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Scan_Doc0020 - 14 Chapter One Chemical Foundations...

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14 Chapter One Chemical Foundations Precision is an indication of accuracy only if there are no systematic errors. Leading zeros are never significant figures. Captive zeros are always significant figures. Trailing zeros are sometimes significant figures. Exact numbers never limit the number of significant figures in a calculation. Following are the results of five trials: Volume Shown by Volume Shown Trial Graduated Cylinder by the Buret 1 25 mL 26.54 mL 2 25 mL 26.51 mL 3 25 mL 26.60 mL 4 25 mL 26.49 mL 5 25 mL 26.57 mL Average 25 mL 26.54 mL Is the graduated cylinder accurate? Solution The results of the trials show very good precision (for a graduated cylinder). The student has good technique. However, note that the average value measured using the buret is sig- nificantly different from 25 mL. Thus this graduated cylinder is not very accurate. It pro- duces a systematic error (in this case, the indicated result is low for each measurement).
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