9.3 Chemical Cells (Voltaic/Galvanic Cells)

Short Answer Questions

1. What is a chemical cell?
   Answer
   A chemical cell is an electrochemical device that converts chemical energy into electrical energy using spontaneous redox reactions.
2. What are the alternative names for a chemical cell?
   Answer
   Chemical cells are also known as voltaic or galvanic cells.
3. What is the role of oxidation and reduction in a chemical cell?
   Answer
   Oxidation occurs at the anode, releasing electrons, while reduction occurs at the cathode, where electrons are gained.
4. What are the two main components of a chemical cell?
   Answer
   A chemical cell consists of two half-cells, each containing a metal electrode immersed in an electrolyte solution.
5. What is the function of a salt bridge in a chemical cell?
   Answer
   A salt bridge maintains electrical neutrality by allowing ion migration between the two half-cells, preventing charge buildup.
6. Which electrode is the anode in a chemical cell?
   Answer
   The anode is the electrode where oxidation occurs and is the negative terminal in a chemical cell.
7. Which electrode is the cathode in a chemical cell?
   Answer
   The cathode is the electrode where reduction occurs and is the positive terminal in a chemical cell.
8. What is the direction of electron flow in a chemical cell?
   Answer
   Electrons flow from the anode (oxidation site) to the cathode (reduction site) through the external circuit.
9. What is electromotive force (EMF) in a chemical cell?
   Answer
   EMF, or voltage, is the potential difference between two half-cells, driving electron flow in a chemical cell.
10. How is the standard cell potential (E°cell) calculated?
    Answer
    E°cell = E°cathode – E°anode
11. What does a positive E°cell value indicate?
    Answer
    A positive E°cell value indicates that the redox reaction is spontaneous, allowing the cell to generate electricity.
12. What does cell notation represent?
    Answer
    Cell notation is a shorthand representation of a chemical cell, showing the anode and cathode reactions and the salt bridge.
13. How is the anode represented in cell notation?
    Answer
    The anode is written on the left side in cell notation, with a single vertical line (|) separating the metal and its ion.
14. What does the double vertical line (||) in cell notation represent?
    Answer
    The double vertical line (||) represents the salt bridge or porous barrier in the chemical cell.
15. What is the function of the electrochemical series?
    Answer
    The electrochemical series ranks half-reactions by their standard electrode potentials, predicting redox reactions and electrode behavior.
16. Which metal acts as the anode in a zinc-copper cell?
    Answer
    Zinc (Zn) acts as the anode because it has a more negative electrode potential (-0.76V).
17. What is the overall reaction in a zinc-copper cell?
    Answer
    Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)
18. How does an electrolytic cell differ from a chemical cell?
    Answer
    An electrolytic cell uses electricity to drive a non-spontaneous reaction, while a chemical cell generates electricity from a spontaneous reaction.
19. List one industrial application of chemical cells.
    Answer
    Batteries, such as those used in cars and electronic devices.
20. What is the function of a voltmeter in a chemical cell?
    Answer
    A voltmeter measures the electrical potential (voltage) generated by the chemical cell.

Explanation Questions

1. Why does oxidation always occur at the anode in a chemical cell?
   Answer
   Oxidation involves the loss of electrons, which must be released into the external circuit. The anode, being the source of electrons, undergoes oxidation.
2. Explain why a salt bridge is necessary in a chemical cell.
   Answer
   The salt bridge prevents charge buildup by allowing the migration of ions, maintaining electrical neutrality and allowing the reaction to continue.
3. Why is the cathode considered the positive terminal in a chemical cell?
   Answer
   Electrons flow to the cathode, where reduction occurs. Since it gains electrons, it becomes relatively positive.
4. How does the choice of electrodes affect the voltage of a chemical cell?
   Answer
   The greater the difference in electrode potentials between the anode and cathode, the higher the voltage of the cell.
5. Why is the Daniell cell a good example of a chemical cell?
   Answer
   It clearly demonstrates the oxidation of zinc and reduction of copper, with a spontaneous redox reaction generating electricity.
6. What happens if the electrolyte concentration changes in a chemical cell?
   Answer
   Changing electrolyte concentration affects ion availability, shifting equilibrium and altering the cell’s voltage.
7. Why do different metals have different standard electrode potentials?
   Answer
   Metals have varying tendencies to lose or gain electrons based on their atomic structure and reactivity.
8. How does a fuel cell differ from a traditional chemical cell?
   Answer
   A fuel cell continuously converts chemical energy from fuel into electricity, whereas a chemical cell operates until reactants are depleted.
9. Why is an external voltage required in an electrolytic cell but not in a chemical cell?
   Answer
   Electrolytic cells drive non-spontaneous reactions, requiring external energy, whereas chemical cells generate spontaneous reactions that produce electricity.
10. How is the voltage of a chemical cell related to its spontaneity?
    Answer
    A positive voltage indicates a spontaneous reaction, while a negative voltage means the reaction is non-spontaneous.