14 points] You perform this same electrochemical analysis on eight of the twenty

Question

14 points] You perform this same electrochemical analysis on eight of the twenty-five aliquots and obtain the concentrations listed below. One of the concentrations appears that it might be an outlier. Use a Q-Test to see if it is an outlier at the 95% confidence level. A Q-Table is located at the back of this exam. d. Aliquot number Electrochemically determined Pb2 concentration in a 40.00 mL. aliquot 1.23 x 103 molar 1.47 x 103 molar 0.74 x 10-3 molar 1.33 x 103 molar 1.49 x 10 molar 1.28 x 103 molar 1.19 x 103 molar 1.32 x 103 molar [2 points] Now that any outliers are removed, report the mean and standard deviation of the Pb2 concentration in a 40.00 mL aliquot using the typical 95% confidence limit format by writing a sentence (AT. Table is attached.) e. [2 points] The measurement of the voltage of electrochemical cells to determine concentrations is a tough analytic technique. Explain why the accuracy of this type of experiment can be such a challenge. f.

Explanation / Answer

(e) Now we have removed the outlier which is the third point.

Now new sample mean x = 1.33 x 10-3 molar

new standard deviation s = 0.1136 x 10-3 molar

Here 95% confidence interval = x +- t60.05 (s/sqrt(n)

= [1.33 +- 2.447 * (0.1136/sqrt(7))] x 10-3 molar

= (1.33 +- 0.105) x 10-3 molar

(f) The accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantity's true value. Here as we don't know the true value and it can only be evaluated by repeated number of attempts and then averaging it out. That makes it very tough process. Their is no standard formula to calculate that voltage so we have to rely on samples mean and their uncertainty. As the example entails that there comes a substantial change due to an outlier. SO, precaution is very necessary while evaluating the voltage.

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