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Chapter 2: Scientific Method Cartoon courtesy of NearingZero.net

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

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Law vs. Theory A law summarizes what happens or describes a wide variety of behaviors in nature. (math equation)A law summarizes what happens or describes a wide variety of behaviors in nature. (math equation) E = MC 2 A theory (model) is an attempt to explain why it happens (a plausible explanation).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 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 Prefixes Common to Chemistry Kind hector does better during classical music PrefixUnit Abbr. Exponent Kilok10 3 Decid10 -1 Centic10 -2 Millim10 -3 Micro 10 -6 Do NOT need in Notes

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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, cm 3 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 oTemperature conversions K=*C + 273.15 *C= K- 273.15 1mL= 1 cm 3

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Section 2-3 Precision and Accuracy Accuracy refers to the agreement of a particular value with the true value.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.Precision refers to the degree of agreement among several measurements made in the same manner. Neither accurate nor preciseNeither accurate nor precise Precise but not accuratePrecise but not accurate Precise AND accuratePrecise 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.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 Nonzero integers always count as significant figures.Nonzero integers always count as significant figures. 3456 has 4 sig figs.3456 has 4 sig figs. Do NOT need in Notes

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Rules for Counting Significant Figures Zeros -Leading zeros do not count as significant figures.Zeros -Leading zeros do not count as significant figures. 0.0486 has 3 sig figs.0.0486 has 3 sig figs. Do NOT need in Notes

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Rules for Counting Significant Figures Zeros -Captive zeros always count as significant figures.Zeros -Captive zeros always count as significant figures. 16.07 has 4 sig figs.16.07 has 4 sig figs. Do NOT need in Notes

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Rules for Counting Significant Figures Zeros -Trailing zeros are significant only if the number contains a decimal point.Zeros -Trailing zeros are significant only if the number contains a decimal point. 9.300 has 4 sig figs.9.300 has 4 sig figs. Do NOT need in Notes

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Rules for Counting Significant Figures Exact numbers have an infinite number of significant figures.Exact numbers have an infinite number of significant figures. 1 inch = 2.54 cm, exactly1 inch = 2.54 cm, exactly Do NOT need in NOTES

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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 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 10 3 s 3 sig figs 0.0054 cm 2 sig figs 3 200 000 2 sig figs Do NOT need in Notes

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Rounding > or = to 5 round up < 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.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)6.38 x 2.0 = 12.76 13 (2 sig figs)

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Steps to solve X or / problems 1)Do the math on your calculator write it down 2)Look at the #’s in the problem determine the # of sig figs in each one 3)Take the lower # and your answer can only have that # of sig figs 4)Round the answer to the correct # of sig figs

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Sig Fig Practice #2 Calculation Calculator says: Answer 3.24 m x 7.0 m 22.68 m 2 23 m 2 100.0 g ÷ 23.7 cm3 4.219409283 g/cm 3 4.22 g/cm 3 0.02 cm x 2.371 cm 0.04742 cm 2 0.05 cm 2 710 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

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

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Steps to solve + or - problems 1)Line the #’s up by the decimal point 2)Do the math on your calculator write it down 3)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 column 5)Round the answer to that column

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Sig 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 Do NOT need in NOTES

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Scientific Notation Scientific notation, numbers are written in the form M x 10 n, where M is a number > or = to 1 but < 10 and n is a whole number. Examples: 65 000 is 6.5 x 10 4 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- boards.html 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/Powerpoin t/Unit0/Unit0_files/frame.htm http://www.sciencegeek.net/Chemistry/Powerpoin t/Unit0/Unit0_files/frame.htm Holt, Rinehart and Winston. Modern Chemistry. Harcourt Brace & Company. 1999.

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