Page 53 - Pharmaceutical Analytical Chemistry II - Pharm D- 02-06-07102
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It responds directly to change in activity of metal ion
Examples:
- Silver electrode Ag+ + e− ↔ Ag (s) E0 = +0.79 V
Ag /AgNO3
Metal electrode solution to be measured
It responds to the activity of Ag+
Eind = E0 − 0.059 log 1
1 [Ag+]
Eind = 0.79 V + 0.059 log [Ag+]
3- Electrode of the second kind: (for anions)
- A metal wire coated with one of its salts precipitate.
- It responds to the activity of anion that form sparingly soluble
precipitate or stable complexes with metal ion
Example Ag/AgCl (Silver metal coated with AgCl paste)
It is used to measure [Cl−] (eg KCl solution)
AgCl(s) + e− ↔ Ag(s) + Cl− E0 = +0.222 V
Eind = E0 Ag/AgCl − 0.059 log [Cl−]
Membrane Electrodes
1. Sensitive to ionic species --- Ion-Selective Electrodes
2. Sensitive to molecular species
Example of Ion-Selective Electrodes
Glass membrane electrode
It is sensitive to changes in H+ concentration --- used to
measure pH
Theory of the glass membrane potential
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