2. Section 2-3 Section 2.3 Uncertainty in Data Define and compare accuracy and precision. Describe the accuracy of experimental data using error and percent error. Apply rules for significant figures to express uncertainty in measured and calculated values.

3. Section 2-3 Section 2.3 Uncertainty in Data (cont.) Measurements contain uncertainties that affect how a result is presented. No measurement of physical quantity is absolutely certain.

4. Section 2.3 Uncertainty in Data (cont.) A. Causes of uncertainty: 1. The skill and care of the person (bias, carelessness) 2. The precision of the measuring instrument 3. procedural errors

5. Sec. 2-3 Precision B. Ways to Evaluate Measurement 1. Precision in a measurement a. Refers to how close to a series of measurements are to one another or the reproducibility of a series of measurements.

6. Sec. 2-3 Precision b. Depends on the scale found on a piece of equipment. 1. Usually it is 1/10 the smallest marked interval on a piece of equipment used. Its related to the area in between markings.

7. Sec. 2-3 Precision e. Example #2: 5 ---------- 4 ---------- 3 ---------- 2 ---------- 1 ---------- 0 ----------

8. Sec. 2-3 Precision 2. Can only guess one tenth beyond the marked interval. This is called a doubtful digit. c. Precision is determined by the instrument.

9. Sec. 2-3 Precision f. Guidelines for precision: Smallest marked intervalRead to: 0.010.001 0.10.01 1 0.1 10 1 Not standard 2 1 5 1 0.20.1 0.50.1

10. Sec. 2-3 Precision d. Example #1: Which student is the most precise?

11. Sec. 2-3 Accuracy 2. Accuracy a. Refers to how close a measurement is to a true or accepted value. b. Reflects the average error that may be present in trying to read the last digit in your measurement. (Doubtful digit) c. You control accuracy.

12. Sec. 2-3 Accuracy d. Examples of accuracy and precision

13. Sec. 2-3 Accuracy Which student is the most accurate?

14. Sec.2-3 Percent Error Error is defined as the difference between and experimental value and an accepted value.Error

15. Sec. 2-3 Percent Error The error equation is error = experimental value – accepted value. - error is always an absolute value - you cannot have a negative error Percent error expresses error as a percentage of the accepted value.Percent error

16. A reference book indicates that a certain amount of chemical will be produced in a particular reaction. This yield is 0.1062 g. The amount that a student obtained during the experiment was 0.0098 g. What is the percent error in this result?