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CHEMISTRY 2101
Name___________________________
Fall 2010
Dr. Philippe Buhlmann
Hour Exam I
October 8, 2009
Page 1
(1)
(30 points in total) Statistics
(a) (20 points) A few brief questions:
•
The concentration of glucose in a blood sample was measured and reported
along with a 95% confidence interval. Describe briefly the meaning of the
confidence interval.
The confidence interval is the range of values within which there is a 95%
probability of finding the true glucose concentration {or the true mean of
the glucose concentration}.
•
Does an increase in the number of measurements decrease the standard
deviation? Answer with yes or no; no justification required.
No
•
The glucose concentration for the above blood sample was reported as
12.01±0.2049. What problem(s) do you see in this result? How would you
report this result?
12.01±0.21 with proper units. A result without units is just as meaningless as
a result without indication of the error. Rounding of 0.2049 must be
correctly performed to give 0.20.
•
Using a newly purchased instrument that just arrived in the lab yesterday,
Peter measured the concentration of potassium in a urine sample three times
and obtained a relative standard deviation of 18.2%. What should Peter do to
make sure that he has an accurate result?
Use another instrument or another technique to measure the same sample.
Measure a standard sample to confirm that his instrument and method are
giving accurate results. Send the sample to another lab for independent
analysis. Note that making more measurements will result in a narrower
confidence interval, but this will not improve accuracy.
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View Full DocumentCHEMISTRY 2101
Name___________________________
Fall 2010
Dr. Philippe Buhlmann
Hour Exam I
October 8, 2009
Page 2
(b) (10 points) The As content of a sample was determined in four
measurements as 3.102%, 3.076%, and 3.030%. What final answer should be
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 Spring '11
 bulman
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