47. Which of the following reactions is a redox reaction?

(a) K₂CrO₄ + BaCl₂ → BaCrO₄ + 2KCl

(b) Pb₂²⁺ + 2Br^- → PbBr

(c) Cu + S → CuS
(A)(a) only
(B)(b) only
(C) (c) only
(D)(a) and (c)

43. Using a 60 MHz spectrometer, the protons in dichloromethane appear at 5.30 ppm. When the same sample is placed in a 100 MHz instrument, where does the signal appear? (A)8.33 (B)5.30 (C) 3.18(D)cannot be determined from information given

44. Which of the following is another name for cyclobutadiene? (A)[2]annulene (B)[4]annulene (C) [6]annulene(D)Dewar benzene

45. In electrophilic aromatic substitution reactions a bromine substituent ________. (A)is a deactivator and a m-director (B)is a deactivator and an o,p-director (C) is an activator and a m-director(D)is an activator and an o,p-director

46. Which element is oxidized in the reaction below?Fe(CO)5 (l) + 2HI (g) → Fe(CO)4I2 (s) + CO (g) + H2 (g) (A)C (B)O (C) H(D)Fe

48. The purpose of the salt bridge in an electrochemical cell is to ________. (A)maintain electrical neutrality in the half-cells via migration of ions (B)provide a source of ions to react at the anode and cathode (C) provide oxygen to facilitate oxidation at the anode (D) provide a means for electrons to travel from the anode to the cathode

49. Consider an electrochemical cell based on the reaction:2H+ (aq) + Sn (s) → Sn2+ (aq) + H2 (g) Which of the following actions would not change the measured cell potential? (A)lowering the pH in the cathode compartment (B)addition of more tin metal to the anode compartment (C) increasing the tin (II) ion concentration in the anode compartment (D) increasing the pressure of hydrogen gas in the cathode compartment

50. What is the cathode in an alkaline battery? (A)MnO2 (B)KOH (C) Zn powder(D)Mn2O3

51. The standard cell potential ( ) for the reaction below is +0.63 V. At 25 °C, the cell potential for this reaction is ________ V when [Zn2+ ] = 3.0 M and [Pb2+ ] =2.0✖10-4M.Pb2+(aq) + Zn (s) → Zn2+(aq) + Pb (s) (A)0.51 (B)0.86 (C) 0.40(D)0.75

52. The first law of thermodynamics can be given as ________. (A)ΔE = q + w (B)(C) for any spontaneous process, the entropy of the universe increases (D) the entropy of a pure crystalline substance at absolute zero is zero

53. When a system is at equilibrium, ________. (A)the reverse process is spontaneous but the forward process is not (B)the forward and the reverse processes are both spontaneous (C) the forward process is spontaneous but the reverse process is not (D) the process is not spontaneous in either direction