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UK CHE 226 - CHEMISTRY 226 EXAM I
Course Che 226-
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Name:_____________________Student ID No.:_______________Trial NumberCHEMISTRY 226 EXAM I SEPTEMBER 26, 2002 Name:_____________________ Student ID No.:_______________ I. (15 pts.) Define five of the following seven terms. Clearly mark the five to be graded. 1. Accuracy 2. Specific Gravity 3. Buoyancy error 4. Parallax 5. Equilibrium Molarity 6. Confidence Interval 7. zII. A. (5 pts) What is the mass in grams of solute in 3.50L of a solution that contains 21.7 ppm of SnCl2 (189.615 g/mol)? B. (3 pts) Calculate the molar concentration of Cl-. C. (3 pts) What is the pCl- ? D. (3 pts) What is the w/v% concentration of SnCl2 in the solution?III. Consider the following set of data: Trial Number Value 1 70.24 2 70.22 3 70.10 4 70.05 For question 1 – 5 calculate the following. Show all work including equations. 1. (3 pts) Mean 2. (3 pts) Median 3. (3 pts) Range 4. (5 pts) Standard Deviation 5. (3 pts) Relative Standard Deviation If the accepted value is 70.30 calculate: 6. (3 pts) Relative error of the mean in pptIV. (5 pts each) Estimate the absolute standard deviation and calculate the result of the following calculations. Round results to include only significant figures. The numbers in parentheses are the standard deviations. 1. Y = 18.97 (± 0.04) + 0.0025 (± 0.0001) + 2.29 (± 0.08) = 2. Y = 251 (±1) X 860 (±2) 1.673 (± 0.006) V. Consider the following set of replicate measurements: 2.3, 2.6, 2.2, 2.4, 2.9 1. (5 pts) Calculate the 95% confidence limit. 2. (5 pts) Calculate the 95% confidence limit if s → σ = 0.05.VI. (8 pts) What mass solid Hg3PO4 (696.74 g/mol) is formed when 50 mL of a 0.423 M solution of Na3PO4 is mixed with 100.00 mL of a 0.5151 M HgNO3 solution? VII. (9 pts) List three types of systematic errors. VIII. (8 pts) How many replicate measurements are necessary to decrease the 99.98% confidence interval to 0.5 µg/mL for an atomic absorption assay that measures copper if the method yields a standard deviation of s → σ = 0.61 µg/mL copper. IX. (3 pts) When a measured result and one standard deviation (µ ± σ) are reported as 10.10 ± 0.12 cm, 68.3% of the population of measurements would be included in what range assuming a Gaussian distribution? (3 pts) Considering the information above, what percent of the population would be included if in the value is reported as 10.10 ± 0.36?z Table Confidence Levels, % z 50 0.67 68 1.00 80 1.29 90 1.64 95 1.96 95.4 2.00 99 2.58 99.7 3.00 99.98 3.29 Values of t for Various Levels of Probability Degrees of Freedom Factor for Confidence Interval 80% 90% 95% 99% 99.9% 1 3.08 6.31 12.7 63.7 637 2 1.89 2.92 4.30 9.92 31.6 3 1.64 2.35 3.18 5.84 12.9 4 1.53 2.13 2.78 4.60 8.60 5 1.48 2.02 2.57 4.03 6.86 6 1.44 1.94 2.45 3.71 5.96 7 1.42 1.90 2.36 3.50


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UK CHE 226 - CHEMISTRY 226 EXAM I

Course: Che 226-
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