对电导法测量乙酸乙酯皂化反应速率常数的一点改进

电导法测量乙酸乙酯皂化反应速率常数的实验,是二级反应动力学的一个较经典实验。目前高等学校物理化学实验教材中均有介绍。但在数据处理中都用到当时间 t→∽时的电导率 L(?)数据。一般采用二种方法进行测量L(?):一是让反应达到平衡后测定其电导率(一     

氧化锆基固体电解质材料与温度无关的离子电导活化能

氧化锆(ZrO2)基固体电解质材料的离子电导率随温度的变化关系呈现非线性Arrhenius特征;相应地,由经典的Arrhenius公式计算得到的电导活化能是一个与温度有关的参数.本文通过对实验获得的几种Y2O3稳定立方ZrO2(YSZ) 材料的电导率－温度关系的分析,对经典的Arrhenius公式进行了修正.由修正后的Arrhenius公式计算得到的电导活化能是一个与温度无关的常数.此外,还进一步借助于物理化学中的过渡状态理论,从材料离子导电机制出发对这一与温度无关的电导活化能的合理性进行了讨论,发现这一活化能在数值上与理论计算结果吻合得很好.     

聚苯胺电极的电导率

采用化学氧化聚合法制备聚苯胺(PANI)。利用四探针技术和电流-电压方法对PANI的电导率进行表征测试。基于电子-空穴导电机理和经典电流密度表达式,建立了PANI的有效导电数学模型,该模型可描述为电流密度、电压、温度的函数。对模型的图形分析表明,得到的电流-电压规律与PANI的实验结果一致。对电流密度与温度的关系分析得到的电导率随温度的变化规律与实验现象相符。结果表明:PANI有机半导体主要以耦合电流为主,电流强度随电压(温度)的增加呈现先增大后减小的趋势;低温时,PANI的导电性较好。     

基于USB接口的有机涂层耐蚀性能快速测试仪

根据多重动电位扫描极化的原理,研制了一种基于USB接口的有机涂层/金属体系耐蚀性能快速测试仪.该仪器便携、简易、实用,有强数据采集和处理功能,不仅可用于实验室的快速实验,更适用于在工业现场对有机涂层/金属体系耐蚀性能快速测试和评价.     

以培养主动性为重点谈分析化学实验教学改革

本文探讨了分析化学实验在教学思想、教学内容和教学方法上的改革。以实验“水中总硬度的测定”为例讨论了增加经典验证性实验之综合性的过程     

溴碘化银T-颗粒晶体中的电子和空穴行为研究

利用Wagner极化法研究了掺杂K₄[Fe(CN)₆]浅电子陷阱掺杂剂的溴碘化银T 颗粒晶体的电子电导率和空穴电导率,并与未掺杂的晶体样品进行对比,分别考察了实验温度、掺杂剂用量、掺杂位置等因素对实验结果的影响.结果表明,随掺杂剂用量的增加,晶体的电子电导率和空穴电导率都相应增加,这说明浅电子陷阱掺杂剂的掺杂有效地抑制了电子和空穴的复合.但其抑制作用却因掺杂位置的不同而不同,当掺杂量一定,掺杂剂掺在碘区附近时,晶体的电子电导率和空穴电导率的变化较明显.随着实验温度的增加,乳剂晶体的电子电导率和空穴电导率都下降.     

综合性化学实验的线上线下混合式教学——以水泥分析为例

水泥熟料分析是一个经典的综合性实验,涉及重量分析和配位滴定分析的很多原理及操作。为了有效开展实验教学、缩短课堂讲解时间、客观评价学生实验数据及结果,我们开展了线上线下混合式教学,引导学生课前自主学习,训练学生综合和创新实验技能。这一改革提高了实验教学质量,取得了较好的教学效果。     

利用手持技术探究氢氧化铝制备实验电导率变化

利用电导率传感器对氢氧化铝制备实验过程中,溶液的电导率变化进行探究,以相同浓度的氨水和氢氧化钠溶液分别滴定硫酸铝溶液,得出反应过程的电导率变化曲线图,并从宏观、微观、符号和曲线4个方面深入分析曲线,从多个角度探究氢氧化铝制备实验的电导率变化,为氢氧化铝的教学提供帮助。     

运用数字化实验技术探究凝聚法制备氢氧化铁胶体的过程

利用数字化实验技术,对氢氧化铁胶体和氯化铁溶液进行了电导率、pH、光照度等性质的测试和比较。通过实验,学生观察到电导率、pH、光照度等数据的差异,直观地感受到实验中电导率、pH、光照度的变化过程,从而认识溶液和胶体的不同。     

基于手持技术的乙酸乙酯水解实验研究

乙酸乙酯水解实验是中学有机化学中的重要实验,通过酯层减少或酯香味消失的时间来判断水解反应速率,实验效果并不理想。利用手持技术中的电导率传感器研究氢氧化钠溶液温度和浓度对乙酸乙酯水解反应速率的影响,以及不同酸碱性条件下的乙酸乙酯水解反应速率。将电导率传感器与pH传感器联用,同时测定乙酸乙酯水解过程的电导率和pH变化。对通过实验得到的电导率变化曲线和pH变化曲线进行分析,帮助中学教师和学生从定量的角度理解乙酸乙酯水解反应规律和微观实质,并阐释了此研究对中学化学实验及其教学的启示。     

Control of voltammetric experiments by means of the Commodore 64 microcomputer

An electronic interface for the Commodore 64 microcomputer suitable for generation of voltammetric waveforms and for data acquisition has been built. Used together with analogue voltammetric instruments the interface makes updating of the measurement techniques possible. Also, fast A/D-conversion and a floppy disk drive make the system useful as a universal data-acquisition unit in the laboratory. The system has been tested together with an amperometric detector in the square-wave voltammetric determination of paracetamol and iodide.     

A semiclassical study of the thermal conductivity of low temperature liquids

The conventional classical energy current auto-correlation function has been extended into a quantum mechanical version and then approximated by the linearized semiclassical initial value representation approach. Comparison of the thermal conductivity to simulation results shows that about 15% quantum correction to the classical molecular dynamics results for liquid neon are quantitatively predicted. For liquid para-hydrogen the quantum effects are sufficiently large that the linearized semiclassical approach is only 20% accurate, while for both liquid He(4) and He(3) the thermal conductivity disagrees by a factor of 2, although exchange effects appear to play a minor role.     

Thermal conductivity of solid argon from molecular dynamics simulations

The thermal conductivity of solid argon in the classical limit has been calculated by equilibrium molecular dynamic simulations using the Green-Kubo formalism and a Lennard-Jones interatomic potential. Contrary to previous theoretical reports, we find that the computed thermal conductivities are in good agreement with experimental data. The computed values are also in agreement with the high-temperature limit of the three-phonon scattering contribution to the thermal conductivity. We find that finite-size effects are negligible and that phonon lifetimes have two characteristic time scales, so that agreement with kinetic theory is obtained only after appropriate averaging of the calculated phonon lifetimes.     

An empirical model to predict temperature‐dependent thermal conductivity of amorphous polymers

Thermal conductivity in polymers has been theoretically and experimentally studied in good detail, but there is a need for more accurate models. Polymeric thermal conductivity exhibits a plateau‐like transition at temperatures around 10 K, which is not well accounted for by existing models. In this work, an empirical model that can predict temperature‐dependent thermal conductivity of amorphous polymers is developed. The model is based on kinetic theory and accounts for three sets of vibrational modes in polymers, and is developed using classical expressions, results of previous simulations, and experimental data. Fundamental material properties like density, monomer molecular weight, and speed of sound are the only input parameters. The model provides estimates for the locations of transitions between different sets of vibrational modes, an upper limit for the thermal conductivity, and temperature‐dependent thermal conductivity, which are in good agreement with experimental data. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1160–1170     

Thermal conductivity of neon in the temperature range 400–2400K

Accurate measurements of the thermal conductivity of neon are given in the temperature range 400–2400K as obtained on an improved thermal conductivity column instrument. These data are found to be in good agreement with the earlier measurements of thermal conductivity from this laboratory and also with the available viscosity values. The present conductivity data are also compared with the predictions of kinetic theory in conjunction with several different forms for the intermolecular potential.     

Application of exploratory data analysis for the characterization of tubular wells of the North of Brazil

Roraima is located in the extreme North of Brazil, in the Western Amazon Region. The groundwater has an important role in the public supply of potable water on the Roraima State. The objective of this work is the application of PCA (Principal Component Analysis) and HCA (Hierarchical Cluster Analysis) for the characterisation of tubular wells of the Roraima State, as regards physical–chemical composition of water. The parameters analyzed in laboratory were the following ones: pH, electric conductivity, Total Hardness, Total Alkalinity, Bicarbonate, Calcium, Potassium, Magnesium, Nitrate, Chloride, Total Iron. The physical–chemical analyses, were carried out during the months of September and October 2000 (winter, period of rains). The laboratory analysis was performed using classical methods (titrimetry and uv–visible spectroscopy), the samples were processed in agreement with the Standard Methods for Examination of Water and Wastewater.The physical–chemical analyses, were accomplished in September and October 2000. In physical–chemical terms, the groundwater samples analyzed do not indicate any restriction to human consumption and the two chemometric methods of exploratory data analysis: PCA and HCA are efficient for the discrimination of bicarbonated (tubular wells locateds in the South of the Roraima State) and not bicarbonated (tubular wells locateds in the North of Roraima) groundwater.     

Effect of counterion on thermodynamic micellar properties of tetradecylpyridinium in aqueous solutions

Electrical conductivity of aqueous solutions of tetradecylpyridinium bromide and chloride has been measured as a function of surfactant molal concentration and temperature. From the molal dependence of conductivity, the critical micelle concentration and the micellar ionization degree were estimated. The temperature dependence of these parameters has been used for calculating the thermodynamic parameters related with the micellization process by using the classical charged pseudophase separation model. The effect of the counterion on the conventional thermodynamic potentials of micellization such as standard Gibbs free energy, enthalpy and entropy has also been a matter of study. Finally, the occurrence of the enthalpy–entropy compensation phenomenon was verified and the relevant parameters discussed.     

Uncertainty of the Thermal Conductivity Measurement Using the Transient Hot Wire Method

This work deals with uncertainty analysis of the thermal conductivity measurement using the transient hot wire method. The characterization is made from a sample of low-density, polyethylene BRALEN SA 200-22. The utilized experimental data are obtained from the test measurements performed on the air at room temperature. The sources of measurement errors are analyzed and the uncertainty of the measured value of the thermal conductivity is evaluated. The analysis shows that in the present case the uncertainty of the thermal conductivity measurement is about ±3.3% for 68% confidence level.This revised version was published online in November 2005 with corrections to the Cover Date.