Calculating Percent Error

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Calculating Percent Error
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What is it??

• Percent Error is used to determine the
  inaccuracy, in percentage, of a measured or
  estimated value, compared to an accepted value.

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The Components of the Formula

• Estimated Value (Measured Value)- The value that
  has been derived from an experiment, or an
  estimated value.
• Actual Value (What you should have gotten!)- This
  value is the exact value excepted throughout the
  scientific community, or the value which is
  determined exact, at a later point in time.

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The formula

• The Formula for Percent Error is a follows
• (EV AV)
  
• AV
  
• Remember
• EV Estimated Value (measured value!)
• AV Actual Value
• PS. We multiply by 100 to make to make the
  decimal a percent.

X 100 Percent Error
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What does it mean if the PE is positive or
negative ?

• Negative if your measurement is too small
• Positive if your measurement is too big

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Practice Problems

• Johnny calculates from an experiment that he has
  22.7 grams of carbon. However, he should have
  gotten 21.8 grams of carbon, which was the
  accepted value for this experiment. What was his
  percent error?
• Remember (EV-AV) X 100 PE
• AV

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Answer

• (EV-AV) X 100 PE
• AV
  
• (22.7 - 21.8) X 100 PE
• 21.8
• .900 X 100 PE
• 21.8
• .0413 X 100 PE
• 4.13 PE

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More Practice

• The actual value for the absorption of carbon is
  .135. Steven calculated that absorption was .235.
  What is the percent error in Stevens experiment?

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Answer

• (EV-AV) X 100 PE
• AV
• (.235 - .135) X 100 PE
• .135
• .100 X 100 PE
• .135
• .741 X 100 PE
• 74.1 PE

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Additional practice

• The boiling point of water is 100C. During an
  experiment, water came to a boil at 97C
  according to the thermometer that was being used.
  What is the percent error of the thermometer?
• answer 3.0

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Additional practice

• 2. An experiment was conducted to find the mass
  of one mole of carbon atoms. The results of the
  experiment showed that a mole of carbon atoms had
  a mass of 15.78 g. The accepted value of a mole
  of carbon atoms is 16.00 grams. What is the
  percent error in this experiment?
• answer 1.38

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Additional practice

• 3. An experiment performed to determine the
  density of lead yields a value of 10.95 g/cm3.
  The accepted value for the density of lead is
  11.342 g/cm3. Find the percent error.
• answer 3.46

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Additional practice

• 4. Find the percent error in a measurement of the
  boiling point of bromine if the laboratory figure
  is 40.6C and the accepted value is 59.35C.
• answer 31.59