Liquid junction potential
Liquid junction potential (shortly LJP) occurs when two solutions of
Calculation
The liquid junction potential cannot be measured directly but calculated. The electromotive force (EMF) of a concentration cell with transference includes the liquid junction potential.
The EMF of a concentration cell without transport is:
where and are activities of HCl in the two solutions, is the
The EMF of a concentration cell with transport (including the ion transport number) is:
where and are activities of HCl solutions of right and left hand electrodes, respectively, and is the transport number of Cl−.
Liquid junction potential is the difference between the two EMFs of the two concentration cells, with and without ionic transport:
Elimination
The liquid junction potential interferes with the exact measurement of the electromotive force of a chemical cell, so its effect should be minimized as much as possible for accurate measurement. The most common method of eliminating the liquid junction potential is to place a salt bridge consisting of a saturated solution of potassium chloride (KCl) and ammonium nitrate (NH4NO3) with lithium acetate (CH3COOLi) between the two solutions constituting the junction. When such a bridge is used, the ions in the bridge are present in large excess at the junction and they carry almost the whole of the current across the boundary. The efficiency of KCl/NH4NO3 is connected with the fact that in these salts, the transport numbers[clarification needed] of anions and cations are the same.
See also
References
- Advanced Physical Chemistry by Gurtu & Snehi
- Principles of Physical Chemistry by Puri, Sharma, Pathania