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Unit 2

Unit 2. Chapter 3 Scientific Measurement. Today…. Turn in: Nothing Our Plan: Daily Challenge Scientific Notation, Accuracy, Precision, Error Notes Worksheet #1 Wrap Up – Rally Robin Homework (Write in Planner): Complete WS #1 by next class. Daily Challenge.

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Unit 2

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  1. Unit 2 Chapter 3 Scientific Measurement

  2. Today… • Turn in: • Nothing • Our Plan: • Daily Challenge • Scientific Notation, Accuracy, Precision, Error Notes • Worksheet #1 • Wrap Up – Rally Robin • Homework (Write in Planner): • Complete WS #1 by next class

  3. Daily Challenge • The number 602200000000000000000000 is used so frequently in chemistry that it has its own name; Avogadro’s number. What would be a better way of writing it?

  4. Scientific Notation • To write a number in scientific notation: • Move the decimal so that the number is between 1 and 10. • The exponent is the number of tens places you moved the decimal • Moving the decimal right = - exponent Moving the decimal left = + exponent

  5. Examples • 65000 m = • 0.0000156 s = • 0.24 m/s = • 6.7 mm = 6.5 x 104 m 1.56 x 10-5 s 2.4 x 10-1 m/s 6.7 x 100 mm

  6. To Write a number in Standard Form • Change it from scientific notation to a standard number by moving the decimal. • Example 1.4 x 106 = 1,400,000 2.6 x 10-4 = 0.00026

  7. Adding & Subtracting • Change the numbers to the same exponent. • Add or subtract the numbers • Example: 4.1 x 106 + 8.5 x 107 • 0.41 x 107 + 8.5 x 107 = 8.91 x 107

  8. Multiplication • Multiply the numbers • Add the exponents • Example: (4 x 106)(2 x 108) • 8 x 1014

  9. Division • Divide the numbers • Subtract the exponents • Example: (9 x 107)/(3 x 104) • 3 x 103

  10. Try It Out! • 3.5 x 104 + 5.1 x 105 • (5.7 x 108)(3.5 x 106) • (6.9 x 106)/(4.5 x 103)

  11. Answers • 5.45 x 105 • 1.995 x 1015 • 1.53 x 103

  12. Or… • Use your scientific calculator. • The EE button means x10^ • Do the Try it Out problems again using your calculator and see if you get the correct answers!

  13. Accuracy & Precision • Accuracy – compare to the CORRECT value • Precision – compare to the values of two or more REPEATED MEASUREMENTS

  14. Accurate, Precise, Both, Neither? Accurate

  15. Accurate, Precise, Both, Neither? Precise

  16. Accurate, Precise, Both, Neither? Neither

  17. Accurate, Precise, Both, Neither? Precise

  18. Accurate, Precise, Both, Neither? Both

  19. Accurate, Precise, Both, Neither? Accurate

  20. Percent Error Percent Error = |experimental - actual| actual value • The absolute value is present so that percent error is always POSITIVE! X 100

  21. Example • Working in the laboratory, a student finds the density of a piece of pure aluminum to be 2.85 g/cm3.  The accepted value for the density of aluminum is 2.699 g/cm3.  What is the student's percent error? Percent Error = |2.85 – 2.699| 2.699 5.59% X 100 =

  22. Try It Out • A student takes an object with an accepted mass of 200.00 grams and masses it on his own balance.  He records the mass of the object as 196.5 g.   What is his percent error? Percent Error = |196.5 – 200.00| 200.00 1.75% X 100 =

  23. STOP! • Complete Worksheet #1 by next class • Worksheets are… • A completion grade (i.e. You do not get a grade until it is 100% finished) • 10 points on time • -2.5 points each day it’s late

  24. Wrap Up • Rally Robin • Pair up with your shoulder partner. Divide a deck of cards in half. Take turns asking each other the questions on the cards. • Be sure to cover the answer with your finger.

  25. Today… • Turn in: • Get out WS#1 to Check • Our Plan: • Scientific Notation Clicker Review • Scientific Notation Quiz • Notes – Significant Figures/Units of Measurement • WS #2 • Bluff • Homework (Write in Planner): • Complete WS #2 by next class (9/12) • QUIZ OVER SIG FIGS NEXT TIME!

  26. Units in Chemistry • When you add or subtract two numbers, they must have the same units. • The answer then has those units as well. • Example: 4 m + 12 m = 16 m • When you multiply, you also multiply the units. • Examples: • 4 m x 5 m = 20 m2 • 2 g x 3 s = 6g·s • When you divide, you also divide the units. • Examples: • 4 m / 2 s = 2 m/s • 8 g / 2 mL = 4g/mL

  27. Challenge! • What does the word “significant” mean?

  28. Significant Figures • The numbers that are known, plus a digit that is estimated

  29. RULES ***All nonzero numbers are significant*** 125, 689 has 6 significant figures (sig figs) 156 has 3 sig figs • Zeros between nonzero numbers are significant. • 40.7 mL has ______ sig figs • 870,009 g has _____ sig figs 3 6

  30. RULES • Zeros in front of nonzero numbers are not significant • 0.00011 s has _____ sig figs • 0.956 g/mL has _____ sig figs 2 3

  31. RULES • Zeros at the end of a number and to the right of a decimal are significant • 85.0000 kg has _____ sig figs • 2.00000000 L has _____ sig figs 6 9

  32. RULES • Zeros at the end of a number are NOT significant. If there is a decimal at the end, they ARE. • 2000. m/s has _____ sig figs • 2000 m/s has _____ sig figs 4 1

  33. EASY RULE! Memorize! Start at the first nonzero number on the left and count every number right Start at the first nonzero number on the right and count every number left

  34. Unlimited Significant Figures • Counting – There are 23 students in the classroom • Could also be expressed as 23.0 or 23.00000000000000 etc. • Conversion Factors – 60 min = 1 hour • Exact quantities do not affect the process of rounding

  35. Try It Out • How many sig figs? • 0.00125 • 1.12598000 • 3,000 • 0.0100103 • 5,500. • 1.23 x 105 3 9 1 6 4 3

  36. Rounding • Round the following numbers so that they have 3 significant figures: • 1.36579 = • 120 = • 145,256,987 = • 0.0001489651 = 1.37 1.20 x 102 OR 120. 145,000,000 0.000149

  37. To Multiply & Divide Sig Figs… • Count the number of sig figs in each number • Round the answer so that it has the same number of sig figs as the number in the problem with the fewest.

  38. Example 1 • 16.19 g / 4.2 mL = 3.8547619 g/mL • 16.19 has 4 sig figs • 4.2 has 2 sig figs, so the answer should have 2 sig figs 3.9 g/mL

  39. Example 2 • 9.3 m x 0.00167 m = 0.015531m2 • 9.3 m has 2 sig figs, 0.00167 has 3 sig figs • Therefore, the answer must have only 2 sig figs. 0.016 m2

  40. Try It Out! 0.014 • (1.23)(0.011) = • 12.63000/100 = • (1.23 x 106)(3.5 x 104) = • 0.0045912/6.570 = 0.1 4.3 x 1010 6.988 x 10-4

  41. Stop • Complete Worksheet #2

  42. Bluff 1A. How many sig figs are in 0.001023? 1B. Solve 456 x 3.2 2A. How many sig figs would the answer have if you calculated 2.1 x 0.01? 2B. How many sig figs are in 123,000? 3A. Solve 2.7 x 3 3B. How many sig figs would the answer have if you calculated 1.4/3.789?

  43. Bluff 4A. What is 235,489 rounded to 2 sig figs? 4B. Solve 1/236 5A. Solve 3.7914/9.2 5B. What is 1,926,560 rounded to 1 sig fig? 6A. How could you write 230 with 3 sig figs? 6B. What is 0.00056798 rounded to 4 sig figs?

  44. Today… • Turn in: • Get out WS#2 to Check • Our Plan: • Sig Fig Race • Sig Fig Quiz • Notes – Significant Figures in Measurement • Practical Lab - Measurement • Wrap Up – Measure Up • Homework (Write in Planner): • Fill out p. 9 – top of 11 using your text by next class!

  45. Sig Figs in Measurements • When doing any measurements in chemistry, it is important that you use the correct precision. • All measurements should be made by writing all units you know and estimating the last unit.

  46. Examples 54 70 10 30 50 20 40 60 38 10 30 50 70 20 40 60 13.9 2 4 6 8 10 12 14

  47. More Examples! 3.4 2 4 6 1.16 0.5 1 1.5 72 20 40 60

  48. Units of Measurement • Every measurement in chemistry MUST HAVE A UNIT! • Without a unit, the number means nothing! • We will use SI units in class

  49. Wrap Up – Clicker! 5.3 2 4 5 6 1.58 0.5 1 1.5 43 20 40 60

  50. Today • Before Class: • Get out Note Booklet, Calculator, & Pencil • Our Plan: • Mix/Group Review (#1-11) • Challenge • Notes - Conversions • WS #3 • Wrap Up – Practice Problem from the Worksheet • Homework (Write in Planner): • Try out some of the problems on the worksheet

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