3.1.11 - Electrode potentials

Cards (29)

  • What is the purpose of the salt bridge in an electrochemical cell? allows ions to flow to complete the circuit
  • What is the salt bridge made up of in an electrochemical cell? filter paper soaked in KNO3 cell
  • EӨ values are always quoted for reductions
  • Soluble ionic compound used in a salt bridge must not react with electrolyte in beaker
  • Reactions are written in the electrochemical series as reductions
  • An oxidising agent will oxidise anything that is in the electrochemical series above
  • Reasons an expected reaction would not happen in a cell:
    1. Kinetically stable
    2. Solution too dilute
  • What are the three types of cells?
    • Rechargeable
    • Non-rechargeable
    • Fuel
  • Advantages of non-chargeable batteries:
    • Cheaper to buy
    • Work for longer
    • Can be recycled
    • Don't contain toxic Pb / Cd so less dangerous in landfill
  • What are the advantages of rechargeable batteries?
    • Can be reused so cheaper long term
    • Can be recycled
  • What are the advantages of fuel cells?
    • No recharging needed
    • H2O is only product
  • What are the disadvantages of fuel cells?
    • Expensive as H2 produced by electrolysis of water
    • H2 highly flammable
  • Features of the electrochemical series:
    • Oxidising agents on the left 
    • Reducing agents on the right
    • Most powerful oxidising agent on the bottom left
    • Most powerful reducing agent on top right
  • Salt bridges are necessary to:
    • Complete the circuit
    • Allows ion movement to balance the charge. Do not react with electrodes
  • What type of species goes is furthest from the salt bridge in standard cell notation?

    The most reduced species
  • What does | indicate?
    Phase boundary (solid/liquid/gas)
  • What happens at the left-hand electrode?
    • Left hand electrode is where oxidation occurs.
    • Left hand electrode is the half cell with the most negative Eo value
  • Right hand electrode:
    • right hand electrode is where reduction occurs.
    • Right hand electrode is the half cell with the most positive Eo value
  • Which side of the cell has the most negative Eo value?

    Left hand electrode
  • Label this standard hydrogen electrode
    A) High resistance voltmeter
    B) Platinum wire
    C) Hydrogen Gas
    D) Salt bridge
    E) Porous platinum metal
    F) Dilute Acid
  • What conditions is the standard hydrogen electrode used in?
    • Temperature = 298 K
    • Pressure = 100 kPa
    • [H+ ] = 1.00 mol dm-3
  • Why might you use other standard electrodes occasionally?
    • They are cheaper/easier/quicker to use and can provide just as good a reference.
    • Platinum is expensive
  • If an Eo value is more negative, what does it mean in terms of oxidising/reducing power? Better reducing agent (easier to oxidise)
  • What factors will change Eo values?
    • Concentration of ions
    • Temperature
  • When would you use a Platinum electrode? When both the oxidised and reduced forms of the metal are in aqueous solution
  • Why is Platinum chosen?
    • Inert so does not take part in the electrochemistry
    • Good conductor to complete circuit
  • Where are lithium-ion cells used? Mobile phones and Laptops
  • A fuel cell is a cell that is used to generate electric current; does not require electrical recharging
  • Label this diagram of a hydrogen fuel cell
    A) Anode
    B) Electrolyte
    C) Cathode
    D) h2
    E) o2
    F) h20