Seat #: Date: Chem 401 Unit 3 Exam F18 (Buffers, Titrations, Ksp, Transition Metals & Electrochemistry) Multiple Choice Identify the choice that best completes the statement or answers the question. (4.2pts ea) 1. Which of the following is TRUE? A) An effective buffer has a [base]/[acid] ratio in the range of 10 100. B) A buffer is most resistant to ph change when [acid] = [conjugate base] C) An effective buffer has very small absolute amounts of acid and conjugate base. D) A buffer cannot be exhausted by adding too much strong base. It can only be exhausted by adding too much strong acid. E) None of the above is true. 2. A solution containing AgNO 3 is mixed with a solution of NaCl to form a solution that is 0.10 M in AgNO 3 and 0.075 M in NaCl. What will happen once these solutions are mixed? K sp (AgCl) = 1.77 10 10. A) Nothing will happen since the molar solubility of AgCl is higher than the solution concentrations. B) Silver chloride will precipitate out of solution, leaving an unsaturated solution of AgCl. C) Silver chloride will precipitate out of solution, leaving a saturated AgCl solution. D) Nothing will happen since NaCl and AgNO 3 are both soluble compounds. E) There is not enough information to say anything about this solution. 3. A complex ion contains A) a central nonmetal ion bound to one or more ligands. B) an anion bound to water. C) water bound to one or more ligands. D) a central metal ion bound to one or more ligands. E) ammonia bound to water. 4. Identify a good buffer. A) small amounts of both a weak acid and its conjugate acid B) significant amounts of both a strong base and a strong acid C) small amounts of both a strong acid and a conjugate acid D) significant amounts of both a weak acid and a strong acid E) significant amounts of both a weak acid and its conjugate base 5. Give the expression for K f for Fe(CN) 6 3. A) C) E) B) D) [Fe 3+ ] [CN ] 6 1
6. Calculate K. AgI(s) Ag + (aq) + I (aq) K sp = 8.5 10 17 Ag(NH 3 ) 2+ 2 (aq) Ag + (aq) + 2 NH 3 (aq) K d = 5.9 10-8 AgI(s) + 2 NH 3 (aq) Ag(NH 3 ) 2+ 2 (aq) + I (aq) K =? A) 1.7 10 7 B) 1.4 10 9 C) 5.0 10 24 D) 2.0 10 23 E) 6.9 10 8 7. A solution is prepared by dissolving 0.23 mol of nitrous acid and 0.27 mol of sodium nitrite in water sufficient to yield 1.00 L of solution. The addition of 0.05 mol of HCl to this buffer solution causes the ph to drop slightly. The ph does not decrease drastically because the HCl reacts with the present in the buffer solution. The K a of nitrous acid is 1.36 10 3. A) H 2 O B) H 3 O + C) nitrite ion D) nitrous acid E) This is a buffer solution: the ph does not change upon addition of acid or base. 8. What is the [CH 3 CO 2 ] / [CH 3 CO 2 H] ratio necessary to make a buffer solution with a ph of 4.34? K a = 1.8 10 5 for CH 3 CO 2 H. A) 0.39:1 B) 0.91:1 C) 1.09:1 D) 2.5:1 9. A buffer solution is 0.100 M in both HC 7 H 5 O 2 and KC 7 H 5 O 2 and has a ph of 4.19. Which of the following ph values would you expect from the addition of a small amount of a dilute solution of a strong base? A) 3.89 B) 3.69 C) 5.79 D) 4.49 E) There is not enough information to determine. 10. Which of the following acids (listed with pk a values) and their conjugate base would form a buffer with a ph of 8.10? A) HC 2 H 3 O 2, pk a = 4.74 B) H 2 SO 3, pk a = 1.77 C) HClO, pk a = 7.54 D) HIO, pk a = 10.64 E) HNO 2, pk a = 3.34 2
11. In which of the following solutions would solid AgCl be expected to be the least soluble at 25 C? A) 0.1 M HCl B) 0.1 M KCl C) 0.1 M BaCl 2 D) 0.1 M NH 4 NO 3 E) H 2 O 12. A ligand is a molecule or ion that acts as a A) Lewis acid. D) Lewis base. B) Brønsted-Lowry base. E) conjugate base. C) Arrhenius base. 13. Describe the solubility of Al(OH) 3 with respect to ph. A) soluble at low ph, insoluble in ph-neutral solution, and soluble at high ph B) soluble at low ph, insoluble in ph-neutral solution, and insoluble at high ph C) insoluble at low ph, insoluble in ph-neutral solution, and soluble at high ph D) soluble at low ph, in ph-neutral solution, and at high ph E) ph has no effect on the solubility. 14. Identify the isomers that have ligands which coordinate to the metal in different ways. A) linkage isomers B) geometric isomers C) coordination isomers D) optical isomers E) stereoisomers 15. Identify the structure that fac-mer isomerism can occur in. A) MA 4 B 2 D) MA 3 B 3 B) MA 5 B E) MAB 2 C) MAB 16. Which of the following complex ions absorbs light of the shortest wavelength? A) [FeCl 6 ] 3 B) [Fe(OH) 6 ] 3 C) [Fe(CN) 6 ] 3 D) [Fe(H 2 O) 6 ] 3+ E) [FeI 6 ] 3 17. How many unpaired electrons would you expect for the complex ion: [Co(OH) 6 ] 3? A) 1 B) 2 C) 4 D) 0 E) 3 3
18. Which of the following pairs of coordination compounds or complex ions are examples of ionization isomers? A) [Fe(NH 3 ) 5 NO 2 ] 2+ and [Fe(NH 3 ) 5 ONO] 2+ B) [Fe(NH 3 ) 2 (H 2 O) 4 ]Cl 2 and [Fe(NH 3 ) 2 (H 2 O) 4 ]Br 2 C) [Fe(NH 3 ) 2 (H 2 O) 4 ]Br 2 and [Fe(NH 3 ) 4 (H 2 O) 2 ]Br 2 D) [Cu(CO) 5 I]F and [Cu(CO) 5 CF]I E) [MnCl 3 Br] 2 and [MnClBr 3 ] 2 19. Which of the following compounds can exhibit cis-trans isomerism? A) [Fe(CO) 5 NO 2 ] 2+ B) [Cu(CO) 5 Br] + C) [MnClBr 3 ] 2 D) [Mn(H 2 O) 6 ] 3+ E) [Ni(CO) 2 (NH 3 ) 2 ] 2+ 20. What is the oxidation number of Co in the compound [Co(NH 3 ) 2 (H 2 O) 2 Br 2 ]Cl? A) 1 B) 2 C) 3 D) 4 E) 5 21. In the compound [Co(en) 3 ]Br 2, the coordination number of cobalt is A) 2 B) 3 C) 4 D) 5 E) 6 22. If you wanted to make a buffer solution from HF, which of the following could you add? A) NaF B) KF C) NaOH D) A & B E) A, B & C 23. A 1.0 L buffer solution is 0.250 M HC 2 H 3 O 2 and 0.060 M NaC 2 H 3 O 2. Which of the following actions will exhaust the buffer? A) adding 0.060 moles of NaC 2 H 3 O 2 B) adding 0.060 moles of HC 2 H 3 O 2 C) adding 0.060 moles of HCl D) adding 0.060 moles of KOH E) All of the above will exhaust the buffer. 4
24. Determine the molar solubility of BaF 2 in pure water. K sp for BaF 2 = 2.45 10 5. A) 1.83 10 2 M B) 1.23 10 5 M C) 2.90 10 2 M D) 4.95 10 3 M E) 6.13 10 6 M 25. Calculate the ph of a solution formed by mixing 250.0 ml of 0.15 M NH 4 Cl with 100.0 ml of 0.20 M NH 3. The K b for NH 3 is 1.8 10 5. A) 9.13 B) 9.25 C) 9.53 D) 4.74 E) 8.98 26. Formic acid (a monoprotic weak acid with K a = 1.8 10 4 ) is the principal component in the venom of stinging ants. What is the molarity of a formic acid solution if 25.00 ml of the formic acid solution requires 44.80 ml of 0.0567 M NaOH to reach the equivalence point? A) 0.0134 M B) 0.0316 M C) 0.0567 M D) 0.102 M 27. A 900.0 ml sample of 0.182 M HClO 4 is titrated with 0.27 M NaOH. Determine the ph of the solution after the addition of 270.0 ml of NaOH. A) 0.86 B) 1.21 C) 2.00 D) 1.12 E) 2.86 5
28. Determine the molar solubility of AgBr in a solution containing 0.150 M NaBr. K sp (AgBr) = 7.7 10 13. A) 8.8 10 7 M B) 3.9 10 13 M C) 5.8 10 5 M D) 5.1 10 12 M E) 0.150 M 29. Calculate the K sp for Sr(OH) 2 if the solubility of Sr(OH) 2 in pure water is 14.2 g/l. A) 1.16 10 1 B) 6.37 10 3 C) 1.42 10 1 D) 1.60 10 3 E) 7.70 10 11 30. Which is true about the following reaction? MnO 4 (aq) + H 2 C 2 O 4 (aq) Mn 2+ (aq) + CO 2 (g) A) C is oxidized and H 2 C 2 O 4 is the oxidizing agent B) Mn is oxidized and MnO 4 is the oxidizing agent C) C is oxidized and H 2 C 2 O 4 is the reducing agent D) Mn is oxidized and MnO 4 is the reducing agent E) None of these are true 31. Balance the following redox reaction if it occurs in acidic solution. What are the coefficients in front of H 2 C 2 O 4 and H 2 O in the balanced reaction? MnO 4 (aq) + H 2 C 2 O 4 (aq) Mn 2+ (aq) + CO 2 (g) A) H 2 C 2 O 4 = 5, H 2 O = 8 B) H 2 C 2 O 4 = 1, H 2 O = 1 C) H 2 C 2 O 4 = 5, H 2 O = 1 D) H 2 C 2 O 4 = 1, H 2 O = 4 E) H 2 C 2 O 4 = 3, H 2 O = 2 6
32. Identify the location of oxidation in an electrochemical cell. A) the anode B) the cathode C) the electrode D) the salt bridge E) the socket 33. What is the oxidizing agent in the redox reaction represented by the following cell notation? Sn(s) Sn 2+ (aq) Ag + (aq) Ag(s) A) Sn(s) B) Ag + (aq) C) Sn 2+ (aq) D) Ag(s) E) Pt 34. Use the standard half-cell potentials listed below to calculate the standard cell potential for the following reaction occurring in an electrochemical cell at 25 C. (The equation is balanced.) A) +4.16 V B) 1.40 V C) 1.32 V D) +1.32 V E) +1.40 V 3 Cl 2 (g) + 2 Fe(s) 6 Cl (aq) + 2 Fe 3+ (aq) 35. Identify the characteristics of a spontaneous reaction. A) DG < 0 B) DE cell > 0 C) K > 1 D) all of the above E) none of the above Cl 2 (g) + 2 e 2 Cl (aq) E = +1.36 V Fe 3+ (aq) + 3 e Fe(s) E = 0.04 V 36. The standard emf for the cell using the overall cell reaction below is +2.20 V: 2 Al(s) + 3 I 2 (s) 2 Al 3+ (aq) + 6 I (aq) The emf generated by the cell at STP when [Al 3+ ] = 4.5 10 3 M and [I ] = 0.15 M is V. A) 2.20 B) 2.30 C) 2.10 D) 2.39 E) 2.49 7
37. Identify the battery that is used as a common flashlight battery. A) dry-cell battery D) NiCad battery B) lithium ion battery E) fuel cell C) lead-acid storage battery 38. Identify a characteristic that does not describe a standard hydrogen electrode. A) 1 M HCl solution with hydrogen gas B) 1 atmosphere C) zinc electrode D) inert platinum electrode E) potential of zero 39. Use the listed half-cell potentials to calculate DG for the following balanced redox reaction. Cu 2+ (aq) + 2 e Cu(s) E = +0.34 V Pb 2+ (aq) + 2 e Pb(s) E = 0.13 V Pb 2+ (aq) + Cu(s) Pb(s) + Cu 2+ (aq) A) 41 kj B) 0.47 kj C) +46 kj D) +91 kj E) 21 kj 40. What mass of aluminum can be plated onto an object in 755 minutes at 5.80 A of current? A) 73.5 g B) 24.5 g C) 220. g D) 147 g E) 8.17 g True/False Indicate whether the statement is true (T) or false (F).(4 pts ea) 1. Weak field ligands lead to low spin complexes. 2. The ph at the equivalence point is above 7 for a WB titrated with a SA. 3. Octahedral complexes feel more repulsions from lignads that approach on-axis than off-axis. 4. The sign of the cathode in a voltaic cell is (+). 8
Short Answer 1. A 100.0 ml sample of 0.20 M HF is titrated with 0.10 M NaOH. Determine the ph of the solution after the addition of 300.0 ml of NaOH. The K a of HF is 3.5 10 4. (6 pts) 2. What is the ph of a solution made by mixing 10.00 ml of 0.10 M acetic acid with 10.00 ml of 0.10 M KOH? K a = 1.8 10 5 for acetic acid. (10 pts) 9
3. EXTRA CREDIT: A 250. ml buffer solution is 0.600 M in HC 7 H 5 O 2 and 1.00 M in LiC 7 H 5 O 2. Calculate the ph of the solution after the addition of 120.0 ml of 1.00 M HCl. The K a for HC 7 H 5 O 2 is 6.5 10 5. (6 pts) 4. EXTRA CREDIT: A solution contains 2.2 10 3 M in Cu 2+ and 0.33 M in LiCN. If the K f for Cu(CN) 4 2 is 1.0 10 25, how much copper ion remains at equilibrium? (8 pts) 10