Chem 115 Practice Final 2 PDF

Exam IV Chem 115 Name _________________________ 110 min vB Tuesday, Dec. 20, 2022 = ( − )...

Exam IV Chem 115 Name _________________________ 110 min vB Tuesday, Dec. 20, 2022 = ( − ) = pH = -log[H3O+] 14 = pH + pOH KaKb= Kw Kw=1.0 x 10-14 [34 ] -. = -/0 + 12 ΔGo=ΔHo-TΔSo PV=nRT R=8.206 x 10-2 L atm/mol K ∆H˚rxn = Σn∆H˚f(products) – Σn∆H˚f(reactants) R = 8.3145 J/mol K ΔGo = -RT ln K T in K = T in C + 273.15 F = 96,485 Coulomb/mol Δ: G = Δ: ; < + => ? Ecello = Eocathode-Eoanode Δ: G =-nFE G.GHIJ 1 kiloJoule = 1000 Joules F = F< − 12? at 25 oC Coulomb = Amp/s K Cl2 + 2e- ⇌ 2Cl- 1.36 V A=Vlc NO3- + 4H+ + 3e- ⇌ NO + 2H2O 0.96 V V = molar absorptivity Ag+ + e- ⇌ Ag 0.80 V l = pathlength Cu2+ + 2e- ⇌ Cu 0.34 V c = concentration 2H+ + 2e- ⇌ H2 0.000V A= absorbance Pb2+ + 2e- ⇌ Pb -0.13 V Ni2+ + 2e- ⇌ Ni -0.23 V Cd2+ + 2e- ⇌ Cd -0.40 V Fe2+ + 2e- ⇌ Fe -0.44 V Zn2+ + 2e- ⇌ Zn -0.76 V Ca2+ + 2e- ⇌ Ca -2.76 V 1 Multiple Choice Problems. 4 points each. Show your work for partial credit. 1. What is the oxidation number of I in IO3-? a. -1 b. -2 c. +5 d. +3 e. +7 2. What is the oxidation number of S in S2O32-? a. +9/2 b. +7 c. +4 d. +2 e. +3 3. What will happen if a 1 M aqueous solution of HNO3 was placed in a copper metal vat? a. Nothing. Acid is not a strong enough oxidizing agent. b. NO gas would be produced c. Cu2+ ions would be produced d. B and C 4. Given the following reaction, what is the oxidizing agent? 10Cl- + 2MnO4- + 16H+  5Cl2 + 2Mn2+ + 8H2O a. Cl2 b. MnO4- c. H+ d. Mn2+ e. Cl- 5. Balance the following ½ reaction in acid: IO3- +_____________________  __ I2 + ____________________________ How many moles of H+ per mole of IO3- are needed? a. 6 b. 3 c. 12 d. 2 e. 5 2 6. Which compound will Fe2+ oxidize? a. Ag+ b. Zn c. Cl- d. All of the above e. None of the above 7. What is the cell potential for the following reaction? Cl2(g) + H2(g)  2Cl- + 2 H+ a. 1.36 V b. -1.36 V c. 0.00 V d. -2.72 V 8. If an electrochemical cell was designed to generate electricity using Pb/Pb2+ and Ca/Ca2+ what would likely be in the cathode compartment? a. 1 M Pb(NO3)2 b. 1 M CaSO4 c. 1 M HNO3 d. Nothing, this cell would never be spontaneous e. An inert electrode 9. What is the cell potential for the following reaction? Zn2+ + Ni(s)  Ni2+ + Zn(s) a. 0.53 V b. -0.99 c. -0.53V d. 1.06 V 3 10. What are the signs of ΔH and ΔS for the following reaction? O2(g)  O2(l) a. ΔH is + and ΔS is + b. ΔH is + and ΔS is - c. ΔH is - and ΔS is + d. ΔH is - and ΔS is - e. Not enough information is given 11. If for a hypothetical reaction, ΔH is -45.2 kJ and ΔS is -452 J/mol K at what temperature would the reaction become spontaneous? a. It is never spontaneous b. Above 100 K c. Below 100 K d. Above 10 C e. Below 0.10 K 12. Given the following standard Gibbs Free Energies of formation, what is the Gibbs free energy of reaction and is it spontaneous? 3C 2A + B ΔGfA = 359.3 kJ/mol ΔGfB = -324.4 kJ/mol ΔGfC = -102.7 kJ/mol a. 702.3 kJ/mol and it is not spontaneous b. -702.3 kJ/mol and it is not spontaneous c. -67.8 kJ/mol and it is spontaneous d. -734.9 kJ/mol and it is spontaneous e. 734.9 kJ/mol and it is not spontaneous 13. Given the standard entropies, calculate the entropy change for the following reaction: Mg(s) + CO2(g)  MgO(s) + C(s) So Mg = 32.7 J/mol K So CO2 =213.6 J/mol K So C = 5.7 J/mol K So MgO = 26.9 J/mol K a. 279.0 J/mol K b. 231.7 J/mol K c. -181.0 J/mol K d. -213.7 J/mol K 4 14. When it snows in the winter, the following reaction is occurring in the atmosphere: H2O (l)  H2O (s) What is the entropy change (ΔS) of the gas molecules in the atmosphere (mainly N2 and O2) surrounding these atmospheric droplets when this happens, if the enthalpy of fusion of water is 6.01 kJ/mol assuming a temperature of the upper atmosphere at -10.0 oC? a. +22.9 J/mol K b. 0.601 kJ/mol K c. -0.601 kJ/mol K d. -22.9 J/ mol K 15. Which of the following reactions represents an increase in entropy of the system? a. CO2(g)  CO2(s) b. H2CO3(aq)  H2O(l) + CO2(g) c. Ba(NO3)2 (aq) + H2SO4 (aq)  BaSO4(s) + 2HNO3(aq) d. HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) 16. What is the Gibbs Free Energy of the following reaction at 298 K? Ni2+ + 4Cl-  NiCl42- Kf = 2.0 x 1021 a. -122 kJ/mol b. +122 kJ/mol c. 307 kJ/mol d. 1.20 kJ/mol 17. What is the pH of a 0.040 M solution of HBr? a. 0.040 b. 1.40 c. 1.00 d. 2.40 e. 12.60 5 18. What is the pH of a 0.50 M solution of CH3COOH (Ka = 1.76 x 10-5) a. 0.0029677 b. 2.53 c. 0.301 d. 2.33 e. 5.4 x 10-4 19. What is the pH of a 0.040 M solution of KOH? a. 0.04 b. 1.40 c. 13.18 d. 13.85 e. 12.60 20. What is the pH of a 500 mL solution prepared by adding 0.983 moles of NH4Cl and 0.235 moles of NH3. The pKa of NH4+ is 9.25. a. 9.84 b. 9.25 c. 8.66 d. 7.14 21. If a small volume 0.10 M NaOH were added to a buffered aqueous solution of CH3COOH and NaCH3COOH at pH of 5.00, what chemical change will happen? a. No change. The buffer solution prevents the NaOH from participating in chemistry b. The NaOH will completely dissociate and flood the solution with OH- ions, increasing the pH to close to 14 c. The OH- from NaOH will react with the CH3COOH forming CH3COO- raising the pH by a small amount d. The OH- from NaOH will react with the CH3COO- forming CH3COOH lowering the pH by a small amount e. The Na+ from NaOH will stress the equilibrium by making more NaCH3COO which will increase the pH 6 22. Which of the following molecular geometries has the highest number of electron domains? a. Tetrahedral b. Trigonal pyramidal c. Trigonal bipyramidal d. Bent e. Square pyramidal 23. What is the bond order for N-O bonds in NO3-? a. 1 b. 1.33 c. 1.66 d. 2 e. 4 24. Which of the following is a correct set of quantum numbers? a. n=2, l=1, ml= -2, ms = +1/2 b. n=6, l=0, ml= 0, ms = +1/2 c. n=2, l=2, ml= -1, ms = -1/2 d. n=7, l=7, ml= +7, ms = -1/2 e. n=0, l=0, ml =0, ms = +1/2 25. How many moles of NaOH are delivered during a titration if the total buret volume dispensed was 28.55 mL and the initial molarity was 0.3394 M? a. 0.009690 moles b. 9.690 moles c. 0.01189 moles d. 84.12 moles 26. Given the following equilibrium 2HI(g) ⇌ H2(g) + I2(g) K=0.022 If a vessel contained these chemicals in equilibrium and the equilibrium was stressed by adding some liquid water to the vessel, what would happen? a. The equilibrium would shift to the right due to H2 and I2 preferentially dissolving in water b. The equilibrium would shift to the left due to HI preferentially dissolving in water c. Nothing – the equilibrium won’t change because water has no effect d. Nothing – the equilibrium won’t change because the change in pressure affects both sides of the equilibrium equally. 7  27. When ammonium nitrate (NH4NO3) dissolves in water, what compounds can be found in solution? a. NH4+ b. NO3- c. A and B d. N3-, O2- and H+ e. N2 and H2O 28. Which of the following processes are exothermic? (i) Freezing of CO2 (ii) Condensation of H2O (iii) Combustion of H2 and O2 to make water a. (i) b. (ii) c. (iii) d. (ii) and (iii) e. all of the above 29. What is a rate determining step? a. The slowest elementary reaction in a reaction mechanism b. The reaction with an activation energy barrier which can be determined by experiment through generating an Arrhenius Plot c. The fastest reaction in a reaction mechanism d. A and B 30. Given the following kinetics experiments, what is the appropriate rate law? Experiment [A] [B] Rate 1 0.10 M 0.10 M 2.4 M s-1 2 0.20 M 0.10 M 4.8 M s-1 3 0.10 M 0.20 M 4.8 M s-1 a. Rate = 2.4 x 104 M-3s-1 [A2][B]2 b. Rate = 240 M-1s-1 [A][B] c. Rate = 2.4 x104 M-2s-1 [A][B]2 d. Rate = 240 M-1s-1 [A]2 e. Rate = 24 s-1 [A] ______/ 120 8 Short answer problems. Partial credit is assigned for work shown. 15 points each. 31. a. Draw the Lewis structures for NO2 and N2O4. b. Write out the equilibrium equation and equilibrium constant expression for NO2 to make N2O4. c. Describe 3 different ways to stress the equilibrium and how the equilibrium will shift from that stress. d. Under what conditions would ΔG be negative for the reaction you wrote in b. above. Explain your reasoning in terms of the signs of ΔS and ΔH and how you determined those signs. ______/15 9 32. If a 0.20 M solution of CoCl2(aq) was prepared in 6.0 M HCl and the temperature was raised to 50 o C when a pink color developed, indicating the presence of CoCl42-. The absorbance = 1.37 for the solution in a cuvette with 1.00 cm pathlength with V = 250 M-1cm-1 for CoCl42-. What is the equilibrium constant at 50oC for the reaction below? Co(H2O)62+ (aq) + 4 Cl-(aq)  CoCl42-(aq) + 6H2O(l) ___/15 10