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Measurements & Calculations

Measurements & Calculations. Chapter 2 Chemistry Review. Scientific Method. Logical approach Observe & collect data (research topic) Form hypothesis (a proposed explanation) Test hypothesis (set up & do experiment) Record & analyze data from experiment Summarize & make conclusions

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Measurements & Calculations

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  1. Measurements & Calculations Chapter 2 Chemistry Review

  2. Scientific Method • Logical approach • Observe & collect data (research topic) • Form hypothesis (a proposed explanation) • Test hypothesis (set up & do experiment) • Record & analyze data from experiment • Summarize & make conclusions • Modify, support, or reject hypothesis • Communicate methods & results

  3. Formulating Hypothesis • Statement must be testable • Can use “If…, then….” statement • If you use Dan’s SureFire Bait, then you’ll always catch premium bass. • Can be worded as if it were a fact • Fisherman using Dan’s SureFire Bait catch more premium bass. • More premium bass are reeled in on Dan’s SureFire Bait.

  4. Planning the Experiment • Independent Variable (I.V.) • What is being tested; what’s different from control • Dependent Variable (D.V.) • What is being measured as a result of I.V. • Control group • Those not receiving/ treated with the I.V. • That to which the experimental group is compared • Experimental group • Those receiving/ treated with the I.V. • Constants • What is the same in both groups

  5. Experimental vs. Control Results [# fish] (D.V)

  6. From Hypothesis to Theory • Hypothesis is supported by data • Methods & Results are published • Others test hypothesis & verify results • Others relate their hypotheses to yours • Others can build models & predict outcomes based on the collective hypotheses • The scientific community adopts a new theory (or expands/ modifies existing one)

  7. International System of Units • Adopted in 1960 by the General Conference on Weights and Measures • Has 7 base units • Length (m, meter); Mass (kg, kilogram); Time (s, second); Temperature (K, kelvin); Amount of substance (mol, mole); Electric current (A, ampere); Luminous intensity (cd, candela) • All scientists understand & use same system

  8. SI Prefixes • tera- T 1012 1 000 000 000 000 • giga- G 109 1 000 000 000 • mega- M 106 1 000 000 • kilo- k 103 1 000 • hecto- h 102 100 • deka da 101 10 • Base unit 100 1

  9. SI Prefixes, negative exponents • Base unit 10 1.000000 • deci- d 10-1 0.1 • centi- c 10-2 0.01 • milli- m 10-3 0.001 • micro- m 10-6 0.000 001 • nano- n 10-9 0.000 000 001 • pico- p 10-12 0.000 000 000 001 • femto- f 10-15 0.000 000 000 000 001

  10. Derived Units • Combinations of base units • Area m2 • Density kg/ m3 ; g/cm3 • Molar mass kg/ mol; g/ mol • Energy kg m2 /sec2 (J, joule) • Volume m3 • Liter = (10 cm)3 = 1000 cm3 = 1000 cc = 1000 mL

  11. Conversion Factors • Ratio derived from equality of 2 different units • 100 cm/ m; 1000 mm/ m; 1 000 000 mm/ m • 102 x 10-2 = 100 = 1 Just change sign of exponent • 1000 m/ km; 1 000 000 m/ Mm • 103 m/ 103 m = 1; kilo = 103, M = 106; 106/ 106 = 1 • Used in dimensional analysis to solve problem • How many mm are there in 2.3 km? • 2.3 km(1000 m/ km)(1000 mm/ m) = 2.3 x 106 mm

  12. Accuracy vs. Precision • Accuracy = close to accepted value • Hits the bull’s-eye • Percentage error % Error= (valueexperimental – valueaccepted)/ valueaccepted Some error always exists with measurements!!! • Precision = close to one another’s values • All hit same area but not necessarily the bull’s-eye

  13. Significant Figures (S.F.) • = All digits known + 1 final digit (estimated) • Rules for S.F. • All digits 1 through 9 are S.F. (327) • All zeros between non-zero digits (30207) are S.F. • All zeros at the end of non-zero digits & right of the decimal point (327.00 or 3.2700) are S.F. • All zeros after non-zero digits & before a decimal point (327000.) are S.F.

  14. Rounding Significant Figures • Products or quotients can have no more S.F. than # of S.F. of what’s multiplied or divided • Sums or differences can have no more decimal places than the least # of decimal places in the problem • Rounding • Must round answer to correct # of S.F. • If the last digit is > 5, increase by 1 UNLESS THE 5 FOLLOWS AN EVEN NUMBER

  15. Scientific Notation • Written in the form of M x 10n • M = all significant figures • n = can be a positive or negative # or zero • (+n) = # is > 10; (-n) = # is between 0 & 1 • When n = 0, # is between 1 & 10, not including 10 • Rule of exponents • 10A x 10B = 10A+B • 10A / 10B = 10A-B

  16. Proportionality • Directly proportional • x k = y, where k is a constant • As x increases, y increases & vice versa • (Pressure) (constant volume) = Temperature • Indirectly proportional • x y = k, where k is a constant • As x increases, y decreases & vice versa • (Pressure)(volume) = Constant Temperature

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