This problem set is worth one lab report. As in your lab reports, correct answer
ID: 957314 • Letter: T
Question
This problem set is worth one lab report. As in your lab reports, correct answers without work will be given no credit, whereas inconvcl answers with work will be given partial credit. Units must be given. Handwritten problem sets arc fine, but you are required to print out the computer data in problem 4. When recording each answer for each section (and subsection) record the correct number of signifigant figures. However, if you then need to use that value to calculate something in the next part of the question use the unrounded number when doing the next calculation! 1. You measure the following retention times in a gas chromotography column 6.79 min, 6.78 min, 6.79 min, 6.77 min. 6.76 min, 6.78 min Calculate the mean retention time, the standard deviation, the standard deviation of the mean, and the 95% confidence interval for these retention times.Explanation / Answer
Mean/average value = (tn)/n= ( 6.79 + 6.78+6.79+6.77+6.76+ 6.78 )/ 6 = 40.67/6= 6.778
Report it as tm = 6.78 min
Standard deviation = [((tm-tn))/(n-1)]1/2 = [0.000683/5]1/2 = 0.0117
Report as 0.012 min
Standard deviation of the mean m = / n1/2 = 0.0117 min / 2.45 = 0.0048
Report as 0.005
At 68 % confidence level, the result is reported as
tm ± m = (6.778 ± 0.005) min
but also (6.78 ± 0.005) min is acceptable.
For a 95% confidence level read in a Student’s t Table the factor for (n-1)= 5 freedom degrees.
This factor is 2.571
The confidence inteval of the mean retention time at 95 % confidence level is:
6.778 - 2.571x0.0048 …..6.778 + 2.571x 0.0048 or
(6.778 – 0.013…..6.778 + 0.013) min or
(6.765…..6.791) min
............................................................(details)
tn
tm-tn
(tm-tn)^2
(SUM(tm-tn)^2 /5)^1/2
6.79
-0.01167
0.000136111
6.78
-0.00167
2.77778E-06
6.79
-0.01167
0.000136111
6.77
0.008333
6.94444E-05
6.76
0.018333
0.000336111
6.78
-0.00167
2.77778E-06
40.67
SUM
0.000683333
0.011690452
6.778333
Average
0.01169
STDEV
tn
tm-tn
(tm-tn)^2
(SUM(tm-tn)^2 /5)^1/2
6.79
-0.01167
0.000136111
6.78
-0.00167
2.77778E-06
6.79
-0.01167
0.000136111
6.77
0.008333
6.94444E-05
6.76
0.018333
0.000336111
6.78
-0.00167
2.77778E-06
40.67
SUM
0.000683333
0.011690452
6.778333
Average
0.01169
STDEV
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