Experiment 2 Scientific Measurement and Experimental Error

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Experiment 2 Scientific Measurement and
Experimental Error

• CHEM 11L
• Summer 2004

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Lab Goals

• Laboratory Glassware
• Accuracy and Precision and Experimental Error
• Statistical Analysis

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1. Glassware

• Types of Glassware
• Volumetric Glassware (designed for accuracy)
• Non-Volumetric Glassware (less accurate, designed
  for routine measurements)

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When Using Glassware

• Always take the volume from the bottom of the
  meniscus
• Note the direction of the numbering.
• Is the number on the top smaller or larger than
  the bottom?
• Always estimate one decimal place beyond the
  scale.

36.4 mL
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2. Accuracy and Precision and Experimental Error

• Accuracy How close our value is to the true
  value.
• true value may be an average or may be provided
  as a literature value
• Example
• I want to add exactly 100.00 mL of water to this
  bottle.
• The closer I get to actually delivering that much
  water, the more accurate my measurement.
• Delivering 100.01 mL is more accurate than
  delivering 100.10 mL of water.

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2. Accuracy and Precision and Experimental Error

• Precision Can I repeat my results?

Precision
Accuracy
Precision and Accuracy
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Two Types of Experimental Error

• Random Error
• Random occurrences
• Cannot be corrected
• Systematic Error
• Error in the instrumentation used
• Can be corrected
• There is NO SUCH THING as Human error

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Statistical Analysis

• We use tools to analyze our accuracy and
  precision.
• Mean/Average (µ) allows us to generate an
  accurate value
• Data 3, 5, 6, 8

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Standard Deviation

• Data 3, 5, 6, 8
• Step 1 Determine the deviation from the
  previously determined mean (5.5)
• Step 2 Standard Deviation (s)

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The Q-Test

• this test allows us to throw out bad data

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Conclusion

• Laboratory Glassware
• Volumetric
• Non-Volumetric
• Accuracy and Precision / Experimental Error
• Accuracy ? Systematic
• Precision ? Random
• Statistical Analysis
• Mean
• Standard Deviation
• Q-Test

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Works Cited

• http//www.umd.umich.edu/casl/natsci/slc/slconline
  /PIPET/sld001.htm