1.11 - Electrode Potentials

• What are the two components of an electrochemical cell?

  Two half-cells
• What connects the two half-cells in an electrochemical cell?

  A salt bridge

  
• What does a simple half-cell consist of?

  A metal and its compound solution
• What happens when two half-cells are connected in a circuit?

  They produce a small voltage
• What is the function of the salt bridge?

  To connect the circuit and conduct charge
• What material is typically used for a salt bridge?

  Filter paper soaked in salt solution
• Why is potassium chloride unsuitable for copper systems?

  Chloride ions can form complexes with copper
• Why is a wire not used to connect half-cells?

  It would create its own electrode system
• What occurs at the zinc half-cell in the electrochemical cell?

  Zinc oxidizes to Zn²⁺ and releases electrons
• What is the potential difference symbol in an electrochemical cell?

  E

  
• What does a high resistance voltmeter measure?

  The maximum potential difference (E)
• What happens when current flows in the circuit?

  The reactions occur at each electrode
• What is the reaction at the most positive electrode?

  Reduction occurs
• What is the reaction at the most negative electrode?

  Oxidation occurs
• How is an electrochemical cell represented in a cell diagram?

  • Zn(s) | Zn²⁺ (aq) || Cu²⁺ (aq) | Cu(s)
  • Solid vertical line: boundary between phases
  • Double line: salt bridge
  • Voltage produced indicated

  
• What must be used if a system does not include a metal electrode?

  A platinum electrode must be used
• Why is platinum used as an electrode?

  It is unreactive and conducts electricity
• What are the components of a standard hydrogen electrode?

  • Hydrogen gas at 100 kPa
  • 1.0 mol dm^-3 H⁺ solution
  • Temperature at 298 K
  • Platinum electrode
• What is the potential of the standard hydrogen electrode?

  0 volts
• What is a secondary standard in electrochemistry?

  A standard calibrated against the SHE
• What are the standard conditions for measuring electrode potentials?

  1 mol dm^-3 solutions, 298 K, 100 kPa
• How is the standard electrode potential measured?

  By connecting to the hydrogen electrode
• How do you calculate the EMF of a cell?

  E_cell = E_red - E_ox
• What is the E_cell for the cell Mg(s) | Mg²⁺ (aq) || Cu²⁺ (aq) | Cu(s)?

  +2.71 V
• What does a positive E_cell indicate?

  A spontaneous redox reaction occurs
• What happens to the more negative half-cell in a redox reaction?

  It oxidizes and goes backwards
• What happens to the more positive half-cell in a redox reaction?

  It reduces and goes forwards
• What is the overall reaction for Mg + Cu²⁺?

  Mg + Cu²⁺ → Cu + Mg²⁺
• How do you determine the strongest oxidizing agent from standard potentials?

  Look for the most positive E_o
• How do you determine the strongest reducing agent from standard potentials?

  Look for the most negative E_o
• What is the significance of the standard electrode potentials table?

  • Indicates tendency to reduce or oxidize
  • Helps predict spontaneous reactions
  • Guides in identifying strong oxidizing/reducing agents
• What is the reaction for fluorine with water?

  F₂ + H₂O → 2HF
• Why does chlorine undergo a redox reaction with water?

  It has a positive E_o value
• What happens to hydrogen peroxide when it is reduced?

  It forms water
• What is the half-equation for the reduction of hydrogen peroxide?

  H₂O₂ + 2H⁺ + 2e^- → 2H₂O
• What is the half-equation for the oxidation of hydrogen peroxide?

  O₂ + 2H⁺ + 2e^- → H₂O₂
• What is the relationship between E_cell and spontaneity of a reaction?

  • Positive E_cell: spontaneous reaction
  • Negative E_cell: non-spontaneous reaction
• What is the formula to calculate Ecell from standard electrode potentials?

  Ecell = Ered – Eox
• What is the standard electrode potential for the reaction of O2 and H2O?

  Eo +1.23V
• Why does fluorine react with water?

  Fluorine has a higher standard electrode potential