AP MCQ 09GHIJ PART 1 Questions 01-02: For Questions 01-02 consider the two standard reduction potentials shown below. Cu2+ + 2e- → Cu (+0.34V) H+ + e- → ½H2 (0.00V) Question 01: If the two half-cells below were combined in a standard, galvanic cell, what would be the correct chemical equation to represent the spontaneous REDOX process? Cu(s) + ½H2(g) → Cu2+(aq) + H+(aq) Cu(s) + 2H+(aq) → Cu2+(aq) + H2(g) Cu(s) + H+(aq) → Cu2+(aq) + ½H2(g) Cu2+(aq) + H2(g) → Cu(s) + 2H+(aq) Question 02: If the two half-cells were combined in a galvanic cell, what would be the voltage generated the spontaneous REDOX process? 0.00 V +0.34 V -0.34 V +0.68 V Question 03: What is always true of all electrolysis processes? They generate electricity They have ∆G° values that are positive They are thermodynamically favored They never need an external source of energy to make them occur Question 04: The metal indium, is known to exist in an oxidation state of +3. What approximate mass of indium (molar mass = 114.82 g) will be produced during the electrolysis of a molten salt that contains In3+, if a current of 10.0 amps is passed through the electrolyte for a period of 50.0 hours? 50.0 g 115 g 714 g 1.80 x 106 g Question 05: The purpose of the salt-bridge in a galvanic cell is To allow the passage of ions and to precipitate out ions of either the reduced or oxidized species To provide electrons to the cell To allow the passage of ions to maintain the potential difference between the two half-cells To allow the passage of electrons between the two half-cells Question 06: Which combination of values for ΔG°, Keq and E°, is the most likely? Negative ΔG°, K < 1 and positive E° Negative ΔG°, K > 1 and negative E° Positive ΔG°, K > 1 and positive E° Negative ΔG°, K > 1 and positive E° Question 07: In a simple galvanic cell constructed from the two half-cells shown below, Cu2+(aq) + 2e- → Cu(s) +0.34V Zn2+(aq) + 2e- → Zn(s) -0.76 V Electrons flow toward the zinc cathode where reduction takes place and negative ions from the salt bridge enter the reduced half-cell Electrons flow toward the copper anode where oxidation takes place and positive ions from the salt bridge enter the reduced half-cell Electrons flow toward the zinc cathode where oxidation takes place and positive ions from the salt bridge enter the reduced half-cell Electrons flow toward the copper cathode where reduction takes place and positive ions from the salt bridge enter the reduced half-cell Questions 08-10: Use the following data for Questions 08-10 . The electrolysis of molten sodium chloride yields different products than the electrolysis of aqueous sodium chloride. The relevant standard electrode potentials are shown below. Question 08: The standard electrode potentials alone, predict that the products from the electrolysis of aqueous sodium chloride should be H2 gas and O2 gas, but it is found that in many situations, the actual products are chlorine gas and hydrogen gas. What is the most likely explanation for this observation? Despite the predicted reaction, the oxidation of water is impossible since in this situation the water cannot conduct electricity Any oxygen produced is immediately converted back to water Any oxygen produced will immediately react with hydrogen to produce water The electrode potentials for the production of chlorine gas and oxygen gas are very similar, and any small deviation from standard conditions may favor the production chlorine over oxygen Question 09: What is the product at the cathode when molten sodium chloride is electrolyzed? Sodium Chlorine Oxygen Hydrogen Question 10: When considering the four reaction reactions listed in the table, it would appear that the reduction of Cl2 gas to chloride ions is the most reduction likely to occur. Why is Cl2 gas not reduced at the beginning of the electrolysis of either aqueous, or molten NaCl? No reduction reaction takes place in electrolysis Positive voltages like chlorine’s reduction to chloride ions, have positive values for ΔGo so cannot occur There is no chlorine gas present in an aqueous or molten sodium chloride The cell is not operating under standard conditions Δ
