What is the difference between accuracy and precision? Good precision Low accuracy = average position Low precision High accuracy

Significant figures: represent the precision of a measurement A 20 g weight is weighed on four different balances, and the four masses shown below were obtained. Which measurement is the most precise? 19.9 g g g g g is the most precise. It has the greatest number of significant figures. # sig figs3456

Determining the number of significant figures: 1. All nonzero figures are significant. 2. The only time zeros are NOT significant is when they precede nonzero numbers. They are merely placeholders. #SigFigs? Sci. Notation x x x x Value

Math with significant figures: Addition/subtraction: line up the decimal points. The answer is rounded to the same number of decimal places as the value with the least number of decimal places cm cm cm cm ( cm) Rounding Rules: 1. Round up if the next number is greater than Round down if the next number is less than If the next number is exactly 5, round up only if the number to be rounded is ODD. Ex: 1.15 and 1.25 both round to 1.2 Rounding Rules: 1. Round up if the next number is greater than Round down if the next number is less than If the next number is exactly 5, round up only if the number to be rounded is ODD. Ex: 1.15 and 1.25 both round to 1.2 For example, add: 28.0 cm cm cm

Math with significant figures: Multiplication/division: the answer is rounded so that it has the same number of sigfigs as the value with the least number of sigfigs. (3.205 cm)(3.65 cm)(2.05 cm) =( cm 3 ) #sigfigs cm 3 What is the answer using the correct number of sigfigs to: (2.005 g/mL)(2.05 mL mL)= (2.005 g/mL)(3.65 mL) The six is underlined because it is the last significant digit. Do not round off any values until the final answer!! = 7.32 g 2 sf’s 7.3 g 2 sf’s

A g weight is weighed on four different balances, and the four masses shown below were obtained. Calculate the percent error for each measurement g g g g error 0.1 g0.04 g0.044 g g Accuracy of a measurement can be determined by calculating the percent error (error = true – experimental). % error0.5%0.2%0.22%0.324% Percent error = error true value x 100