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Metal-Metal- Insoluble salts electrode:

These consist of a metal (M) which is covered by a layer of sparingly soluble salt (MX), immersed in solution containing common ions (X-). And it is represented as anode or anion electrode.

M I MX (sat’d) I X-  for example  Ag I AgCl (sat’d) I Cl-  II  Cathode

We Know that AgX (F, Cl, Br,I) Silver salt’s are insoluble in water.

Other examples:

(1) Hg(s) I Hg2SO4(sat’d) I SO4-2 II    (Cathode)  used in the standard Weston Cell.

(2) Hg(s) I Hg2Cl2(sat’d) I Cl- (KCl paste) II    (Cathode) used as Calomel electrode

(3) Pb(s) I PbSO4(sat’d) I SO4-2 II    (Cathode)  used in lead batteries

(4) Cu(s) I CuCl2(sat’d) I Cl- (KCl paste) II    (Cathode)

(1) Silver electrode as Anode or anionic electrode:

Ag I AgCl (sat’d) I Cl-  II  Cathode

The electrode reaction can be considered as taking place in two steps as.

This electrode reaction involve only the concentration of chloride ion, the electrode is said to be reversible with respect to chloride ions (Cl-).

The above reaction show how an electron can be released or taken up in such electrode.

Nernst equation for this electrode (Anode) is written as:

Silver electrode as cathode or cationic electrode:

   Anode   II Cl- aq I AgCl(sat’d)IAg(s)

Nernst equation for this electrode (Cathode) is written as:

(2) Calomel electrode:

A calomel cell consist of a platinum electrode dipping into mercury in contact with calomel (dimercury (I) chloride,Hg2Cl2 and potassium chloride solution.

As Anode:

Hg(s) I Hg2Cl2(sat’d) I Cl- (KCl paste) II    (Cathode) :

As Cathode:

  Anode          II Cl- (KCl paste)I Hg2Cl2(sat’d) I Hg(s)    

Related Questions:

(1) The conductivity of 0.0011028 mol per liter acetic acid is 4.95 × 10–5 S per cm. Calculate its dissociation constant if ^°m for acetic acid is 390.5 S cm2 per mol–1 .

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