I II III I. Using Measurements CH. 2 - MEASUREMENT

A. Accuracy vs. Precision  Accuracy - how close a measurement is to the accepted value  Precision - how close a series of measurements are to each other ACCURATE = CORRECT PRECISE = CONSISTENT

A. Accuracy vs. Precision Precise Accurate Precise Not Accurate Not Precise Not Accurate

B. Percent Error  Indicates accuracy of a measurement your value accepted value

B. Percent Error  A student determines the density of a substance to be 1.40 g/mL. Find the % error if the accepted value of the density is 1.36 g/mL. % error = 2.9 %

C. Significant Figures  Indicate precision of a measurement.  Recording Sig Figs  Sig figs in a measurement include the known digits plus a final estimated digit 2.35 cm

C. Significant Figures 6.34 cm

C. Significant Figures  Rule 1- any # other than 0 is significant  Example has 5 SF

C. Significant Figures  Rule 2- any 0’s between significant figures are significant  Example has 6 SF 1002 has 4 SF

C. Significant Figures  Rule 3- All final 0s after a decimal are significant  Example has 5 SF has 6 SF

C. Significant Figures  Rule 4- )s used for spacing are not significant  Example has 3 SF has 3 SF

, C. Significant Figures Counting Sig Fig Examples , sig figs 3 sig figs 2 sig figs

C. Significant Figures  Rounding  If the digit to be removed is:  < 5, round down  > 5, round up  = 5, round to the nearest even number

kg cm m g C. Significant Figures Rounding Examples Round each number to 3 sig figs 42.7 g 17.3 m 2.78 cm 78.6 kg

C. Significant Figures  Calculating with Sig Figs  Multiply/Divide - The # with the fewest sig figs determines the # of sig figs in the answer. (13.91g/cm 3 )(23.3cm 3 ) = g 324 g 4 SF3 SF

C. Significant Figures  Calculating with Sig Figs (con’t)  Add/Subtract - The # with the lowest decimal value determines the place of the last sig fig in the answer mL mL 7.85 mL 224 g g 354 g  7.9 mL  350 g 3.76 mL mL 7.86 mL 224 g g 354 g

C. Significant Figures  Calculating with Sig Figs (con’t)  Exact Numbers do not limit the # of sig figs in the answer.  Counting numbers: 12 students  Exact conversions: 1 m = 100 cm  “1” in any conversion: 1 in = 2.54 cm

C. Significant Figures 5. (15.30 g) ÷ (6.4 mL) Practice Problems = g/mL  18.1 g g g g 4 SF2 SF  2.4 g/mL 2 SF

D. Scientific Notation  Converting into Sci. Notation:  Move decimal until there’s 1 digit to its left. Places moved = exponent.  Large # (>1)  positive exponent Small # (<1)  negative exponent  Only include sig figs. 65,000 kg  6.5 × 10 4 kg

D. Scientific Notation 7. 2,400,000  g kg 9.7  km  10 4 mm Practice Problems 2.4  10 6  g 2.56  kg km 62,000 mm

D. Scientific Notation  Calculating with Sci. Notation (5.44 × 10 7 g) ÷ (8.1 × 10 4 mol) = 5.44 EXP EE ÷ ÷ EXP EE ENTER EXE = = 670 g/mol= 6.7 × 10 2 g/mol Type on your calculator: