Effects of hydrochloric acid and salts on the absorption of light by beta-naphthoquinonesulfonic acid

Abstract

In order to evaluate t he effects of hydrochloric acid and neutral salts on the absorption of light by an organic acid dye, spectrophotometric measurements were made of a series of solutions of hydrochloric acid and of neutral salts plus hydrochloric acid, each containing 3 X 10-4 M I'l-naphthoquinonesulfonic acid.The dye in these solutions showed small differences in spectral absorption. Similar differences may contribute to the changes of absorption shown by true indicators . Most of the data were compatible with the assumption that new absorption bands were not produced or that there was no considerable shift in the position of the original bands with respect to wave number.The increase in the absorption by the dye in the presence of salts was proportional to the square root of the m olar activity of the electrolyte. The proportionality factor was different for each salt and varied from 0.144 to 0.353.The results suggest that the specific effects of ions on the absorption indices of positive, neutral, and negative forms of an indicator must be taken into account, as well as the normal effects of the ions on the dissociation of the indicator, for accurate pI-I measurements.

Basic ionization constant of metacresolsulfonphthalein; pH values and salt effects

“…The discussion below seems to eliminate the possibility that repression of the ionization of the sulfonate group accounts for these phenomena. As metacresolsulfonphthalein at pH 7.2 to 9 also shows such shifts of the absorption bands in concentrated salt solutions, we can conclude that the specific salt effect of the concentrated hydrochloric acid is due to the alteration of the spectral properties of the indicator chiefly by the change in the surrounding electrical field of the solutions [8]. The transmittancy values were read at even wavelength intervals from the graph sbeet and then cor rected to their true wavelengths.…”

“…Hence, as expressed linearly in eq 2, if a mixture of these two forms alone determines the observed absorp&If polar states (electronic tatitomers orelectromers) ofeacb ion, indicated by [+) and [-) signs in figUre 1, are present in instantaneous equilibrium witb tbe nonpolar forms. tbe absorption bands .may still be' used at any given temperature to calculate tbe over-all values of a and (1-a) for tbe red and yellow ions, including tbeir natural polar states or tbose "induced" by other ions [1,4,7,8 tion curve in their overlapping regions of spectral absorption, the isosbestic point must r emain unchanged with respect to both index and wave number for all stages of the color transformation. This may not be true when specific salt effects, association, or colored impurities affect this part of the spectrum, as shown in.…”

“…The acid in concentrations from 0.5 to above 2 M begins noticeably to cause two compensating effects. The first is the completion of the normal reaction of hydrogen ions with the yellow form, which should slightly increase the index at wave number 18,960 (527.5 m,u), and the second is the "abnormal" or specific, effect [1,8,21,22] of the increased electrolyte and surrounding electrical field in decreasing the absorptive properties and index of the indicator, together with the shift of the absorption bands for the red and yellow forms toward the lower wave numbers. The net result is that the acid in concentrations above 2 M causes little additional change in the position and height of the main absorption band, except g, slight shift, untiJ a concentration of over 4 M is reached.…”

pH values of acid-salt mixtures of some aromatic sulfonic acids at various temperatures and a criterion of completeness of dissociation

“…It may be concluded that the same group in indicators of similar structure will likewise be completely dissociated in dilute solutions, a conclusion previously arrived at by Wingfield and Acree [1]. An extension of this conclusion to more complex compounds must be made with caution, however, since sulfonic acids of large molecular weight have a tendency to exhibit colloidal characteristics.…”

“…The emf of this cell at a pressure of 1 atmosphere of hydrogen is given by E=Eo-RJ In(l4Iacl)=Eo-RJ In (jHfClmHmd, (1) in which E is the measured emf in international volts; EO is the potential of the silver-silver-chloride electrode in international volts for unit activity of hydrochloric acid; a, m, andf represent, respectively, the activity, molality, and activity coefficient of the ionic species denoted by subscripts; and R, T, and F have their usual significance. In table 1 values of the observed emf corrected to unit hydrogen pressure in the usual manner r131 are given for the temperatures of 10°, 25°, 40°, and 60° C and for the various solutions of concentrations recorded in columns 2 and 3.…”