Abstract
The heat of adsorption of hydrohalogenic acids (HCl, HBr and HI) on polyamide was measured by the flow method at 30°, 40° and 50°C. From the heat of adsorption at saturated adsorption and -Δμ°I (obtained from adsorption isotherm), the entropy change of adsorption (ΔS°C•I) was calculated. The value of at same temperature was HCl<HBr<HI and ΔS°C•I was HCl>HBr>HI, and as the temperature increases increases and ΔS°C•I decreases.
From the measurement of NMR absorption spectra of water proton in D2O+H2O solution of these acids, a parameter (Δδ) which corresponded with the state of hydration of these acids in aqueous solution was obtained. The positive value of, Δδ shows the destructiveness of water structure and the negative one shows the formativeness. The Δδ of these acids shows a negative value and this value is equal to the sum of ΔδH+ (water structure formation) and ΔδX- (Water structure destruction). The value of ΔδX- was Cl-<Br-<I-, that is, I- is more destructive than Cl- for the water structure. Plots of ΔS°C•I against Δδ show a straight line.
From these results, it is assumed that the difference of entropy change of adsorption of these acids correspond with the difference of the water structure destructiveness of acid anions, i.e., the difference of correspond with the difference of the endothermic process of acid anions. It is also assumed that the increase in with increasing temperature is closely related to the decrease in the structure of water.
