1 / 28

Chemistry 139

Chemistry 139. Davis. Chapter 1 – Goals. Chapter 2 - Goals. Measurements Understand Uncertainty in Measurement Know, understand, and be able to apply significant figures to calculations. Know, understand, and be able to apply scientific notation to calculations. Measurement….

monet
Download Presentation

Chemistry 139

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. Chemistry 139 Davis

  2. Chapter 1 – Goals

  3. Chapter 2 - Goals • Measurements • Understand Uncertainty in Measurement • Know, understand, and be able to apply significant figures to calculations. • Know, understand, and be able to apply scientific notation to calculations.

  4. Measurement… • Defined: determination of the quantities related to an object. • Dimensions • Volumes • Time • Etc… • Requires that someone actually

  5. I’m certainly uncertain… • Two terms: • Exact numbers – • Exactly • Exactly • Exactly _____ desks in this room. • Inexact numbers – • Flaws in • Uncalibrated • User

  6. Accuracy and Precision • Defined • Precision –

  7. Accuracy – Volume measurements for a titration: Trial 1 = 25.5 mL Trial 2 = 25.6 mL Trial 3 = 25.5 mL

  8. Is this accurate or precise or…?

  9. Sample data • Mass readings for a magnesium sample: Evaluate these measurements for precision and accuracy

  10. From the book: • Two teams of three students count birds sitting on a power line. Team counts are: The actual count was 76 birds. Who was most accurate? Which team was most accurate? Which team’s count was most precise?

  11. Uncertainty in Measurement • Why are digits in measurements uncertain? • Instruments • Differences • Always involves estimation • Choose the right instrument for the job • Volumetric vs ‘to hold’ glassware • May be estimated for you (electronic scales) • Scale is marked but you estimate the in-between

  12. Glassware/proper equipment

  13. Measurements • MUST Which is correct?

  14. Significant Figures (Digits)… • Method to deal with • All digits known

  15. What Sig Figs mean… • All KNOWN numbers 15023.557

  16. Significant Digits • The Rules – Memorize these. • All non-zeros are • A zero is significant when : • It is • It is • A zero is not significant when: • It is • It is at

  17. Significant Digits - PRACTICE How many significant digits? • 54.23 • 23.00005 • 0.0004 • 35000 • 0.000504 • 45.623200 • 5,000,000 • 4,000,000.1

  18. Calculations with Significant Figures • Add/subtract – • Multiply/divide – • Only round after problem is complete

  19. Practice Add/Subtract 122.53 + 6.448 + 145.3 274.278

  20. Significant Digits - Calculations • Addition and Subtraction • Round answer to have final digit in the SAME PLACE as the last digit in the LEAST ACCURATE MEASUREMENT • 1.21 + 5.002 + 10. = • 34.5 + 12.45 + 23.0505 = • 186.31 + 11.1 = • 12.0231 + 3.86 = • 0.100012 + 120. = • 1200 + 12 + 15 + 0.5 =

  21. Significant Digits - Calculations • Multiplication and Division • The answer has as many sig figs as the number with the fewest sig figs • 14.8 x 3.1 = • 18.2 x 3.0 = • 52/1.5 = • 321.868783 x 1 = • 2400 x 2.123 = • 15000/12.354 =

  22. Practice Multiply/Divde 452.11 x 78.5 = 35490.635

  23. Practice 1524.57 / 32.15 = 47.4205287714

  24. Significant Figures and Exact Numbers • Exact numbers are never used to determine the number of significant figures to report in your answer. 6.25 ft * 1 mile = 0.00118371212 mile 5280 ft

  25. Scientific Notation • Convenient way of writing very large or very small numbers and showing only significant figures • Number between • 5120 becomes • Move decimal point in original number to make number 1-10 • Move left = • Move right =

  26. Scientific Notation Practice • 123,000 = • 0.000045 = • 23.45 = • 0.0000000003 = • 1,000,000 =

  27. Scientific Notation and Significant Figures • Express the number 275,364,145 with: • 4 sig fig: • 2 sig fig: • 6 sig fig:

  28. Scientific Notation • Math with: • Use the EE or EXP button on your calculator. • For example:

More Related