# Unit 2

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## Unit 2

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1. Unit 2

2. Bell work • Turn in Unit 2 preview. What pieces of laboratory equipment are you familiar with? What are they used for or what do they measure?

3. Agenda • Bell work • Scientific discovery lab • Textbook overview

4. Measurement lab edits • Station 1 – Write what each line represents. • Station 2 • You will be using pipettes, but it’s a different type of pipette than described in the lab. There is no wheel or anything, you just squeeze the bulb. • Station 6 • Ignore the page numbers. Just look through chapter 2 for the answers.

5. Textbook questions • If you finish early, grab a textbook from the shelf and peruse chapter 2. • What is the SI system? What is a base unit? What is a derived unit? • Copy the first 5 rows of table 2.1 into your notes • Copy all of table 2.2 into your notes

6. Bell work • Turn in measurement lab. • What is the volume in each of these (mL): 70 50 60 60 40 40 50 30 20

7. Agenda • Bell work • Scientific notation overview • SI Prefixes and metric to metric conversions • Homework: Metric to metric conversions

8. Scientific notation • Used to express numbers that are really big or really small • Move the decimal place • (+) : move decimal place to the right • Make number bigger • (-) : move decimal place to the left • Make number smaller

9. Scientific notation examples • Express the following in scientific notation: 51,200,000 3640 0.00432 • Express the following in standard notation: 7.6 x 10-4 8.98 x 103 5.321 x 10-6

10. Scientific notation practice • Express the following in scientific notation: 72,000 0.0129 0.000056 • Express the following in standard notation: 9.10 x 105 4.33 x 10 -5 8.01 x 103

11. Adding and subtracting • You need to have the same power of ten, so adjust one to match the other • Then add or subtract the numbers • Give answer in scientific notation • 2 × 103 + 3.6 × 104 • 0.2 x 104 + 3.6 x 104 • (0.2 + 3.6) x 104 • 3.8 x 104

12. Example • 7 × 105 – 5.2 × 104 • 70 x 104 – 5.2 x 104 • (70-5.2) x 104 • 64.8 x 104 • 6.48 x 105

13. Multiplying and dividing • Multiply decimal numbers • For multiplying, add exponents on powers of 10 • For dividing, subtract exponents on powers of 10 • (2.6 x 107) (6.3 x 104 ) • (2.6 x 6.3) = 16.38 • 107 x 104 = 1011 • 16.38 x 1011 • 1.638 x 1012

14. Example • (2 x 108) (3.2 x 105) • 2 x 3.2 = 6.4 • 108 + 105 = 1013 • 6.4 x 1013

15. Dividing • Divide decimal numbers • Subtract exponents on powers of 10 • (2.4 x 1011) / (1.2 x 104) • 2.4 / 1.2 = 2 • 1011 / 104 = 107 • 2 x 107

16. Example • (5.76 x 109) / (3.2 x 103) • 5.76 / 3.2 = 1.8 • 109 / 103 = 106 • 1.8 x 106

17. Measurement • Base units – basic units of measure • Ex: • Derived units – formed from a combination of base units • Ex: • Metric vs English • 1 in = 0.0254 m or 2.54 cm • 1 ft = 0.3048 m • 1 mi = 1.61 km or 1609 m • 1.8°F = 1°C • 1 Gal = 0.003785 m3 • 2.2 lb = 1 kg

18. Table 2.1 • SI Base units – there are 7 but we’re concentrating on 5 • SI (SystemeInternacionale) • Internationally standardized measurement notation • Copy this table into your notes

19. Table 2.2 • SI Prefixes – added to base units • Copy this table into your notes

20. Metric to Metric Conversions • All you’re doing is moving the decimal point • You need to think about what the prefix means (10whatever) and if you’re going from a bigger unit to a smaller unit or vice versa • Small  big ; your number should be smaller 10 cm = ________ m • Big  small; your number should be bigger 5 L = ______ dL

21. Practice • Use the table of SI prefixes to complete the following metric to metric conversions • h = hecto; means 102 • This will be your homework

22. Bell work • Turn your metric to metric conversions practice into the tray. • What is the length shown on each of these (cm): 5 70 6 4 60 4 3 50 2

23. Agenda • Overview of measurement lab • Precision vs accuracy • Precision vs accuracy lab • Dimensional analysis • Exit ticket: scientific notation practice • Homework: Precision vs accuracy lab 4 problems at end of this lecture

24. Measurement lab • Station 1 • What we’ve been doing in the bell work • What volume does each line on the equipment measure? 30 125 3 6 80 100 60 20 2 4 40 10 50 1 2 20 75

25. Station 1 • What did you notice when you measured 100 mL with the Erlenmeyer flask and beaker? • If you wanted 100 mL exactly, which piece of glassware would you use?

26. Station 2 • Which most accurately measured 10 mL of water: pipette or beaker? • Which piece of glassware would be best to use when measuring small quantities of liquid?

27. Station 3 • Uncertain digit • Meter sticks on paper – bottom is more precise (has more decimal places) and has less uncertainty • Table dimensions in meter • Table dimensions in centimeters • Volume of table

28. Station 4 • We’ve done some practice with reading volumes during bell work • Any questions on that? • When would you NOT want to use the most precise graduated cylinder?

29. Station 5 • Mass of rubber stopper, 150 mL beaker, and watch glass • What decimal place is the estimated place for our balances?

30. Percent Error • Used to evaluate accuracy • % error = (error / accepted value) x 100 • Error = experimental value – actual value (should always be positive so take absolute value) • Smaller % error is more accurate • % accuracy = experimental / accepted x 100 • Greater % accuracy is more accurate

31. Percent Error • % error + % accuracy = 100 • 22.) 5.45 % • 23.) 7.27% • 24.) You did because you have a lower % error, which means your value was closer to the accepted value.

32. Station 6 • Quantitative vs qualitative • Precise measurement – more decimal places in measurement, more precise • Precision vs accuracy

33. Precision vs accuracy • Precision: repeatable, several measurements close together • Accuracy: close to the accepted value

34. Accuracy How close you are to the accepted value. Good Accuracy

35. Accuracy How close you are to the accepted value. Bad Accuracy

36. Precision How close you are to repeating a result. Good Precision

37. Precision How close you are to repeating a result. Bad Precision

38. Good Precision and Accuracy You want both: repeatedly getting a result close to the accepted or desired value. Good Accuracy and Precision

39. Precision vs Accuracy lab • Read through the lab • Everyone is going to get a chance to see how precise/accurate they are • Same lab groups as before

40. Dimensional analysis • Converting by cancelling units • Steps • Write down what you are given • Find the appropriate conversion factors • Figure out what goes on top and what goes on the bottom • What you want to cancel goes on the bottom • What you want goes on the top • Multiply across the top and divide by what’s on the bottom • 10 hL = ____ L 5 mi = ______ ft 15 km = ______ in

41. Dimensional analysis practice • Try the following conversions using the dimensional analysis method: 15 s = _______ min 7 m = ______ mi 30° C = _____ K 63 in = ________ dm

42. Bell work • Turn in your precision vs accuracy lab. Pull out the 4 dimensional analysis problems I asked you to try from last class. • The accepted mass of a rock is 20.1 g. Jon used a balance and found the mass to be 18.3 g. Jeff found the mass to be 21.3 g. Find both Jon and Jeff’s percent error. Whose balance was more accurate?

43. Agenda • Bell work • Review 4 dimensional analysis problems • Significant figures • Whiteboard practice • Cut and paste dimensional analysis lab • Homework: Cut and paste dimensional analysis lab

44. Dimensional analysis practice • Try the following conversions using the dimensional analysis method: 15 s = _______ min 7 m = ______ mi 30° C = _____ K 63 in = ________ dm

45. All nonzeronumbers aresignificant 7 km has one sig. fig. 55 km/s has two sig. figs. 11,257 kg has five sig. figs.

46. Zeros between nonzero numbers are significant 703 J has three sig. figs. 7.03 V has three sig. figs. 7003 kg has four sig. figs.

47. Zeros in front of nonzero digits are not significant 0.753 m/s has three sig. figs. 0.00753 N has three sig. figs.