Vibrational spectral studies of solutions at elevated temperatures and pressures. VI. Raman studies of perchloric acid

Abstract

. J. Chem. 62, 1134Chem. 62, (1984.Raman spectra of perchloric acid in water have been measured for solutions spanning a wide concentration range and, for two specific concentrations, a wide range of temperatures. The acid is completely dissociated down to a water:acid mole ratio of about 1.8 at room temperature. At elevated temperatures it is still a very "strong" acid. As the concentration increases the apparent symmetry of the C10,-ion decreases and a small amount of a new species assigned as associated C10,-(H,,)' can be detected. The effects on the OH stretching bands of water, of temperature, C10,-, and the excess acid protons are discussed.C. I. RATCLIFFE et D. E. IRISH. Can. J. Chem. 62, 1134 (1984.On a mesurC les spectres Raman de l'acide perchlorique en solution aqueuse pour un large intervalle de concentrations et Cgalement, pour deux concentrations spkcifiques, pour un large intervalle de tempkratures. A la tempCrature ambiante, I'acide est completement dissociC jusqu'i un rapport molaire eau : acid d'environ 1,8. A des temperatures plus ClevCes, I'acide demeure un acide trks "fort". Lorsque la concentration augmente, la symttrie apparente de I'ion CIO,-diminue et on peut dtceler la presence d'une faible quantitC d'une nouvelle espkce identifite comme Ctant I'ion associC C 1 0 , -(H,,)'. On discute des effets de la tempirature, du C10,-et des protons acides en excks sur les bandes d'klongation OH de I'eau.[Traduit par le journal] Introduction As the temperature of water rises K, increases (1, 2) and hydrolysis reactions are encountered more frequently in salt-water mixtures (3, 4). Such reactions can be controlled or prevented, of course, by controlling the acidity. At ambient temperatures perchloric acid is often used to control pH because the perchlorate ion does not complex with most cations and the acid is strong. (A recent determination suggests that there is no association above a water:acid mole ratio, N = nH20/n,,,d, of 1.8 ( 3 . ) Thus competing equilibria can frequently be neglected. When studying the properties of salts in water at elevated temperatures, it is important to know if these useful properties of perchloric acid are retained. Also, for the measurement of relative integrated Raman band intensities, an internal intensity standard is generally employed and at moderate temperatures the v , line of the perchlorate ion is most frequently the preference for the reasons cited above. Thus, for our longer term goals, knowledge of the temperature dependence of the Raman spectra of aqueous solutions of perchloric acid is essential. It was also of interest to see if the much reduced dielectric constant of water at higher temperatures might promote formation of HC104. (Nitric and sulfuric acids show markedly enhanced association as the temperature increases.)Swaddle et al. (6) have studied the kinetics of decomposition of 1.1-6.6 m aqueous perchloric acid in the range 295-332°C. (At 250°C very little, if any, decomposition occurs at these concentrations.) The reaction is autocatalytic and t...

Vibrational spectral studies of solutions at elevated temperatures and pressures. VII. Raman spectra and dissociation of nitric acid

“…Raman spectra between 3 and 250°C were obtained using the same furnace and spectrometer described in earlier papers in this series (2,4,5). Since the pressures used in this apparatus to maintain the liquid state at high temperatures are insufficient to keep the density constant it is most convenient to describe the solutions in terms of molality tn (mol kg-' H,O) or stoichiometric mole ratio N (=H20:HN07) which are density independent.…”

“…As part of a larger program of research in this area we have studied the effects of increasing temperature on the Raman spectra of several acids in water, at pressures sufficient to maintain the liquid state. Perchloric acid remains a "strong" acid at high temperatures (2). However, for solutions of nitric and sulphuric acid, large increases occur in the populations of the ionogens (i.e.…”

SERS study of hydrogen peroxide electroreduction on a Pb‐modified Au electrode

“…Peak 5 at 927 cm 1 is well understood to be the symmetric stretch mode of the perchlorate ion s ClO 4 . 37 The intensity of this peak increases as the potential moves positively and decreases as the potential scans back. This behavior has been observed previously and is attributed to the enhanced adsorption of perchloric ion on the Au surface at high potentials.…”

Raman spectral studies of solutions at elevated temperatures and pressures.13. Sodium formate – water

“…A structure breaker is an ion that decreases the intermolecular coupling between water molecules. Common structure breakers include BF; (17), I- (17), and C10, (18).…”