Houston Community College System Chemistry 1412 Exam # 2 Summer 2011 CHEM 1412 Exam #2 Summer 2011 Name: ____________________________ Score: PART I - ( 3 points each) - Please write your correct answer next to each question number. ____1. What is the conjugate acid of HSO4-? A. H2SO4– B. H2SO4 C. SO4-2 D. H3O+ ____2. Which of these species will have the lowest entropy (S°) at 25°C? A. CH3OH(l) B. CH3OH(g) C. C2H5OH(l) D. C2H5OH(g) ____3. A sample of orange juice has a hydroxide concentration of 3.5 x 10-11 M. What is the pH? A. 3.11 B. 3.31 C. 3.54 D. 10.46 ____4. An aqueous solution of Cu(NO3)2 will have a pH that is A. Acidic B. Basic C. Neutral D. cannot be determined ____5. What is the pH of a buffer solution consisting of 0.400 M HCN (Ka = 6.2x10-10) and 0.600 M sodium cyanide, NaCN A. 9.21 B. 9.61 C.9.03 D. 9.38 ____6. Which of the following do you predict to be the strongest acid? A. HClO2 B. HBrO2 C. HBrO D. HClO ____7. If X is the molar solubility of a salt, which of the following solubility product expressions is incorrect? A. Ag2CO3, Ksp=4X3 B. AgClO3, Ksp=X2 C. CaS, Ksp=X2 D. FePO4, Ksp=16X2 C. 0.40 D. Cannot be determined ____8. What is pH of 0.10M HClO4(aq) A. 0.10 B. 1.0 ____9. The molar solubility of silver sulfate, Ag2SO4, in pure water is 0.0144 M. Calculate the value of Ksp for silver sulfate from this data. A. 2.99 x 10-6 B. 1.19 x 10-5 C. 2.39 x 10-6 D. 5.97 x 10-6 ____10. Determine the pH of a Ba(OH)2 solution made by dissolving 0.200 mol Ba(OH)2 in 500 mL of solution. A. 13.6 B. 13.9 C. 13.3 D. 13.0 _____11. Which response includes all of the following processes that are accompanied by an decrease in entropy? 1) I2(s) → I2(g) 2) 2I(g) → I2(g) 3) 2NH3(g) → N2(g) + 3H2(g) 4) Mg2+(aq) + 2OH–(aq) → Mg(OH)2(s) A. 1,2 B. 1, 3 C. 3,4 D. 2,4 ____12. Calculate the entropy change (J/mole.K) of the reaction. The molar entropies [So] are given in brackets after each substance. Bi2O3(s) [151.5] + 3 CO(g) [197.7] A. 35.2 B. 9.9 2 Bi(s) [56.7] + 3 CO2(g) [213.7] C. 79.5 D. -79.5 ____13. Which of the following has Gf°=0 & Hf°=0? A. I2(g) B. O3(g) C. H2O(l) D. Br2(l) ____14. Which one of the following is a buffer solution? A. 1.0 M HCl and 1.0 KCl C. 1.0 M NH3 and 1.0 M NH4Cl B. 1.0 M HNO3 and 1.0 M HNO2 D. 1.0 M HNO3 and 1.0 M NaOH ____15. Sodium carbonate can be made by heating sodium bicarbonate: 2NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(g) Given that ΔH° = 128.9 kJ/mol and ΔG° = 33.1 kJ/mol at 25°C, calculate ΔS°. A. 3.83 kJ/K-mol B. -3.83 kJ/K-mol C. 0.321 kJ/K-mol -9.73 x 103kJ/K-mol ____16. Consider a reaction for which ΔH° = –199.0 kJ/mol; ΔS° = –41.00J/K-mol Which of the following statements is true? A. The reaction is spontaneous at all temperatures B. The reaction becomes spontaneous at low temperatures below 4854 K C. The reaction becomes spontaneous at high temperatures above 48.54 K D. The reaction is never spontaneous ____17. What is the pH of 0.100 M HCHO2 (Ka for HCHO2 = 1.77 × 10-4) A. 1.00 B. 3.75 C. 2.38 D. 4.75 ____18. At 1500°C the equilibrium constant for the reaction CO(g) + 2H2(g) CH3OH(g) has the value Kp = 1.4 × 10–7. Calculate ΔG° for this reaction at 1500°C. A. 105 kJ/mol B. 233 kJ/mol C. -105 kJ/mol D. 1.07 kJ/mol ____19. The pH of a 0.020 M solution of an unknown weak acid, HA, is 5.0. The % ionization of the acid is A. 10-3 B. 2.5 C. 0.050 D. 0.40 ____20. Which of the following is not a hydrolysis reaction? A. NH3(aq) + H2O(l) H3O+(aq)+OH-(aq) B. Sn+4(aq) +H2O(l)SnOH+3(aq) + H+(aq) C. NH3(aq) + HCl(aq) NH4Cl(aq) D. All are hydrolysis reactions Part II (8 points each) Please show all your work for full credit. 1. a. What will be the pH upon addition 30 mL of 0.200 M NaOH to 25 mL of 0.300 M HNO3. b. What will be the pH upon addition 40 mL of 0.200 M NaOH to 25 mL of 0.300 M HNO3. 2. The solubility product constant Ksp of Mn(OH)2 is 2.1x1013 at 25°C. The molar mass of Mn(OH)2 is 88.96 g/mol. a. Calculate its molar solubility b. Calculate its solubility in g/L 3. The equilibrium constant for the reaction PbI2 (s) Pb+2(aq) + 2I– (aq) is Ksp = 8.5 × 10–9 at 25°C. a. Calculate ΔGo for the reaction. b. Calculate ΔG for the reaction when [Pb+2] = 2.0 × 10–3 M and [I–] = 1.0 × 10–3 M. c. Is the reaction spontaneous or nonspontaneous at these concentrations? 4. Consider a 0.10 M KF solution; [Ka(HF) = 6.8 × 10–4]. a. What is the Kb of F-? b. Write the associated chemical EQUATION for hydrolysis by Fc. Calculate the pH of a 0.10 M KF solution. 5. Calculate the standard free energy change, ΔG° and the equilibrium constant, K, at 298 K for the reaction SO2(g) + NO2(g) → SO3(g) + NO(g). ΔG°f SO2(g) –300.4 kJ/mol SO3(g) –370.4 kJ/mol NO(g) 86.7 kJ/mol NO2(g) 51.8 kJ/mol Bonus Question A 25.0 ml sample of 0.200 M HClO. (Ka for HClO = 3.0 × 10-8) is titrated with 0.200 M KOH. a. Calculate the pH of the solution when 10.00 ml of KOH has been added b. What will be the pH at the half-equivalence point? c. What is the pH at the equivalence point?