Lecture 1.106- Silver- Silver Chloride Electrode

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,–                   ag-agcl

                         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)

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