APCE Electrochemistry 1 — Questions and Answers
Question 1: What is the definition of oxidation in a redox reaction?
- Gain of electrons.
- Loss of electrons. (Correct answer)
- Gain of protons.
- Loss of protons.
Correct answer: Loss of electrons.
In a redox (reduction-oxidation) reaction, oxidation is defined as the loss of electrons by a chemical species. This process results in an increase in the oxidation state of the atom or ion undergoing oxidation. A common mnemonic is OIL RIG: Oxidation Is Loss (of electrons).
Question 2: What is reduction in a redox reaction?
- Loss of electrons.
- Gain of electrons. (Correct answer)
- Loss of protons.
- Gain of protons.
Correct answer: Gain of electrons.
Reduction in a redox reaction is defined as the gain of electrons by a chemical species. This process leads to a decrease in the oxidation state of the atom or ion undergoing reduction. The mnemonic OIL RIG helps remember this: Reduction Is Gain (of electrons).
Question 3: What does the electrode potential indicate?
- The likelihood of a substance to donate protons.
- The tendency of a substance to gain or lose electrons. (Correct answer)
- The amount of heat released in a reaction.
- The temperature at which a reaction occurs.
Correct answer: The tendency of a substance to gain or lose electrons.
The electrode potential indicates the tendency of a substance to either gain electrons (be reduced) or lose electrons (be oxidized). A higher positive reduction potential signifies a greater tendency for reduction, while a more negative reduction potential indicates a greater tendency for oxidation. This value is crucial for predicting the spontaneity of redox reactions.
Question 4: What is the role of a salt bridge in an electrochemical cell?
- To facilitate the movement of electrons.
- To allow ion exchange and maintain electrical neutrality. (Correct answer)
- To act as a power source.
- To store energy.
Correct answer: To allow ion exchange and maintain electrical neutrality.
In an electrochemical cell, a salt bridge connects the two half-cells, allowing for the migration of ions between them. Its crucial role is to maintain electrical neutrality in each half-cell by balancing the charge buildup that occurs as electrons flow. This ion exchange completes the electrical circuit, enabling continuous electron flow.
Question 5: What is the standard electrode potential for the hydrogen ion (H⁺) half-cell?
- 0.00 V. (Correct answer)
- 1.00 V.
- 0.50 V.
- -1.00 V.
Correct answer: 0.00 V.
The standard electrode potential for the hydrogen ion (H⁺) half-cell, also known as the Standard Hydrogen Electrode (SHE), is conventionally assigned a value of 0.00 V. This serves as the reference point against which the electrode potentials of all other half-cells are measured and compared. It allows for the determination of relative tendencies for reduction or oxidation.
Question 6: What is a galvanic cell?
- A cell that requires an external power source.
- A cell that generates electricity from spontaneous reactions. (Correct answer)
- A cell that uses energy to drive a non-spontaneous reaction.
- A cell that stores chemical energy.
Correct answer: A cell that generates electricity from spontaneous reactions.
A galvanic cell, also known as a voltaic cell, is an electrochemical cell that generates electrical energy from a spontaneous redox reaction. The chemical energy released during the spontaneous reaction is converted into electrical energy as electrons flow from the anode (where oxidation occurs) to the cathode (where reduction occurs) through an external circuit.
Question 7: What is the Nernst equation used for?
- To calculate the number of electrons involved in the reaction.
- To calculate the cell potential under non-standard conditions. (Correct answer)
- To calculate the activation energy of the reaction.
- To determine the concentration of ions in a solution.
Correct answer: To calculate the cell potential under non-standard conditions.
The Nernst equation is used to calculate the cell potential (E_cell) of an electrochemical cell under non-standard conditions. It accounts for variations in reactant and product concentrations, as well as temperature, from the standard conditions (1 M concentrations, 1 atm pressure, 25°C). This equation allows for a more accurate prediction of cell voltage in real-world scenarios.
Question 8: What is the purpose of electrolysis?
- To generate electricity from spontaneous reactions.
- To use electricity to induce a chemical reaction. (Correct answer)
- To create electrical energy.
- To separate ions from a solution.
Correct answer: To use electricity to induce a chemical reaction.
Electrolysis is a process that uses electrical energy to drive a non-spontaneous chemical reaction. Unlike galvanic cells, which produce electricity, electrolytic cells consume electricity to force a redox reaction to occur in the desired direction. This technique is used for various applications, such as plating metals or producing elements like chlorine and sodium.
Question 9: What is the relationship between the cell potential and the spontaneity of a reaction?
- A positive cell potential indicates a non-spontaneous reaction.
- A negative cell potential indicates a spontaneous reaction.
- A positive cell potential indicates a spontaneous reaction. (Correct answer)
- Cell potential does not affect spontaneity.
Correct answer: A positive cell potential indicates a spontaneous reaction.
A positive cell potential (E_cell > 0) indicates that a redox reaction is spontaneous under the given conditions. This means the reaction will proceed on its own to generate electrical energy. Conversely, a negative cell potential signifies a non-spontaneous reaction, requiring an external energy input (like in electrolysis) to occur.
APCE Electrochemistry 1
What is the definition of oxidation in a redox reaction?