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

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

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

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

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.

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)

How many sig figs?  Answer in notebook  4,675,  3, 075,  3,075, x 10 17

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 = Using sig figs = x 324 = 162,000 Using Sig figs = 200, = Sig figs = 22.04

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

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