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Quantitative Chemical Analysis Seventh Edition Quantitative Chemical Analysis Seventh Edition Chapter 3 Experimental Error Copyright © 2007 by W. H. Freeman.

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Presentation on theme: "Quantitative Chemical Analysis Seventh Edition Quantitative Chemical Analysis Seventh Edition Chapter 3 Experimental Error Copyright © 2007 by W. H. Freeman."— Presentation transcript:

1 Quantitative Chemical Analysis Seventh Edition Quantitative Chemical Analysis Seventh Edition Chapter 3 Experimental Error Copyright © 2007 by W. H. Freeman and Company Daniel C. Harris

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3 a cubic decimeter of water at its point of maximum density, 3.984 °C, has a mass that is 25.05 parts per million less than the kilogram.parts per million Cleaning the prototypes removes between 5 and 60 µg of contamination short-term instability of about 30 µg over a period of about a month in its after-cleaned mass

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6 Random error Systematic error

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8 0.234 58.3

9 In experimental data, the first uncertain figure is the last significant figure. 0.234 58.3

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11 significant figure: The number of significant digits in a quantity is the minimum number of digits needed to express the quantity in scientific notation..

12 Adding and subtracting with sig figs: Keep least sig figs beyond the decimal point 121.795

13 Adding and subtracting with sig figs: Keep least sig figs beyond the decimal point WATCH OUT: SAME POWERS OF 10!

14 Multiplying and dividing with sig figs: Keep least sig figs.

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16 logarithms with sig figs: sig figs. in mantissa = sig figs in number

17 logarithms with sig figs: sig figs. in mantissa = sig figs in number log(3.39 x 10 2 ) = log(3.39) + log (10 2 ) = 0.530 + 2 = 2.530 log(3.39 x 10 -5 ) = log(3.39) + log (10 -5 ) = 0.530 – 5 = -4.470

18 NB 1 sig fig!

19 Propagation of Uncertainty from Random Error

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21 This is like adding systematic errors

22 Propagation of Uncertainty from Random Error

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27 The real rule: The first uncertain figure is the last significant figure. TIP: In our calculations, we retain extra insignificant digits and round off only at the end.

28 For systematic uncertainty, we add the uncertainties of each term in a sum or difference.

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30 0.71 1.18 Vernier scale


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