Density of salt solutions: Effect of ions on the apparent density of water
Density of salt solutions: Effect of ions on the apparent density of water
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DOI：
10.1021/jp010097r
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发表时间：
2001-05-17
影响因子：
3.3
通讯作者：
Dougherty, RC
中科院分区：
文献类型：
--
作者：
Dougherty, RC
水溶液中水的表观密度是通过假设离子所占据的体积来分析的，在没有接触离子对的情况下，可以通过具有适当离子半径的球体可靠地近似。离子溶液的X射线数据用于识别离子半径与晶体半径。对氯化物和氟化物的大小进行了小的修正。向水中添加离子改变了水的堆积密度以及平均氢键长度。水的表观密度与浓度的关系（在无限稀释时）的斜率在298 K，1臂时单价电解质从负到正变化。在蔗糖溶液的情况下，水的表观密度不随蔗糖浓度变化。对于具有表观水密度随浓度的正斜率的盐，通常根据溶解度范围观察到作为浓度的函数的表观密度的最大值。室温下的表观密度最大值在多价电解质中更常见。这些现象进行了讨论，在水的平衡结构和添加的盐对结构介导的氢键强度的变化的影响。该分析预计，在低温（较高的氢键强度）下，氯化钠溶液应显示出水的表观密度随浓度变化的最大值。自1937年以来就有数据证实存在这种最大值。水的氢键强度的变化被解释在涉及阳离子，阴离子和水的电子离域。A.微扰分子轨道（PMO）模型较好地描述了表观水密度的极限斜率。模型值远溶液密度在低浓度比较有利的实验结果。由离子的存在引起的液态水结构平衡的变化将反映在溶液自由能的变化中，即使是最低浓度的离子。
The apparent density of water in aqueous solutions is analyzed by assuming that the volume occupied by the ions, in the absence of contact ion pairs, can be approximated reliably by spheres with appropriate ionic radii X-ray data for ionic solutions are used to identify the ionic radii with crystal radii. Small corrections for the sizes of chloride and fluoride are made. Addition of ions to water changes the packing density of the water as well as the average hydrogen bond length. The slope of the apparent density of water versus concentration (taken at infinite dilution) varies from negative to positive for univalent electrolytes at 298 K, 1 arm. in the case of sucrose solutions, the apparent density of water does not change with sucrose concentration. For salts that have a positive slope of apparent water density with concentration, a maximum in apparent density as a function of concentration is generally observed depending on the solubility range. Apparent density maxima at room temperature are more frequently observed with polyvalent electrolytes. These phenomena are discussed in terms of the equilibrium structure of water and the influence of added salts on the structure mediated by changes in hydrogen bond strength. This analysis anticipated that at low temperatures (higher hydrogen bond strength) sodium chloride solutions should show a maximum in the apparent density of water as a function of concentration. Data confirming the existence of such a maximum has been available since 1937. Changes in hydrogen band strength for water are interpreted in terms of electron delocalization involving cations, anions, and water. A. perturbation molecular orbital (PMO) model gives a good account of the Limiting slope of apparent water density. Model values far solution densities at low concentrations compare favorably with experimental results. Changes in the structural equilibrium for liquid water caused by the presence of ions will be reflected in changes in the free energy of solution for even the lowest concentration of ions.