Useful EquationsCritical Values for the Rejection Quotient QValues of t for Various Levels of ProbabilityCHEMISTRY 226 EXAM II OCTOBER 24, 2002 Name: Student ID No.: Email Address:______________________ I. (14 pts.) Match the following terms and definitions. 1. _______ In statistics the postulate that two observed quantities are the same. 2. _______ (Q-S)/S 3. _______ Precipitate that settles spontaneously and is readily filtered. 4. ________ A few atoms or molecules come together to form a stable solid. 5. ________ Process by which a coagulated colloid reverts to its original dispersed state. 6. _______ Contaminating ions are trapped in a pocket during rapid crystal growth. 7. _______ Species produced when an acid gives up a proton. A. Activity Coefficient H. Mechanical Entrapment B. Amphiprotic Solvent I. Nucleation C. Bronsted Base J. Null Hypothesis D. Conjugate Base K. Occlusion E. Colloidal Suspension L. Particle Growth F. Crystalline Suspension M. Peptization G. Digestion N. Relative Supersaturation II. (6 pts) Consider the following set of replicate measurements: 0.624, 0.613, 0.596, 0.607, 0.582 Is the 0.582 value an outlier at the 95% CL?III. (12 pts) The percent lindane was assayed in two lots of an insecticide preparation. The results were: Lot 1 (% Lindane) Lot 2 (% Lindane) 7.47 6.90 6.98 7.50 7.27 6.85 7.01 7.33 Is there a significant difference between lots at the 95% CL? IV. (7 pts) Calculate the solubility product constant for Ag3PO4 given the molar concentration of the saturated solution is 4.7 X 10-6 M. V. (7 pts) At 25º C what are the molar H3O+ and OH- concentrations in a 0.100M chloroacetic acid (ClCH2COOH) solution (Ka = 1.36 X 10-3)?VI. A plot of the following data for Zn analysis by atomic absorption spectrometry yields a straight line. Zn Concentration (µg/dL) Concentration2 Absorbance Absorbance2 Conc X Absorbance 0.0 0.0 0.06 0.0036 0.0 5.0 25.0 1.48 2.19 7.40 10.0 100.0 2.28 5.20 22.8 15.0 225.0 3.98 15.84 59.7 20.0 400.0 4.61 21.25 92.2 Using least squares analysis calculate: 1. (5 pts) The slope of the line 2. (5 pts) The equation for the least squares line. 3. (5 pts) For an atomic absorption reading of 3.67, calculate the Zn concentration.VII. (10 pts) A 0.1799 g sample of an organic compound was burned in a stream of oxygen and the resultant CO2 collected in a solution of barium hydroxide. Calculate the percent carbon in the sample if 0.5613 g BaCO3 (MW = 197.336g/mol) is recovered. VIII. (7 pts) Explain why the solubility of a salt is increased in the presence of an electrolyte solution. Consider the solubility of BaSO4 in a solution of NaCl compared to a solution of BaSO4 in water. IX. (7 pts) Calculate the solubility of SrF2 (8.6 X 10-4 mol/L) in which [F-] = 0.050M if the Ksp = 2.5 X 10-9.X. (15 pts) Using activities calculate the solubility of Zn(OH)2 in a 0.0167 M solution of Ba(NO3)2. Ksp Zn(OH)2 = 3.0 X 10-16. The effective diameters are 0.5 nm for Ba2+, 0.3 nm for NO3-, 0.6nm for Zn2+ and 0.35 nm for OH-. Useful Equations Sxx = Σxi2 – [(Σxi)2/N] Syy = Σyi2 – [(Σyi)2/N] Sxy = Σxiyi – [ΣxiΣyi/N] m = Sxy/Sxx Sr = Syy – m2Sxx Sm = Sr2/Sxx N-2 Critical Values for the Rejection Quotient Q # Observations 90% Confidence 95% Confidence 99% Confidence 3 0.941 0.970 0.994 4 0.765 0.829 0.926 5 0.642 0.710 0.821 6 0.560 0.625 0.740 7 0.507 0.568 0.680Confidence Levels of Various Values of z. 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 99.9 3.29 Values of t for Various Levels of Probability Degrees of Freedom 90% CI 95%CI 99%CI 1 6.31 12.7 63.7 2 2.92 4.30 9.92 3 2.35 3.18 5.84 4 2.13 2.78 4.60 5 2.02 2.57 4.03 6 1.94 2.45 3.71 7 1.90 2.36 3.50 8 1.86 2.31 3.36 9 1.83 2.26 3.25 10 1.81 2.23
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