CH204 Expt 1 sp10 - 2/3/2010 FYI Please do not e-mail Dr....

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1 FYI b Please do not e-mail Dr. Lyon with questions regarding lab assignments. b Please include your name in your e-mail message. 1 CH204 Experiment 1 Are the Densities of Coke and Diet Coke Different? Dr. Donna Lyon Spring 2010 volume mass density = 2 Error in Measurements b Accuracy and precision s Accuracy refers to how closely the measured value of a quantity corresponds to its “true” value. s Precision expresses the degree of reproducibility, or agreement between repeated measurements. 3 Error in Measurements b Random error will cause some of the measurements to be a little high and some to be a little low. b An example of random error is the fluctuation of the readings of an electronic balance during a mass determination, which are caused by tiny vibrations, voltage fluctuations, and air currents. While random errors can be minimized, they can never be eliminated. s Random error can be reduced by averaging several measurements. s Random errors are errors that affect the precision of a set of measurements. s Random error scatters measurements above and below the mean, with small random errors being more likely than large ones. 4 Error in Measurements s Systematic errors are ones that cause readings to be always high or always low. These are generally due to mistakes, equipment malfunction, and poor laboratory technique. b Systematic errors have an identifiable cause and affect the accuracy of results. b For example, if a balance reads 0.25 g when there is no mass on it, this would introduce a systematic error to each mass measurement—they would all be too large by 0.25 g. This can be corrected by zeroing the balance. b Other systematic errors can only be eliminated by using a different experimental setup. Most of the simple experiments you do will have some systematic error. 5 Error in Measurements s Gross errors are undetected mistakes that cause a measurement to be very much farther from the mean measurement than other measurements. 6
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CH204 Expt 1 sp10 - 2/3/2010 FYI Please do not e-mail Dr....

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