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Chapter 3 Section 2

Chapter 3 Section 2. p recision - how close a series of measurements are to one another a ccuracy - the closeness of measurements to the true value of what is being observed *Can be precise, but not accurate or vice versa -page 54 figure 3.4

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Chapter 3 Section 2

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  1. Chapter 3 Section 2 precision- how close a series of measurements are to one another accuracy- the closeness of measurements to the true value of what is being observed *Can be precise, but not accurate or vice versa -page 54 figure 3.4 -to evaluate the accuracy you must compare with the actual value

  2. accepted value- correct value based on reliable references ex- boiling point of water = 100°C or 212°F experimental value- the value measured in the lab ex- measured bp of water = 99.1°C error- │experimental value – accepted value│ ex- error = │ 99.1°C - 100°C │ = 0.90°C

  3. percent error= error X 100 accepted value ex- 0.90°C X 100 100°C =0.90%

  4. Significant Figures -all the digits that can be known precisely in a measurement plus a last estimated digit Rules for Counting Sig Figs • all non zero digits are significant • all zeroes between two #’s are significant • all zeroes to the right of a # without a decimal point are NOT significant • all zeroes to the right of a # with a decimal point are significant

  5. 5) all zeroes to the left of a number containing a decimal point are NOT significant • if counting, all numbers are significant Examples 1100m 0.00130ML 2003g (2) (3) (4) 3000 cars 456 17.80 (4) (3) (4)

  6. Atlantic Rule -if a decimal point is absent, start counting from the first non-zero digit from the Atlantic Ocean side inland (right →left) Pacific Rule -if a decimal point is present, start counting from the first non-zero digit from the Pacific Ocean side inland (left →right) **All #’s significant when counting 10400L 308g 0.00240m 0.40500L 230L 0.04020g 5600mg 200 pens

  7. Rounding Sig Figs Round each number to 2 sig figs: 15698 1304 560 16000 1300 560 34.29 487.20 62.17 34 490 62

  8. Multiplying/Dividing Sig Figs -the answer must have the same number of sig figs as the factor with the fewest sig figs Ex- (40)(56)(340) 761600 800000 (1 sig fig) Ex- 2.0035 ÷ 3.20 0.626094 0.626 (3 sig figs)

  9. Adding/Subtracting Sig Figs -the result must have the same number of decimal places as the quantity with the fewest decimal places Ex- 2.345 + 0.07 + 2.9975 5.4125 5.41 (2 decimal places) Ex- 5.9 – 0.221 5.679 5.7 (1 decimal place)

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