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Unformatted text preview: Name:________________________________________________________________________ Chemistry 3600 Fall, 2003 First Examination October 3, 2003 Read over all the questions before you start to answer, as some are more difficult than others. Each question shows the number of points that it is worth in parenthesis. Show the formulas you used and all your work to get full credit. Express all answers with the correct number of sigfigs! Formulas: x= x i i n s= (x - x) i i 2 =x n -1 ts n For Fcalc>Ftable tcalculated = x1 - x2 2 s12 / n1 + s2 / n2 gap s12 Q= F= 2 range s2 2 2 2 ( s1 / n1 + s 2 / n 2 ) d.f. = 2 -2 2 2 2 ( s1 / n1 ) + ( s 2 / n 2 ) n1 + 1 n2 + 1 For Fcalc<Ftable tcalculated = x1 - x2 spooled n1n2 n1 + n2 s pooled = 2 s12 (n1 - 1) + s2 (n2 - 1) n1 + n2 - 2 Tables: Q table @ 90% confidence: Q 0.94 0.74 0.64 N 3 4 5 0.56 6 0.51 7 0.47 8 0.44 9 0.41 10 t table @ 95% confidence: t 12.71 4.30 3.18 2.78 2.57 2.45 2.36 2.31 2.26 d.f. 1 2 3 4 5 6 7 8 9 F table @ 95% confidence: d.f. (s2) 2 3 4 5 6 2 19.00 9.55 6.94 5.79 5.14 3 19.16 9.28 6.59 5.41 4.76 d.f. (s1) 4 19.25 9.12 6.39 5.19 4.53 5 19.30 9.01 6.26 5.05 4.39 6 19.33 8.94 6.16 4.95 4.28 1) List the steps involved in a chemical analysis (10) 2) A 56.0 wt % solution of perchloric acid (HClO4, MW=100.458 g/mol) has a density of 1.35 g/mL. (10 total) a) What is the formal concentration of HClO4? (5) b) Which is more accurate to state concentration in for this case, formality or molarity? Why? (5) 3) Repeated measurements of the zirconium concentration (Zr, 91.224 g/mol) from a soil sample gave values of 185.7, 177.4, 167.6, 181.45, and 189.3 ppm. (30 total) a) What are the mean concentration, standard deviation, and 95% confidence interval of the Zr concentration? (10) b) Use the Q-test to determine if the lowest measurement can be dropped from the set with 90% confidence. (10) c) A second soil sample analyzed 6 replicate times for Zr content gave mean=0.0195 % and standard deviation=0.00208 %. At the 95% confidence level, does this soil sample differ in Zr concentration from the soil sample in part (a)? (10) 4) Aluminum hydroxide, Al(OH)3 (s) (MW=78.003) has a Ksp of 5.81x10-33. (30 total) a) How many nanograms of Al(OH)3 will dissolve in 1.00 L of pure water? (10) b) Aluminum can also form a series of complex ions in solution with hydroxide: Al(OH)2+(aq), 1=1.0x109; Al(OH)2+(aq), 2=5.0x1018; Al(OH)3(aq), 3=1.0x1027; Al(OH)4-, 4=1.1x1033. Calculate the concentration of Al3+(aq) and all four complex ions in a solution containing Al(OH)3(s) where the pH is held constant at 7.8. (20) 5) Identify each of the following chemical species as a strong acid, strong base, weak acid, weak base, or none of the above. (10 total) a) Ammonium (NH4+) b) Bromide ion (Br-) c) Hydrogen iodide (HI) d) Oxalate ion (C2O42-) e) Tetraethylammonium hydroxide (CH3CH2)4N+OH- 6) Diprotic sulfurous acid (H2SO3) is a weak acid unlike its cousin sulfuric acid. H2SO3 has a Ka1=1.3x10-2 and a Ka2=5.1x10-6. (10 total) a) Write the association reactions for the conjugate base forms of sulfurous acid in water (5) b) Determine the Kb1 and Kb2 equilibrium constants for the reactions in part (a) (5) ...
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This note was uploaded on 12/10/2008 for the course CHEMISTRY CHEM 3600 taught by Professor Philipj.silva during the Fall '07 term at Uni. Tartu.

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