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More on “Signal”

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Presentation Transcript

  1. More on “Signal” • Interference • Method blank • Matrix effect • Detection limit

  2. The “Scales” of Analytical Chemistry

  3. Review Significant Figures • What are sig figs? • Rules: Addition/subtraction Multiplication/division Log/antilog Exact numbers • When to round?

  4. Significant Figures Examples • Add the numbers 1.0556, 7.113*10-2, and 0.81 • How many kilometers is 9.3 miles? (Use the conversion factor 1 km = 0.62137 mi.) • A student measures the mass and volume of a liquid to determine its density. The volume is 25.00 mL. An empty beaker has a mass of 74.881 g, and the beaker with liquid is 99.437 g. What is the density? • What is the pH of a 1.56*10-3 M hydrochloric acid solution?

  5. Accuracy • What is accuracy? • Quantifying accuracy • Assessing accuracy • No true value?

  6. Precision • What is precision? • Quantifying precision • Assessing precision

  7. Characterizing Data Example Calculate the average, mode, standard deviation, relative standard deviation, and percent relative error for the following data set (density of pennies, post 1982 = 7.18 g/mL). (By hand first, then use your calculator’s stat mode…) • 7.22 g/ml • 6.87 g/ml • 7.03 g/ml • 7.30 g/ml

  8. Two Types of Error • Determinate error • Sampling • Method • Measurement • Personal **can be constant or proportional**

  9. Class A Tolerances

  10. Two Types of Error • Indeterminate/random Visualizing these: Determinate Indeterminate

  11. Uncertainty • What is uncertainty? • DUI example

  12. If you don’t learn anything else in this class…