Liquid junction potential between dilute electrolytes and saturated potassium chloride

Abstract

A novel method is presented of calculating the liquid junction potential between saturated potassium chloride and dilute electrolytes (10^–2 M and less), in which no assumption has to be made about the ion distribution at the liquid junction. Calculations have been made for a number of electrolytes at 25°C, those for potassium hydrogen phthalate and for equimolar mixtures of sodium acetate and acetic acid having been confirmed by experiment. For all these electrolytes, the liquid junction potential obeyed the same linear relationship with the logarithm of the specific conductance, and this may be universally true. This gives rise to a method of correcting the measured pH of dilute solutions for error due to liquid junction potential. A standard dilute solution of known pH is necessary, and 10^–3M potassium hydrogen phthalate is proposed, the provisional pH being 4.334 at 25°C. An alternative method using the customary 0.05 M phthalate standard is also given.