1. CHEMISTRY Thursday, August 14, 2014 Sig Figs, Accuracy and Precision

2. Bell Work 8/14  Convert the Following Units using dimensional analysis 15Km = _____ cm 20lbs = _____ g 48°F = ______K

3. Agenda  Discuss Significant Figures  Accuracy vs Precision  Multiplying and Dividing Scientific Notation  Complete Measurement Activity Packet

4. Objectives Students will be able to:  Determine the correct number of significant figures for a number  Distinguish between accuracy and precision  Multiply and Divide using scientific notation

5. Significant Figures  When we write numbers in science it turns out that some numbers are more important than others.  Numbers that are important are called significant, numbers that aren’t are insignificant.  Especially in Chemistry, significance is important, because we need to keep measurements and calculations on the same track.

6. What makes a number significant?  It all comes down to zeroes. 1. All non-zeroes digits are significant—455 (3 significant) 2. Trapped zeroes are significant—5005 (4 significant) 3. Preceding Zeroes are insignificant—00045 or.0045 (2) 4. Trailing zeroes are insignificant---5,000,000 (1) unless there is a decimal point included in the number— 5,000,000. (7) or.4000 (4) 5. If a number is written in scientific notation, only the numbers before the x 10 x are considered significant following the rules above—7.04 x 10 5 (3)

7. How many sig figs?  Answer in notebook  4,675,000.0000535000  3, 075, 000.0000000003  3,075,000.0050 x 10 17

8. Using Sig Figs in Chemistry  When taking measurements, you should always go one number beyond what the increments are on the measuring device.  When multiplying/dividing your answer should have the same number of sig figs as the least amount in the problem.  Adding/Subtracting answer should have the same number of decimal places as least in problem 584 x 13.82 = 8070.88 Using sig figs = 8070 5000 x 324 = 162,000 Using Sig figs = 200,000 18.4756 + 3.56 = 22.0356 Sig figs = 22.04

9. Accuracy vs Precision  What does it mean to be accurate?  Accuracy means that your measured values are as close to the true value as possible.  Precise?  Your measured values for each trial are as close together as possible

10. Finish Measurement Activity Packet  Tasks 1-4 should be completed by end of period.  I will collect!