and technology, it is extremely important to be able to make proper measurements. The quantitative determination of common extrinsic physical properties such as length, mass, and volume, as well as common intrinsic properties like density or heat of reaction per mole, can only be accurately determined by carefully performing experiments which depend on making particular measurements correctly. Therefore the quality of any physical-property determination is only as good as the measurements used in determining that physical property. Proper Measurements. A properly recorded measurement consists of two basic parts, the number and the label (or units) associated with it. Both must be stated clearly when quoting a measurement. The numerical portion of a measurement relates the actual value obtained and the accuracy to which it is known. In your own work, you will always want to convey, exactly, the accuracy to which a value is known. This is so because, even if the exact degree of accuracy is not important to you in your work, it may be important to someone else who, at some later time, may try to use your results for a different purpose. Remember that whenever a measurement is made, there is always some degree of uncertainty in the value of the measurement, i.e., an estimate is involved. One needs to know how to treat this uncertainty in a number and in subsequent calculations. In addition to the numerical portion of a measurement, its units must be clearly stated to avoid any confusion. For example, if you were told the distance between New York and Los Angeles is 125, you would be perplexed since no units are quoted. You are left to guess the units used to make this measurement, and no units with which you are likely familiar seem appropriate. Clearly, units are needed to remove the confusion. Thus, a proper measurement consists of two basic parts, the number and the label (or units) associated with it . 8 Measurements. When making a measurement, you must decide how best to report the value that you obtain. To illustrate the procedure, consider the following measurement: Clearly, a measurement of the length of the line should be reported to two significant figures because the line is obviously longer than 0.3 D but less than 0.4 D. That is, by estimating the second decimal place, a total of two significant figures is obtained. Therefore, to complete our measurement, we need only to make an estimate of the length of the line that extends beyond the 0.3 D marking. To do this, we divide (in our minds) the distance between the 0.3 D marking and the 0.4 D marking into 10 parts.we divide (in our minds) the distance between the 0....
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- Fall '08