Topic 14

• What are the two components of an electrochemical cell?

  Two half-cells
• Why must the two half-cells be connected with a salt bridge?

  To complete the circuit and allow ion flow

  
• What does a simple half-cell consist of?

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

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

  To connect the circuit and conduct charge
• What material is commonly used to make 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 created between the electrodes called?

  Voltage
• What is the symbol for the potential difference in a cell?

  E
• What is the measured voltage for the cell described?

  E = +1.1V
• Why does a high resistance voltmeter need to be used?

  To measure maximum potential difference without current
• What happens when current is allowed to flow in the circuit?

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

  Reduction takes place
• What is the half-equation for copper reduction?

  Cu²⁺ + 2e^- → Cu(s)
• What occurs at the most negative electrode?

  Oxidation takes place
• What is the half-equation for zinc oxidation?

  Zn(s) → Zn²⁺ + 2e^-
• What is the structure of a cell diagram for electrochemical cells?

  • Represents half-cells and their components
  • Solid vertical line: boundary between phases
  • Double line: salt bridge
  • Voltage produced indicated
  • More positive half-cell on the right (if possible)

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

  A platinum electrode must be used
• How is a platinum electrode represented in a cell diagram?

  By including it in the diagram
• What is the purpose of the platinum electrode?

  To provide a conducting surface for electron transfer
• What is the equilibrium for the hydrogen electrode?

  H₂(g) ⇌ 2H⁺(aq) + 2e^-
• What is the potential of the standard hydrogen electrode?

  0 volts
• What are the conditions for a standard hydrogen electrode?

  • Hydrogen gas at 100 kPa
  • Solution of H⁺ at 1.00 mol dm^-3
  • Temperature at 298K
• What is a secondary standard in electrochemistry?

  A standard calibrated against the SHE
• What are common secondary standards?

  Silver/silver chloride and calomel electrodes
• What are the standard conditions for measuring electrode potentials?

  • All ion solutions at 1.00 mol dm^-3
  • Temperature at 298K
  • Gases at 100 kPa pressure
  • No current flowing
• What is the standard electrode potential?

  The potential difference measured under standard conditions
• How is the standard electrode potential quoted?

  In data books and as half equations
• What is the equation to calculate Ecell?

  Ecell = E_red - E_ox
• How do you calculate Ecell for Mg and Cu half-cells?

  Ecell = 0.34 - (-2.37)
• What does a positive Ecell indicate?

  A spontaneous change will occur
• What does the more negative half-cell do in a redox reaction?

  It will oxidize
• What does the more positive half-cell do in a redox reaction?

  It will reduce
• What is the overall reaction for Zn and Fe half-cells?

  Zn + Fe²⁺ → Fe + Zn²⁺
• How do standard electrode potentials indicate reducing and oxidizing agents?

  • More positive: stronger oxidizing agents
  • More negative: stronger reducing agents
• What is the half-equation for lithium reduction?

  Li⁺ + e^- → Li
• What is the half-equation for silver reduction?

  Ag⁺ + e^- → Ag
• What is the half-equation for fluorine reduction?

  F₂ + 2e^- → 2F^-