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CH. 2 - MEASUREMENT

I. Using Measurements. CH. 2 - MEASUREMENT. Activity – Significant figures & measurement. With a partner, read all the instructions for the activity!

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CH. 2 - MEASUREMENT

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  1. I. Using Measurements CH. 2 - MEASUREMENT

  2. Activity – Significant figures & measurement • With a partner, read all the instructions for the activity! • Go to one of the lab stations in the back of the room and, using materials provided, complete the procedure and answer the questions that follow…on your own paper!! • Return to your seats to read the passage on the back and complete the questions.

  3. 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

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

  5. 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 = ____ %

  6. 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

  7. C. Significant Figures Counting Sig Figs Count all numbers EXCEPT: Leading zeros -- 0.0025 Trailing zeros without a decimal point -- 2,500

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

  9. 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/cm3)(23.3cm3) = 324.103g

  10. 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 224 g + 130 g 354 g 224 g + 130 g 354 g 3.75 mL + 4.1 mL 7.85 mL 3.75 mL + 4.1 mL 7.85 mL  ___ g  ___ mL

  11. 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

  12. C. Significant Figures 5. (15.30 g ) ÷ (6.4 mL) Practice Problems = 2.390625 g/mL 6. 18.9 g - 0.84 g  _____g 18.06 g

  13. D. Scientific Notation Converting into Sci. Notation: Move decimal until there’s 1 digit to its left. # Places moved = exponent Large # (>1)  positive exponentSmall # (<1)  negative exponent Only include sig figs 65,000 kg  6.5 × 104 kg

  14. D. Scientific Notation 7. 2,400,000 g 8. 0.00256 kg 9. 7  10-5 km 10. 6.2  104 mm Practice Problems

  15. D. Scientific Notation Calculating with Sci. Notation EXE EXP EXP ENTER EE EE (5.44 × 107 g) ÷ (8.1 × 104 mol) = Type on your calculator: 5.44 7 8.1 4 ÷

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