The Silver/Silver Chloride Electrode

 

A diagram of a silver/silver chloride electrode is shown in figure 10.

 

The silver/silver chloride electrode is the most common and popular electrode used in electrochemistry. The electrode consists of a silver wire coated with silver chloride and immersed in a solution of potassium chloride saturated with silver chloride. Thus,

 

                             Ag | AgCl(saturated), KCl (xM)

 

 

Figure 10. The Silver/Silver Chloride Electrode.

 

And the half reaction is,       AgCl + eР   Ag + ClÐ

 

The actual "redox" action occurring at the electrode is

 

      

 

And the potential developed will be a function of the (Ag⁺) concentration. Now as the (Ag⁺) concentration depends on the solubility product equilibrium of AgCl then the electrode potential will also depend on the chloride ion concentration. The standard potential of the Ag/AgCl electrode at 25oC is 0.2223 V. The silver/silver chloride electrode is easily constructed, can be used over a relatively wide range of temperatures and can be used in non-aqueous solutions.

 

The commercial electrode shown in figure 11 is a long-life electrode suitable for permanent installation. The electrode element is produced by the electrolytic precipitation of silver chloride onto the silver metal.

 

 

Figure 11. Diagram of a Silver/Silver Chloride Electrode Manufactured by Castle Electrodes

 

The electrode is then embedded in a "mortar" containing a known concentration of chloride ions and an anti-drying agent. The whole is contained in a white Nylon tube with Nylon inserts. The silver/silver chloride is one of the more commonly used reference electrodes in the measurement of pH.