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September 2, 2008

September 2, 2008. Lab/Demo Makeup Notes: Metric Measures & Dimensional Analysis (a.k.a. Factor/Label ) Homework: Read 1.2, SR 1-14. Introduction to Chemistry Unit 1.2. 1.2 Measures & Calculations. Unit 1.2 Goals. Know values of metric prefixes Convert metric units

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September 2, 2008

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  1. September 2, 2008 • Lab/Demo Makeup • Notes: Metric Measures & Dimensional Analysis (a.k.a. Factor/Label) • Homework: • Read 1.2, SR 1-14

  2. Introduction to ChemistryUnit 1.2 1.2 Measures & Calculations

  3. Unit 1.2 Goals • Know values of metric prefixes • Convert metric units • Use Scientific Notation • Solve using dimensional analysis • Measure & calculate using Sig. digs • Understand the purpose of the Sci. Method • Chapters: 1.2, 2.2, 2.3

  4. Thinker • Sort the following words into three categories (matter, not matter, unsure) • PEANUT BUTTER, WATER, FISH, LIGHT, GARBAGE, TIME, MOTION, THE HUMAN BRAIN, CARBON DIOXIDE, AIR, YOURSELF, AN IDEA, TREE, ENERGY

  5. Measures

  6. Why Use Metric (pt. 1)? • U.S. uses British Units • Only U.S. & a few Caribbean Countries • How many inches in a foot? • How many feet in a yard? • How many yards in a mile? • How many pints per gallon? • What IS a slug?

  7. Why Use Metric (pt. 2)? • Metric System (S.I.) is used worldwide. • How many mm in a cm? • How many cm in a m? • How many m in a km? • How many ml in a L? • Metric is Base 10! • Other Units are on p 12 in Table 2

  8. Metric Prefixes • Which ones do we need to know? • T, G, M, k, base, c, m, µ, n • Know symbol, prefix, exponent multiplier & mathematical meaning. • http://en.wikipedia.org/wiki/Metric_prefixes for more.

  9. Dimensional Analysis • A.K.A. Factor/Label • We use Factors & Labels to convert one measure to another. • EX: Convert 4.5 kg to g • 1. Copy the number & units • 2. Use factors to cancel units & generate new units • 3. Repeat as necessary • 4. Do the math!

  10. Example: • Convert .851 g to mg .851 g 1000 mg 851 mg 1 g

  11. Example 2: • Convert 34.2 cm to m 34.2 cm 1 m .342 m 100 cm

  12. Example 3: • Convert 23.2 kg to mg 23,200,000 23.2 kg 1000 g 1000 mg mg 1 kg 1 g

  13. Let’s Try These • Convert: • 1.34 g to mg • 34.2 mg to g • 17.3 m to cm • 2.56 L to cL • 5.13 m to mm • Answers: • 1340 mg • .0342 g • 1730 cm • 256 cL • 5130 mm

  14. Homework: • Read Chapter 1.2, SR 1-14

  15. Derived Units • Meters, liters, grams, kelvin, moles, amps, Celsius, etc. are base units. • Care must be used w/ factor/label • Derived units contain 2 or more base units. • m2 • km/h • cm3 (all chem students know = 1 ml) • g/cm3 • These are factors already!

  16. For Example: • Convert 200 g/cm3to kg/mL 200 g 1 kg 1 cm3 kgmL .2 1 cm3 1000 g 1 mL

  17. Let’s Try These • Convert: • Answers:

  18. September 6, 2007 • Deriving Units • More fun with Dimensional Analysis • Homework: Re-read Chap 1.2 & do RQ 1-14 on p.19

  19. SunBurn • Research has indicated that in 1997: • Fossil Fuels were burned • The fossil Fuels burned, took 400 years of photosynthesis to capture the energy. • A single gallon of gasoline represents the remains of 200,000 lbs of plant material. “Burning buried sunshine: Human consumption of ancient solar energy.” Climatic Change 61:31-34, November 2003

  20. September 7, 2007 • HW X & Go Over • More Factor/Label • Derived Units

  21. September 7, 2007 • Using Scientific Notation • Homework: • Scientific Notation W.S. • Read Chap 1.2 & do (p.19) RQ 1-14

  22. Scientific Notation • Used to easily communicate large and small numbers. • For instance: • .000 000 001 • 1 x 10-9 • 1,300,000,000 • 1.3 x 109

  23. September 10, 2007 • “Pop” Quiz • HW X & Go Over • Measurements: Accuracy & Precision • Significant Digits • HW: peruse p54-58 & Sig Figs W.S. Front • Remember Tomorrow ACT Prep

  24. Measurements & Calculations • Must use the right equipment! • Calibrations • 10’s of ml • 1’s ml • .1’s of ml • .01’s of ml • .001 of ml • Different measurements require different tools.

  25. Accuracy • How close a measure is to its true value • In an experiment: • Measuring chemicals as close as possible: • When 46 ml are needed: • 45.2 ml, and 46.9 ml • Analogy: Dart Board • More Accurate means more darts hit the bull’s eye.

  26. Precision • How close a measured value is to its other measured values. • If you were measured one aspect of a chemical several times: • 50.4 ml • 50.3 ml • 50.5 ml • Analogy: Dart Board • More Precision means the darts are clustered

  27. Accuracy & Precision

  28. Suppose: • Students do a lab to determine the composition of a metal block: • Group A % Cu = 23.53 • Group B % Cu = 23.47 • Group C % Cu = 23.55 • Mixture actually contains 23.94% • I compliment the lab work. Why?

  29. Answer: • The results are consistent • This indicates good lab techniques • The results were consistent, and therefore precise. • The accuracy of the results is the problem. • Likely the measuring equipment needs to be checked.

  30. September 12, 2007 • H.W. X & Go Over • Discuss Sig. Fig Rules • Discuss Math Sig. Fig Rules • Practice!!!!! • Test Friday • Chapter 1.2 & 2.3 • Scientific Method (browse Chap 2.2)

  31. Significant Figures • Helps to define the accuracy and precision of our calculations. • The last digit in any number is always the least certain. • Ex: 10 g • Does not indicate the accuracy of the device • Can mean 8 – 10 g, or 9.999 – 10.001 • Ex: 10.0 g • Indicates accuracy to the .1 • Can mean 9.95 – 10.05 g

  32. Significant Figures Rules • A. All non-zero numbers are sig. • B. Zeros b/t non-zeros are sig. • C. Zeros in front of non-zeros are not sig. • D. Trailing zeros are only sig. if a decimal is involved.

  33. How many Sig. Figs.? • 10,000 • 1 • 100. • 3 • 3.0456 • 5 • -0.001 • 1

  34. How many Sig. Figs. 2? • 46.3 dm • 3 • 40.7 cm • 3 • .009 587 m • 4 • 58.00 g • 4 • 2000 • 1

  35. Special Case: • Exact values have an unlimited number of significant digits. • EX: Count Values • Number of trees on the lawn. • Number of Mc Nuggets in a box • Number of H atoms in H2O • EX: Conversion Factors • 1 kilometers = 1000 meters • When doing math operations ignore values with unlimited sig. figs.

  36. Doing Math w/ Sig Figs • CALCULATORS DO NOT DO SIG FIGS • Multiplication & Division • Count the # of sig figs in each value • Do the operation • Round the answer to have the same # of sig figs as the SMALLEST #. • EX: • 20.4 * 17.32 = 353.328 • Can only have 3 sig figs: 353.

  37. Addition & Subtraction • The answer cannot be more certain than the least certain value. • Pay attention to the PLACE value here. • Round to PLACE of least significance. • EX: • 20.4 + 17.32 = 37.72 • Can only have 1/10ths place • 37.7

  38. Homework • WS #1-5, 8-11, 14 • .

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