SCIENTIFIC MEASUREMENT

1. SCIENTIFIC MEASUREMENT • CHEM IH: CHAPTER 3

2. What is Scientific Notation? • Scientific notation is a way of expressing really big numbers or really small numbers. • For very large and very small numbers, scientific notation is more concise.

3. Scientific notation consists of two parts: • A number between 1 and 10 • A power of 10 N x 10x

4. Examples • Given: 289,800,000 • Use: 2.898 (moved 8 places) • Answer:2.898 x 108 (how many sig figs? Honors only) • Given: 0.000567 • Use: 5.67 (moved 4 places) • Answer:5.67 x 10-4 (How many sig figs? Honors only)

5. Stating a Measurement In every measurement there is a • Number followed by a • Unit from a measuring device The number should also be as precise as the measuring device.

6. Ex: Reading a Meterstick . l2. . . . I . . . . I3 . . . .I . . . . I4. . cm First digit (known) = 2 2.?? cm Second digit (known) = 0.7 2.7? cm Third digit (estimated) between 0.05- 0.07 Length reported =2.75 cm or 2.74 cm or 2.76 cm

7. UNITS OF MEASUREMENT Use SI units — based on the metric system Length Mass Volume Time Temperature Meter, m Kilogram, kg Liter, L Seconds, s Celsius degrees, ˚C kelvins, K

8. Metric Prefixes

9. Significant Figures (Honors only) • The numbers reported in a measurement are limited by the measuring tool • Significant figures in a measurement include the known digits plus one estimated digit

10. Counting Significant Figures: Non-Zero Digits (Honors Only) RULE 1. All non-zero digits in a measured number ARE significant. #of Significant Figures 38.15 cm 4 5.6 ft 2 65.6 lb ___ 122.55 m___

11. Counting Significant Figures:Leading Zeros (Honors Only) RULE 2. Leading zeros in decimal numbers are NOT significant. #of Significant Figures 0.008 mm 1 0.0156 oz 3 0.0042 lb ____ 0.000262 mL ____

12. Counting Significant Figures:Sandwiched Zeros (Honors Only) RULE 3. Zeros between nonzero numbers ARE significant. (They can not be rounded unless they are on an end of a number.) # of Significant Figures 50.8 mm 3 2001 min 4 0.702 lb ____ 0.00405 m ____

13. Counting Significant Figures:Zeros @ the End of a # & to the Right of a Decimal (Honors Only) RULE 4. Trailing zeros at the end of a number and to the right of a decimal numbers ARE significant. # of Significant Figures 43.00 m. 4 200.00 yr 5 1.10 gal ____ 0.04500 g ____

14. Counting Significant Figures:Trailing Zeros (Honors Only) RULE 5. Trailing zeros in numbers without decimals are NOT significant. They are only serving as place holders. # of Significant Figures 25,000 in. 2 200. yr 3 48,600 gal ____ 25,005,000 g ____

15. Counting Significant Figures:Unlimited Sig Figs (Honors Only) RULE 6. 2 instances in which there are an unlimited # of sig figs. • Counting. Ex: 23 people in our classroom. • Exactly defined quantities. Ex: 1hr = 60 min. • Both are exact values. There is no uncertainty. • Neither of these types of values affect the process of rounding an answer.

16. Shortcuts to Sig Figs The Atlantic-Pacific Rule says: "If a decimal point is Present, ignore zeros on the Pacific (left) side. If the decimal point is Absent, ignore zeros on the Atlantic (right) side. Everything else is significant."

17. Learning Check (Honors Only) A. Which answers contain 3 significant figures? 1) 0.4760 2) 0.00476 3) 4760 B. All the zeros are significant in 1) 0.00307 2) 25.300 3) 2.050 x 103 C. 534,675 rounded to 3 significant figures is 1) 535 2) 535,000 3) 5.35 x 105

18. Learning Check (Honors Only) In which set(s) do both numbers contain the samenumber of significant figures? 1) 22.0 and 22.00 2) 400.0 and 40 3) 0.000015 and 150,000

19. Significant Numbers in Calculations (Honors Only) • A calculated answer cannot be more precise than the measuring tool. • A calculated answer must match the least precise measurement. • Significant figures are needed for final answers from 1) adding or subtracting 2) multiplying or dividing • If you must round to obtain the right # of sig figs, do so after all calcs are complete

20. Adding and Subtracting (Honors Only) The answer has the same number of decimal places as the measurement with the fewest decimal places. 25.2one decimal place + 1.34two decimal places 26.54 answer 26.5one decimal place

21. Learning Check (Honors Only) In each calculation, round the answer to the correct number of significant figures. A. 235.05 + 19.6 + 2.1 = 1) 256.75 2) 256.8 3) 257 B. 58.925 - 18.2 = 1) 40.725 2) 40.73 3) 40.7

22. Multiplying and Dividing (Honors Only) Round (or add zeros) to the calculated answer until you have the same number of significant figures as the measurement with the fewest significant figures.

23. Learning Check (Honors Only) A. 2.19 X 4.2 = 1) 9 2) 9.2 3) 9.198 B. 4.311 ÷ 0.07 = 1)61.582) 62 3) 60 C. 2.54 X 0.0028 = 0.0105 X 0.060 1) 11.3 2) 11 3) 0.041

24. Conversion Factors Fractions in which the numerator and denominator are EQUAL quantities expressed in different units Example: 1 hr. = 60 min Factors: 1 hr. and 60 min 60 min 1 hr.

25. How many minutes are in 2.5 hours? Conversion factor 2.5 hr x 60 min = 150 min 1 hr cancel By using dimensional analysis / factor-label method, the UNITS ensure that you have the conversion right side up, and the UNITS are calculated as well as the numbers!

26. Learning Check How many seconds are in 1.4 days? Unit plan: days hr min seconds 1.4 days x 24 hr x _60min x 60 s = 1 day 1 hr 1 min ANSWER: 120,960 s. FINAL ANSWER (in sig figs) = 120,000 s

27. Scientific Notation & Your Calculator • Video Instructions- Using Calculator