拡散電位

WordNet

existing in possibility; "a potential problem"; "possible uses of nuclear power" (同)possible
the inherent capacity for coming into being (同)potentiality, potency
(physics) the process in which there is movement of a substance from an area of high concentration of that substance to an area of lower concentration
the spread of social institutions (and myths and skills) from one society to another

PrepTutorEJDIC

可能性のある,潜在的な / 可能性,潜在力 / 電位
放散,発散,拡散[作用] / 普及,流布 / (文体などの)散漫,冗漫

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/03/27 18:52:50」(JST)

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Liquid junction potential occurs when two solutions of different concentrations are in contact with each other. The more concentrated solution will have a tendency to diffuse into the comparatively less concentrated one. The rate of diffusion of each ion will be roughly proportional to its speed in an electric field. If the anion diffuses more rapidly than the cation, it will diffuse ahead into the dilute solution, leaving the latter negatively charged and the concentrated solution positively charged. So an electrical double layer of positive and negative charges will be produced at the junction of the two solutions. So at the point of junction, a potential difference will develop because of the ionic transfer. This potential is called liquid junction potential or diffusion potential. The magnitude of the potential depends on the relative speeds of the ions.

Calculation

The liquid junction potential can not be measured directly but calculated. The Electromotive force (EMF) of a concentration cell with transference includes the liquid junction potential.

E_{without transference} = RT/F . ln(a₂/a₁)

where a₁ and a₂ are activities of HCl in the two solutions, R is the Universal Gas Constant, T is the temperature and F is Faraday's Constant.

E_{with transference} = t_M RT/F . ln (a₂/a₁)

where a₂ and a₁ are activities of HCl solutions of right and left hand electrodes respectively and t_M be transport number of Cl^–

Liquid Junction potential = E_{with transference}– E_{without transference} = (t_M – 1) RT/F . ln (a₂/a₁)

Elimination of liquid junction potential

The liquid junction potential interferes with the exact measurement of EMF of a chemical cell. So it should be eliminated or at least its effect should be minimized. The general practice to eliminate the liquid junction potential is to place a salt bridge consisting of usually 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 of anion and cation are the same.

References

Advanced Physical Chemistry by Gurtu & Snehi
Principles of Physical Chemistry by Puri, Sharma, Pathania

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