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

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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

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

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

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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 %

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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

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C. Significant Figures 6.34 cm

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C. Significant Figures Rule 1- any # other than 0 is significant Example 123.45 has 5 SF

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C. Significant Figures Rule 2- any 0’s between significant figures are significant Example- 1002.05 has 6 SF 1002 has 4 SF

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C. Significant Figures Rule 3- All final 0s after a decimal are significant Example- 12.740 has 5 SF 92100. has 6 SF

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C. Significant Figures Rule 4- )s used for spacing are not significant Example- 921000 has 3 SF.00000233 has 3 SF

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4. 0.080 3. 5,280 2. 402 1. 23.50 C. Significant Figures Counting Sig Fig Examples 1. 23.50 2. 402 3. 5,280 4. 0.080 4 sig figs 3 sig figs 2 sig figs

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

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4. 78.5543 kg 3. 2.7851 cm 2. 17.32 m 1. 42.68 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

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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 ) = 324.103g 324 g 4 SF3 SF

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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. 3.75 mL + 4.1 mL 7.85 mL 224 g + 130 g 354 g 7.9 mL 350 g 3.76 mL + 4.1 mL 7.86 mL 224 g + 130 g 354 g

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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

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C. Significant Figures 5. (15.30 g) ÷ (6.4 mL) Practice Problems = 2.390625 g/mL 18.1 g 6. 18.9g - 0.84 g 18.06 g 4 SF2 SF 2.4 g/mL 2 SF

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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

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D. Scientific Notation 7. 2,400,000 g 8. 0.00256 kg 9.7 10 -5 km 10.6.2 10 4 mm Practice Problems 2.4 10 6 g 2.56 10 -3 kg 0.00007 km 62,000 mm

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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 78.1 4 = 671.6049383= 670 g/mol= 6.7 × 10 2 g/mol Type on your calculator:

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