Accuracy & Precision Worksheet Accuracy: refers to how close a measurement is to a true, accepted or target value. Precision: Refers to the reproducibility of a series of measurements Percent Error (Difference): (Measurement – Target Value)*100 Target Value 1. The following measurements were made to determine the density of a material whose value was, according to the Handbook of Chemistry and Physics, 1.24 g/mL Trial #1 1.20 g/mL Trial #2 1.22 g/mL Trial #3 1.22 g/mL a. make a general comment on the accuracy of these results b. make a general comment on the precision of these results c. use the average of the three trials as the “measured value” and determine the numerical value for the percent error. 2. The following measurements were made to determine the density of a material whose value was, according to the handbook of Chemistry and Physics, 1.15 g/mL Trial #1 Trial #2 Trial #3 0.95 g/mL 1.16 g/mL 1.26 g/mL a. make a general comment on the accuracy of these results b. make a general comment on the precision of these results c. use the average of the three trials as the “measured value” and determine the numerical value for the percent error. 3. In a chloride ion determination which you will do this year, assume that when you titrated 50.0 mg/L standard chloride solution you got 46.2 mg/L. Calculate your percent error.
