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Chapter 2 – Measurements and Calculations

Chapter 2 – Measurements and Calculations. Evidence of Chemical Change. Evolution of a Gas (Bubbles, Odor) Formation of a Precipitate (Formation of Cloudiness in a Clear Solution, Solids Collecting at the Bottom or Top) Release of Energy (Heat, Light) Color Change. Scientific Method.

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Chapter 2 – Measurements and Calculations

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  1. Chapter 2 – Measurements and Calculations Honors Chemistry, Chapter 2 Page 1

  2. Evidence of Chemical Change • Evolution of a Gas (Bubbles, Odor) • Formation of a Precipitate (Formation of Cloudiness in a Clear Solution, Solids Collecting at the Bottom or Top) • Release of Energy (Heat, Light) • Color Change Honors Chemistry, Chapter 2 Page 2

  3. Scientific Method • Observing and Collecting Data • Qualitative (Bubbles Formed) • Quantitative (1 gram/liter of catalyst speeded the reaction by 25%) • Chemists Study Systems (Region Selected for Study) • Formulate Hypothesis • Generalization about Data • Testable Statement Honors Chemistry, Chapter 2 Page 3

  4. Scientific Method • Testing Hypothesis (Experimentation) • Supported, Retained • Not Supported, Discarded, Modified • Theorizing – Create a Model • Model: An Explanation of How Phenomena Occur and How Data or Events are Related. • Visual • Verbal • Mathematical Honors Chemistry, Chapter 2 Page 4

  5. JFHICW FH VHHVLBFND FL N ZGVHFIVLB, BTV NZZVNGNLPV CY JFHICW JFDD IC FL N PNLIFINBV. – VGFP HVRNGVFI. (Wisdom is essential in a president, the appearance of wisdom will do in a candidate. – Eric Severeid) Honors Chemistry, Chapter 2 Page 5

  6. Units of Measure • Measurements Are Quantitative Information • Quantity: Something That Has Size or Amount Honors Chemistry, Chapter 2 Page 6

  7. SI Measurement • SI Units Are Defined in Terms of Standards of Measurement • Seven Basic Units • All Others Derived From Seven Basic Units Honors Chemistry, Chapter 2 Page 7

  8. SI Base Units Honors Chemistry, Chapter 2 Page 8

  9. SI Prefixes Honors Chemistry, Chapter 2 Page 9

  10. SI Prefixes Honors Chemistry, Chapter 2 Page 10

  11. Derived Units • Area A m2 • Volume V m3 • Density D kg/m3 (=m/V) • Molar Mass M kilograms/mol • Concentration c mol/liter • Molar Volume Vm m3/mol • Energy E joule Honors Chemistry, Chapter 2 Page 11

  12. Helpful Hint • Relationship Between D, m, and V: m V D Honors Chemistry, Chapter 2 Page 12

  13. Factor Label Method • Express 4.5 kg as grams • Begin by Expressing as a Fraction: 4.5 kg 1 • Identify Conversion Factor: 1 kg = 1000 grams • Express as a Fraction: 1 kg 1000 g 1 = --------------- or -------------- 1000 g 1 kg Honors Chemistry, Chapter 2 Page 13

  14. Factor LabelContinued • Write Equation Including Proper Factor • Cancel Units • Multiply Numbers to Get Final Result 4.5 kg 1000 g --------- x -------------- = 4500 g 1 1 kg Honors Chemistry, Chapter 2 Page 14

  15. Scientific Measurements • Accuracy – The Closeness of Measurements to the Correct or Accepted Value • Precision – The Closeness of a Set of Measurements Honors Chemistry, Chapter 2 Page 15

  16. Accuracy vs. Precision XX XX XX XX High Precision High Accuracy High Precision Low Accuracy Honors Chemistry, Chapter 2 Page 16

  17. Accuracy vs. Precision X X X X X X X X Low Precision Low Accuracy Low Precision High Accuracy (on average) Honors Chemistry, Chapter 2 Page 17

  18. Percent Error Valueaccepted - Valueexperimental %Error = --------------------------------------- Valueaccepted Honors Chemistry, Chapter 2 Page 18

  19. Significant Figures • All the Digits Known With Certainty Plus One Final Digit Which is Somewhat Uncertain • | I I I I | I I I I | I I I I | I I I I | • 8 9 • 8.36 Honors Chemistry, Chapter 2 Page 19

  20. Rules for Significant Figures • Zeros Appearing Between Nonzero Digits are Significant • Zeros Appearing in Front of All Nonzero Digits are Not Significant • Zeros Appearing to the Right of the Decimal Point And at the End of the Number are Significant Honors Chemistry, Chapter 2 Page 20

  21. Rules for Significant Figures 4. Zeros at the End of a Number but to the Left of the Decimal Point May or May Not be Significant. If a Zero Has Not Been Measured or Estimated but is Just a Placeholder, it is Not Significant. A Decimal Point Placed After Zeros Indicates They are Significant. Honors Chemistry, Chapter 2 Page 21

  22. Rules for Rounding If the Digit Following the Last Digit to be Retained is: > 5 Then Round Up < 5 Then Round Down 5 Followed by non Zero Digits Then Round Up Honors Chemistry, Chapter 2 Page 22

  23. Rules for Rounding If the Digit Following the Last Digit to be Retained is: 5 Followed by Non-Zero Digit(s), and Preceeded by an Odd Digit Round Up 5 Followed by Non-Zero Digit(s), and Preceeded by an Even Digit Leave Unchanged Honors Chemistry, Chapter 2 Page 23

  24. Significant Figures With Addition/Subraction • When Adding or Subtracting Decimals, the Answer Must Have the Same Number of Digits to the Right of the Decimal Point as There are in the Measurement Having the Fewest Digits to the Right of the Decimal Point. Honors Chemistry, Chapter 2 Page 24

  25. Significant Figures With Multiplication/Division • When Multiplying or Dividing, the Answer Can Have no More Significant Figures Than are in the Measurement with the Fewest Number of Significant Figures. • (Conversion Factors Have Unlimited Digits of Accuracy.) Honors Chemistry, Chapter 2 Page 25

  26. Scientific Notation • Move the Decimal Point Left or Right Until the Mantissa is Greater Than or Equal to 1.0 and Less Than 10 • Express the Number as: M x 10n Where n Represents the Number of Places the Decimal Point was Moved, Positive if the Decimal is Moved Left and Negative if the Decimal is Moved Right Honors Chemistry, Chapter 2 Page 26

  27. Direct Proportion • Y = kX • Example Mass vs. Volume Data for Aluminum • Slope of the Line (k) is the Density Honors Chemistry, Chapter 2 Page 27

  28. Measurement of a Series of Blocks Honors Chemistry, Chapter 2 Page 28

  29. Plot Mass vs. Volume Honors Chemistry, Chapter 2 Page 29

  30. Calculate Slope and Intercept • Y = mX + b = slope x Volume + intercept • Slope = 2.69 g/cm3 • Intercept = 0.09 grams (!) (Actually Zero) • From Table of Densities: Sample is Aluminum (Al) Honors Chemistry, Chapter 2 Page 30

  31. Inversely Proportional • k = XY or Y = k/X • As X Increases, Y Decreases • Example: Pressure-Volume Data Honors Chemistry, Chapter 2 Page 31

  32. Pressure Volume Data for Nitrogen Honors Chemistry, Chapter 2 Page 32

  33. Volume vs. Pressure For Nitrogen Honors Chemistry, Chapter 2 Page 33

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