Chem 287_Chapter 4

# Chem 287_Chapter 4 - Lectures: Classical Methods of...

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Lectures: Classical Methods of Chemical Analysis 1 Analytical Chemistry Chapter 4 To be covered Pages: 83-101 Problems: 3,6,12,15,18 To be covered: 1) Standard Error and Confidence Interval 2) Statistical Comparison 3) Linear Regression Accuracy and Precision Accuracy= How close the measurements are to the tr e al e are to the true value. Precision= How close the measurements are to each other. Inaccurate Imprecise Inaccurate Precise Accurate Imprecise Accurate Precise

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Lectures: Classical Methods of Chemical Analysis 2 General Statistical Principles Descriptive statistics (DS) Used to describe the nature of data Inductive statistics Used DS to make a statement, prediction/estimation or decision DS are commonly reported but both are needed to interpret results Measurement Errors Indeterminate Errors (random) can greatly affect the precision of results. For truly random processes, the distribution of the errors will follow a normal curve (Gaussian), where: 2 2 2 2 1 f(x)  x x e x -
Lectures: Classical Methods of Chemical Analysis 3 Mean and Standard Error Standard Error (in Text as Standard Deviation, s= ) is one measure of precision. For small number of measurements:   x - x) 2 s =     where i - x = average x (mean value) = x i /N N = number of points - Coefficient of Variation s CV =  * 100 x Often variation in a measurement is given relative to the measurement.

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## This note was uploaded on 07/15/2011 for the course CHEM 287 taught by Professor Burns during the Fall '08 term at McGill.

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Chem 287_Chapter 4 - Lectures: Classical Methods of...

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