redox equilibria

• when a metal is put into a solution with its ions it forms an electric potential. such as, a copper rod being placed in a aqueous solution of copper ions forms a copper half-cell
• during electrode potentials the metal can either gain electrons to become a salt or it can lose electrons to become copper ions. however copper is a unreactive metal so it tends to gain electrons (reduced).
• more reactive metal rends to lose electrons so is oxidised.
• voltages of metals can be measured by comparing with the standard hydrogen electrode
• the standard hydrogen electrode consists of:

  • hydrogen gas at 1 atm pressure
  • H+ ions of concentration 1 mol/dm3
  • platinum electrode covered with platinum black
• platinum black is finely divided platinum. it acts as a catalyst to allow equilibrium, a large surface area for close contact, and it is inert so it does not take part in the reaction.
• standard electrode potential is the potential of an electrode of any metal that is compared against standard hydrogen electrode under standard conditions
• salt bridge is a inverted U-tube that contains a solution of ions. it allows the flow of negative and positive ions to connect the circuit together
• standard electrode potential can be measured using:

  • metals or non-metals in contact with their ions
  • ions of the same element at different oxidation states
• standard cell potential = voltage of ion - voltage of hydrogen (0)
• a more positive voltage value indicates that it is easier to be reduced
• in metal ion/metal half-cell

  • half cell is connected to a standard hydrogen electrode
  • salt bridge is used