MCAT Physical : Voltaic/Galvanic Cells
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Example Questions
Example Question #1 : Voltaic/Galvanic Cells
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.
In the above diagram, a KOH salt bridge is used. Which species would you anticipate finding at the tip of the arrow numbered 4?
The reduction potential for 
The correct answer is 
Example Question #2 : Voltaic/Galvanic Cells
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.
The student in the passage creates a new cell, but uses the same element at both the anode and the cathode. What is likely to be true of this new cell?
Reduction and oxidation are not occuring in the cell
This cell can generate energy, but only after energy is input into the system
This cell cannot generate energy
Different concentrations of the species are present in each cell
The Gibbs free energy of this cell is zero
Different concentrations of the species are present in each cell
This is an example of a concentration cell. If you have two half cells, each made of the same chemical species, and connect them with a wire, the cell will generate a voltage as it attempts to correct the disequilibrium induced by the concentration difference.
Example Question #3 : Voltaic/Galvanic Cells
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.
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?
Acetic acid
Ethane
Heptane
Benzene
Carbon tetrachloride
Acetic acid
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.
Example Question #4 : Voltaic/Galvanic Cells
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.
If the structure labeled X were removed from the cell, which of the folllowing would be true?
The reduction potential for 
Copper ions forming during cell function would be increasingly repelled by existing ions in solution
Ag ions forming during cell function would be inceasingly attracted by existing ions in solution
Ag ions forming during cell function would be inceasingly repelled by existing ions in solution
The cell would generate an uncontrolled burst of high energy
Copper ions forming during cell function would be increasingly attracted by existing ions in solution
Copper ions forming during cell function would be increasingly repelled by existing ions in solution
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.
Example Question #5 : Voltaic/Galvanic Cells
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.
The student in the passage disassembles the cell, and attempts to rebuild it the next day. He forgets, however, to include 
The cell will not function at all
The cell will function, but for a shorter period of time before it reaches equilibrium and ceases to produce energy
The cell requires 
The cell will produce more energy, because there is no existing ion to repel further ionization into solution
The cell will function without 
The cell will not function at all
There must be 
Example Question #4 : Voltaic/Galvanic Cells
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.
Which of the following compounds could be used to construct the structure labeled "X"?
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.
Example Question #21 : Electrochemistry
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?
The ions will distribute evenly in the salt bridge
The potassium will remain bound to chlorine, and will not ionize
Toward the cathode
Toward the anode
Toward the cathode
Potassium ions (K+) will be positively charged, which means they will travel towards the side of the cell that is more negative. Reduction takes place at the cathode, because electrons flow from the anode to the cathode. Since negative charge accumulates at the cathode, the cations will travel in that direction, while the anions will travel towards the anode.
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