Statistics Problem Set #2e
-
A sample was prepared from 1.3452 g of soil (weighed on an analytical balance).
The mercury in this sample was extracted and diluted to 100.0 mL in a class
A volumetric flask.
-
Use the data from the standards to construct a calibration curve.
-
Based upon this calibration curve, what is the concentration of mercury
in the solution that was analyzed.
-
Based on the concentration of mercury in the solution, what is the concentration
of mercury in the original soil sample?
-
What is the uncertainty in the concentration of the mercury in the solution
(based upon the uncertainty in the calibration curve)?
-
What is the uncertainty in the concentration of mercury in the original
soil sample (by propagating the error from each step)? (Note: the uncertainty
in the balance and the volumetric glassware may be treated as population
statistics since these are standard deviations for a very large number
of measurements.)
- Based upon the above calculations, how would you report your results?
-
How could you verify the accuracy of your determination?
Concentration
(ppm) |
Signal
LOG(Po/P) |
|
|
0 |
0.00236 |
0.001 |
-0.00610 |
0.002 |
0.00149 |
0.005 |
0.00282 |
0.01 |
0.00377 |
0.05 |
0.02093 |
0.07 |
0.02235 |
0.09 |
0.03336 |
0.12 |
0.04990 |
0.15 |
0.05834 |
0.18 |
0.06637 |
Unknown |
0.0353 |
-
A unknown sample was prepared for analysis by inductively coupled plasma
emission.
-
Solution A; 0.0153±0.0001 g of unknown was weighed out on an analytical
balance, dissolved and diluted to 250.0±0.1 ml in a volumetric flask.
-
Solution B; 100.0±0.2 ml of solution A was transferred to a second
flask and diluted to 250.0±0.1 ml.
-
Solution C; 0.0026±0.0001 g of iron was dissolved, 100.0±0.2
ml of solution A was added, and the solution diluted to 250 ml.
-
Giving the following data:
|
Trial 1 |
Trial 2 |
Trial 3 |
Blank |
0.026 |
0.037 |
0.029 |
Solution B |
11.312 |
11.292 |
11.299 |
Solution C |
17.399 |
17.401 |
17.390 |
-
What is the concentration of Fe in solution B?
-
What is the weight percent Fe in the unknown sample?
-
Based upon the replicate samples what is the uncertainty in the concentration
of Fe in solution B?
-
Use propagation of error to determine the uncertainty in the weight percent
of Fe in the unknown sample. Report your results at the 90% confidence
level using the t-test.
This page is maintained by
Scott Van Bramer
Department
of Chemistry
Widener University
Chester, PA 19013
Please send any comments, corrections, or suggestions to
svanbram@science.widener.edu.
This page has been accessed times
since 1/8/98.
Last Updated 1/8/98