希托夫法求离子迁移数计算通式

在研究电解质溶液理论时,通过计算离子迁移数,可以求出电解质溶液中离子电导、离子淌度、电位梯度等一系列重要物理量。离子迁移数常用的实验室测定方法有:希托夫(Hittof)法、界面移动法和电动势法。其中希托夫法在目前物理化学教材中没有简便统一的计算公式可循。笔者结合教学实践,根据离子迁移数定义与不同情况下离子在阴、阳极区电解前后浓度变     

无限稀释氯化氢水溶液中离子迁移数的测定

基于Debye-Hückel-Onsager理论讨论了离子迁移数与电解质溶液浓度的关系,并介绍了测定无限稀释条件下离子极限迁移数的实验方法。实验证明,测得的迁移数与溶液浓度关系可以计算为一个线性拟合函数,并外推至零浓度,从而得到极限迁移数。因此,这个传统教学实验可以做出改进,以增进学生对电解质理论的理解。     

不同浓度下NaCl水溶液的分子动力学模拟

采用分子动力学模拟的方法在298K时对1.33mol/L,2.71mol/L,4.14mol/L和5.12mol/L的NaCl水溶液的微观结构进行了研究。模拟发现浓度对离了近程水化结构的影响不大,浓溶液中Na^+,Cl^-之间有两种缔合方式,接触缔合离子对和溶剂分隔的缔合离子对。这表明在建立可适用于高浓度条件下的电解质溶液热力学模型时应考虑离子缔合的贡献。     

不同浓度下NaCl水溶液的分子动力学模拟

采用分子动力学模拟的方法在298K时对1.33mol/L,2.71mol/L,4.14mol/L和5.12mol/L的NaCl水溶液的微观结构进行了研究。模拟发现浓度对离了近程水化结构的影响不大,浓溶液中Na^+,Cl^-之间有两种缔合方式,接触缔合离子对和溶剂分隔的缔合离子对。这表明在建立可适用于高浓度条件下的电解质溶液热力学模型时应考虑离子缔合的贡献。     

离子迁移数测定中各物质的量的关系

离子迁移数测定中各物质的量的关系张光玺（云南大学化学系昆明６５００９１）在物理化学教材中，离子迁移数测定方法之一是希托夫（Ｈｉｔｔｏｒｆ）法。其基本原理是：通电于电解质溶液之后，溶液中的正、负离子分别向阴－阳两极移动，并在相应的两极界面上发生还原或氧...     

聚合物电解质离子迁移数的测定方法

介绍了用于测定理想聚合物电解质中离子迁移数的三种比较常用的电化学方法,阐述了实际聚合物电解质输运性质和理想聚合物电解质输运性质之间的区别,并说明了实际聚合物电解质的离子迁移数的测定方法。     

高温及超临界条件下 MgCl2与CaCl2水溶液中离子水化与缔合的量子化学计算

对NaCl等碱金属水溶液的研究表明,室温条件下,离子在溶液中以水合形式存在,而在高温及超临界时,阴阳离子将结合成为离子对．采用量子化学计算,研究了MgCl2与CaCl2水溶液中水化与缔合的情况．通过Gaussian98软件包计算了阳离子的水化自由能以及离子对的生成能,从而获得水合离子与离子对的热力学稳定性及其随温度、压力的变化情况．通过比较热力学稳定性,考察了两种溶液中水化与缔合的变化情况．研究结果表明,MgCl2与CaCl2水溶液中离子水化与缔合的变化趋势与碱金属溶液基本一致,但是存在一个过渡区域,该区域内离子对与水合离子共存,因此需要采用不同于碱金属溶液的方法处理MgCl2与CaCl2水溶液．     

用电解法采集钢样和测定不锈钢中固溶钛

用由阴离子交换膜隔开的三室电解池作为采样器,电解法采集１Ｃｒ１８Ｎｉ９Ｔｉ不锈钢样品,并测定其中固溶钛的含量。测定结果和酸溶样法的一致。文中讨论了采样原理、采集质量的确定方法,电解质及电解电流的选择。     

电解质溶液界面结构的分子动力学模拟研究

电解质溶液界面结构的研究不仅具有重要的理论意义, 而且具有一定的实用价值. 采用分子动力学模拟研究了LiCl, LiBr, LiI, NaI, KI, CsI水溶液中阴阳离子在1×105 Pa和300 K下的气液界面分布情况, 探讨离子水化与电解质溶液界面结构的关系, 并分析阳离子水化能力的强弱对共存阴离子在界面富集分布的影响. 通过对模拟结果的分析发现, 离子的水化能力越强, 就越能形成稳定的水化结构而处于本体相中, 水化能力越弱, 则越易在界面富集. 该机理合理地解释了离子在界面的分布现象, 阳离子水化能力一般较其共存阴离子强而处于本体相, 阴离子则趋向在界面处富集; 不同阴离子在界面的密度分布也与阴离子的水化能力相关, 阴离子水化能力越弱, 其在界面富集程度越高, 不同阴离子在界面的富集趋势为Cl－＜Br－＜I－; 阳离子水化能力的强弱也影响其共存阴离子在界面的富集程度, 阳离子的水化能力越弱, 其共存阴离子在界面的富集程度就越低.     

物理化学教学中是否一定要定义a±?

电解质活度的问题是物理化学中的一个基本问题,涉及的范围较广。而我国现行的《物理化学》教科书中,论述电解质活度定义时,认为电解质在溶液中以离子形式存在,而单独离子的活度和活度系数a_+、a_-、γ_+、γ_-则无法用实验测量。因此需定义能用实验方法测定的电解质平均活度a_±、平均活度系数γ_±及与之有关的平均浓度m_±。     

Studies on silver(I) solvation in binary solvent mixtures containing dimethylsulfoxide. IV determination of solvent transference numbers for AgSCN and ionic coordination numbers of Ag+ in methanol-dimethylsulfoxide mixtures at 25°C

Solvent transport by AgSCN in the methanol (M)+dimethylsulfoxide (DMSO) system has been studied at 25°C by e.m.f. measurements. The solvent transference number of DMSO is positive as its concentration increases in the cathode compartment during electrolysis. The solubility of AgSCN has been determined in methanol, in DMSO and in methanol-DMSO mixtures. Using the known Gibbs free energy of solvation for the Ag⁺ ion, the corresponding energy for SCN, was found to be independent of the mole fraction. The experimental solvent transference numbers therefore only represent the contribution of Ag⁺, this is because it is preferentially solvated by DMSO. A coordination model has been applied to the Gibbs free energy of transfer of Ag⁺ in order to obtain coordination numbers thereby allowing calculation of solvent transference numbers. The experimental and the calculated solvent transference numbers are in good agreement at mole fractions of DMSO greater than 0.5. In highly methanolic solutions the assumption that the solvation of Ag⁺ in the solvent system studied is adequately represented by a total coordination number of four, proves to be too simple.     

Technique for measurement of transference numbers in membranes involving minimal concentration changes : Application to cellophane in potassium hydroxide solutions

True transference numbers may be determined by measuring the quantities of ions and solvent transported across a membrane on passing an electric current. In most previous work concentrations on one or both sides of the membrane have been allowed to change during the run. Ideally, the concentrations should be maintained invariant during the electrolysis to minimise transfer of solvent and solute by osmosis and diffusion, respectively. The maintenance of constant concentrations may also be important if the membrane characteristics show irreversibility on changing concentrations as is found with Cellophane in alkaline solutions.In the present paper a technique is described for holding solution compositions constant requiring only relatively simple equipment. Reversible electrodes are not essential and the method allows determination of both ionic and solvent transference numbers simultaneously. The cell described is rapid to assemble and an excellent membrane-cell seal is obtained eliminating solution leakage. Transference number data for Cellophane in potassium hydroxide solutions covering a wide concentration range, determined using the technique described, are presented.     

Development of highly sensitive cadmium iondashselective electrodes by titration method and its application to cadmium ion determination in industrial waste water

Characteristics of cadmium iondashselective electrode made cadmium sulphide (CdS)-silver sulphide (Ag(2)S) mixture were studied. CdS-Ag(2)S mixtures were obtained by gas/solid-phase reaction between silver-cadmium mixed powder and hydrogen sulphide gas (dry method) and by ionic reaction between cadmium-silver mixed ions and sulphide ion (wet method). As a result, it was found that the CdS-Ag(2)S mixture had to be made in the condition of excess existence of sulfur and had better regulate the excess sulfur quantity minimum, for the CdS-Ag(2)S pressed membrane gave a good Nernstian response against the cadmium ion concentration change. As the best way, CdS-Ag(2)S mixture was obtained by adding sulphide ion solution to 5 mol% cadmium ion and 95 mol% silver ion mixed solution while measuring silver sulphide (Ag(2)S) electrode potential as an indicator electrode. According to the reaction was stopped when the potential variation from the initial potential in the sulphide ion solution reached at 87-116 mV which the sulphide ion concentration became 10(-3) - 10(-4) of the initial concentration, the cadmium ion membrane pressed diameter of 8 mm and thickness of 2 mm showed a Nernstian response from 10(-8) to 10(-1) M of cadmium ion concentration. Furthermore, aiming to its application for industrial waste water, masking buffer for interfering metal ions such as lead ion (Pb(2+)) and copper ion (Cu(2+)), which were possibly coexisted and to adjust total ionic strength and pH of sample was developed. The present Cd(2+) iondashselective electrode was applied to the determination of Cd(2+) in the industrial waste water. The good regression line with correlation factor of 0.984 was obtained compared with the conventional atomic absorption spectroscopy.     

Modification of the direct moving boundary method for the determination of transference numbers for concentrated solutions

The upper concentration limit for the direct moving boundary method for measuring transference numbers can be appreciably extended by introducing three new concepts. First, the closed side of the cell must contain an electrolyte whose apparent molar volume changes relatively little with concentration. Second, the closed electrode chamber must be stirred to avoid the build-up of regions of differing concentration. Third, the solution in this chamber should be pre-saturated with the insoluble salt involved in the electrode reaction. These three modifications allow the large volume correction for concentrated solutions to be calculated much more exactly. The new technique was tested with fair success for 3M KCl in water at 25°C using the KCl LiCl system. The high current dependence of the transference number was mainly attributed to the Soret effect at the boundary.     

A Study on the Competitive Permeability of Anions in Anion Exchange Membrane

The selective permeability of two species of critical ions coexisting in Solution 1 for a third species of ions of the same charge in Solution 2 penetrate through the anion exchange membrane has been studied. The competitive permeability of coexisting ions depends on various concentrations, compositions and reaction time with the restriction that the volume of solution in each compartment is finite. The species which is easy to exchange across the membrane in multi-ionic system has a high selective permeability at small composition and high total concentration condition. The experimental result shows that there exist overshooting and depletion effects for the fast ion when the reaction time is long enough, and the higher the permselectivity T^CL_OH is, the more appreciable the overshooting effect is. An explanation of the overshooting and depletion effects with finite volume of solution has been made specifically in discussion.     

Synthesis and characterisation of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) Zr(IV) monothiophosphate composite cation exchanger: analytical application as lead ion selective membrane electrode

A Pb²⁺ ion selective membrane electrode based on poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) Zr(IV) monothiophosphate composite cation exchange material was fabricated using solution casting method. The effect of membrane composition on the proton exchange capacity was investigated by using varying amounts of electroactive material. The membrane with 250 mg of electroactive material and 10 µL of plasticiser exhibited higher proton conductivity. The optimised membrane composition was used for the fabrication of ion selective membrane electrode which exhibited typical Nernstian response towards Pb²⁺ ions in the concentration range 20.70 gL^?1–20.7 µgL^?1 (1 × 10^–1–1 × 10^–7 mol L^?1) with a sub-Nernstian slope of 27.429 mV per decade change in Pb²⁺ ion concentration. The response time of the electrode under study for Pb²⁺ ions was found to be 11 s and the electrode can be used for 120 days without any considerable divergence in response potential. It can also be successfully used in the pH range from 3.0 to 6.5. It was found selective for Pb²⁺ ions in the presence of various monovalent, divalent and trivalent interfering metal ions. It was also employed as an indicator electrode in the potentiometric titration of Pb²⁺ ions using ethylenediaminetetraacetic acid, disodium salt, as a titrant.     

Water-in-salt electrolytes: An interfacial perspective

Liquid electrolytes with high ionic conductivity, high transference number for the target ions, and excellent electrochemical, chemical, and thermal stability are essential for electrochemical energy storage devices. Water-in-salt (WIS) electrolytes, in which the salt–water ratio is larger than one, are gaining intensive attention in the electrochemical community. Here, we review the recent work on WIS electrolytes and the closely related water-in-ionic liquid electrolytes. We highlight the fact that many properties of these electrolytes, in bulk and at electrolyte–electrode interfaces, are underpinned by the physics and chemistry of the interfaces formed between water and ions (or aggregated water/ion clusters). Manipulating these interfaces by tailoring the selection of ions and water–ion ratio opens up new dimensions in the optimization of liquid electrolytes but also poses new challenges. We conclude the review by highlighting several directions for research on WIS electrolytes, in particular, the study of WIS electrolyte–electrode interfaces using surface force measurements.     

连续电提取浓缩技术

电去离子技术结合了电渗析和离子交换使离子在树脂中瞬时积累、降低体系电阻、电极上水解产生氢离子与氢氧根离子使树脂在线再生,以去除离子为目的制备纯水和高纯水. 这些被去除的离子在浓室中富集,可发展一种新型浓缩分离提取技术,现已逐渐应用于微量重金属、稀有金属、营养盐、有机酸碱,甚至气体的回收. 本文论述了这一连续电提取浓缩技术的原理及应用并探讨发展趋势,以期引起电化学研究工作者的关注.     

Sorption equilibrium of aromatic anions in an anion exchange membrane

Ion exchange and water content measurements were performed with an anion exchange membrane, ADS XL 10 (Solvay), equilibrated in aqueous solutions containing mineral electrolyte as NaCl, and/or organic electrolyte as sodium benzene carboxylate (ΦCO₂Na) and sodium 4-hydroxy-1-naphthalenesulfonate (ΦΦOHSO₃Na). By using radiotracers, it was possible to determine the amount of the total mineral and organic ionic species present inside the membrane. The fixation of big organic ions balancing the exchanging sites of the membrane can modify the membrane structure, creating micropores able to sorb more electrolytes. It was established that the sorption of hydrophobic organic ions corresponds to a ‘micelle mechanism’, The penetration of hydrophobic ions into the membrane induces a change in the molar volume of the wet membrane in relation to the variation of the water content.