4. cannot occur. occurring within the same system. (A) I, III (B) II, V (C) III, IV (D) IV, V (E) V, II

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1 Practice Exercises Oxidation-Reduction Reactions and Electrochemistry 483 Multiple-Choice For the first four problems below, one or more of the following responses will apply; each response may be used more than once or not at all in these questions. 1. Nernst equation II. spontaneous III. reduction IV oxidation V electrolysis 1. The loss of electrons is atn) process (C) III 2. In order to produce aluminum, large amounts of electricity are used to perform the _ of aluminum oxide. (C)III 3. This is used to determine cell voltages when standard state conditions are not present. (C) III 4. cannot occur without also occurring within the same system., III, V (C) III, IV, V, II 5. Balance the following half-reaction in acid solution: NO~ ---)NH~ When balanced with the smallest whole-number coefficients, the sum of all the coefficients is (A) 13 (B) 26 (C) 15 (D) 23 (E) 21

2 484 AP Chemistry 6. For the reaction between the permanganate ion and iron(ii), the, reaction is Which of the following is the correct form of the Nernst equation for this reaction? (A) E - EO R_T In.:;,-[M_n_2+-=][=-=-Fe_ 3 +-,,-H-=-::-H_20--=-] - cell 5?J [MnO:][Fe 2 +][H+] o RT [Mn 2 +][Fe 3 +Y (B) E = E - - In -"--~'-"---::-"-- cell 5?J [MnO:][Fe2+nH+] o RT [Mn 2 +][Fe 3 +Y (C) E = E - - In --"--~"-"--~--;::- cell 5?J [MnO:] [Fe 2 +n H+]8 o RT [Mn 2 +][Fe 3 +Y (D) E = E - - In --"--~"-"--~--;::- cell 8?J [MnO:][Fe2+nH+r o RT [Mn2+ ][Fe 3 + y (E) 5E = 5E - - In _-"--~!.!o--;:--"---;::- cell 8?J [MnO:][ Fe 2 +n H+]8 7. The following reactions are known to occur spontaneously: Cu + 2Ag+ ~ Cu Ag Zn + 2Ag+ ~ Zn Ag Zn + Cu 2 + ~ Zn Cu The activity series for the three elements from the strongest to the weakest reducing agent is (A) Cu > Ag > Zn (B) Zn> Cu > Ag (C) Ag > Cu > Zn (D) Ag > Zn > Cu (E) Zn > Ag > Cu 8. The standard reduction potential for Pb0 2 ~ Pb 2 + is V, and the standard reduction potential for Fe 3 + ~ Fe 2 +is V What is the standard cell voltage for the reaction (A) V (B) V (C) V (D) V (E) V

3 Oxidation-Reduction Reactions and Electrochemistry Which of the following 13. Which of the following elements compounds includes an element has the largest number of possible with an oxidation number of +5? oxidation states? (A) ClO~ (A) Fe (B) MnO~ (B) CI (C) NO; (C) Ca (0) SO~- (0) Mn (E) NO~ (E) Na 10. Which of the following metals 14. For the reaction does NOT react with water to produce hydrogen? zr + Cl2 ~ zcr + 12 (A) Zn the standard cell voltage is (B) Li V What is the equilibrium (C)Ca constant for this reaction at (0) Na 45 DC? (R= V C mor l K- I, (E) Rb and?jf = 96,485 C mol") 11. In the electrolysis of an aqueous (A) 9.8 X solution of CU(N0 3 )2' which of (B) 1.0 x the following is expected to occur? (C) 1.6 X 10 5 (0) 6.3 X 10-6 (A) formation of 02 at the anode (E) 2.27 (B) formation of H2 at the cathode 15. Which of the following cell (C) deposition of copper metal voltage values represents a on the anode nonspontaneous reaction that (0) formation of hydroxide ions produces the greatest amount of at the cathode product? (Assume the same (E) formation of H+ at the number of electrons is transferred cathode in each reaction.) 12. Sodium metal cannot be (A) V electrolyzed from an aqueous (B) V Na2S0 4 solution because (C) V (0) V (A) the voltage needed is too (E) V high for any available instrument to achieve 16. A metal is electrolyzed from (B) wateris reduced to 02 before aqueous solution by using an Na+ electrical current of 1.23 A for (C) Na+ has a high over-potential 21/2h, and 3.37 g of metal is that keeps it from being deposited. In a separate reduced experiment the number of (0) H+ has a more favorable electrons used for the reduction of reduction potential than Na+ the metal is 2. What is the metal? (E) Na+ does electrolyze, but it (A) AI immediately reacts with (B) Ni water again (C) Sn (0) Mg (E) Au

4 486 AP Chemistry 17. A galvanic cell is set up under nonstandard state conditions, and EceU is measured as V Which of the following is true about this system? (A) The galvanic cell is set up incorrectly because of the negative cell voltage value. (B) If the contents of the two cells are mixed, the reaction will proceed in the forward direction. (C) The reaction is definitely nonspontaneous. (D) If the contents of the two cells are mixed, the reaction will proceed in the reverse direction. (E) The reaction is definitely spontaneous. 18. A galvanic cell is constructed; and when the temperature of the cell is increased from 20 C to 30 C, the cell voltage changes by a factor of Which of the following conclusions may be drawn from this observation? 1Go must be positive since the reaction is not spontaneous. (B) The increase is due solely to the temperature term in I1Go = -RT In K (C) The information indicates that 115 for this reaction must be negative. (D) The reaction is spontaneous because I1GO is negative. (E) The voltage change must be due to the change in the equilibrium constant with temperature. 19. Which of the following is NOT commonly produced by electrolysis? (A) NaOCl (bleach) (B) Al (C) Fe (D) NaOH (E) H2 20. Which of the following compounds includes an element that has the same oxidation number as the chlorine in sodium chlorate, NaClO/ (A) K 3 Fe(CN)6, (B) KMn04 (C) Al(N0 3 )3 (D) (NH4)2S04 (E) KCl With a current of 1.25 A, how many minutes will be required to deposit 2.00 g of copper on a platinum electrode from a copper(ii) nitrate solution? (Faraday'sconstant = 96,485 C mol") (A) 4859 (B) 81.0 (C) 40.5 (D) 1.35 (E) What is the minimum number of electrons needed to balance the following half-reaction with whole number coefficients? (A) 1 (B) 2 (C) 5 (D) 10 (E) 12

5 Oxidation-Reduction Reactions and Electrochemistry Which of the following pairs of constants are NOT mathematically related to each other? (A) equilibrium constant and Gibbs free energy (B) rate constant and activation energy (C) standard cell voltage and equilibrium constant (D) standard cell voltage and rate constant (E) Gibbs free energy and standard cell voltage 24. Which of the following statements is FALSE? (A) Reduction involves a gain of electrons. (B) Batteries are galvanic cells. (C) A spontaneous reaction always has a positive E ~ell. (D) Electrolysis reactions always produce a gas at at least one electrode. (E) Galvanic cells can be used to determine equilibrium constants. ANSWER KEY l.d 6. C 11. A 16. B 21. B 2. E 7. B 12. D 17. D 22. D 3. A 8. B 13. B 18. B 23. D 4. C 9. E 14. A 19. C 24. D 5. D 10. A 15. C 20. C See Appendix 1 for explanation of answers. Free-Response (a) Balance the following skeleton reaction in acid solution r + 10; ~ I; (b) Describe in words what to do to convert the balanced equation in part (a) into a reaction in basic solution. (c) Write the Nernst equation for the reaction in part (a). (d) A galvanic (voltaic) cell is set up with a copper wire immersed in a Cu2+ solution and a strip of magnesium immersed in a Mg2+ solution. If the magnesium ion concentration is M and the cell voltage is measured as 2.15 volts, what is the concentration of the copper ion solution? (e) A solution containing Cu 2 + is electrolyzed for 45.0 minutes. The mass of a platinum electrode increases from to grams when the copper is reduced onto it. What was the average electrical current through this electrolytic cell?

6 528 AP Chemistry Important Concepts Arrhenius theory Brensted- Lowry theory Lewis theory Neutralization Titration Buffers Strong vs weak acids and bases Predicting relative strengths of acids Hydrolysis Important Equations ph = -log [H+] and poh = -log [OH-] [conjugate base]] p H = pk a + Iog (.. [conjugate acid] [H+][A-] [HB+][OH-] K= K==-----=--=------= a [HA] b [B] Kw = [H+ ][ 0 H- ].Practice Exercises Multiple-Choice For the first four problems below, one or more of the following responses will apply; each response may be used more th~n once or not at all in these questions. I. Cu(NH3)~+ II. KOH III. HCO~ IV: CO~v: SO~- 1. Which of the above is the product of a Lewis acid reacting with a Lewis base? and II (C) I and III (E) IV and V 2. Which ion is the strongest base? (C) III 3. Which of these imparts a color to a solution? (C) III

7 Acids and Bases When an equal number of moles of each is mixed, which of these can be used to prepare a buffer solution? and II and III (C) III and IV and V and I 5. Which of the following has the highest ph? (A) MHCI (B) MHC z H 3 0 Z (C) MNazC0 3 (D) MNaCl (E) MNaCzH 3 0 Z 6. Which of the following CANNOT occur together in solution? (A) H 3 P0 4 and HzPO~ (B) HCO; and CO~- (C) Na+ and SO~- (D) C20~- and H Z C Z 0 4 (E) HPO~- and PO!- 7. When mol ofnaoh is added to 1.00 L of MHl04, the solution will contain (A) HPO~- (B) H2PO~ (C) PO~- (D) A and B (E) A and C 8. A buffer with a ph of 10.0 is needed. Which of the following should be used? (A) ethanoic acid with a f\, of 1.8 X 10-5 (B) ammonia with a ~ of 1.8 X 10-5 (C) nitrous acid with a I\. of 7.1 X 10-4 (D) H2PO~ and PO!- with a I\. of 4.5 X (E) dimethylamine with a ~ of 1.05 X ph is equal to pi\. (A) when [conjugate acid] = [conjugate base] (B) at the end point of a titration (C) in the buffer region (D) in the Henderson-Hasse1balch equation (E) at equilibrium 10. The ph of a 1.23 X 10-3 M solution of Ba(OH)2 aqueous solution is (A) 2.61 (B) 2.43 (C) (D) (E) An indicator has a I\. of 6.4 X 10-6, the conjugate acid is red, and the conjugate base is yellow. At what ph will the solution be red? (A) 5.2 (B) 5.5 (C) 4.0 (D) 4.7 (E) A buffer has a ph of If the buffer is made from a weak acid (I\. = 3.30 X 10-5 ), and its conjugate [conjugate base] base, the [weak acid] (A) 4.87 (B) 4.48 (C) 1.00 (D) 2.45 (E) 0.41 ratio is 13. Which of the following statements is correct? (A) HCl0 2 is a stronger acid than HCI0 3 (B) HI is a weaker acid than HCl. (C) CH 3 COOH is a stronger acid than CH 2 BrCOOH. (D) HN0 3 is a stronger acid than HNOz' (E) H 3 P0 4 is a stronger acid than HCI0 4

8 530 AP Chemistry 14. What is the ph of a M solution ofk2hpoi (For H 3 P0 4, pk; = 2.15; pi<; = 7.20; p~ = ) (A) 1.00 (B) (C) 9.78 (D) 6.67 (E) Which of the following is the correct method for preparing a buffer solution? (A) Mix the correct amounts of a weak acid and its conjugate base. (B) Neutralize a weak base partially with strong acid. (C) Neutralize a weak acid partially with a strong base. (D) Add the appropriate amount of strong acid to an acid salt. (E) All of the above methods may be used to prepare buffers. 16. The only acid that is both a strong and a weak acid on dissociation is (A) hydrochloric acid (B) perchloric acid (C) nitric acid (D) sulfuric acid (E) phosphoric acid 17. Which of the following is the acid anhydride of a monoprotic acid? (A) CaO (B) 50 3 (C) FeO (D) CO 2 (E) N Which of the following CANNOT be either a Lewis acid or a Lewis base? (A) CH 4 (B) Cu 2 + (C) CO (D) Fe 3 + (E) NH3 19. In the complex ion Cu(NH3)~+ the NH3 is called (A) a cation (B) a ligand (C) a Lewis acid (D) an anion (E) a conjugate acid 20. The ph of a M solution of a weak base is What is the p~ of this base? (A) 3.5 x (B) 6.4 x 10-7 (C) 2.8 X 10-4 (D) 2.3 X 10-3 (E) 1.2 X A solution containing HF is titrated with KOH. At the end point of the titration the solution contains (A) equal amounts ofhf and KOH (B) H 2 0, H+, OH-, K+, F, and HF (C) K+ and F (D) KF and H 2 0 (E) K+, F-, and H A buffer at ph 5.32 is prepared from a weak acid with a pi\, = If 100 ml of this buffer is diluted to 200 ml with distilled water, the ph of the dilute solution is (A) 5.62 (B) 5:02 (C) 5.32 (D) The identity of the acid is needed to answer the question. (E) The concentrations of the acid and the salt are needed to answer the question.

9 I CHALLENGE I 23. If 50.0 ml of a MHCl solution is mixed with 24.0 ml of a MNaOH solution, what is the ph of the final mixture? (A) 1.87 (B) (C) 5.29 (D) 3.02 (E) I CHALLENGE ~ 24. If 50.0 g offormic acid (HCH0 2, K"= 1.8 X 10-4)and 30.0 g of sodium formate (NaCH0 2 ) are dissolved to make 500 ml of solution, the ph of this solution is (A) 4.76 (B) 3.76 (C) 3.35 (D) 4.12 (E) 3.02 Acids and Bases 531 ANSWER KEY 1. C 6. D 11. C 16. D 21. B 2. D 7. E 12. D 17. E 22. C 3. A 8. B 13. D 18. A 23. D 4. C 9. A 14. C 19. B 24. C 5. C 10. C 15. E 20. B ee Appendix 1 for explanations of answers. Free-Response Answer the following questions using the concepts and procedures discussed in this chapter and preceding chapters. (a) Rank the strengths of phosphoric acid, sulfuric acid, and perchloric acid. Explain your reasoning. (b) Calculate the ph, poh, Ba(OH)2' [H+], and [OH-] of a molar solution of (c) Sketch and fully label a titration curve for 50.0 ml of M ammonia titrated with M HBr. (d) Describe a comprehensive method for preparing a buffer. Be sure to mention all the data you need and calculations that need to be performed. (e) Write the chemical reaction for propanoic acid (CH 3 CH 2 COOH) reacting with ammonia. Identify the conjugate acid-base pairs, and if the position of the equilibrium lies toward the product side, indicate their strengths.