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Measurement book reference p. 51 -62 Accuracy The accuracy of the measurement refers to how close the measured value is to the true value. For example, if you used a balance to find the mass of a 100.00 g object. If you got a measurement of 78.55 g, your measurement would not be very accurate. Precision Precision refers to how close together a group of measurements actually are to each other.

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Accuracy and precision examples Preciseaccurate and precise

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Errors Accuracy with error & precision with error

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Electron configuration practice Give the electron configuration: Pb Fe Identify the element: [Kr]4d 10 5s 2 5p 2 [Ne]3s 2 3p 1

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Significant figures sig fig (sf) Rules for reporting meaningful experimental results. Prevents propagation of error.

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Sig figs Any non-zero number is significant Zeros between sig figs are significant Zeros in front of all nonzero digits are not significant Zeros at the end of number and to right of the decimal point are significant Zeros to the left of the decimal are tough. If they were measured they are significant. Use scientific notation.

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Sig fig examples 24.7 g 0.346 g 2005 m 3.509 ml 0.00067 g 56.00 6.010 600 720 3 sf 4 sf 2 sf 4 sf 1 or 3 6.00 x 10 2 2 or 3 7.20 x 10 2

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Calculations and sig fig Addition subtraction An answer can not be more precise than the least precise measurement 4.34 cm - 2.3 cm = 2.04 so 2.0 cm Rounding rules if the digit after the last significant digit is 5 or greater round up 10.345 g + 2.3 g = 12.645 so 12.6 g

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Calculations and sig fig multiplication division The LEAST MOST rule - the most sig fig reported in your answer comes from the least number of sig fig in the calculation 3.4 cm x 5.43 cm = 18.462 so 18 cm 2 18.45 g /3.45 g = 5.347826087 so 5.35

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