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1.
Simple two-parameter Hückel and Pitzer equations were used for the calculation of the activity coefficients of aqueous hydrochloric acid at 25°C up to a molality of 2.0 mol-kg–1. The data obtained by Harned and Ehlers(12,13) from galvanic cells without liquid junction were used in the analysis and the parameters obtained were compared to those obtained from all reliable data presented in the literature for HCl at this temperature. A good agreement between the parameters was always observed. The activity coefficients obtained by the new equations were compared to those suggested by Robinson and Stokes,(8) Hamer and Wu,(1) and Pitzer and Mayorga,(9) and good agreement was also found. The data from the most important literature data sets for HCl were also predicted using the new activity coefficient equations, and the magnitude of the resulting errors was close to the precision of the measurements, the errors forming an almost random pattern for all data sets. 相似文献
2.
Published thermodynamic data measured in aqueous mixtures of sodium or potassium dihydrogen phosphate with hydrogen phosphate
and chloride at 25°C were used to test recently developed methods for calculation of the pH of phosphate buffer solutions.
Equations for ionic activity coefficients are used in these methods. It is shown that all data used in the tests up to an
ionic strength of about 0.5 mol-kg-1 can be accurately predicted by the two methods recommended. In one of these methods, equations of the Hückel type are used
for ionic activity coefficients and in the other equations of the Pitzer type. Several sets of phosphate buffer solutions
are recommended,e.g., for calibrations of glass electrode cells. In the recommended sets, the pH of the buffer solutions can be calculated either
by the Hückel or Pitzer method, and the pH predictions of these methods agree in most cases within 0.005 at least up to ionic
strengths of about 0.2 mol-kg-1. The pH values of the two primary pH standards endorsed by IUPAC based on aqueous mixtures of KH2PO4 and Na2HPO4,i.e., pH values of 6.865 and 7.413, can also be accurately predicted by the equations recommended in this study. 相似文献
3.
Khoroshko LO Takhistov VV Petrova VN Viktorovskii IV Lahtiperä M Paasivirta J 《European journal of mass spectrometry (Chichester, England)》2004,10(5):731-736
Structures of six cyclic polysulfides, previously unknown as organic environmental pollutants, were analyzed from a sediment sample from the Eastern Gulf of Finland. The determinations were done by gas chromatography connected to mass spectrometry. High resolution (HRMS) measurements of the isotopic composition of four compounds could be done to confirm their molecular formulae. Total low resolution (LRMS) spectra were used to elucidate structures of all six compounds by thermochemical approach, application of fragmentation rules and by ICLU simulation of the spectra. The compounds were deduced to be (in the order of GC- retention) 1,2,4-trithiacycloheptane, tetrathiacyclopentane, 1,2,4,5-tetrathia-cyclohexane, 1,2,3,4- tetrathiacycloheptane, 1,2,3,4-tetrathiacyclohexane and 1,2,4,6-tetrathiacyclooctane. 相似文献
4.
Simple two-parameter Hückel and Pitzer equations were used for the calculation of the activity coefficients of aqueous hydrochloric acid at temperatures 0–60°C up to a molality of 2.0 mol-kg–1. The data obtained by Harned and Ehlers(2,3) on galvanic cells without a liquid junction were used in the parameter estimations of these equations. These data consist of sets of measurements at the temperature intervals of 5°C. It was observed that all estimated parameters follow very simple equations with respect to temperature. They are either constant or depend linearly on the temperature. The values for the activity coefficient parameters calculated by these simple equations are recommended here. The recommended parameter values were tested by predicting the data of Gupta, Hills, and Ives,(5) consisting of cell measurements from 5 to 45°C and molalities up to 1.0 mol-kg–1, and the data of Bates and Bower,(4) which extend to 95°C but measurements were only made on molalities less than about 0.1 mol-kg–1. The activity coefficients obtained by the new equations were also compared to those calculated by the Pitzer equations with the parameter values determined by Saluja, Pitzer, and Phutela(6) from calorimetric data. The agreement observed was excellent up to a molality of 1.5 mol-kg–1 at temperatures from 0 to 60°C. 相似文献
5.
Saukkoriipi J Sillanpää A Laasonen K 《Physical chemistry chemical physics : PCCP》2005,7(22):3785-3792
Cationic aluminium(chloro) hydroxide complexes with two to four aluminium atoms were studied using quantum chemical methods. Complexes were studied in both gas and liquid phase. The liquid environment was modeled by using a conductor-like screening model (COSMO). COSMO calculations were carried out as a single point calculation at the optimized gas phase structures. Water (epsilon = 78.54) was used as the solvent. The minimum energy structures obtained from the gas phase studies were mostly compact cyclic structures. Aluminium preferred to be five-coordinated in oxygen rich clusters. Core oxygen preferred three-fold coordination but in the largest clusters the four-coordinated oxygen was observed. Water reacted dissociatively with hydrogen poor clusters. The COSMO calculations showed that the optimal structures of cationic aluminium(chloro) hydroxides tend to be more open in the liquid than in the gas phase. 相似文献
6.
Marja Pitkänen Heli Kangas Ossi Laitinen Asko Sneck Panu Lahtinen Maria Soledad Peresin Jouko Niinimäki 《Cellulose (London, England)》2014,21(6):3871-3886
A finely ground fibrillated cellulose was fractionated into separate size fractions. The characteristics of the smallest size fractions were studied, and the toxicity to humans was tested as part of a safety assessment. Morphological studies performed with state-of-the-art methods, such as scanning electron microscopy and atomic force microscopy, showed that the fraction obtained consisted of long thin fibrils but also larger fibril agglomerates, and spherical particles were present. The finest fraction did not show any sub-lethal effects as assessed by RNA inhibition test in vitro, nor were there any indications of genotoxicity as tested by the Ames test in vitro. Systemic effects tested in vivo with the nematode were also absent. No cytotoxic effects were seen in the highest tolerated dose test in vitro, but some indication of cytotoxicity was observed in the total protein content test in vitro at the highest sample concentration. The significance of this toxicity test result should be addressed in relation to the other toxicity tests, in which no toxicity was observed, with special emphasis on the in vivo test. Given this, the overall toxicity analyses support the conclusion that nano-scale cellulose fibrils can be considered to be safe towards humans. However, the reason for the positive cytotoxicity test result and, in addition, the effect of the biocide used in sample preservation on the toxicity tests need to be clarified before generalizing these results and declaring nanocellulose to be unambiguously safe. 相似文献
7.
Marika E. Nissil? Ya-Chieh Li Shu-Yi Wu Jaakko A. Puhakka 《Applied biochemistry and biotechnology》2012,168(8):2160-2169
Concentrated acid hydrolysis of cellulosic material results in high dissolution yields. In this study, the neutralization step of concentrated acid hydrolysate of conifer pulp was optimized. Dry conifer pulp hydrolysis with 55?% H2SO4 at 45?°C for 2?h resulted in total sugar yields of 22.3?C26.2?g/L. The neutralization step was optimized for solid Ca(OH)2, liquid Ca(OH)2 or solid CaO, mixing time, and water supplementation. The highest hydrogen yield of 1.75?mol?H2/mol glucose was obtained with liquid Ca(OH)2, while the use of solid Ca(OH)2 or CaO inhibited hydrogen fermentation. Liquid Ca(OH)2 removed sulfate to below 30?mg SO4 2?/L. Further optimization of the neutralization conditions resulted in the yield of 2.26?mol?H2/mol glucose. 相似文献
8.
9.
Kaarina Kekäläinen Henrikki Liimatainen Jouko Niinimäki 《Cellulose (London, England)》2014,21(5):3691-3700
Periodate–chlorite oxidized bleached hardwood kraft pulp fibre samples with six levels of charge densities ranging from 0.5 to 1.8 mmol/g were gradually disintegrated to microfibrils using a high-shear homogenizer. The disintegration kinetics and mechanisms were studied by a flow fractionation method, and the properties of the resulting particles were determined using low shear viscosity and transmittance measurements. The particles formed during the disintegration were visualized with a charge-coupled device camera and by field-emission scanning electron microscopy. The result showed that cellulose fibres with a low charge density disintegrated at a low rate and produced ragged fibres and bunches of microfibrils via bursting of the fibre walls, whereas those with a higher charge density broke down at a high rate and microfibrils were formed through swelling and the creation of balloon structures. A carboxyl content of 1.2 mmol/g was found to be the threshold value for the efficient formation of high aspect ratio microfibrils and also for the change in the disintegration mechanism in the high-shear homogenizer. 相似文献
10.