Hi, Ag/AgCl reference electrode uses an electrolyte of KCl solution saturated with AgCl. The most often seen reaction in literature is AgCl= Ag++ Cl-.
But what are the actual reactions going on there between Ag/AgCl electrode, KCl solution and AgCl solution? what if we don't use AgCl? Why are we using KCl? Why not NaCl?
A variety of filling solutions are used. The most commonly used are saturated KCl or 3.0 M KCl. KCl has the ability to form a crusty layer of solid KCl where the solution is exposed to the air. NaCl (3M ) is preferred and used. LiCl is used in special instances.
Advantage
Saturated solutions of KCl or NaCl are used because the concentration is reproducible even if the temperature changes (if solid salt is present) and are immune to the effects of water evaporation.
Disadvantage
However, the solid salts harden into an impenetrable block which may lead to a high impedance electrode. A "nearly saturated" solution (3.5M KCl or 3M NaCl) can change concentration due to evaporation.
Dear Mr. Abrar, completing the answer of Dr. Najib, the Ag/AgCl is immersed in a high concentration of chloride ions to maintain the measured potential independent of the chloride ions concentration present in the sample. If you just use a wire of silver covered with silver chloride, the reference electrode also responds to chloride ions. Therefore, this affect the measurements of the indicator electrode. Generally, is used a concentration from 1 to 3 M, because these are about ten times higher than chloride ions concentration in the sample. But, other anions can also affect the potential of reference electrode. The subject is very interesting and complex. See the best review about new developments of reference electrodes: U. Guth, F. Gerlach, M. Decker, W. Oelßner, W. Vonau; Solid-state reference electrodes for potentiometric sensors. Journal of Solid State Electrochemistry. January 2009, Volume 13, Issue 1, pp 27-39. I think this paper can help you in your doubts. Kind regards.
I have problem obtaining inner filling solution for my electrolyte analyser.
The manufacturer only says the inner solution is nacl and kcl.
Can I use 3.5molar kcl or 3molar nacl or both?
The mobility difference of K+ and Cl- in KCl is the least among chlorides, which creates smaller liquid junction potential and a minor correction to the standard potential.Therefore, 3.5 M KCl is recommended.
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