Primary and Secondary Cells in Galvanic Cells
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Questions and Answers

What is the primary characteristic that distinguishes primary cells from secondary cells?

  • The ability to be recharged (correct)
  • The presence of complex ions
  • The shape of the electrodes
  • The type of electrolyte used

    • What is the purpose of the electrolyte in a galvanic cell?

  • To convert chemical energy to electrical energy
  • To separate the electrodes
  • To facilitate the flow of electrons
  • To provide a pathway for ions to move between electrodes (correct)

    • What type of galvanic cell is the Leclanche cell?

  • Wet cell
  • Secondary cell
  • Fuel cell
  • Dry cell (correct)

    • What occurs at the anode (zinc) electrode in the Daniell cell?

    <p>It loses mass</p> Signup and view all the answers

    What is the common feature of all galvanic cells?

    <p>They contain two electrodes in contact with an electrolyte</p> Signup and view all the answers

    What is the purpose of the copper sulphate solution in the Daniell cell?

    <p>To react with the zinc strip</p> Signup and view all the answers

    What is the primary function of the reaction between Zn2+ and NH3 in a Leclanche cell?

    <p>To prevent the buildup of ammonia gas around the cathode</p> Signup and view all the answers

    What is the overall cell reaction in a Leclanche cell?

    <p>Zn(s) + 2NH4+(aq) + 2MnO2(s) → Zn2+(aq) + Mn2O3(s) + H2O(l) + 2NH3(aq)</p> Signup and view all the answers

    In the voltaic cell described in Exercise 4.4, which half-cell reaction involves the reduction of silver ion?

    <p>Silver rod half-cell</p> Signup and view all the answers

    What is the purpose of the salt bridge in the voltaic cell described in Exercise 4.4?

    <p>To connect the two half-cells</p> Signup and view all the answers

    What is the effect of cold weather on the voltage of a Leclanche cell?

    <p>It decreases the voltage</p> Signup and view all the answers

    What type of ion is formed by the reaction between Zn2+ and NH3 in a Leclanche cell?

    <p>Complex ion</p> Signup and view all the answers

    What is the role of manganese dioxide in a Leclanche dry cell?

    <p>It acts as a depolarizer</p> Signup and view all the answers

    What is the primary difference between a Daniell cell and a Leclanche cell?

    <p>The Leclanche cell uses a moist electrolyte paste while the Daniell cell uses solutions</p> Signup and view all the answers

    What is the purpose of the salt bridge in a Daniell cell?

    <p>To maintain electrical neutrality between the two solutions</p> Signup and view all the answers

    What is the half-cell reaction at the anode of a Daniell cell?

    <p>Zn(s) → Zn2+(aq) + 2e</p> Signup and view all the answers

    What is a significant advantage of dry cells over wet cells?

    <p>Dry cells are more portable than wet cells because they do not contain solutions</p> Signup and view all the answers

    What is the primary function of a salt bridge in a galvanic cell?

    <p>To maintain electrical neutrality between the two solutions</p> Signup and view all the answers

    Study Notes

    Redox Reactions and Electrochemistry

    • A zinc-carbon dry cell (Leclanche cell) produces electricity through spontaneous redox reactions:
      • Anode reaction: Zn(s) → Zn2+(aq) + 2e
      • Cathode reaction: 2NH4+(aq) + 2MnO2(s) + 2e → Mn2O3(s) + H2O(l) + 2NH3(aq)
      • Overall (cell) reaction: Zn(s) + 2NH4+(aq) + 2MnO2(s) → Zn2+(aq) + Mn2O3(s) + H2O(l) + 2NH3(aq)

    Preventing Ammonia Buildup

    • Ammonia gas buildup around the cathode can disrupt the current, but this is prevented by:
      • Reaction between Zn2+ and NH3 to form a complex ion, [Zn(NH3)2]2+
      • Crystallization of the complex ion as a chloride salt through reaction with chloride (spectator ion)

    Leclanche Cell Reaction

    • The overall reaction occurring in a Leclanche cell is:
      • Zn(s) + 2NH4Cl(aq) + 2MnO2(s) → Zn(NH3)2Cl2(s) + Mn2O3(s) + H2O(l)

    Characteristics of Leclanche Cells

    • Voltage: initially about 1.5 V, but decreases as current is drawn off and deteriorates rapidly in cold weather

    Voltaic Cells

    • A voltaic cell is constructed from two half-cells connected by a salt bridge
    • Example: cadmium rod in Cd(NO3)2 solution and silver rod in AgNO3 solution

    Classification of Galvanic Cells

    • Primary cells: non-rechargeable, examples include Daniell's cell and zinc-carbon (Leclanche) dry cells
    • Secondary cells: rechargeable, not discussed in this text
    • Fuel cells: to be discussed in grade 11

    Primary Cells

    • Characteristics:
      • Not rechargeable
      • Chemical energy is converted into electrical energy when in use
      • Examples: Daniell's cell and zinc-carbon (Leclanche) dry cells
    • Features:
      • Contain two electrodes in contact with an electrolyte
      • Electrolyte can be in the form of a solution (wet cells) or a paste (dry cells)

    Daniell Cell

    • A wet primary cell
    • Consists of:
      • Zinc strip in ZnSO4 solution
      • Copper strip in CuSO4 solution
    • Half-cell reactions:
      • Anode reaction: Zn(s) → Zn2+(aq) + 2e
      • Cathode reaction: Cu2+(aq) + 2e- → Cu(s)
    • Overall (cell) reaction: Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)

    Salt Bridge

    • Purpose: to maintain electrical neutrality between the two solutions in a Daniell cell
    • Allows the cell to produce electricity

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    Description

    Explore the classification and functions of primary and secondary cells in galvanic cells. Learn how these cells store electrical energy as chemical energy and convert it back when in use. Discover the differences between primary cells and secondary cells.

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