This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Electrochemical Cells”.
1. An electrochemical cell can only convert electrical energy to chemical energy.
Explanation: An electrochemical cell can convert electrical energy to chemical energy and can also convert electrical energy to chemical energy. There are two types of electrochemical cells- Galvanic cell and Electrolytic cell.
2. An electrochemical cell generally consists of a cathode and an anode. Which of the following statements is correct with respect to the cathode?
a) Oxidation occurs at the cathode
b) Electrons move into the cathode
c) Usually denoted by a negative sign
d) Is usually made up of insulating material
Explanation: Cathodes are usually metal electrodes. It is the electrode where reduction takes place. The cathode is the positive electrode in a galvanic cell and a negative electrode in an electrolytic cell. Electrons move into the cathode.
3. When equilibrium is reached inside the two half-cells of the electrochemical cells, what is the net voltage across the electrodes?
a) > 1
b) < 1
c) = 0
d) Not defined
Explanation: A half-cell is half of an electrochemical cell (electrolytic or galvanic), where either oxidation or reduction occurs. At equilibrium, there is no transfer of electrons across the half cells. Therefore, the potential difference between them is nil.
4. Which of the following is not a generally used electrolyte in the salt bridges used to connect the two half-cells of an electrochemical cell?
Explanation: A salt bridge is a device used to connect the oxidation and reduction half-cells of a galvanic cell (a type of electrochemical cell). Strong electrolytes are generally used to make the salt bridges in electrochemical cells. Since ZnSO4 is not a strong electrolyte, it is not used to make salt bridges.
5. When no current is drawn through an electrochemical cell, the sum of the electrode potentials of the two electrodes is called cell emf. True or False?
Explanation: Emf of a cell is equal to the maximum potential difference across its electrodes, which occurs when no current is drawn through the cell. It can also be defined as the net voltage between the oxidation and reduction half-reactions.
6. Which of the following statements is correct regarding Electrochemical cells?
a) Cell potential is an extensive property
b) Cell potential is an intensive property
c) The Gibbs free energy of an electrochemical cell is an intensive property
d) Gibbs free energy is undefined for an electrochemical cell
Explanation: Cell potential is an intensive property as it is independent of the amount of material present. Gibbs free energy is defined for an electrochemical cell and is an extensive property as it depends on the quantity of the material.
7. Which of the following factors does not affect the electrode potential of an electrode?
a) Nature of the electrode (metal)
b) Temperature of the solution
c) Molarity of the solution
d) Size of the electrode
Explanation: Electrode potential is the tendency of an electrode to accept or to lose electrons. Electrode potential depends on the nature of the electrode, temperature of the solution and the concentration of metal ions in the solution. It doesn’t depend on the size of the electrode.
8. Why are the saturated solutions of electrolytes for the salt bridge prepared in agar-agar jelly or gelatin?
a) The jelly acts as an electrolyte
b) It helps the electrolytes to mix with the contents of the half cells
c) It helps maintain the electrical polarity between the two half-cell solutions
d) It keeps the electrolyte in semi-solid phase and prevents it from mixing with the two half-cell solutions
Explanation: The salt bridge connects the two half-cell solutions to complete the circuit of the electrochemical cell. The electrolytes of the salt bridge are generally prepared in agar-agar or gelatin so that the electrolytes are kept in a semi-solid phase and do not mix with the half-cell solutions and interfere with the electrochemical reaction.
9. Which of the following is not a characteristic feature of a salt bridge?
a) Salt bridge joins the two halves of an electrochemical cell
b) It completes the inner circuit
c) It is filled with a salt solution (or gel)
d) It does not maintain electrical neutrality of the electrolytic solutions of the half-cells
Explanation: A salt bridge is a junction that connects the anodic and cathodic compartments in a cell or electrolytic solution. It maintains electrical neutrality within the internal circuit, preventing the cell from rapidly running its reaction to equilibrium.
10. Which of the following is not a type of electrochemical cell?
a) Voltaic cell
b) Photovoltaic cell
c) Electrolytic cell
d) Fuel Cell
Explanation: A Voltaic or Galvanic cell is a type of electrochemical cell that converts chemical energy into electrical energy. Photovoltaic cells are used to convert light energy into electrical energy. An Electrolytic cell is a type of electrochemical cell that converts electrical energy into chemical energy. A fuel cell is an electrochemical cell that converts the chemical energy of a fuel and an oxidizing agent into electricity.
11. What is the direction of flow of electrons in an electrolytic cell?
a) Anode to cathode externally
b) Anode to cathode internally
c) Cathode to anode externally
d) Cathode to anode in the solution
Explanation: An electrolytic cell is a type of electrochemical cell. An electrolytic cell converts electrical energy into chemical energy. Electrons flow from anode to cathode through the external supply in an electrolytic cell. In the solution, only ions flow and not the electrons.
12. Which of the following is a not a secondary cell?
a) Nickel-cadmium cell
b) Lead storage cell
c) Mercury cell
d) Leclanche cell
Explanation: A secondary battery (a series of cells) is one which can be charged, discharged into a load, and recharged many times. Nickel-cadmium cell, Lead storage cell and Mercury cell are examples of secondary cells. Leclanche cell is an example of a primary cell.
13. Which of the following statements regarding primary cells is false?
a) Primary cells cannot be recharged
b) They have low internal resistance
c) They have an irreversible chemical reaction
d) Their initial cost is cheap
Explanation: Primary cells cannot be used again and again. Since there is no fluid inside, these cells are also known as dry cells. The internal resistance is high and the chemical reaction is irreversible. Their initial cost is cheap.
14. What is the observation when the opposing external applied potential to an electrochemical cell is greater than the cell’s potential?
a) The electrochemical cell behaves like an electrolytic cell
b) The electrochemical cell stops functioning
c) Only oxidation reactions occur in the cell
d) Only reduction reactions occur in the cell
Explanation: In an electrochemical cell, when an opposing externally potential is applied and increased slowly, the reaction continues to take place. When the external potential is equal to the potential of the cell, the reaction stops. Once the externally applied potential is greater than the potential of the cell, the reaction goes in the opposite direction and the cell behaves like an electrolytic cell.
15. Which of the following conditions are satisfied when the cell reaction in the electrochemical cell is spontaneous?
a) ΔG° > 0
b) E°cell < 0
c) E°cell = 0
d) ΔG° < 0
Explanation: For all spontaneous chemical reactions, the change in Gibbs free energy (ΔG°) is always negative. For a spontaneous reaction in an electrolytic cell, the cell potential (E°cell) should be positive.
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