Chapter 2:Chapter 2:Scientific MethodScientific Method

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Section 2-1Section 2-1Steps in the Scientific MethodSteps in the Scientific Method

1.1. ObservationsObservations-- quantitative quantitative - - qualitative qualitative

2.2. Formulating hypothesesFormulating hypotheses - - possible explanation for the possible explanation for the

observation or testable statementobservation or testable statement 3.3. Performing experimentsPerforming experiments

- gathering new information to decide - gathering new information to decide whether the hypothesis is valid whether the hypothesis is valid

Outcomes Over the Outcomes Over the Long-TermLong-Term

TheoryTheory (Model) (Model) - - A set of tested hypotheses A set of tested hypotheses that give an overall explanation of that give an overall explanation of some natural phenomenon.some natural phenomenon.

Natural LawNatural Law-- The same observation applies The same observation applies to many to many different systems different systems -- Example - Law of Conservation Example - Law of Conservation of Massof Mass

Law vs. TheoryLaw vs. Theory

• A A lawlaw summarizes what happens summarizes what happens or describes a wide variety of or describes a wide variety of behaviors in nature. (math behaviors in nature. (math equation) equation) E = MC2

• A A theorytheory (model) is an attempt to (model) is an attempt to explain explain whywhy it happens (a it happens (a plausible explanation).plausible explanation). Usually a broad generalization.

Section 2-2 Section 2-2 Units of Units of

MeasurementMeasurement

MeasurementMeasurement - quantitative - quantitative observation observation

consisting of 2 partsconsisting of 2 partsPart 1 -Part 1 - number number Part 2 - scale Part 2 - scale (unit)(unit)

Examples: Examples: 20 grams 20 grams 6.63 x 106.63 x 10-34-34 Joule seconds Joule secondsQuantityQuantity is something that has is something that has

magnitude, size or amount.magnitude, size or amount.

The Fundamental SI UnitsThe Fundamental SI Units (le Système International, SI)(le Système International, SI)

Physical Quantity Name AbbreviationPhysical Quantity Name AbbreviationMassMass kilogram kilogram kg kgLengthLength meter meter m mTimeTime second s second sTemperature Kelvin KTemperature Kelvin KAmount of a substance mole molAmount of a substance mole molElectric current Ampere AElectric current Ampere ALuminous intensity candela cdLuminous intensity candela cd

SI PrefixesSI PrefixesCommon to ChemistryCommon to Chemistry

• Kind hector does better during classical music

Prefix Unit Abbr.

Exponent

Kilo k 103

Deci d 10-1

Centi c 10-2

Milli m 10-3

Micro 10-6

Do NOT need in Notes

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.

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

o Temperature conversions K=*C + 273.15 *C= K- 273.15 1mL= 1 cm3

Section 2-3 Section 2-3 Precision and AccuracyPrecision and Accuracy

• AccuracyAccuracy refers to the agreement of a refers to the agreement of a particular value with the true value.particular value with the true value.

• PrecisionPrecision refers to the degree of refers to the degree of agreement among several measurements agreement among several measurements made in the same manner.made in the same manner.

• Neither accurate nor preciseNeither accurate nor precise• Precise but not accuratePrecise but not accurate• Precise AND accuratePrecise AND accurate

Percent Error

Percent Error = accepted value – experimental value accepted value

X 100

Uncertainty in Uncertainty in MeasurementMeasurement

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

Why Is there Why Is there Uncertainty?Uncertainty?

• Measurements are performed with instruments

• No instrument can read to an infinite number of decimal places

Rules for Counting Rules for Counting Significant Figures Significant Figures

• Nonzero integersNonzero integers always count always count as significant figures. as significant figures.

• 34563456 has 4 sig figs. has 4 sig figs.

Do NOT need in Notes

Rules for Counting Rules for Counting Significant FiguresSignificant Figures

• Zeros Zeros -Leading zeros do not -Leading zeros do not count as significant figures.count as significant figures.

• 0.04860.0486 has 3 sig figs. has 3 sig figs.

Do NOT need in Notes

Rules for Counting Rules for Counting Significant Figures Significant Figures

• Zeros Zeros -Captive zeros always -Captive zeros always count as significant figures.count as significant figures.

• 16.0716.07 has 4 sig figs. has 4 sig figs.

Do NOT need in Notes

Rules for Counting Rules for Counting Significant Figures Significant Figures

• Zeros Zeros -Trailing zeros-Trailing zeros are are significant only if the number significant only if the number contains a decimal point. contains a decimal point.

• 9.3009.300 has 4 sig figs. has 4 sig figs.

Do NOT need in Notes

Rules for Counting Rules for Counting Significant Figures Significant Figures

• Exact numbersExact numbers have an infinite have an infinite number of significant figures. number of significant figures.

• 11 inch = inch = 2.542.54 cm, exactly cm, exactly

Do NOT need in NOTES

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

Sig Fig Practice #1Sig Fig Practice #1

• 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

Do NOT need in Notes

Rounding•> or = to 5 round up•< 5 round down

Rules for Significant Rules for Significant Figures in Figures in

Mathematical Mathematical OperationsOperations

• Multiplication and DivisionMultiplication and Division: # sig figs : # sig figs in the result equals the number in the in the result equals the number in the least precise measurement used in least precise measurement used in the calculation. the calculation.

• 6.38 x 2.0 = 12.76 6.38 x 2.0 = 12.76 13 (2 sig figs)13 (2 sig figs)

Steps to solve X or / problems1) Do the math on your calculator write it

down2) Look at the #’s in the problem

determine the # of sig figs in each one3) Take the lower # and your answer can

only have that # of sig figs4) Round the answer to the correct # of sig

figs

Sig Fig Practice #2Sig Fig Practice #2

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 lb·ft 5870 lb·ft

• 1.030 g ÷ 2.87 mL 2.9561 g/mL 2.96 g/mL

Do NOT need in NOTES

Rules for Significant Rules for Significant Figures in Figures in

Mathematical Mathematical OperationsOperations

• Addition and SubtractionAddition and Subtraction: The : The number of decimal places in the number of decimal places in the result equals the number of decimal result equals the number of decimal places in the least precise places in the least precise measurement. measurement.

• 6.8 + 11.934 = 18.734 6.8 + 11.934 = 18.734 18.7 (3 sig figs)18.7 (3 sig figs)

Steps to solve + or - problems1) Line the #’s up by the decimal point2) Do the math on your calculator write it

down3) Underline the last digit # of each # you

added or subtracted 4) The underlined digit that is over to the

left the most circle the entire column5) Round the answer to that column

Sig Fig Practice #3Sig Fig Practice #3

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 > or = to 1 but < 10 and n is a whole number.

Examples: 65 000 is 6.5 x 104

0.00012 is 1.2 x 10-4

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.

Work Cited• “Dart board”. Image. July 27, 2006.

http://www.shopnbu.com/games/electronic-dart-boards.html

• “North America map”. Image. July 27,2006. http://www.lifelinks.org/serv01.htm

• July 25, 2006. http://www.sciencegeek.net/Chemistry/Powerpoint/Unit0/Unit0_files/frame.htm

• Holt, Rinehart and Winston. Modern Chemistry. Harcourt Brace & Company. 1999.