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Chapter 4: Q30P (page 93)
Explain the following statement: "The validity of a chemical analysis ultimately depends on measuring the response of the analytical procedure to known standards."
The given statement should be accepted.
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The equation for the Gaussian curve in Figure 4 - 1is
where is the mean value is the standard deviation , total bulbs = 4768, and hours per bar ( = 20) is the width of each bar in Figure 4 - 1. Set up a spreadsheet like the one with this problem to calculate the coordinates of the Gaussian curve in Figure 4 - 1 from 500to 1200hin 25 - hintervals. Note the heavy use of parentheses in the formula at the bottom of the spreadsheet to force the computer to do the arithmetic as intended. Use Excel to graph your results.
Which statement about the F test is true? Explain your answer.
(i) If, there is more than a 5%chance that the two sets of data are drawn from populations with the same population standard deviation.
(ii) If, there is at least 95%probability that the two sets of data are drawn from populations with the same population standard deviation.
Now we use a built-in routine in Excel for the paired t test to see if the two methods in Problem 4-15 produce significantly different results. Enter the data for Methods 1 and 2 into two columns of a spreadsheet. For Excel 2007 and 2010, find Data Analysis in the Data ribbon. If Data Analysis does not appear, follow the instructions at the beginning of Section 4-5 to load this software. Select Data Analysis and then select t-Test: Paired Two Sample for Means. Follow the instructions of Section 4-5 and the routine will print out information including (labeled "tStat")(labeled " t Critical two-tail"). You should reproduce the results of Problem 4-15.
The ratio of the number of atoms of the isotopes andin eight samples from different sources was measured in an effort to understand differences in reported values of the atomic mass of gallium:
Find the (a) mean, (b) standard deviation, (c) variance, and (d) standard deviation of the mean. (e) Write the mean and standard deviation together with an appropriate number of significant digits.
Calibration curve. (You can do this exercise with your calculator, but it is more easily done by the spreadsheet in Figure.) In the Bradford protein determination, the color of a dye changes from brown to blue when it binds to protein. Absorbance of light is measured.
(a) Find the equation of the least-squares straight line through these points in the form with a reasonable number of significant figures.
(b) Make a graph showing the experimental data and the calculated straight line.
(c) An unknown protein sample gave an absorbance of0.973. Calculate the number of micrograms of protein in the unknown and estimate its uncertainty.
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