The Adsorption Behavior of Phenolphthalein at a Mercury Electrode in Water-Ethanol Solutions

Abstract

A complete characterization of the adsorption of phenolphthalein at the hanging mercury drop electrode in aqueous buffer solutions containing 10% (v/v) ethanol was obtained employing cyclic voltammetry and double potential step chronocoulometry. At pH 3.4, a sharp symmetric cyclic voltammetric wave due to an irreversible weak adsorption of the monoanionic form is obtained at a concentration of 5.1 mmol Á dm À3 . Under these conditions, phenolphthalein adsorbs in a compact layer in which the triphenylmethan moiety is arranged perpendicular to the electrode surface. Upon increasing the concentration, the symmetry of the wave decreases; it can now be attributed to a mixed diffusion-adsorption process. In acidic solutions (pH<3.4) the observed electroactivity is ascribed to the adsorption of the neutral lactone form. In solutions of pH 10.58, no adsorption was detected.

Iridium-catalyzed reductive γ-lactonization of ortho-acylbenzoic acids in water: sustainable access to phthalides

“…Phenolphthalein is a commonly used acid–base indicator, which turns colorless in acidic solutions (pH < 8.3) and pink in basic solutions (8.3 < pH < 10.0). 29 As an analog of phenolphthalein, 2k was also capable of playing the same role. 100 mL of NaOH solution (0.1 mol L −1 ) containing 0.25 mg of 2k was titrated with HCl solution (0.1 mol L −1 ).…”