Electrodes of the second kind-respond to changes in ion activity through formation of complex Example:Silver works as halide indicator electrode if coated with silver halide Silver wire in KCl (sat'd)forms AgCl layer on surface AgCl(s)+e>Ag(s)+CI-E=+0.222 V Eind=+0.222-0.0592 n log aci- =+0.222+0.0592pCl Electrodes of the third kind-respond to changes of different ion than metal electrode CEM 333 page 11.6
• Electrodes of the second kind - respond to changes in ion activity through formation of complex Example: Silver works as halide indicator electrode if coated with silver halide Silver wire in KCl (sat'd) forms AgCl layer on surface AgCl(s) + e - « Ag(s) + Cl- E 0 = +0.222 V Eind = +0.222 - 0.0592 n log a Cl - = +0.222 + 0.0592pCl • Electrodes of the third kind - respond to changes of different ion than metal electrode CEM 333 page 11.6
Membrane (or Ion Selective)Electrodes: Membrane: Low solubility -solids,semi-solids and polymers Some electrical conductivity -often by doping Selectivity-part of membrane binds/reacts with analyte Two general types-crystalline and non-crystalline membranes Non-crystalline membranes: Glass-silicate glasses for H+,Na+ Liquid-liquid ion exchanger for Ca2+ Immobilized liquid-liquid/PVC matrix for Ca2+and NO3 Crystalline membranes: Single crystal-LaF3 for F- Polycrystalline or mixed crystal-AgS for S2-and Ag+ CEM333 page 11.7
Membrane (or Ion Selective) Electrodes: Membrane: • Low solubility - solids, semi-solids and polymers • Some electrical conductivity - often by doping • Selectivity - part of membrane binds/reacts with analyte Two general types - crystalline and non-crystalline membranes • Non-crystalline membranes: Glass - silicate glasses for H+, Na+ Liquid - liquid ion exchanger for Ca2+ Immobilized liquid - liquid/PVC matrix for Ca2+ and NO3 - • Crystalline membranes: Single crystal - LaF3 for FPolycrystalline or mixed crystal - AgS for S2- and Ag+ CEM 333 page 11.7