1 / 23

MEASUREMENT: Ch. 2

MEASUREMENT: Ch. 2. Using Measurements. I. Units of Measurement. II. Unit Conversions. III. Honors Chem 1. MEASUREMENT: Ch. 2. Using Measurements (p.44 - 57). A. Accuracy vs. Precision. accuracy - how close a measurement is to the accepted value

vhoggan
Download Presentation

MEASUREMENT: Ch. 2

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. MEASUREMENT: Ch. 2 Using Measurements I Units of Measurement II Unit Conversions III Honors Chem 1

  2. MEASUREMENT: Ch. 2 Using Measurements (p.44 - 57)

  3. A. Accuracy vs. Precision • accuracy - how close a measurement is to the accepted value • precision - how close a series of measurements are to each other ACCURATE = CORRECT PRECISE = CONSISTENT

  4. H/L Accuracy? H/L Precision? Low accuracy Low precision

  5. H/L Accuracy? H/L Precision? Low accuracy High precision

  6. H/L Accuracy? H/L Precision? High accuracy High precision

  7. your value you get from lab ‘known’ value B. Percent Error • indicates accuracy of a measurement - actual accepted = ´ % error 100 accepted

  8. % error = 2.9 % Example • A student determines the density of a substance to be 1.40 g/mL. Find the % error if the accepted value of the density is 1.36 g/mL.

  9. C. Significant Figures • aka sig figs or S.F. • indicate precision of a measurement. • recording sig figs • sig figs in a measurement include the known digits plus a final estimated digit 2.36 cm

  10. C. Significant Figures • Counting Sig Figs Three rules: < 1 [less than one]– start at first non-zero and count all numbers to the RIGHT > 1 [greater than one] with NO decimal – count from non-zero to non-zero > 1 [greater than one] WITH decimal – count all numbers

  11. Example Counting sig figs: 1. 23.50 1.23.50 4 sig figs 3 sig figs 2. 402 2.402 3. 5,280 3.5,280 3 sig figs 2 sig figs 4. 0.080 4. 0.080

  12. 3 SF C. Significant Figures • Calculating with Sig Figs • multiply/divide - the # with the fewest sig figs determines the # of sig figs in the answer (13.91g/cm3)(23.3cm3) = 324.103g 4 SF 3 SF 324g

  13. C. Significant Figures • Calculating with Sig Figs (cont.) • add/subtract - the # with the least # of decimal places determines the # of decimal places in the answer 224 g + 130.2 g 354.2 g 224 g + 130.2 g 354.2 g 3.75 mL + 4.1 mL 7.85 mL 3.75 mL + 4.1 mL 7.85 mL  354 g  7.9 mL

  14. D. Scientific Notation • converting into scientific notation: • move decimal until there’s 1 digit to its left, places moved = exponent • large # (>1)  positive exponentsmall # (<1)  negative exponent • only include sig figs! 65,000 kg  6.5 × 104 kg

  15. 2,400,000 g 6.72  102 L Example Convert TO sci. notation: 2.4  106 g Convert FROM sci. notation: 672 L

  16. a. accurate b. precise (but not accurate) c. both accurate and precise d. neither accurate nor precise 1. These values were obtained as the mass of products from the same reaction: 6.62 g; 6.67 g; 6.63 g. The known mass of products from that reaction is 7.60 g. The values are

  17. a. good precision b. good accuracy c. poor precision d. poor accuracy 2. Using the same balance, a chemist obtained the values 4.225 g, 5.326 g, and 4.85 g for the mass of a sample. These measurements have

  18. Student A Student B Student C Student D 3. Four students each measured the mass of one 1.43 g sample four times. The results in the table above indicate that the data collected by ____ reflect the greatest accuracy and precision. Mass Data of Sample Trial 1 Trial 2 Trial 3 Trial 4 Student A 1.43 g 1.52 g 1.47 g 1.42 g Student B 1.43 g 1.40 g 1.46 g 1.44 g Student C 1.54 g 1.56 g 1.58 g 1.50 g Student D 0.86 g 1.24 g 1.52 g 1.42 g

  19. a. (13.30 g) ÷ (2.4 mL)  5.5 g/mL 2 SF 4. Calculating with sig figs: 4 SF 2 SF = 5.54166 g/mL b. 14.9 g - 0.14 g  14.8 g 14.76 g

  20. 2.17  10-3 8.472  102 9.13  10-1 3.20615  102 7.48  10-6 9.042  1011 5. Write in exponential/scientific notation: • 0.00217 • 847.2 • 0.913 • 320.615 • 0.00000748 • 904,200,000,000

  21. 356,000 2,700 0.0000824 0.000000000145 30,320,000 0.000341 6. Write out in full: • 3.56 x 105 • 2.7 x 103 • 8.24 x 10-5 • 1.45 x 10-10 • 6.032 x 107 • 3.41 x 10-4

  22. 4 5 5 5 3 5 2 4 7. How many significant figures are in the following numbers? • 4015 • 0.16985 • 405,060 • 0.00032505 • 1.35 • 56.681 • 0.000020 • 79.54

  23. 201.0 cm 19.3 g 21 kg 0.03 mL 2.3 403.37 mm 10. Solve the following, giving your answer with the correct number of significant figures and the correct UNITS: • 125.3cm + 75.7cm • 6.2 g + 13.11g • 43.1 kg – 22 kg • 0.0225 mL / 0.75 mL • 153.33 x 0.015 • 151.81 mm x 2.65734 mm

More Related