Heterogeneous equilibria at the glass electrode-solution interface

Abstract

H eterogeneous eq uili 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 Br-io 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-CaOSi02, 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\Il"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.

Atypical pH response of some nonsilicate glasses

“…Each of the presen t glasses was attacked vigorously at all pH values, and non e of them exhibi ted s'wellin g in acid buffers, as was so ch aracteristic of many of the silicate glasses [2 , 4]. This iDdicates th ere was no prefer en tial leaching at an y pH of certain constituen ts of th e glass, h ence no leaving b ehind of a chemically durable, negatively charged framework [5], which in t urn suggests t h at no satisfactory elect.rical eq uilibrium, eith er real, pseudo , or transient, could be set up s ui tably for indicating hydrogen-ion activi ty ot aqueous solutions. Furth er, the hygroscopicity of th ese glasses (water sorbed in 1 hour), was considerably less than for most pH responsive silicate glasses [4,6).3 Thus the second require- 3 The lower limit of hygroscopicity for a satisfactory pH responsive glass has not yet been established .…”

Effect of temperature on the electrical resistance and voltage departures (errors) of glass electrodes, and upon the hygroscopicity of glass

“…These r esults show that t he voltage departures in t he biah alkaline and s up eracid ranges are not attributable to excessively hig h electrical r esistances, nor are they associa ted with m arked c hanges in electrical resistance. Their causes have been discussed elsewb er e in connection with the water activity of the solu tions [1], chemi cal durability of the glass [2], heterogen eous equilibria at the glass electrode solution interface [15], and equilibra tive response to ion other th a,n bydrogen [1,16]. Although the hygroscopicity curves for the three glasses reported must be classified as being of uncertain reliability, they do warrant a brief evaluation.…”