Chem Exam 4 Review Part 2

46. A concentration cell is constructed by using the same half-reaction for both the cathode and anode. What is the value of Ecell for a concentration cell that combines silver electrodes in contact with 0.10M silver nitrate and 0.00003 M silver nitrate solutions? (see question) a. +0.21 V b. +0.59 V c. +0.80 V d. -0.21 V e. +1.01 V

A. +0.21 V

40. Using the following data, determine the standard cell potential E°cell for the electrochemical cell constructed using the following reaction, where zinc is the anode and lead is the cathode. (see question) a. +0.637 V b. -0.637 V c. +1.274 V d. -0.889 V e. +0.889 V

A. +0.637 V

41. Which statement about a cathode in a voltaic cell is NOT correct? a) Oxidation occurs at the cathode. b) Reduction occurs at the cathode. c) Usually the cathode is a metal strip. d) In the external circuit, electrons flow toward the cathode. e) Chemical species can have their oxidation number decreased at the cathode.

A. Oxidation occurs at the cathode

36.The following reaction occurs in basic solution. Identify the reducing agent (Note:equation is not balanced) Zn(s)+NO3-(aq)-->Zn(OH)4^2-(aq)+NH3(aq) a. Zn(s) b. NO3-(aq) c. OH-(aq) d. H2O(l) e. NH3(aq)

A. Zn (s)

29. Reduction is the ___ a. gain of electrons b. loss of electrons c. gain of protons d. loss of protons e. loss of mass

A. gain of electrons

37.In the smelting of iron from iron oxide according to the equation Fe2O3(s)+3CO(g)-->2Fe(s)+3CO2(g) What is the change in oxidation number for iron? a. +3 b. -3 c. +2 d. -2 e. 0

B. -3

45. An electrochemical cell is constructed with a zinc metal anode in contact with a 0.052M solution of zinc(II) nitrate and a silver cathode in contact with a 0.0042M solution of silver(I) nitrate. What is the emf of this cell at 5°C? (see question) a. 1.656 V b. 1.465 V c. 1.561 V d. 1.370 V e. 1.609 V

B. 1.465 V

48. Copper metal is purified by electrolysis. How much copper metal could be produced from copper(II) oxide by applying a current of 10.0 amps at the appropriate negative potential for 12.0 hours? a. 284 g b. 142 g c. 28.4 g d. 14.2 g e. 4.48 g

B. 142 g

39. You have a job as a summer intern in an orange juice processing plant. Part of your job is to determine the amount of vitamin C in a given quantity of orange juice. To make this determination, you titrate the orange juice with I3-, the triiodide ion. To make sure you know what you are doing, your supervisor asks you how many electrons are transferred in the reaction. The reaction describing the titration is given below. What is your response? ascorbate+H2O+I3- -->dehydroascorbate+2H+3I- a. 1 b. 2 c. 4 d. 0 e. It is impossible to tell

B. 2

35. The following reaction occurs in basic solution. Identify the oxidizing agent (Note:equation is not balanced) Zn(s)+NO3-(aq)-->Zn(OH)4^2-(aq)+NH3(aq) a. H2O (l) b. NO3- (aq) c. OH- (aq) d. Zn (s) e. NH3 (aq)

B. NO3-

30. Oxidation is the ___ a. gain of electrons b. loss of electrons c. gain of protons d. loss of protons e. loss of mass

B. loss of electrons

32. Glancing at a periodic table, where do you expect to find elements that are good reducing agents? a. in groups 16 and 17 b. on the left c. in the middle d. at the bottom e. in group 17

B. on the left

42. The standard hydrogen electrode is ___ a) used to calibrate voltmeters. b) used to produce a set of standard reduction potentials. c) needed to activate electrochemical cells. d) often overlooked in measuring standard reduction potentials. e) used to produce a standard cell potential of exactly 1 V.

B. used to produce a set of standard reduction potentials

34. When hydrogen reacts with a metal to form a hydride (e.g CaH2) what are the oxidation numbers of the calcium and hydrogen, respectively, in the product? a. -2 and +1 b. +1 and -2 c. +2 and -1 d. 0 and 0 e. +2 and -2

C. +2 and -1

27. What is indicated by the shape of the titration curve? (see graph) a. A diprotic acid was titrated with a strong base. b. A triprotic acid was titrated with a strong base. c. A diprotic base was titrated with a strong acid. d. A triprotic base was titrated with a strong acid. e. A strong acid was titrated with a strong base.

C. a diprotic base was titrated with a strong acid

44. The Nernst equation can be used to calculate a) standard cell potentials from standard reduction potentials. b) the change in standard Gibbs free energy from standard cell potentials. c) cell potentials from standard cell potentials when the conditions of concentration and temperature are not standard. d) cell potentials given the temperature and reactant concentrations. e) cell potentials from standard oxidation potentials.

C. cell potentials from standard cell potentials when the conditions of concentration and temperature are not standard

28.What is the pH of a buffer solution where [HA]=[A-] a. pH=1 b. pH=Ka c. pH=pKa d. pH=pOH e. pH=7.0 pH=pKa+log[A-]/[HA]=pKa+log[base]/[acid]

C. pH=pKa

33. What is the oxidation number of chromium in the ionic compound ammonium dichromate, (NH4)2Cr2O7? a. +3 b. +4 c. +5 d. +6 e. +7

D. +6

25. Acid-base indicators need to have very intense colors so that a very low concentration is visible. Could there be a problem in using too much indicator? a.No, the colors would just be darker b.No, indicators are inert c.Yes, more indicator requires more extreme pH values to change color d. Yes, the indicator could affect the acid-base chemistry being measured e.No, the colors would just be sharper

D. Yes, the indicator could affect the acid-base chemistry being measured

43. The spontaneous redox reaction in a voltaic cell has __ a) a negative value of Ecell and a negative value of ΔG. b) a positive value of Ecell and a positive value of ΔG. c) a negative value of Ecell and a positive value of ΔG. d) a positive value of Ecell and a negative value of ΔG. e) a positive value of Ecell and a value of zero for ΔG.

D. a positive value of Ecell and a negative value of ΔG.

47. A voltaic cell is constructed based on the oxidation of zinc metal and the reduction of silver metal. Solutions of silver nitrate and zinc nitrate also were used. Locate the silver metal on the diagram. (see question) A.a B. b C. c D. d

D. d

26. In a titration of monoprotic acids and bases, there is a large change in pH___ a. at the point where pH = pKa of the acid. b. when the volume of acid is exactly equal to the volume of base. c. when the concentration of acid is exactly equal to the concentration of base. d. when the number of moles of acid is exactly equal to the number of moles of base. e. at the point where pH = pKb of the base

D. when the number of moles of acid is exactly equal to the number of moles base

38. Which one of the following items does not characterize an oxidizing agent? a) An oxidizing agent gains electrons. b) An oxidizing agent causes another species to be oxidized. c) The oxidation number of an oxidizing agent decreases. d) A good oxidizing agent is a metal in a high oxidation state, such as Mn7+. e) An example of a good oxidizing agent is an alkali metal, such as Na.

E. an example of a good oxidizing agent is an alkali metal, such as Na

31. Glancing at a periodic table, where do you expect to find elements that are good oxidizing agents? a. at the bottom left b. in the top left c. in the transition metals d. at the bottom e. on the right (expect for the last group)

E. on the right (expect for the last group)