Electrode potential

• Characteristics of cells

  • 2 half-cells
  • have to be connected with a salt bridge
  • will produce of a small voltage if connected into a cicuit
• what doe simple half cells consist of?

  the metal that acts as the electrode and a solution of a compound containing the metal
• why do voltage form?

  the half-cell has higher oxidising power will oxidise to release electrons. More electrons will build up on one electron than the other. The potential difference created between the two electrodes, on is positive terminal, the other negative
• why use a high resistance voltmeter?

  voltmeter needs to be of very high resistance to stop the current from flowing in the circuit. Possible to measure the maximum possible potential difference.

  • The reaction will not occur because high resistance voltmeter stops current from flowing
• why is salt bridge used to connect up the circuit ?

  The free moving ions can conduct the charge
• What is salt bridge made of and what is required from it?

  • made from filter paper soaked in salt solution, KNO3
  • unreactive with electrodes and electrode solutions
• why are wires not used for the salt bridge?

  Metal wire would set up its own electrode system with the solutions
• What happens if current flow?

  Reaction will occur separately at each electrode, voltage will fall to zero as the reactants are used up
• How to let current flow?

  -remove high resistance voltmeter

  -replaced bulb

  -short circuited
• The most positive electrode will always undergo reduction
• The most negative electrode will always undergo reduction
• If a system does not include a metal as an electrode then a platinum electrode must be used.
• Why are platinum electrodes used?

  -provides conducting surface for electron transfer

  -unreactive and can conduct electricity
• Standard hydrogen electrode = 0 volts
• Potential of all electrodes are measured by comparing their potential to that of the standard hydrogen electrode
• Platinum electrode in SHE

  -equilibrium does not include a conducting metal surface

  -platinum wire is used which is coated in finely divided platinum
• Why is platinum black used?

  porous and can absorb hydrogen gas