混合酸、多元酸滴定的教学探讨

为解决混合酸(碱)、多元酸(碱)滴定教学中出现的问题,提出一些思路:(1)应在搞清滴定反应及其优先次序前提下,充分利用滴定曲线这一有力工具解决各种问题。(2)教学中,应遵循由易到难、步步深入的原则。在充分讲授单种一元酸滴定的基础上,可按强碱滴混合一元酸、强碱滴多元酸、强碱滴复杂混合酸的顺序安排教学内容。由于规律相似,所以在学生学完强碱滴定酸之后,只需对强酸滴定碱略作介绍即可。另外,提出一种无需复杂计算,仅利用单种一元酸(碱)滴定曲线拼合出复杂酸(碱)体系的近似滴定曲线的新方法,获得的曲线虽不十分精确,但足以给滴定分析可能性判断以及指示剂选择等问题提供有力的支持。     

线性作图法求混合酸中各组分酸的含量

用传统的分段滴定法测定混合酸中各组分酸的含量,一般要求各组分酸的电离常数间比值要大于10~4,各组分酸浓度相差不能太大,否则不能由一次滴定分别求得各组分酸含量。例如由定量的二氯乙酸(K′=3.32×10~(-2))和定量的醋酸(K′=1.76×10~(-5))所组成的混合酸,在分步滴定曲线上,第一突跃十分不明显,第二突跃较明显(见图1中A线所示)。测定范围受到了很大限制。     

金属离子酸的离解常数与金属离子存在下滴定游离酸的理论处理

金属离子酸的离解常数可推导为Ka=Kw·K_(MOH)及Ka_n=Kw·K_(M(OH)n)。在金属离子存在下滴定游离酸,可以作为混合酸进行理论处理,使用相同的滴定条件与等当点pH计算公式。在加入掩蔽剂滴定时,可以使用金属离子酸的条件稳定常数作出相似的理论处理。     

无需标准溶液的酸碱滴定计算分析研究

无需标准溶液的滴定计算分析能同时求出滴定剂与被测物质浓度.本文用非线性规划问题的单纯形加速法对无需标准溶液的酸碱滴定进行了研究.单元酸、多元酸及混合酸的测定得到了比较满意的结果.     

络合滴定中的掩蔽效应 络合掩蔽效应公式及其应用

(一)前言在若干种离子的混合溶液中,欲不经分离而进行个别离子的氨羧络合滴定,必须控制滴定条件。根据作者提出的酸效应公式,可以计算在混合溶液中,控制酸度滴定个别离子的最高和最低酸度范围。但是,对于氨羧络合物的稳定性相近的一些离子(例如△pK<5时),欲不经分离而进行选择滴定,单     

多元酸及混合酸滴定规律的讨论——可编程序计算器的应用

多元酸和混合酸的滴定,近年来国内外教材和专著均有所介绍。但一般都沿用一元酸的滴定规律来判断多元酸及混合酸分级或分别滴定的可能性,于是出现了一些与实验事实相矛盾的现象。现从酸碱平衡质子条件出     

氨基乙酸的测定——水-乙醇混合溶剂的滴定法

在混合溶剂中的极弱酸的滴定分析工作报道得很少。氨基乙酸的测定通常是使用冰醋酸介质的非水滴定法,由于其实验耗资较大,一般学校均难以开出此实验。据报道,对CKa<10~(-8)的极弱酸的测定,除非水滴定法外,还有直线法等。本文研究了乙醇混合溶剂中测定氨基乙酸的条件。实验结果表明,该滴定体系的pH突跃明显,做电位滴定和指示剂滴定均可,其耗资仅为用冰醋酸介质的四分之一左右。     

混合酸线性滴定的一种新图解法

混合酸的滴定是滴定分析中比较难处理的问题,采用巳有线性滴定图解法也必须对相互干扰进行修正,其缺点是计算量大、线性方程复杂。因此,本文提出一种新图解法。新图解法原理设C_(0B)为NaOH标准溶液的浓度,V为滴入的体积;V_0为被滴液的体积;混合酸中HAⅠ的形成常数为K_(HA1)~H,初始浓度为C_(0A1),瞬时浓度为C_(A1);HAⅡ的形成常数为K_H~HA_(11),初始浓     

多种(多元)混合酸的图象计算分析法

以酸碱电位滴定然后进行曲线拟合分析多种(多元)混合酸的方法,可以在不分离的情况下一次滴定分析出多种及多元混合酸的含量和电离常数。Ingman、Johansson、汪葆俊等人已经在这方面做了大量的工作。本文提出了图象计算分析法(即从图形上确定各种酸的pκ_A及个数m,并以线性回归法计算出各个酸的浓度)。这种方法的分析与计算简单、直观、可靠,能有效地应用于实际样品分析。     

混合酸的滴定判据及终点误差

关于混合酸的滴定，在分析化学教材和参考书中，详细论述的不多。有的教材根本没有讲授混合酸的滴定，有的只简单的谈到关于混合酸的滴定，情况跟多元酸相似，有的则直接给出第一化学计量点时溶液中的H^ 浓度的计算公式。笔者在多年的分析化学教学中发现，学生对此有较多的疑问，不知道计算公式从何而来等。本文就混合酸的滴定作一较为详细的讨论。     

Combination of the Metropolis Monte Carlo and Lattice Statics method for geometry optimization of H‐(Al)‐ZSM‐5

In this article, the combination of the Metropolis Monte Carlo and Lattice Statics (MMC‐LS) method is applied to perform the geometry optimization of crystalline aluminosilicate zeolite system in the presence of cationic species (H⁺), i.e., H‐(Al)‐ZSM‐5. It has been proved that the MMC‐LS method is very useful to allow H⁺ ions in (Al)‐ZSM‐5 extra‐framework to approach the global minimum energy sites. The crucial advantage of the combination MMC‐LS method is that, in stead of simulating over thousands random configurations via the only LS method, the only one configuration is needed for the MMC‐LS simulation to achieve the lowest energy configuration. Therefore, the calculation time can be substantially reduced via the performance of the MMC‐LS method with respect to the only LS method. The calculated results obtained from the MMC‐LS and the only LS methods have been comparatively represented in terms of the thermodynamic and structural properties. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010     

Simultaneous separation of mercury and lignosulfonate from aqueous solution using supported liquid membrane

This paper presents an experimental investigation on facilitated and simultaneous transport of mercury and lignosulfonate (LS) through a flat sheet supported liquid membrane (SLM) having Nylon 6,6 as support, trioctylamine (TOA) as carrier and dichloroethane as solvent. The experiments were performed at various operating conditions such as strip phase concentration, feed pH, carrier concentration and feed concentration to find the best set of parameters that would yield the maximum separation of pure mercury as well as its mixture with LS. The experiments were performed in co-transport mode using NaOH as the strip phase. It was observed that extraction of mercury as well as its mixture increases with increase in concentration of NaOH up to a certain limit 0.1 M NaOH in case of pure solution and 0.2 M NaOH in case of mixture). Feed phase pH significantly affects the mercury separation process. However, initial feed concentration does not affect the extraction process appreciably. Separation of mixture of mercury and LS behaves in a similar way as their pure solution; however the extraction is low in comparison to pure solution. The extraction of mercury from its pure solution is about 81% in 1 h. The extraction of mercury and LS from their mixture is about 52.6% and 50.2%, respectively at optimum condition and in a period of 2 h.     

二元复杂共混体系组成的SEC-LS分析

提供了一种利用体积排阻色谱-光散射(SEC-LS)联用技术来解决二元复杂共混体系组成的定量分析问题.基于体积排除色谱的绝对定量化原则,首先从理论上分析了共混物的光散射响应因子与组成呈线性关系.通过分析六组复杂共混体系的光散射响应因子与组成的关系,验证了该线性关系确实存在.进而利用该线性关系计算了共混体系的组成.在某些共混体系中,通过光散射响应因子得出的组成比利用示差法得出的组成更加接近原料组成.通过分析这两种方法产生误差的来源,阐述了产生该现象的原因.     

目标转换因子分析与库检索相结合用于红外混合体系定性分析

将库检索与目标转换因子分析相结合利用抽象浓度的分布信息确定可能解域，其最大可能解即为体系包含的物种。可能解域的确定大大减少了计算量，应用于严重重叠的甲苯和乙苯二组份和苯，甲苯及乙苯三组份混合体系，结果令人满意。     

亚氯酸盐-硫代硫酸盐非缓冲体系的动力学

研究了亚氯酸盐-硫代硫酸盐反应体系在非缓冲条件下的复杂动力学行为.结果发现,在开放体系中反应的pH值和Pt电位存在准周期振荡分叉和混合模式振荡分叉通向混沌的过程，且pH峰与Pt电位峰反相位.当与起始浓度比相对较小时，随着流速的逐渐升高，体系的pH值和Pt电位从简单的小振幅振荡(S)经过准周期振荡分叉到混沌，最后回到简单大振幅振荡(L)；而当与起始浓度比相对较高时，随着流速的降低，体系的pH值和Pt电位出现LS1、LS2、LS3…LSn的混合模式振荡,并在每对(LSn、LSn＋1)振荡区间发现了LSn、LSn＋1随机出现的非周期振荡行为.运用硫价态变化的一般动力学模型，模拟出了反应体系的混合模式振荡及非周期振荡.     

Adsorption of sophorolipid biosurfactants on their own and mixed with sodium dodecyl benzene sulfonate, at the air/water interface

The adsorption of the lactonic (LS) and acidic (AS) forms of sophorolipid and their mixtures with the anionic surfactant sodium dodecyl benzene sulfonate (LAS) has been measured at the air/water interface by neutron reflectivity, NR. The AS and LS sophorolipids adsorb with Langmuir-like adsorption isotherms. The more hydrophobic LS is more surface active than the AS, with a lower critical micellar concentration, CMC, and stronger surface adsorption, with an area/molecule ～70 ?(2) compared with 85 ?(2) for the AS. The acidic sophorolipid shows a maximum in its adsorption at the CMC which appears to be associated with a mixture of different isomeric forms. The binary LS/AS and LS/LAS mixtures show a strong surface partitioning in favor of the more surface active and hydrophobic LS component but are nevertheless consistent with ideal mixing at the interface. In contrast, the surface composition of the AS/LAS mixture is much closer to the solution composition, but the surface mixing is nonideal and can be accounted for by regular solution theory, RST. In the AS/LS/LAS ternary mixtures, the surface adsorption is dominated by the sophorolipid, and especially the LS component, in a way that is not consistent with the observations for the binary mixtures. The extreme partitioning in favor of the sophorolipid for the LAS/LS/AS (1:2) mixtures is attributed to a reduction in the packing constraints at the surface due to the AS component. Measurements of the surface structure reveal a compact monolayer for LS and a narrow solvent region for LS, LS/AS, and LS/LAS mixtures, consistent with the more hydrophobic nature of the LS component. The results highlight the importance of the relative packing constraints on the adsorption of multicomponent mixtures, and the impact of the lactonic form of the sophorolipid on the adsorption of the sophorolipid/LAS mixtures.     

Mechanical and thermal properties of rigid polyurethane foams derived from sodium lignosulfonate mixed with diethylene-, triethylene- and polyethylene glycols

Sodium salt of lignosulfonic acid (LS), which was obtained as by-product of cooking process in sulfite pulping, was solved in diethylene, triethylene or polyethylene glycol. Three series of polyurethane foams (LSPU) were synthesized by varying the LS content from 0 to 33 wt%. Apparent density (ρ) of LSPU foams ranged from 0.08 to 0.18 g cm⁻³ and was affected by both LS content and oxyethylene chain length. Glass transition temperatures increased with increasing amount of LS and with decreasing oxyethylene chain length. Thermal gravimetry analysis indicated that the LS component decomposes first and that the thermal stability increases with decreasing oxyethylene chain length. Compression strength and compression modulus increased linearly with increasing apparent density. It is concluded that LS is successfully utilized as a hard segment of rigid PU foams, whose thermal and mechanical properties can be tuned by changing the amount of LS and the length of soft oxyethylene chains.     

Influence of peak-broadening and interdetector volume error on size-exclusive chromatographic analysis with dual viscometric-concentration detection using the universal calibration method

The effect of peak-broadening and error in interdetector volume on the local calibration curve and experimental molecular-mass averages obtained by size-exclusion chromatography (SEC) with dual concentration/viscosity detection, and determination of molecular mass using the universal calibration (UC) method, is theoretically examined using a polymer sample with a molecular-mass distribution (MMD) approximated by the log-normal function. Although peak-broadening is often neglected, its effect on the slope of the local calibration curve and, consequently, on the experimentally obtained values of the weight-to-number average ratio is large. To obtain the right values of these parameters, a numerical correction is usually recommended. While using the UC method, the relationships between the extent of peak broadening, calibration slopes and interdetector volume are complex and can contribute to the occurrence of undiscovered errors. For this reason, an understanding of this problem, using a model, is necessary. The results of the UC method are compared with those obtained using dual-detection with known Mark-Houwink-Kuhn-Sakurada parameters (MHKS method), light-scattering (LS)/concentration detection as well as with the results obtained using conventional calibration. Due to peak-broadening, the slope of a local calibration curve and the weight-to-number average ratio, (Mw/Mn)", obtained using the UC method, increase compared to the theoretical values, whereas they decrease using the MHKS or LS methods. The increase when using the UC method is even larger compared to evaluation using conventional calibration. The effect of the error in interdetector volume on the slopes of local calibrations and the weight-to-number average ratios is opposite in the UC method to that found using the MHKS and LS methods.     

Comparison of different methods to estimate the uncertainty in composition measurement by chromatography

Natural gas is a mixture that contains hydrocarbons and other compounds, such as CO₂ and N₂. Natural gas composition is commonly measured by gas chromatography, and this measurement is important for the calculation of some thermodynamic properties that determine its commercial value. The estimation of uncertainty in chromatographic measurement is essential for an adequate presentation of the results and a necessary tool for supporting decision making. Various approaches have been proposed for the uncertainty estimation in chromatographic measurement. The present work is an evaluation of three approaches of uncertainty estimation, where two of them (guide to the expression of uncertainty in measurement method and prediction method) were compared with the Monte Carlo method, which has a wider scope of application. The aforementioned methods for uncertainty estimation were applied to gas chromatography assays of three different samples of natural gas. The results indicated that the prediction method and the guide to the expression of uncertainty in measurement method (in the simple version used) are not adequate to calculate the uncertainty in chromatography measurement, because uncertainty estimations obtained by those approaches are in general lower than those given by the Monte Carlo method.     

Assay of uranium in scrap and waste produced at natural uranium metal production and fuel fabrication plants

The paper describes the results and observations on the analyses of uranium in calcium fluoride slag, silica cake and fused salt cake obtained in uranium metal and fuel plants. The analysis is done by (1) non-destructive assay by passive gamma ray counting, (2) chemical analysis, and (3) solid state nuclear track detector (SSNTD) technique. The details of the development of NDA method to suit the requirements of the sample are given. The difficulties encountered in chemical assay are described. SSNTD method has been applied to such materials for the estimation of the uranium for the first time. A simple scheme for the recovery of uranium and the salt mixture from the fused salt cake is also described.