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Accuracy and Precision

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Presentation on theme: "Accuracy and Precision"— Presentation transcript:

1 Accuracy and Precision

2 Accuracy Accuracy – how closely a measurement agrees with an accepted value. For example: The accepted density of zinc is 7.14 g/cm3 Student A measures the density as 5.19 g/cm3 Student B measures the density as 7.01 g/cm3 Student C measures the density as 8.85 g/cm3 Which student is most accurate?

3 Error Error = experimental value – accepted value
All measurements have some error. Scientists attempt to reduce error by taking the same measurement many times. Example: The accepted value for the specific heat of water is J/gºC. Mark measures the specific heat of water as J/gºC. What is Mark’s error? Error = exp.value – acc.value Error = J/gºC – J/gºC Error = J/gºC

4 Percent Error │error │ %Error = x 100% acc.value
Example: The accepted value for the molar mass of methane is g/mol. Jenny measures the molar mass as g/mol. What is Jenny’s percent error?

5 Precision Precision – describes the closeness of a set of measurements taking under the same conditions. Good precision does not mean that measurements are accurate.

6 Accuracy and Precision

7 Example Problem Working in the laboratory, a student finds the density of a piece of pure aluminum to be 2.85 g/cm3.  The accepted value for the density of aluminum is g/cm3.  What is the student's percent error?


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