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Titolo:
DETERMINING ACID EQUILIBRIUM-CONSTANTS BY MEANS OF CHROMATIC PARAMETERS
Autore:
ESCOLAR D; HARO MR; SAUCEDO A; AYUSO J; JIMENEZ A; ALVAREZ JA;
Indirizzi:
UNIV CADIZ,DEPT QUIM FIS,APDO 40 PUERTO REAL 11510 CADIZ SPAIN
Titolo Testata:
Applied spectroscopy
fascicolo: 10, volume: 50, anno: 1996,
pagine: 1290 - 1294
SICI:
0003-7028(1996)50:10<1290:DAEBMO>2.0.ZU;2-S
Fonte:
ISI
Lingua:
ENG
Soggetto:
SEAWATER; INDICATORS; PH;
Keywords:
PK(A) BY CHROMATIC COORDINATES METHOD; BROMOPHENOL BLUE; CHROMATIC PARAMETERS OF THE CIE L-ASTERISK, A-ASTERISK, B-ASTERISK SYSTEM; THERMODYNAMIC VALUES;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Science Citation Index Expanded
Citazioni:
24
Recensione:
Indirizzi per estratti:
Citazione:
D. Escolar et al., "DETERMINING ACID EQUILIBRIUM-CONSTANTS BY MEANS OF CHROMATIC PARAMETERS", Applied spectroscopy, 50(10), 1996, pp. 1290-1294

Abstract

A method has been developed for the determination of acid-base equilibrium constants, which is applicable to compounds that absorb in the visible, The tristimulus (X, Y, Z) and the colorimetric coordinate values (L, a*, b*) of the chromatic space CIELAB 1976 are calculated by means of the transmittances of the entire spectral range. The curves, in the a,b plane, of chromatic differences vs. pH intersect at a pH value agreeing with the pK(a); this configuration occurs because a chromatic equilibrium of both species takes place at this point, which corresponds to the chemical equilibrium, With this method, the acidity constants are found easily and quickly, and they yield very good results, The validity of the method has been tested with the acid-base indicator bromophenol blue, obtaining pK(a) = 3.943 at 25 degrees C; this result is compared with those obtained through the usual spectrophotometric methods. Also, thermodynamic magnitudes obtained from pK, values at different temperatures from 20 to 70 degrees C have been determined, resulting in Delta H-o = -(13.93 +/- 0.88) kJ mol(-1), Delta S-o = -(122.6 +/- 2.8) J K-1 mol(-1).

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Documento generato il 28/01/21 alle ore 08:05:08