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

2. 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 19.94 g19.935 g19.9351 g 19.9351 g is the most precise. It has the greatest number of significant figures. # sig figs3456

3. 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? 1.15 101.5 0.015 Sci. Notation 0.00150 101.50 1.153 1.015 x 10 2 4 1.0150 x 10 2 5 1.5 x 10 -2 2 1.50 x 10 -3 3 Value

4. 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. 28.0 cm 23.542 cm 25.64 cm + 77.2 cm (77.182 cm) Rounding Rules: 1. Round up if the next number is greater than 5. 2. Round down if the next number is less than 5. 3. 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 5. 2. Round down if the next number is less than 5. 3. 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 + 23.542 cm + 25.64 cm

5. 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) =(23.814 cm 3 ) #sigfigs4 33 23.8 cm 3 What is the answer using the correct number of sigfigs to: (2.005 g/mL)(2.05 mL + 1.6 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

6. A 20.0000 g weight is weighed on four different balances, and the four masses shown below were obtained. Calculate the percent error for each measurement. 19.9 g 20.04 g20.044 g19.9351 g error 0.1 g0.04 g0.044 g0.0649 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