Ch 3 Scientific Measurement

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Ch 3 Scientific Measurement
2
Observing Collecting Data

• Quantitative Observations
• Qualitative Observations
• Inferences

3
Accuracy and Precision

• Accuracy
• Precision
• Percent Error
• Error Experimental - Accepted Value x 100
  
• Accepted Value
• Error/Uncertainty in Measurement You must
  estimate 1 place beyond what is known for the
  instrument you are using Do class examples

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Accuracy / Precision in Measurement
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Measurement
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Significant Figures

• All nonzero digits are significant
• 321 698 both have 3 significant figures
• All (Captive) zeros between nonzero digits are
  significant
• 506 30.3 both have 3 significant figures
• (Leading) Zeros to the left of nonzero digits are
  not significant
• 0.00321 00405 both have 3 significant figures
• (Trailing) Zeros to the right of a nonzero digit
  when a decimal is present are significant
• 300. and 3.00 both have 3 significant figures
• (Trailing) Zeros to the right of a nonzero digit
  when a decimal is not present are not significant
  
• 230 has 2 significant figures
• Counting numbers and definitions are considered
  to have an unlimited number of significant digits
  
• 1000 mm 1 m Unlimited significant figures

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Significant Figures in Calculations

• Multiplication Division
• The answer should have no more digits than the
  measurement with the least number of significant
  figures
• 4.562 x 2 9.124 The final answer should be
• rounded to 9 since 2 has only 1 significant
  figure
• Addition Subtraction
• The answer should have the same number of decimal
  places as the measurement with the least number
  of decimal places. Place value is important!
• 4.0025 2.3 6.3025 The final answer should be
  rounded to 6.3 since 2.3 has only 1 digit to the
  right of the decimal point.

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Units of Measurement

• Any measurement recorded in this class must
  include the QUANTITY and the UNIT.
• SI Measurements Single measurement system based
  on the metric system.
• Length meter m
• Mass kilogram kg
• Time second s
• Amount of Substance mole mol
• Temperature kelvin K
• Other Units (Derived Units)
• Volume
• Solids cubic meters m3
• Liquid Capacity Liter L

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Metric Prefixes
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Scientific Notation

• This should be review for most students.
• Check Appendix C in the back of the book,
• Check out the math skill help link if you need
  help with this.
• See me before or after school or during SRT

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Conversion Factors

• Ratios (fractions) that represent an equality of
  two different units. ex. sec per hour or cm per
  m
• Each ratio can be written as two different
  conversion factors ex. 100 cm 1 m
• 100 cm or 1 m
• 1 m 100 cm

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• How many inches are in .150 m?
• EX.PL.OR.E.
• Examine Given .150 m Unknown ? in.
• known ratios100 cm 1 m 2.54 cm 1in
• Plan Convert from m to in. using conversion
  factors (use the factor label method)
• Organize/Implement
• .150 m x 100 cm x 1 in___ 5.91 in
• 1 m 2.54 cm
• Evaluate Does the answer make sense? Do all of
  the units divide out as needed?
• Link to a handy conversion chart.

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Density

• Density
• Formula D m
• V
• Units - ratio of mass to volume
• Temperature dependent
• Pure substances have constant density, mp, bp,
  etc.
• Mixtures will vary in these physical properties

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Density Examples

• An unknown substance has a mass of 6.0 g and a
  volume of 3.0 cm3. What is the density of the
  substance?
• A sample of aluminum has a mass of 12.0 g. If
  the density of aluminum is 2.7 g/cm3, what is the
  volume of the sample?

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Graphing

• Descriptive Title
• Use Axes Labels and Include Units
• Convenient, Easy to Read Scale
• Label Points or Circle Around Them
• NEAT and CLEAN Use pencil or computer
• Choose the best type of graph for the
  data/appropriate trend line
• Direct Proportions
• y / x k y kx
• Indirect Proportions
• y 1 / x xy k

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Graphing
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