Chapter 2: Scientific Method

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Chapter 2Scientific Method
Cartoon courtesy of NearingZero.net
2
Section 2-1Steps in the Scientific Method

• 1. Observations
• - quantitative
• - qualitative
• 2. Formulating hypotheses
• - possible explanation for the observation or
  testable statement
• 3. Performing experiments
• - gathering new information to decide
  whether the hypothesis is valid

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Outcomes Over the Long-Term

• Theory (Model)
• - A set of tested hypotheses that give an
  overall explanation of some natural phenomenon.
• Natural Law
• - The same observation applies to many
  different systems
• - Example - Law of Conservation of Mass

4
Law vs. Theory

• A law summarizes what happens or describes a wide
  variety of behaviors in nature. (math equation) E
  MC2
• A theory (model) is an attempt to explain why it
  happens (a plausible explanation). Usually a
  broad generalization.

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Section 2-2 Units of Measurement

• Measurement - quantitative observation
• consisting of 2 parts
• Part 1 - number
• Part 2 - scale (unit)
• Examples
• 20 grams
• 6.63 x 10-34 Joule seconds
• Quantity is something that has magnitude,
  size or amount.

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The Fundamental SI Units (le Système
International, SI)

• Physical Quantity Name
  Abbreviation
• Mass kilogram kg
• Length meter m
• Time second
  s
• Temperature Kelvin
  K
• Amount of a substance mole mol
• Electric current Ampere
  A
• Luminous intensity candela
  cd

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SI PrefixesCommon to Chemistry
Do NOT need in Notes
Prefix Unit Abbr. Exponent
Kilo k 103
Deci d 10-1
Centi c 10-2
Milli m 10-3
Micro ? 10-6

• Kind hector does better during classical
  music

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Derived SI units

• Derived unit is a unit that can be obtained from
  combinations of fundamental units. Examples
  volume, Density, area, concentration.
• Volume is the amount of space occupied by an
  object, units mL, cm3
• Density mass/Volume
• Density is the quantity of matter per unit
  volume.

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Conversion Factors

• Conversion Factor is a ratio derived from the
  quantity between two different units and can be
  used to convert from one unit to another.
  Examples 365.25 days or 1 year
• 1 year
  365.25days
• Temperature conversions
• KC 273.15
• C K- 273.15
• 1mL 1 cm3

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Section 2-3 Precision and Accuracy

• Accuracy refers to the agreement of a particular
  value with the true value.
• Precision refers to the degree of agreement
  among several measurements made in the same
  manner.
• Neither accurate nor precise
• Precise but not accurate
• Precise AND accurate

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Percent Error

• Percent Error accepted value experimental
  value
• accepted
  value

X 100
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Uncertainty in Measurement

• A digit that must be estimated is called
  uncertain. A measurement always has some degree
  of uncertainty.

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Why Is there Uncertainty?

• Measurements are performed with instruments
• No instrument can read to an infinite number of
  decimal places

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Rules for Counting Significant Figures
Do NOT need in Notes

• Nonzero integers always count as significant
  figures.
• 3456 has 4 sig figs.

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Rules for Counting Significant Figures
Do NOT need in Notes

• Zeros -Leading zeros do not count as significant
  figures.
• 0.0486 has 3 sig figs.

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Rules for Counting Significant Figures
Do NOT need in Notes

• Zeros -Captive zeros always count as significant
  figures.
• 16.07 has 4 sig figs.

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Rules for Counting Significant Figures
Do NOT need in Notes

• Zeros -Trailing zeros are significant only if the
  number contains a decimal point.
• 9.300 has 4 sig figs.

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Rules for Counting Significant Figures
Do NOT need in NOTES

• Exact numbers have an infinite number of
  significant figures.
• 1 inch 2.54 cm, exactly

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Atlantic Pacific Rule

• Pacific
• Decimal is Present
• Start at the left most digit that is a nonzero.
• 0.00234

• Atlantic
• Decimal is Absent
• Start at the right most digit that is a nonzero.
• 567000

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Sig Fig Practice 1
Do NOT need in Notes

• How many significant figures in each of the
  following?
• 1.0070 m ? 5 sig figs
• 17.10 kg ?4 sig figs
• 100 890 L ?5 sig figs
• 3.29 x 103 s ?3 sig figs
• 0.0054 cm ?2 sig figs
• 3 200 000 ?2 sig figs

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Rounding

• gt or to 5 round up
• lt 5 round down

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Rules for Significant Figures in Mathematical
Operations

• Multiplication and Division sig figs in the
  result equals the number in the least precise
  measurement used in the calculation.
• 6.38 x 2.0 12.76 ? 13 (2 sig figs)

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• Steps to solve X or / problems
• Do the math on your calculator write it down
• Look at the s in the problem determine the of
  sig figs in each one
• Take the lower and your answer can only have
  that of sig figs
• Round the answer to the correct of sig figs

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Sig Fig Practice 2
Do NOT need in NOTES

• Calculation Calculator says
  Answer
• 3.24 m x 7.0 m 22.68 m2
  23 m2
• 100.0 g 23.7 cm3 4.219409283 g/cm3
  4.22 g/cm3
• 0.02 cm x 2.371 cm 0.04742 cm2
  0.05 cm2
• 710 m 3.0 s 236.6666667 m/s
  240 m/s
• 1818.2 lb x 3.23 ft 5872.786 lbft
  5870 lbft
• 1.030 g 2.87 mL 2.9561 g/mL
  2.96 g/mL

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Rules for Significant Figures in Mathematical
Operations

• Addition and Subtraction The number of decimal
  places in the result equals the number of decimal
  places in the least precise measurement.
• 6.8 11.934 18.734 ? 18.7 (3 sig figs)

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• Steps to solve or - problems
• Line the s up by the decimal point
• Do the math on your calculator write it down
• Underline the last digit of each you added or
  subtracted
• The underlined digit that is over to the left the
  most circle the entire column
• Round the answer to that column

27
Sig Fig Practice 3
Do NOT need in NOTES

• Calculation Calculator says
  Answer
• 3.24 m 7.0 m 10.24 m
  10.2 m
• 100.0 g - 23.73 g 76.27 g
  76.3 g
• 0.02 cm 2.371 cm 2.391 cm
  2.39 cm
• 713.1 L - 3.872 L 709.228 L
  709.2 L
• 1818.2 lb 3.37 lb 1821.57 lb
  1821.6 lb
• 2.030 mL - 1.870 mL 0.16 mL
  0.160 mL

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Scientific Notation

• Scientific notation, numbers are written in the
  form M x 10n , where M is a number gt or to 1
  but lt 10 and n is a whole number.
• Examples
• 65 000 is 6.5 x 104
• 0.00012 is 1.2 x 10-4

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Direct vs. Inverse Proportions

• Two quantities are inversely proportional to each
  other if their product is constant.
• The graph of an inverse proportion is a curved
  line.
• Two quantities are directly proportional to each
  other if dividing one by the other gives a
  constant value.
• The graph of a direct proportion is a straight
  line.

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Work Cited

• Dart board. Image. July 27, 2006.
  http//www.shopnbu.com/games/electronic-dart-board
  s.html
• North America map. Image. July 27,2006.
  http//www.lifelinks.org/serv01.htm
• July 25, 2006. http//www.sciencegeek.net/Chemistr
  y/Powerpoint/Unit0/Unit0_files/frame.htm
• Holt, Rinehart and Winston. Modern Chemistry.
  Harcourt Brace Company. 1999.