Heterogeneous equilibria at the glass electrode-solution interface

bria a t the glass-solution in terface we re investigated in co nnection with t he pH r esp o nse of glasses. The preferentia l leaching of a lka li an d oth er cations fr o m the glass surface by ac id aq ueous solu t ion s, leav ing a s ilica-rich layer to act as a nonmigratable negatively charged ion, caused a n un e\'en d istr ibu t ion of t he migratable ions of t h e system in accordance with t he d ictates of t he Donnan membra ne equilibria an d the "equation of p rodu cts." The un even d istribution of Ag (KH 3)1i, and Brio ns for various experimental con dition s wa s readi ly foll owed potentiomet r icall y for Corn in g 015, a series of Ka20-CaO-Si02, a nd a series of Na20-Si02 glasses. T he Don nan membrane theory is compat ible with the vario us experimentall y observed phen omena su ch as t he s we llin g of the glass s"face, repr ession of swelli ng by h igh con ce ntrations of elcctr olytes, vo ltage departure~ in a lkalin e an d hydrofluoric-aci d solutions, vo ltage departures in the "superacid" region, and asymmetr.v p otentials. H owever, t h e Don nan membr a ne con sideration s do not accou nt for t h e p refere nt ia l voltage response of t he glass electr ode t o hydr ogen ions wi th t he complete or parLial exclusion of other ions.