Solubility of Elemental Sulfur in Water at 298 K

Abstract

The solubility of elemental rhombic sulfur in water is 1.9(±0.6) × 10^?8 mole S₈·kg^?1. This value is in agreement with thermodynamic considerations on the solubility of sulfur and experimental data on sulfur hydrosols.     

Raman spectroscopy of likasite at 298 and 77 K

Raman spectroscopy at 298 and 77K has been used to study the structure of likasite, a naturally occurring basic copper(II) nitrate of formula Cu3NO3(OH)5.2H2O. An intense sharp band is observed at 3522 cm(-1) at 298 K which splits into two bands at 3522 and 3505 cm(-1) at 77 K and is assigned to the OH stretching mode. The two OH stretching bands at 3522 and 3505 provide estimates of the hydrogen bond distances of these units as 2.9315 and 2.9028 angstroms. The significance of this result is that equivalent OH units in the 298 K spectrum become two non-equivalent OH units at 77 K suggesting a structural change by cooling to liquid nitrogen temperature. A number of broad bands are observed in the 298 K spectrum at 3452, 3338, 3281 and 3040 cm(-1) assigned to H2O stretching vibrations with estimates of the hydrogen bond distances of 2.8231, 2.7639, 2.7358 and 2.6436 angstroms. Three sharp bands are observed at 77 K at 1052, 1050 and 1048 cm(-1) attributed to the nu1 symmetric stretching mode of the NO3 units. Only a single band at 1050 cm(-1) is observed at 298 K, suggesting the non-equivalence of the NO3 units at 77 K, confirming structural changes in likasite by cooling to 77 K.     

Organically-Modified Silica Xerogels for Adsorption of CH4 at 298 K

Organic tethers have been incorporated into acid- and base-catalysed silica sol–gels. The surface area is modified by this insertion suggesting an interaction at a molecular level. The HCl-catalysed SiO₂ sol–gel had its relative extent of adsorption at 298 K of CH₄ relative to H₂O:

1. depressed by the addition of 5% bis(triethoxysilyl)methane
2. increased by the addition of 5% bis(trimethoxysilyl)hexane

which attributed the tether hydrophilic-lipophilic balance (HLB). The reasons for this unexpected physical adsorption of CH₄ at a temperature far above its boiling point are now being explored, along with the potential of these materials for selective hydrocarbon sensors and separators.     

Raman spectroscopy of nacrite single crystals at 298 and 77 K

A Raman microscope in conjunction with a thermal stage has been used to determine the Raman spectra of single crystals of nacrite at 298 and 77 K. The spectra obtained are a function of the physics of the spectrometer and were orientation dependent. Bands are observed at 3710, 3646, 3630 and 3623 cm(-1). Upon obtaining the Raman spectra at liquid nitrogen temperature, the band at 3648 cm(-1) was not observed but an additional band at 3603 cm(-1) appeared. This latter band may be attributed to the hydroxyl stretching of non-hydrogen bonded interlayer hydroxyls in the nacrite. The bands attributed to both the inner and inner surface hydroxyls moved to lower frequencies upon cooling to liquid nitrogen temperatures. Low frequency bands also showed orientation dependence.     

Reaction of phenylperoxy radicals with NO(2) at 298 K

In the present work, phenylperoxy radicals were generated by stationary 254 nm photolysis of iodobenzene and nitrosobenzene in the presence of O(2) and NO(2) at 298 K and a total pressure of 1 bar (M = N(2)). Experiments were performed on time scales of seconds or minutes in a temperature controlled photoreactor made of quartz (v = 209 L). Major gas phase products identified and quantified in situ by long-path IR absorption include N(2)O(5), NO, HONO, HNO(3), CO, and o-nitrophenol. In addition, evidence is presented for the formation of an aerosol consisting of p-nitrophenol. The occurrence of N(2)O(5) as a major product in both reaction systems, the strong loss of NO(2) in the iodobenzene system and the comparison of measured product distributions with the results of numerical model calculations suggest that the reaction C(6)H(5)O(2) + NO(2) --> C(6)H(5)O + NO(3), k(5)occurs in both photolysis systems, a major part of the NO(3) being scavenged as N(2)O(5). The results of ab initio calculations imply that proceeds via a short-lived peroxynitrate intermediate. In the photolysis of nitrosobenzene-NO(2)-O(2)-N(2) mixtures, NO and NO(2) compete for C(6)H(5)O(2) radicals. Comparison of measured and modelled product distributions allows to set a lower limit of k(5) > 1 x 10(-12) cm(3) molecule(-1) s(-1) at 298 K. This lower limit is consistent with the assumption that k(5) is equal to the high pressure recombination rate constant of RO(2) + NO(2) --> RO(2)NO(2) reactions, i.e. with k(5) approximately 7 x 10(-12) cm(3) molecule(-1) s(-1) at 298 K, 1bar.     

在298K标准镉汞齐电极的标准电极势

固体金属镉电极和饱和镉汞齐电极的标准电极势,Harned等^[1]已有过综合性的评述.两年前我们^[2]从饱和硫酸镉标准电池在298K的电动势测定值出发,用热力学方法计算得饱和镉汞齐电极和固体金属镉电极的标准电极势值分别为-0.35215绝对伏和-0.40264绝对伏.     

在298K标准锌汞齐电极的标准电极电势

饱和锌汞齐电极的标准电极电势,一般是指含锌量10％的锌汞齐电极对活度为1的锌离子所产生的电极电势,ε_(Zn~2+)~0+Zn-Hg(Zn10％)=—0.7618±0.0008V。固体金属锌电极的标准电极电势是指金属锌电极对活度为1的锌离子所产生的电极电势ε_(Zn~2+)~0-Zn=0.7618V。     

Standard enthalpy of solution of ammonium nitrate in water at 298 K

We have made calorimetric measurements of the enthalpy of solution of NH₄NO₃(c, IV) in water at 298 K, where (c, IV) indicates the crystal form of amomonium nitrate that is stable from 256 to 305 K. Results of our measurements have been combined with enthalpy of dilution values from Parker to obtain the standard enthalpy of solution of NH₄NO₃ (c, IV) in water at 298.15 K to be ΔH^o = 25.41 kJ mol^?1.     

Thermodynamical characteristics of acid-base equilibria in glycyl-glycyl-glycine aqueous solutions at 298 K

The constants and enthalpies of acid dissociation of glycyl-glycyl-glycine peptide in aqueous solutions at 298.15 K and ionic strength values of 0.1, 0.5, and 1.0 M containing NaCl as a background electrolyte, were determined by potentiometry and calorimetry. The standard values of pK ₁^° and pK ₂^° constants, the change of Gibbs energy, enthalpy, and entropy for the dissociation processes were calculated. It was found that the acidic properties of the carboxylic group in aqueous solution subside upon the transition from α-amino acids to peptides due to the lower entropy effect of dissociation. It was concluded that the increase of dissociation constant of a protonated peptide amino group upon an increase in the length of its molecule is determined by entropy factor associated with the attenuation of amino group solvation.     

Oxygen phase equilibria near 298 K

Raman spectra of fluid and solid oxygen have been measured at temperatures near 298 K to pressure greater than 180 kbar (18 GPa). At 298 K, fluid oxygen freezes at 59.1±0.5 kbar which is 2 kbar higher than the freezing pressure of n-H₂ at this temperature. Solid—solid phase transitions are observed near 96 and 99 kbar. The phase boundaries near room temperature and the intense visible absorption spectra of the very high pressure phase are described.     

Thermodynamics of ionization of benzoic acid in water at 298°K

The standard heat of ionization of aqueous benzoic acid has been determined by solution calorimetry. The value obtained for H ^o of ionization, 0.11±0.04, is in good agreement with H ^o from other calorimetric values; 0.10±0.05 kcal-mole ^–1 is suggested to be the best value for this ionization at 298° K.     

The enthalpy of solution of ferrous chloride in water at 298 K

We have made calorimetric measurements of the enthalpy of dissolving solid ferrous chloride in water at 298 K and have derived ΔH° = −19.82 kcal mol⁻¹ for the standard enthalpy of this process. This ΔH° is related by way of some thermodynamic calculations to other properties of iron.     

Thermodynamic analysis of denatured lysozyme folded on moderately hydrophobic surface at 298 K

Both calorimetric determination of displacement adsorption enthalpies ΔH and measurement of adsorbed amounts of lysozyme (Lyz) denatured by 1.8 mol L⁻¹ guanidine hydrochloride (GuHCl) on a moderately hydrophobic packings at 298 K, pH 7.0 and various salt concentrations were carried out. Based on the thermodynamics of stoichiometric displacement theory (SDT) the fractions of thermodynamic functions, which related to four subprocesses of denatured protein refolding on the surface, were calculated and thermodynamic analysis that which one of the subprocesses plays major role for contribution to the thermodynamic fractions was made in detail. The moderately hydrophobic surface can provide denatured Lyz energy and make it gain more conformation with surface coverage or salt concentration increment. The displacement adsorptions of denatured Lyz onto PEG-600 surface are exothermic, more structure-ordered and enthalpy driven processes.     

Constants of acid-base equilibria of glycylglycine in water-dimethyl sulfoxide solutions at 298 K

Constants of acid-base equilibria of glycylglycine were obtained by potentiometry at a temperature of 298 K and an ionic strength of 0.1 M (NaClO₄) in water-dimethyl sulfoxide solutions. It was determined that upon an increase in the content of the organic component in solution, the dissociation constant of the glycylglycinium ion declines stepwise. It was concluded that the pK of the dissociation of glycylglycine versus the composition of a mixed solvent is of a critical character with a minimum in the water-organic solvent composition range of 0.1 to 0.3 molar fractions of DMSO. It is suggested that upon an increase in the concentration of DMSO, the zwitter-ion form of glycylglycine transitions to the molecular form.     

Rate constant and products of the BrO + BrO reaction at 298 K

The overall rate coefficient k of the self recombination of BrO radicals has been measured at 298 K with use of the discharge flow/mass spectrometry technique. The rate coefficient k₂ for the reaction channel forming Br₂ has been also determined. The results are: k = (3.2 ± 0.5) × 10^?12 and k₂ = (4.7 ± 1.5) × 10^?13 (in cm³ molecule^?1 s^?1). These results are discussed with respect to previous literature data.     

Dependence of the volume and viscosity of naphthalene-ethanol-octane solutions on composition at 298 K

The solubility of naphthalene in ethanol-octane mixtures was measured by the isothermal saturation method. The solution densities were determined and the partial and apparent molar volumes of naphthalene were calculated. The viscosity was measured with an Ubbelohde viscosimeter with a suspended level. All measurements were performed at 298.15 K. The results were discussed based on interactions in solution.     

Absolute rate constants for the reactions between amino and alkyl radicals at 298 K

The absolute rate constants for the reactions of NH₂ radicals with ethyl, isopropyl, and t-butyl radicals have been measured at 298 K, using a flash photolysis–laser resonance absorption method. Radicals were generated by flashing ammonia in the presence of an olefin. A new measurement of the NH₂ extinction coefficient and oscillator strength at 597.73 nm was performed. The decay curves were simulated by adjusting the rate constants of both the reaction of NH₂ with the alkyl radical and the mutual interactions of alkyl radicals. The results are k(NH₂ + alkyl) = 2.5 (±0.5), 2.0 (±0.4), and 2.5 (±0.5) × 10¹⁰ M^?1·s^?1 for ethyl, isopropyl, and t-butyl radicals, respectively. The best simulations were obtained when taking k(alkyl + alkyl) = 1.2, 0.6, and 0.65 × 10¹⁰M^?1·s^?1 for ethyl, isopropyl, and t-butyl radicals, respectively, in good agreement with literature values.     

298.15 K下氨基酸在D-木糖水溶液中的体积性质

报道了甘氨酸、L-丙氨酸和L-丝氨酸3种典型氨基酸在D-木糖水溶液中的体积性质.     

The phase diagrams of the CdCl2-NaCl-H2O system at 298 K

Solid-liquid equilibrium of ternary system Cd²⁺, Na⁺//Cl^?-H₂O at 298 K were studied by an isothermal solution saturation method. Experimental results indicate that there are three univariant curves AE, EF, and FB, two invariant points E, F, and three crystallization fields in the ternary system. The ternary system has one double salt Na₂CdCl₄ · 3H₂O. The crystallization zones of equilibrium solid phases are CdCl₂ · H₂O (AEG field), Na₂CdCl₄ · 3H₂O (EFM field), and NaCl (FBN field), respectively. The composition of the invariant point E is CdCl₂ · H₂O and Na₂CdCl₄ · 3H₂O of which content was 52.70 and 4.11%, respectively. The composition of the invariant point F is Na₂CdCl₄ · 3H₂O and NaCl of which content was 27.92 and 14.95%, respectively. The density of solution in the ternary system show regular changes along with the increased cadmium concentration. The results indicated that CdCl₂ · H₂O possessed the highest solubility among those three salts, which means a strong transfer of Cd ion and a high pollution risk of soil environment. And the solubility of NaCl would be restrained as the three salts existing together.