MCAT Physical : Electrochemistry
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Example Question #3 : Half Reactions And Reduction Potential
Imagine a galvanic cell which uses solid zinc and aqueous iron ions to produce a voltage.
Assuming standard conditions, what is the free energy for the reaction?
Since the reaction is taking place under standard conditions, we can determine the free energy of the reaction by using the equation
n is the number of moles of electrons transferred in the balanced reaction, F is Faraday's constant, and Eo is the cell potential for the reaction.
Example Question #4 : Half Reactions And Reduction Potential
Determine the cell potential of the following reaction.
Reduction potentials of 
In the given reaction calcium, 
We are only given the reduction potentials. The oxidation potential of 
Recall that only the moles of electrons must balance for these reactions, therefore no multiplication of the standard potentials is needed when balancing mole atoms; thus the cell potential is the sum of the calcium oxidation potential and the gold reduction potential.
Example Question #1 : Half Reactions And Reduction Potential
Consider the following half reactions and corresponding reduction potentials:
Based on the above information, which substance can oxidize 
The reduction potential of 
For a substance to oxidize 
The only choice that meets this requirement is 
Example Question #11 : Electrochemistry
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 voltaic cell drawn above, what is true about the species Ag?
The reduction potential for 
It is reduced and gains electrons
It is oxidized and loses electrons
It is oxidized and gains electons
It is reduced and loses electrons
It is neither reduced nor oxidized
It is reduced and gains electrons
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.
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 #11 : Electrochemistry
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.
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