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Anal ysis

Anal ysis. f o n o i t a c i f i t

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Anal ysis

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  1. Analysis f o n o i t a c i f i t n e d i of Glass a n d

  2. Scenario: A body has been discovered by the side of the road – it appears to have been struck by a car. Upon closer examination, fragments of glass are found embedded in the skin. It is possible that these fragments may be from the windshield of a vehicle, or could come from another source, such as glass from broken bottles thrown along the roadside.

  3. Objective: To determine if the glass recovered on the victim is (uniquely) consistent with windshield glass. Problem: What methods can we use to distinguish between types of glass? Density (d=m/v) Refractive index (RI)

  4. Objective: To measure the density of you glass sample (A, B, C) and see which (if any) correspond to windshield glass (or if we can tell). Problem: What procedure(s) can we use to measure the density of glass fragments? Displacement (one or more pieces?) Flotation

  5. Objective: To measure the density of you glass sample (A, B, C) and see which (if any) correspond to windshield glass (or if we can tell). Problem: Which density method is best? How can we tell? Precision Accuracy

  6. Accuracy can be determined from %error Precision can be determined from standard deviation, s Accuracy and Precision

  7. Concepts covered/things to consider • Density • Precision • Mean (average) values • Standard deviation • Accuracy • Percent Accuracy • Significant figures

  8. Writeup (Short written report) • Objective • Procedure • Results • table (samples A, B, C) • sample calcs for density (one from each method with correct sig figs!), stdev (one method, your 3 values), % error (one method, your 3 values)

  9. Writeup (Short written report) • Objective • Procedure (describe steps foreeach method) • Results • table (samples A, B, C) • sample calcs for density (one from each method with correct sig figs!), stdev (one method, your 3 values), % error (one method, your 3 values) [use 2.47 g/mL for windshield glass dens.]

  10. Discussion Conclusion – answer the following questions: • 1. Which method was most precise? How do you know? • 2. Which method was most accurate? How do you know? • 3. How does the number of sig. figs. determined for your density values relate to the accuracy and precision of the method? (see also question 4) • 3. An analytical balance can measure mass in grams to the fourth decimal place. For which method (if any) might this have been useful? Why or why not? • 4. What kind of glass was your sample (see table 2.3)? Can you tell which sample is consistent with glass from a car windshield? Why or why not? • 5. Are there any other variables that you think are important to the lab? How might it be improved?(if something went wrong, what and why)

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