Determinação de parâmetros físico-químicos com um sensor potenciométrico sensível ao íon p-aminobenzoato

Abstract

The paper describes the construction and determination of physical chemical parameters with a second kind electrode, Pt|Hg|Hg2(PABA)| Grafite, sensitive to p-aminobenzoate ion (PAB). Electrode construction is easy, presents a fast response time (30 sec), low-cost, excellent response stability and (lifetime > 12 months, under continuous use). Using of the mercury(I) p-aminobenzoate electrode, the molar single activity coefficient associated with PAB (yPAB) was estimated at 250C and ionic strengths between 0.700-3.000 mol L-1 (NaClO4). The standard molal potential of the electrode at 25°C is 445.5 ± 0.5 mV. The thermodynamic solubility-product constant of mercurous p-aminobenzoate determined with the mentionated electrode, in aqueous solution, at 25°C was TKps = 2.50 x 10-12 mol3 L-3 . An important feature of the electrode is that it permits the determination of the concentration of free p-aminobenzoate ions in complex systems of metallic ions.