measuring a standard electrode potential

• to measure a standard electrode potential, the half-cell is connected to a standard hydrogen electrode

  • the two electrodes are connected by a wire to allow controlled flow of electrons
  • the two solution are connected by a salt bridge which allows ions to flow
• the salt bridge typically contains a concentrated solution of an electrolyte that does not react with either solution e.g. strip of filter paper soaked in aqueous potassium nitrate KNO3 (aq)
• std electrode potentials have been measured for many solutions and these are listed in data reference tables
• equilibrium is always shown so that forward reaction is the reduction
• the more negative the std electrode potential:

  • the greater the tendency to lose an electron and undergo oxidation
  • the less the tendency to gain an electron and undergo reduction
• the more positive the std electrode potential:

  • the greater the tendency to gain electrons and undergo reduction
  • the less the tendency to lose electrons and undergo oxidation
• metals tend to have negative std electrode potential values and lose electrons
• non-metals tend to have positive std electrode potential values and gain electrons
• in general:

  • the more negative the std electrode potential value, the greater the reactivity of a metal in losing electrons
  • the more positive the std electrode potential value, the greater the reactivity of a non-metal in gaining electrons
• cells can easily be assembled using any half cells - the e.m.f measured is then the cell potential Ecell