Questions Question 1 How does a fuel cell differ from conventional methods of energy generation? Why is fuel cell better than the conventional methods of energy generation? Relate the answers to the two questions using a concept map. Question 2 Illustrate how a galvanic cell uses a spontaneous chemical reaction to generate electricity. Label your illustration properly and show the flow of electrons. Name the electrodes properly and indicate the specific redox reaction involved in each. Write the half-cell reactions. Explain why it is necessary to physically separate the oxidizing and reducing reagents from each other. Question 3 Illustrate a diagram showing what is happening inside a hydrogen fuel cell? Label the diagram properly and briefly explain the process. Name byproduct(s) of an active hydrogen fuel cell and explain the role of an electrolyte in a fuel cell. Question 4 List different types of fuel cells. Which of these cells is the most efficient? Explain your answer. Question 5 When a galvanic cell contains two different solutions, a salt bridge is often required. The salt bridge allows the two solutions to remain isolated by providing ionic interactions for both solutions, without severely reducing the potential difference. The salt bridge is commonly composed of a potassium chloride solution. In what direction would you expect the potassium ions to travel in a galvanic cell? If a salt bridge is removed between the half cells, what happens to the voltage? Explain. Question 6 You are charging your cell phone battery with your cell phone charger. What can you conclude about this process? Is it acting as a galvanic or an electrolytic cell? Is it acquiring or releasing voltage? Explain. Question 7 A battery and a fuel cell are both examples of galvanic cells, but what is/are their difference(s)? Question 8 Fuel cells are promising forms of alternative energy because of its advantages over conventional sources of energy. However, petroleum products are still the most prevalent energy sources in the world. Why do you think this is the case? Can you list limitations and issues of fuel cells? Cite your literature source. Quiz Time!!! Question 1 In an electrolytic cell, oxidation takes place at the __________. A salt bridge C cathode B anode D Oxidation does not take place in an electrolytic cell. Question 2 Which of the following is not true of electrolytic cells? A Electricity is conducted by the motion of ions C No battery is required for electrolysis to take place B The cell potential is negative D Oxidation occurs at the anode Question 3 Which of the following is false about anodes and cathodes? I. In a galvanic cell only, reduction occurs at the anode whereas oxidation occurs at the cathode II. Electron flows from anode to cathode in both galvanic and electrolytic cells III. Cathodes are only found in galvanic cells A II and III C I, II, and III B I and III D III Question 4 Electrons are __________ in cathodes and __________ in anodes. A products . . . products C products . . . reactants B reactants . . . reactants D reactants . . . products Question 5 Which of the following is the correct direction of electron flow in an electrochemical cell? A Cathode to anode C The electron flow direction depends on the type of electrochemical cell B The electron flow direction depends on the metals involved in the half-reactions D Anode to cathode Problem-Solving Time!!! A student conducts an experiment for a chemistry class. The student wishes to explore power generation from different types of voltaic cells. He sets up three different cells, and then compares the amount of energy generated from each one. One of his cells is shown below as an example. Both remaining cells follow the same layout. Question 1 How would the voltaic cell depicted above differ from an electrolytic cell? A B An electrolytic cell requires energy input An electrolytic cell produces more energy C An voltaic cell requires energy input to begin the reduction process D An electrolytic cell produces energy based on differences in concentrations between the half cells Question 2 Instead of silver, a scientist uses a strip of zinc in the opposite half cell from copper. Which of the following is true when comparing this new cell to the cell in the diagram? A The cathode is the same in both cells C Energy can be produced in both cells B The direction of ion migration in the salt bridge is the same in both cells D The direction of electron flow is the same in both cells Question 3 In the voltaic cell drawn above, what is true about the species Ag? A It is oxidized and loses electrons C It is neither reduced nor oxidized B It is reduced and gains electrons D It is oxidized and gains electons Question 4 If there is a net production of copper ions in the half cell on the left as the reaction proceeds, which of the following must be true? A Silver has a more positive reduction potential than copper C Copper is reduced in the reaction B There is no net electron flow D Copper has a more positive reduction potential than silver Question 5 The student in the passage wants to replace the water, represented by the blue in the diagram, with an alternative solvent. Which solvent would be most likely to produce a functioning cell? A Acetic acid C Heptane B Carbon tetrachloride D Ethane Question 6 If the structure labeled X were removed from the cell, which of the following would be true? A Ag ions forming during cell function would be increasingly repelled by existing ions in solution B Copper ions forming during cell function would be increasingly attracted by existing ions in solution C Copper ions forming during cell function would be increasingly repelled by existing ions in solution D Ag ions forming during cell function would be inrceasingly attracted by existing ions in solution Question 7 The student in the passage disassembles the cell, and attempts to rebuild it the next day. He forgets, however, to include Ag+ in the solvent of the half cell on the right side of the diagram. Which of the following is likely to happen? 2+ + A The cell will produce more energy, because there is no existing ion to repel further ionization into solution C The cell requires Cu , not Ag , in the right-side half reaction to function properly B The cell will function without Ag+ pre2+ existing in solution, but not without Cu D The cell will not function at all Question 8 Which of the following compounds could be used to construct the structure labeled "X"? A As C CCl 4 B KOH D Ne Answer Keys Quiz Question 1 In an electrolytic cell, oxidation takes place at the __________. B anode Explanation: Electrolytic cells have a negative electromotive force and require an outside energy source to power a non-spontaneous reaction. Galvanic cells, in contrast, have positive potentials and facilitate spontaneous reactions without the need of a power source. Regardless of cell type, however, oxidation always takes place at the anode and reduction always takes place at the cathode. The flow of electrons is always from the anode to cathode. Question 2 Which of the following is not true of electrolytic cells? C No battery is required for electrolysis to take place Explanation: For electrolytic cells, the cell potential is negative; in contrast, galvanic/voltaic cells have positive cell potentials. Electrolysis reactions can only occur if the total potential is positive. An additional voltage input, such as a battery, is required so that the sum of potentials in the electrolytic cell is greater than zero. Oxidation always occurs at the anode, regardless of cell type, and electrons always travel toward the site of reduction (the cathode). In a galvanic cell, the cathode is positively charged, naturally drawing the flow of electrons. In an electrolytic cell, the cathode is negatively charged, but still requires the flow of electrons to allow reduction to occur. An induced current from a battery is used to propel these electrons against their natural flow. Question 3 Which of the following is false about anodes and cathodes? I. In a galvanic cell only, reduction occurs at the anode whereas oxidation occurs at the cathode II. Electron flows from anode to cathode in both galvanic and electrolytic cells III. Cathodes are only found in galvanic cells B I and III Explanation: An electrochemical cell undergoes two half-cell reactions (one oxidation reaction and one reduction reaction). Each half-cell reaction occurs either in a cathode or an anode; therefore, an electrochemical cell always has a cathode and an anode. Recall that there are two types of electrochemical cells: a galvanic cell and an electrolytic cell. Regardless of the type of the electrochemical cell, the reduction half-cell reaction always occurs in the cathode and the oxidation half-cell reaction always occurs in the anode; therefore, both galvanic and electrolytic cells have reduction occurring in the cathode and oxidation occurring in the anode. In both galvanic and electrolytic cells, electrons flow from the anode to the cathode. Anodes have free electrons because electrons are products of an oxidation reaction whereas cathodes require electrons because electrons are reactants of a reduction reaction; therefore, the free electrons flow from the anode to the cathode where they are used up in the reduction reaction. Cathodes are found in both galvanic and electrolytic cells. Recall the cathodes are the site of reduction half-reaction and anodes are the site of oxidation half-reaction. Question 4 Electrons are __________ in cathodes and __________ in anodes. D reactants . . . products Explanation: The cathode is the site of reduction half-reaction, whereas the anode is the site of the oxidation half-reaction. In a reduction reaction molecules acquire electrons, whereas in an oxidation reaction molecules lose electrons. Electrons act as reactants during reduction reactions in the cathode, whereas they serve as products during oxidation reactions in the anode. Question 5 Which of the following is the correct direction of electron flow in an electrochemical cell? D Anode to cathode Explanation: Electron flow, especially the electrical energy associated with electron flow, is an important characteristic of an electrochemical cell. In a galvanic cell, electrical energy is harnessed from a spontaneous chemical reaction and is used to drive other unfavorable processes. In an electrolytic cell, electrical energy is supplied by an outside voltage source that is used to drive a nonspontaneous chemical reaction. Recall that cathodes are the site of reduction and anodes are the site of oxidation. Electrons are used up (reactants) in a reduction reaction and electrons are produced (products) in an oxidation reaction; therefore, anodes produce and have an excess of free electrons whereas cathodes use and have a deficiency of free electrons. Since there are fewer electrons in the cathode, the electrons in an electrochemical cell will flow from the anode to the cathode. Answer Keys Problem-Solving Question 1 How would the voltaic cell depicted above differ from an electrolytic cell? A An electrolytic cell requires energy input Explanation: Electrolytic cells require an input of energy, and are used to plate metals by functionally running a voltaic cell in reverse. Question 2 Instead of silver, a scientist uses a strip of zinc in the opposite half cell from copper. Which of the following is true when comparing this new cell to the cell in the diagram? C Energy can be produced in both cells Explanation: In the new cell, energy can still be produced, but because zinc ions have a lower reduction potential than copper ions, the copper will be reduced and the direction of electron flow will be reversed, as compared to the cell with silver in which copper was oxidized. Question 3 In the voltaic cell drawn above, what is true about the species Ag? B It is reduced and gains electrons Explanation: As drawn above, the reaction must involve the oxidation of copper (lower reduction potential) and the reduction of silver (higher reduction potential). Reduction always means that a species gains electrons. Question 4 If there is a net production of copper ions in the half cell on the left as the reaction proceeds, which of the following must be true? A Silver has a more positive reduction potential than copper Explanation: As drawn above, the reaction must involve the oxidation of copper (lower reduction potential) and the reduction of silver (higher reduction potential). Reduction always means that a species gains electrons. Question 5 The student in the passage wants to replace the water, represented by the blue in the diagram, with an alternative solvent. Which solvent would be most likely to produce a functioning cell? A Acetic acid Explanation: The function of a voltaic cell requires the generation and dissolution of ions. Acetic acid is the only answer choice with a net dipole moment, and would therefore be the only one to dissolve the ions produced. The other choices would be unable to dissolve the ions, and the cell would not function. Question 6 If the structure labeled X were removed from the cell, which of the following would be true? C Copper ions forming during cell function would be increasingly repelled by existing ions in solution Explanation: As the cell runs, only copper produces ions. Silver actually loses ions from solution. If this continues without balance by the salt bridge, the positive ions build up in the solution on the left side of the diagram, without any balanced negative ions, and repel the formation of new copper ions more and more strongly. Question 7 The student in the passage disassembles the cell, and attempts to rebuild it the next day. He forgets, however, to include Ag+ in the solvent of the half cell on the right side of the diagram. Which of the following is likely to happen? D The cell will not function at all Explanation: There must be Ag+ pre-existing in the right-side half reaction for the cell to function at all. Without the pre-existing ions, the cell has no electron acceptor dissolved in solution, and no electron transfer can therefore take place. Electron transfer is the fundamental energyproducing process that takes place in a voltaic cell. Question 8 Which of the following compounds could be used to construct the structure labeled "X"? B KOH Explanation: Structure "X" corresponds to the slat bridge. Its main function is balancing the ionic charge that builds up as a voltaic cell functions; therefore, there needs to be an ability for the salt bridge to ionize and send appropriate ions to each half cell. KOH is the only ionizable salt among the answer choices.
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