CHEM 1211k 1st Edition Lecture 2 Outline of Last Lecture I Chapter 1 Matter Measurement and Problem Solving Chapter 1 Matter Measurement and Problem Solving continued II 1 7 Counting Significant Figures A All nonzero digits are significant Ex 1 5 has 2 sig figs Interior zeros are significant Ex 1 05 has 3 sig figs Leading Zeros are NOT significant Ex 0 00105 has 3 sig figs Trailing zeros may or may not be significant Trailing Zeros after a decimal point are significant and only significant if the number contains a decimal point Ex 1 050 has 4 sig figs B Exact numbers have an unlimited number of significant figures Ex 1 cm is exactly equal to 0 01m 1cm 0 01m unlimited Radius of a circle diameter of the circle 2 C Practice Problems 1 0 04450 m 4 sig figs 2 5 003 km 5 sig figs 3 10 dm 1m unlimited sig figs 4 1 000 X 10 5 s 4 sig figs 5 0 00002 mm 1 sig fig 6 10 000 m 1 sig fig D Significant Figures in Calculations These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute When multiplying or dividing measurements with significant figures the result has the same number of significant figures as the measurement with the fewest significant figures Ex 5 02 X 89 665 X 0 10 45 0018 45 because the number with the fewest significant figures is 0 10 and it has 2 significant figures When adding or subtracting measurements with significant figures the result has the same number of decimal places as the measurement with the lowest number of decimal places Ex 2 345 0 07 2 9975 5 4125 5 41 because the number with lowest number of decimal places is 0 07 and it only has two decimal places When doing different operations with significant figures 1 Do whatever is in parentheses first 2 Evaluate the significant figures in the intermediate answer 3 Then do the remaining steps Ex 3 489 x 5 67 2 3 3 37 3 4 3 489 x 3 4 11 8626 12 III 1 8 Solving Chemical Problems A Always write every number with its associated unit B Conversion factors are relationships between two units may be exact or measured C Arrange conversion factors so the starting unit cancels You don t need to know the relationship as long as you can find something else the starting and desired units are related to D Precision and Accuracy Precision is an indication of how close repeated measurements are to each other how reproducible a measurement is Random error can result in the inconsistency Accuracy is an indication of how close a measurement comes to the actual value of the quantity Random error error that has equal probability of being too high or too low Systematic error error that tends toward being either too high or too low Chapter 1 Matter Measurement and Problem Solving continued