This is another highly used Secondary reference Electrode, It consists of a silver wire covered with AgCl, dipped in Potassium Chloride solution of known concentration standard with AgCl. The porous plug at the bottom provides electrical contact. Partial deposition of AgCl on a Ag wire is electrolytic, anodic ally carried out, in a solution of chloride ions.The electrode is represented as:
Ag, AgCl (s) | KCl (x M) saturated with AgCl
It is a reversible electrode and if oxidation occurs at the Electrode, then
Ag(s) < ————– > Ag+ (aq) + e–
If reduction occurs at the electrode, the reaction is :
Ag+ (aq) + Cl– < ———– > AgCl (aq)
AgCl (aq) + e– < ————- > Ag + Cl–
So the overall reaction is, Ag(s) + Cl– (aq) < ———– > AgCl (aq) + e . The working mechanism are same as we have seen till now in other reference and other kind of electrode. The Nerst equation,–
E electrode = E0Ag/AgCl – K * log [Cl–]
Where K = 2.303 RT/nF from the nerst equation.
The electrode potential at 298K of Saturated KCl, normal (1N KCl), and deci-normal KCl (.01N KCl) electrodes are 0.290 V , 0.224 V and 0.199 V respectively. Here from the equilibrium, we can conclude the values. The Applications of Ag-AgCl electrode-
- As a secondary reference electrode in place of Calomel electrode/glass electrode/ion selective electrodes.
- In determining whether the potential distribution is uniform or not is ship hulls and old pipelines protected by cathodic protection (sacrificial anode method or impressed current method).
- As a portable reference electrode for measuring for different depths of oil rigs ad platforms, submerged oil pipeline etc. Usually such probe is powered by Ni-Cd portable battery and can operate up to a depth of 300-400 m precision of +/- 1m V.
Next, there are certain electrodes which have a special property of giving potential to only a certain ions in the solution and not to others called and ion-selective Electrode(1.107).
Abhishek kumar jha
(Chemistry at Utkarshini)