The application of hydrogen-palladium electrode for potentiometric acid-base determinations in tetrahydrofuran

Abstract

The application of the hydrogen-palladium electrode (H2/Pd) as an indicator electrode for the determination of the relative acidity scale (Es, mV) of tetrahydrofuran (THF) and potentiometric titrations of acids in this solvent were investigated. The relative acidity scale of THF was determined from the difference between the half-neutralization potentials of perchloric acid and tetrabutylammonium hydroxide (TBAH), which were measured using both H2/Pd-SCE and glass-SCE electrode pairs. The experimentally obtained value of the Es scale of THF with the H2/Pd-SCE electrode pair was 1155 mV, while that obtained with the glass-SCE electrode pair was 880 mV. By using an H2/Pd indicator electrode, the individual acids (benzoic acid, palmitic acid, maleic acid, acetyl acetone and α-naphthol) and two component acid mixtures (benzoic acid + α-naphthol, palmitic acid + α-naphthol, maleic acid + α-naphthol and maleic acid + phthalic acid) were titrated with a standard solution of TBAH. In addition, sodium methylate and potassium hydroxide proved to be very suitable titrating agents for the titrations of the individual acids and the acids in mixtures, respectively. The relative error of the determination of acids in the mixtures was less than 3 %. The results are in agreement with those obtained using a conventional glass electrode. The advantages of the H2/Pd electrode over a glass electrode in the potentiometric acid-base determinations in THF lie in the following: this electrode gives a wider relative acidity scale for THF, larger potential jumps at the titration end-point and relatively fast response times. Furthermore, it is very durable, simple to prepare and can be used in the titrations of small volumes. © 2013 (CC) SCS.