Summer 2003 CHEMISTRY 115 EXAM 3(A)

Transcription

1 Summer 2003 CHEMISTRY 115 EXAM 3(A) 1. In which of the following solutions would you expect AgCl to have the lowest solubility? A M BaCl 2 B. pure water C M NaCl D M KCl 2. Calculate the ph of a 1L solution containing 0.40 mol HF and 0.1 mol HCl. (K a = 6.8x10 4 for HF) A B. 1.0 C. 2.6 D What is the effect of addition of an acid to a buffered solution of HF and KF? A. [HF] will increase, [F ] will decrease B. [HF] will increase, [F ] will increase C. [HF] will decrease, [F ] will decrease D. [HF] will decrease, [F ] will increase 4. Calculate ph of a buffer composed of M HNO 2 (K a =4.5x10 4 )and 0.1 M KNO 2 A. 8.4 B. 7.0 C. 5.6 D Which of the following substances, when added to a solution of hydrofluoric acid, could be used to prepare a buffer solution? A. NaF B. NaNO 3 C. NaCl D. NaBr 6. Consider the titration diagram shown on the plot below. What type of substance was originally in the flask? A. weak acid B. weak base C. strong acid D. strong base ml of 0.1 M HF (K a =6.8x10 4 ) is titrated with 0.1 M NaOH. What is the ph of the solution when 10 ml of NaOH have been added? A. 7.2 B. 6.3 C. 3.2 D. 2.1

2 8. What is the molar solubility of MgC 2 O 4 (K sp =8.6x10 5 )? [H 2 C 2 O 4 is the oxalic acid.] A. 9.3 x 10 3 B. 6.4 x C. 7.1 x 10 9 D. 2.8 x Which of the following substances will increase in solubility if the ph of the saturated solution of the compound is lowered? A. AgCl B. AgI C. Cr(OH) 3 D. PbCl Which substance is serving as a reducing agent in the following reaction? Fe 2 S HNO 3 2Fe(NO 3 ) 3 + 3S + 6NO 2 + 6H 2 O A. HNO 3 B. S C. NO 2 D. Fe 2 S What is the oxidation number of manganese in KMnO 4? A. 0 B. +1 C. +7 D What is the coefficient of iodine when the following reaction (acidic solution) is correctly balanced? MnO 4 + I Mn 2+ + I 2 A. 5 B. 7 C. 2 D Which of the following transformation could take place at the cathode of an electrochemical cell? A. MnO 2 MnO 4 B. Br 2 BrO 3 C. Mn 2+ MnO 4 D. HSO 4 H 2 SO The standard reduction potentials for Pb 2+ and Ag + are 0.13 V and +0.8 V, respectively. Calculate E 0 for a cell in which the overall reaction is Pb + 2Ag + Pb Ag A B C D Respective standard reduction potentials of Pb 2+ and Ni 2+ are 0.13 V and 0.28 V. An electrochemical cell is built from Pb electrode in Pb 2+ solution and Ni electrode in Ni 2+ solution. The reduction reaction will occur on the electrode which is called: A. Pb, anode

3 B. Pb, cathode C. Ni, anode D. Ni, cathode 16. Calculate G (in J) for the reaction of elemental bromine Br 2 (E 0 red = 1.09 V) with chloride ion (Cl 2, E o red = 1.36) A. 2.1 x 10 4 B x 10 4 C x 10 5 D x The standard emf for Zn/Cu voltaic cell is 1.10 V. Calculate the cell emf when the concentration of Zn 2+ and Cu 2+ in the solution are 0.01 M and 1.0 M, respectively. A V B V C V D V 18. Using the table of standard reduction potentials indicate the metal which could provide cathode protection to zinc: A. Fe B. Ag C. Al D. Cu 19. The electrolysis of NiCl 2 produces Ni and Cl 2. What is the minimum external emf needed to drive electrolysis under standard conditions? A V B V C V D V 20. Identify the products of electrolysis of an aqueous solution of CuI 2 and FeCl 2 (acidic solution). [Hint: Assume that the concentration of OH is equal to zero.] A. Cu and O 2 B. Fe and Cl 2 C. Fe and O 2 D. Cu and I 2 EXAM 3(B) 1. In which of the following solutions would you expect AgCl to have the lowest solubility? A. pure water B M BaCl 2 C M KCl D M NaCl

4 2. Calculate the ph of a 1L solution containing 0.40 mol HF and 0.1 mol HCl. (K a = 6.8x10 4 for HF) A B C. 2.6 D What is the effect of addition of an acid to a buffered solution of HF and KF? A. [HF] will decrease, [F ] will increase B. [HF] will increase, [F ] will increase C. [HF] will decrease, [F ] will decrease D. [HF] will increase, [F ] will decrease 4. Calculate ph of a buffer composed of M HNO 2 (K a =4.5x10 4 )and 0.1 M KNO 2 A. 5.6 B. 7.0 C. 8.4 D Which of the following substances, when added to a solution of hydrofluoric acid, could be used to prepare a buffer solution? A. NaCl B. NaNO 3 C. NaF D. NaBr 6. Consider the titration diagram shown on the plot below. What type of substance was originally in the flask? A. weak acid B. strong acid C. weak base D. strong base ml of 0.1 M HF (K a =6.8x10 4 ) is titrated with 0.1 M NaOH. What is the ph of the solution when 10 ml of NaOH have been added? A. 3.2 B. 6.3 C. 7.2 D What is the molar solubility of MgC 2 O 4 (K sp =8.6x10 5 )? [H 2 C 2 O 4 is the oxalic acid.] A. 6.4 x B. 9.3 x 10 3 C. 2.8 x 10 2 D. 7.1 x Which of the following substances will increase in solubility if the ph of the saturated solution of the compound is lowered? A. PbCl 2 B. AgCl C. Cr(OH) 3 D. AgI

5 10. Which substance is serving as a reducing agent in the following reaction? Fe 2 S HNO 3 2Fe(NO 3 ) 3 + 3S + 6NO 2 + 6H 2 O A. HNO 3 B. Fe 2 S 3 C. NO 2 D. S 11. What is the oxidation number of manganese in KMnO 4? A. +7 B. 0 C. +5 D What is the coefficient of iodine when the following reaction (acidic solution) is correctly balanced? MnO 4 + I Mn 2+ + I 2 A. 7 B. 5 C. 4 D Which of the following transformation could take place at the cathode of an electrochemical cell? A. Mn 2+ MnO 4 B. MnO 2 MnO 4 C. Br 2 BrO 3 D. HSO 4 H 2 SO The standard reduction potentials for Pb 2+ and Ag + are 0.13 V and +0.8 V, respectively. Calculate E 0 for a cell in which the overall reaction is Pb + 2Ag + Pb Ag A B C D Respective standard reduction potentials of Pb 2+ and Ni 2+ are 0.13 V and 0.28 V. An electrochemical cell is built from Pb electrode in Pb 2+ solution and Ni electrode in Ni 2+ solution. The reduction reaction will occur on the electrode which is called: A. Ni, cathode B. Ni, anode C. Pb, cathode D. Pb, anode 16. Calculate G (in J) for the reaction of elemental bromine Br 2 (E 0 red = 1.09 V) with chloride ion (Cl 2, E o red = 1.36) A x 10 5 B x 10 5 C. 2.1 x 10 4 D x The standard emf for Zn/Cu voltaic cell is 1.10 V. Calculate the cell emf when the concentration of Zn 2+ and Cu 2+ in the solution are 0.01 M and 1.0 M, respectively.

6 A V B V C V D V 18. Using the table of standard reduction potentials indicate the metal which could provide cathode protection to zinc: A. Cu B. Fe C. Al D. Ag 19. The electrolysis of NiCl 2 produces Ni and Cl 2. What is the minimum external emf needed to drive electrolysis under standard conditions? A V B V C V D V 20. Identify the products of electrolysis of an aqueous solution of CuI 2 and FeCl 2 (acidic solution). [Hint: Assume that the concentration of OH is equal to zero.] A. Fe and O 2 B. Fe and Cl 2 C. Cu and I 2 D. Cu and O 2