AP Chemistry: Electrochemistry 3 — Questions and Answers
Question 1: The Nernst equation at 25 °C is E = E° − (0.0592/n) log Q. As Q increases, the cell potential:
- Decreases (Correct answer)
- Increases
- Stays constant
- Becomes zero immediately
Correct answer: Decreases
A larger Q makes the log term larger, subtracting more from E° and lowering E.
Question 2: When an electrochemical cell reaches equilibrium, the cell potential E equals:
- 0 V (Correct answer)
- E°cell
- A maximum
- The standard reduction potential of the cathode
Correct answer: 0 V
At equilibrium no net reaction occurs, so the measured cell potential is zero.
Question 3: For a cell with n = 2 and E° = +0.46 V, what is log K at 25 °C?
- About 15.5 (Correct answer)
- About 7.8
- About 2.0
- About 0.46
Correct answer: About 15.5
log K = nE°/0.0592 = (2 × 0.46)/0.0592 ≈ 15.5.
Question 4: Increasing the concentration of reactant ions in the cathode compartment will generally:
- Increase the cell potential (Correct answer)
- Decrease the cell potential
- Have no effect
- Reverse the cell polarity
Correct answer: Increase the cell potential
More cathode reactant lowers Q, which raises E according to the Nernst equation.
Question 5: A concentration cell generates voltage because of a difference in:
- Ion concentration between the two half-cells (Correct answer)
- Electrode metals
- Temperature only
- Salt bridge composition
Correct answer: Ion concentration between the two half-cells
A concentration cell uses identical electrodes but differing ion concentrations to produce potential.
Question 6: In a concentration cell, the half-cell with the lower ion concentration acts as the:
- Anode (Correct answer)
- Cathode
- Salt bridge
- Reference electrode
Correct answer: Anode
The dilute side undergoes oxidation to raise its ion concentration, making it the anode.
Question 7: What is the standard temperature assumed when using the 0.0592/n form of the Nernst equation?
- 298 K (25 °C) (Correct answer)
- 273 K (0 °C)
- 373 K (100 °C)
- 310 K (37 °C)
Correct answer: 298 K (25 °C)
The constant 0.0592 V is derived assuming 298 K.
AP Chemistry: Electrochemistry 3
The Nernst equation at 25 °C is E = E° − (0.0592/n) log Q.
As Q increases, the cell potential: