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Tools for Chemists

Tools for Chemists. Measurements and Numbers. The King ’ s Foot. The story of a King, a Queen, and a carpenter who almost lost his life for the lack of a system of standard measurements. Number of Pennies in a Jar. Exact or Inexact?. Height of Pennies in a Stack. Exact or Inexact?.

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Tools for Chemists

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  1. Tools for Chemists Measurements and Numbers

  2. The King’s Foot The story of a King, a Queen, and a carpenter who almost lost his life for the lack of a system of standard measurements.

  3. Number of Pennies in a Jar • Exact or Inexact?

  4. Height of Pennies in a Stack • Exact or Inexact?

  5. The Great Penny Count

  6. The Great Penny Count Machine Count = 116. Which team is accurate? Precise?

  7. The Great Penny Count Are errors random? Systematic?

  8. Does Your Measuring Tool Matter? • Try it!

  9. Uncertainty • What creates it? • How do we indicate it?

  10. The “Recording Uncertainty” Rule • Record all digits which you can read with certainty off the measuring device, plus one estimated digit. The resulting numbers will all be significant.

  11. Student Balance 22 23 Research Balance 22.5 Try It!

  12. Significant Figures The Horse and the Ribbon 0.19 lbs 1270 lbs

  13. How much do they weigh together? 1270 lbs + 0.19 lbs 1270.19 lbs

  14. Communicating Significance • Significant Numbers and Place holders • Non-zero digits • Zeros • Leading: 0.0256 • Confined: 20056 • Trailing: 347000 or 347000.

  15. Practice • 72.0 • 51.700 • 0.03400 • 3.060 • 450 • 360,000

  16. Vocabulary Summary • Exact Number • Inexact number • Precision • Accuracy • Random error • Systematic error • Uncertainty • Significant figures

  17. Sig Figs and Mathematical Operations • Rounding • < 5: drop • > 5 round up • = 5: Round up if odd, drop if even • If rounding to left of decimal, replace dropped digits with placeholder zeros.

  18. Rounding Practice • Round to 3 sig figs • 72.311 • 72.382 • 72.353 • 64.453 • 72311 • 72382 • 72356

  19. Multiplying and Dividing with Sig Figs • The number of sig figs in the answer (product or quotient) equals the number of sig figs in the multiplier or divisor with the fewest sig figs. • Huh? • Area: 62.059 in x 72.6 in = 4505.4834 in2

  20. Addition and Subtraction • The precision of the number resulting from an addition or subtraction operation is the same as that of the least precise number used to carry out the operation. • Huh? Huh?

  21. Small Group Practice • Carry out the following operations and write the answer with correct sig figs, rounding properly. • 350.00 x 0.00072 • 3554/2.22 • 237 + 37 + 7 • 4.111 - 3.07 • 1.20 x (3.45 + 4.5) • 0.500 x0.1723 x (0.6772 + 0.31)

  22. Assignment • Read 2.1-2.6 • Do Problems in range 2.1 – 2.77

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