3343t1fall98 - as Zn 2 P 2 O 7 If the Zn 2 P 2 O 7 weighed...

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Chem 3343 Fall’98 Test 1 NAME 1. A sample of steel was analyzed for percentage of manganese. The following percentages were the obtained: 1.01, 0.95, 0.99, 1.06, 0.94, 0.85, 1.05, 1.05, 1.05. a. Calculate the average of the sample. b. calculate the standard deviation for the samples. c. Calculate the relative standard deviation for the samples. d. Calculate the 95% confidence interval. 2. A second sample of steel was analyzed for percentage manganese. The average of 5 measurements was 1.07 % with a standard deviation of 0.08. Is there any evidence that the second sample was different from the sample in #1? 3. A sample that contains 8 ppb of Pb 2+ contains how many Pb 2+ ions per liter? 4. A 1.0000 g sample of zinc ore was dissolved and the zinc precipitated as the phosphate and weighed
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Unformatted text preview: as Zn 2 P 2 O 7 . If the Zn 2 P 2 O 7 weighed 0.6611 g, what was the percent Zn in the ore? 5. Solve the following problem: (50.00 ± 0.02 - 37.00 ± 02)(0.1395 ± 0.0005) 6. What are the problems associated with drying a sample prior to running the analysis and how are they normally handled? 7. How are elemental (C, H, etc.) analyses performed today? Give a general description of the procedure. 8. What is a confidence interval? What are (is) the assumptions in our calculations? 8. How many analyses should we do if we want to be 95% certain that the error is less than 5% (0.05) if the standard deviation is 6% (0.06)? 7. Why do we normally do analyses in triplicate rather than some other number of analyses?...
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This note was uploaded on 10/01/2011 for the course CHEM 3332 taught by Professor Thummel during the Spring '08 term at University of Houston.

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