Behaviour of the mercury, mercuric oxide electrode in alkaline solutions in the temperature range 298–363 K

Abstract

Electromotive-force measurements of mercury, mercuric oxide electrodes against the silver, silver chloride and the hydrogen electrodes in mixed KCl + NaOH solutions have been made in the range 298–363 K. After digesting the crystals of HgO, bias potentials between the electrodes never exceeded 0.2 mV; they were much smaller between electrodes having HgO of the same colour. The thermodynamics of the reaction HgO(c)+ H₂(g)= Hg(1)+ H₂O were established; the ΔS values obtained differ from those reported in thermodynamic tables. In the experimental temperature range, pK_w was also determined with good precision and this allowed the calculation of the standard potential of the mercury, mercuric oxide electrode having the electrode reaction 2e + HgO(c)+ H₂O(l)= Hg(l)+ 2OH^–(aq).