Electrode potentials

• What are the two main components of an electrochemical cell?

  Two half-cells
• Why do the two half-cells need to be connected with a salt bridge?

  To complete the circuit and allow charge conduction

  
• What does a simple half-cell consist of?

  A metal and a solution of a compound containing that metal
• What happens when the two half-cells are connected into a circuit?

  They produce a small voltage
• What is the function of the salt bridge in an electrochemical cell?

  To connect the circuit and conduct charge

  
• What is a common material used to make a salt bridge?

  Filter paper soaked in potassium nitrate solution
• Why is potassium chloride not suitable for copper systems?

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

  Because it would set up its own electrode system
• What occurs at the zinc half-cell in the electrochemical cell?

  It oxidizes to Zn²⁺ and releases electrons
• What is the potential difference created between the two electrodes called?

  Voltage
• Why does a high resistance voltmeter need to be used?

  To stop current from flowing and measure maximum potential difference
• What happens to the voltage when current is allowed to flow?

  The voltage falls to zero as reactants are used up
• Which electrode undergoes reduction in an electrochemical cell?

  The most positive electrode
• Which electrode undergoes oxidation in an electrochemical cell?

  The most negative electrode
• What is the structure of a cell diagram for an electrochemical cell?

  • Oxidized form next to the double line
  • Solid vertical line represents phase boundaries
  • Double line represents the salt bridge
  • Voltage produced is indicated
  • More positive half-cell is written on the right (if possible)

  
• What must be used if a system does not include a metal that can act as an electrode?

  A platinum electrode
• Why is a platinum electrode used in electrochemical cells?

  Because it is unreactive and can conduct electricity
• What are the conditions required for a standard hydrogen electrode?

  1. Hydrogen gas at 100 kPa
  2. Solution with hydrogen ion at 1.0 mol dm^-3
  3. Temperature at 298 K
  4. Platinum electrode
• What is a secondary standard in electrochemistry?

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

  • All ion solutions at 1 mol dm^-3
  • Temperature at 298 K
  • Gases at 100 kPa pressure
  • No current flowing
• How is the standard electrode potential measured?

  By connecting it to another half-cell of known potential
• What happens to the more positive half-cell in a redox reaction?

  It will reduce and go forward
• What happens to the more negative half-cell in a redox reaction?

  It will oxidize and go backward
• How do you determine the overall reaction from two half-reactions?

  1. Add the two half-reactions together
  2. Cancel out the electrons
  3. Write the full equation
• What does the series of standard electrode potentials indicate about reducing and oxidizing agents?

  The most powerful reducing agents are found at the most negative end, and the most powerful oxidizing agents at the most positive end
• Why does fluorine react with water?

  Because it has a high standard electrode potential
• What happens to hydrogen peroxide when it is reduced?

  It forms water
• Why does fluorine react with water?

  Fluorine has a higher standard electrode potential than water, allowing it to oxidize water.
• Write the equation for the reaction that occurs when fluorine reacts with water.

  2F2(g) + 2H2O(l) → 4F–(aq) + O2(g) + 4H+(aq)
• Why should chlorine undergo a redox reaction with water?

  Chlorine has a higher standard electrode potential than water, allowing it to oxidize water.
• Write the equation for the reaction that occurs when chlorine reacts with water.

  2Cl2(g) + 2H2O(l) → 4Cl–(aq) + O2(g) + 4H+(aq)
• What happens to hydrogen peroxide when it is reduced in terms of oxidation states?

  Hydrogen peroxide is reduced from an oxidation state of -1 to 0 in O2 and -2 in H2O.
• Write the equation for the reduction of hydrogen peroxide.

  H2O2(aq) + 2H+(aq) + 2e– → 2H2O(l)
• How do you determine which half-equation will reduce and which will oxidize?

  The half-equation with the more positive Eo will reduce, while the more negative Eo will oxidize.
• What is the conventional cell diagram for the reaction involving fluorine and water?

  Pt|H2O|O2 || F2|F–|Pt
• What happens to Ecell as the reaction proceeds and reactant concentrations drop?


  Ecell will fall to zero as the reaction proceeds and the reactant concentrations drop.
• How does changing the concentration of reactants affect Ecell?

  Increasing the concentration of reactants increases Ecell, while decreasing them causes Ecell to decrease.
• What happens to Ecell when the concentration of Fe2+ is increased and Zn2+ is decreased?


  Ecell will increase.
• How does temperature affect Ecell in exothermic reactions?

  Applying a temperature rise to exothermic reactions results in a decrease in Ecell.
• What are the types of electrochemical cells?

  Non-rechargeable, rechargeable, and fuel cells.