Electrode potentials

Cards (56)

  • Electrode or reduction potentials
    Half equations are always written as reduction processes, with the particle on the left gaining electrons to form the particle on the right
  • Oxidation states
    Half equations always have two different oxidation states
  • Standard electrode potential (E standard)
    A measure of the ability of a species to accept electrons, also known as reduction potential
  • More positive standard electrode potential

    Greater ability to gain electrons
  • Relative ability to gain electrons
    • Chlorine (Cl2) most able
    • Copper (Cu2+) middle
    • Vanadium (V2+) least able
  • How the half equation is balanced does not affect the standard electrode potential
  • Balancing half equations

    The important thing is to get the electrons to cancel, not to change the standard electrode potential
  • Standard electrode potentials give a measure of the ability of a species to gain electrons
  • Combining two half equations/cells
    The more positive standard electrode potential will proceed in the forward direction, forcing the less positive one to go in reverse
  • Cell voltage (E cell)
    Calculated by taking the more positive standard electrode potential and subtracting the less positive one
  • Determining if chlorine can oxidise Fe2+ to Fe3+
    1. Compare standard electrode potentials
    2. Cl2 is more positive, so it can oxidise Fe2+ to Fe3+
    3. Calculate cell voltage as 0.59V
  • Determining if iodine can oxidise Fe2+ to Fe3+
    1. Compare standard electrode potentials
    2. Fe3+/Fe2+ is more positive, so it can oxidise I- to I2
    3. Iodine is not a powerful enough oxidising agent
  • Copper 2+ copper half cell
    Copper metal electrode dipping into 1 M aqueous Cu2+ solution
  • V2+ V half cell
    Vanadium metal electrode dipping into 1 M aqueous V2+ solution
  • Electrochemical cell formation
    1. Connect the two half cells with a platinum wire and a salt bridge
    2. The more positive standard electrode potential half-reaction will occur in the forward direction, forcing the less positive half-reaction to occur in the reverse direction
  • More positive standard electrode potential

    Substance can gain electrons more readily
  • Reaction in the electrochemical cell
    1. Cu2+ ions are reduced to Cu metal at the cathode
    2. V metal is oxidized to V2+ ions at the anode
  • Anode
    • The electrode with the less positive (more negative) standard electrode potential
    • Oxidation reaction occurs here
  • Cathode
    • The electrode with the more positive standard electrode potential
    • Reduction reaction occurs here
  • Electrons flow from the anode to the cathode through the external circuit
  • Salt bridge
    Allows the flow of ions to maintain charge balance between the two half-cells
  • Standard hydrogen electrode
    Half-cell with a standard electrode potential of 0 V, used as a reference to measure the standard electrode potentials of other half-cells
  • Measuring standard electrode potentials
    1. Connect the unknown half-cell to the standard hydrogen electrode
    2. The voltage measured is the standard electrode potential of the unknown half-cell
  • Electrochemical cell

    Formed when two half cells are combined
  • Example electrochemical cell
    • Copper 2+ copper half cell + Vanadium 2+ Vanadium half cell
  • Electrochemical cell setup
    1. Copper 2+ copper half cell on left
    2. Vanadium 2+ Vanadium half cell on right
    3. External circuit with voltmeter
    4. Salt bridge connecting solutions
  • Salt bridge
    Allows flow of ions to balance charge imbalance between half cells
  • Standard electrode potential
    Measure of how readily a substance can gain electrons
  • Copper 2+ standard electrode potential
    More positive than Vanadium 2+ standard electrode potential
  • Electrochemical cell reaction
    1. Copper 2+ ions accept electrons from Vanadium
    2. Vanadium 2+ ions formed
    3. Copper deposited on electrode
    4. Vanadium electrode disintegrates
  • Cell voltage (E_cell)
    Calculated as most positive standard electrode potential minus least positive standard electrode potential
  • Summary
    • Electrochemical cells made from two half cells
    • Standard electrode potential indicates which species accepts/donates electrons
    • Positive electrode has most positive standard electrode potential
    • Electrons flow from negative to positive electrode
    • E_cell = most positive - least positive standard electrode potential
  • Standard electrode potential
    The voltage of a half cell when connected to a standard hydrogen electrode
  • Standard conditions for standard electrode potential
    • 298 Kelvin temperature
    • 100 kilopascals pressure
    • Solutions at 1 mole per decimeter cubed
  • Standard hydrogen electrode
    An electrode used as a reference to measure the standard electrode potential of other half-cells
  • Standard hydrogen electrode
    1. Hydrogen gas at 100 kilopascals pressure
    2. Platinum electrode
    3. H+ ions at 1 mole per decimeter cubed
    4. Assigned 0 volts potential
  • Positive standard electrode potential

    Indicates the half-cell has a greater tendency to accept electrons than the standard hydrogen electrode
  • Negative standard electrode potential
    Indicates the half-cell has a lesser tendency to accept electrons than the standard hydrogen electrode
  • Salt bridge
    Allows flow of ions between half-cells to address charge imbalance
  • Types of half-cells
    • Metal-metal ion
    • Ion-ion
    • Gas-ion