Quiz-1-07F-Solutions

Quiz-1-07F-Solutions - 1 CHEM 119 H Quiz 1 Show work neatly...

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1 CHEM 119 H Quiz 1 09/27/07 ____________________________________ Show work neatly on these pages. Use backs as needed. I have neither given nor received aid while If we cannot follow your work QUICKLY, it is wrong. taking this quiz USE PENCIL & ERASE CLEANLY. Pay attention to decimals in answers. 1. (5) What is meant by “confidence interval”? The confidence interval is the range around the average value in which we believe that the true value lies. 2. (35) The analyses of trace amounts of material are inherently more difficult than analyses of samples with concentrations in the range we are using. There will almost always be a “relatively large” uncertainty in the results. Harris reports the following results for the analysis of concentrations of xylenes (isomeric C 8 H 10 compounds) in air in two places: average, standard deviation, number of measurements. As you can see, there is a wide variation (large standard deviation) for these measurements. A microgram of material per cubic meter of air is not much. Place C{xyl, µ g/m 3 } #measurements Turnpike 31.4 ± 30.0 32 Tunnel 52.9 ± 29.8 32 e. (10) Use the appropriate statistical equations to determine whether or not these average values differ at the 95 % confidence level () 12 1 2 22 11 22 XX n * n t = sn + n n-1s + (n-1 )s s = n+n-2 s = 29.9 X-X 21 .5 = 2 21.5 32 t{calc}= 2.88 29.9 64 = ⎜⎟ t{table, 60} t{62} = 2.00 t{calc} > t{table}; therefore, the two results are
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Quiz-1-07F-Solutions - 1 CHEM 119 H Quiz 1 Show work neatly...

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