2.7 Accuracy And Precision

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2.7 Accuracy And Precision

Although rarely used properly in everyday conversation, accuracy and precision are not the same things. Learn the difference here. For scientists, accuracy and precision are very different and can be very confusing. Accuracy is the correctness of your answer meaning the closeness of your data to the accepted value by chemists, usually accessible online somewhere. When you're thinking accuracy, think percent error. Precision regards the consistency of your results. This is the reason we always do more than one trial of an experiment, to determine precision. When thinking precision, compare it to the average of your results. &n


Questions and Answers
  • 1. 
    My watch says it is 9:00 exactly and my iPod says 12:52.  The atomic clock says it is 3:33 exactly.  Are these two times accurate, precise, or neither?
    • A. 

      Accurate

    • B. 

      Precise

    • C. 

      Neither

  • 2. 
    My watch and an atomic clock which is never wrong both say 3:34.  My friend's watch says 3:34 also.  In relation to the atomic clock, are my friend and my watches
    • A. 

      Accurate?

    • B. 

      Precise?

    • C. 

      Both?

    • D. 

      Neither?

  • 3. 
    I want to measure exactly 24.53 mL of hydrochloric acid.  Which of the following would give me the best precision in my measurement?
    • A. 

      Using a beaker that is labeled every 25 mL

    • B. 

      Using a graduated cylinder that measures to the nearest tenth of a mL

    • C. 

      Using a cracked old bottle and spilling some in the process

  • 4. 
    If you want a result to be accurate, then you are looking for it to be reasonably close to __________. 
    • A. 

      Results from other trials that you conducted

    • B. 

      The value accepted by professional chemists

    • C. 

      100

  • 5. 
    To a scientist, the words accuracy and precision are interchangeable.
    • A. 

      True

    • B. 

      False

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