中学化学实验产物的综合利用

在传统中学化学实验中,实验的产物常常不被重视。只要实验者观察到了有关的现象和数据,就算达到了实验目的。     

化学教学中如何引导学生正确描述实验现象

在高中化学教学过程中,发现有许多教师不太注重学生对化学实验现象的正确描述,许多学生在描述过程中也存在语言不规范,条理不清或者根本就不知道从哪里说起。本文主要针对高中化学教学中常出现的一些误区进行归纳总结。     

化学演示实验应重视"对比"效果

在中学和中师化学的演示实验中,有一大类是属于“对比性”的实验,教师通过对实验中出现的不同现象之间的比较,得出相应的一些结论,以支持和验证所教授的化学理论。这类实验成功与否主要看现象之间的“对比”效果是否明显、强烈、突出,只有教师在实验操作中做出了这种“对比”的效果,同时学生也看到了化学现象之间在对比中产生的区别、差别,才算达到了演示实验的预期目的。反之,若对比不突出,对问题的说服力就不强。但在实际教学中我们发现：一方面,一些教师对实验的“对比性”认识不够,除了一些直接了当的对比性实验外,把一些原本是分步操作的先后对比的一个实验做成了前后联系似乎不大的2个近乎“孤立”的实验,弱化了对比的效果。另一方面,有些实验我们可以通过操作程序的改变,将其由不是对比性的或是对比性不太强的改造成对比性的或对比性较强的实验,以增强实验的演示效果。本文就这一方面的问题谈一些自己的想法和做法。     

谈有机化学实验中的开放实验模式

化学是一门以实验为手段 ,以应用性、创造性为特征的学科 ,因此化学实验是大学化学教学中极其重要的一部分 ,也是培养学生创新意识、创新能力的重要途径。但是原有的实验教学模式存在许多缺点与不足 ,培养的学生越来越不适应社会的要求 ,突出表现在以下几方面 :　　 (1 )原有的实验教学体系采用的是单一验证式知识型的教学模式。大部分化学实验是起验证作用 ,学生学习兴趣低 ,对所面对的实验只是粗略了解 ,无法深刻地理解实验的设计思想。学生的观察能力弱 ,从观察事物现象中获得的东西甚少 ,久而久之对观察不感兴趣 ,缺乏应有的求知欲。　…     

中学生化学实验设计初探

中学生化学实验设计是指按照实验目的及有关要求,遵循中学化学实验基本原理,制定的合理的实验方案。完整的实验设计应包括实验目的要求、实验仪器药品、实验步骤及现象、实验分析及结论等。     

基于实验的探究教学开发

实验既是化学学科发展的基础,又是化学教学的有效手段,以实验为基础开展探究教学是化学教学的方向之一。以实验目的、实验原理、实验装置、实验步骤、实验现象和实验结论等实验方案的要素为切入点为实验探究教学创造更多的实践途径,从而实现基于实验的探究教学在理念、思维和操作层面的发展。     

青霉素瓶在微型有机化学实验中的应用

由杭州师范学院研制的成套塑料微型仪器 ,被誉为“化学实验的重大改革 ,素质教育的得力工具”。现在已成功、广泛地应用于基础化学实验和无机定性实验。但其材料聚乙烯耐高温极差 ,易溶于有机溶剂 ,无法完成大多数有机实验。试用不同型号青霉素瓶做诸类有机实验 ,效果很好。1　强溶剂类实验烃类实验中用到松节油、苯、甲苯 ;醛、酮、醚 ,实验中用到的酮、乙醚这些物质是常见的有机溶剂 ,用井穴板做上述性质实验 ,瞬间软化 ,表面变粗 ,透明度降低。若改用带盖子青霉素瓶做该类实验 ,现象明显 ,空气污染程度小 ,实验后废液可统一回收处理。⑴…     

科学论证在化学实验探究中的应用——以氢氧化钠潮解现象的教学为例

化学实验探究中, 论证教学以学生对氢氧化钠潮解现象的不一致解释为契机, 然后通过实验收集证据, 以证据、推理和结论3个要素为框架做出论证, 最后修改与评价论证, 有目的地将论证融入到探究活动中。     

用实验指证几个错误的"想当然"

"实践是检验真理的唯一标准",对于化学问题中可能的现象以及对现象的解释我们都应通过实验验证或是结合其他资料来寻求合理的答案,而不可凭空臆测或是想当然.下面给出几个例证.希望借此让我们重视对引起因素的全面思考并重视通过实验探索求证.     

对氢硫酸变质(浑浊)、失效的再实验与再思考

半瓶装或敞口置放的氢硫酸容易变质(浑浊)、失效,这似乎是尽人皆知的常识,可我们的实验却意外地发现了许多新的实验事实和实验现象,很值得研究.     

利用手持技术改进测定乙醇分子结构实验

利用压强传感器代替排水集气法,改进测定乙醇分子结构实验的仪器装置,并探索最佳反应条件。另外,设计两个空白实验,结合压强变化曲线对实验误差进行相关讨论。     

光谱仪测试范围的扩展

由于石化行业的生产需要，其材质的使用具有多样性和广泛性，经常会出现顾客委托的测试样品的一个或几个元素跨越光谱仪现有测试程序测量范围的情况。本法通过对光谱仪测试原理的认识，根据光谱仪的测试能力及标样的采集，实现了一个或几个元素测量范围的扩展，并对其测量的影响因素进行了研究。     

Influence of viscosity of medium on processes of oxygen quenching of excited states of mesoporphyrin

The oxygen quenching rate constants for singlet and triplet excited states of the dimethyl ester of mesoporphyrin IX increase with decreasing viscosity of the medium and reach a maximum at a viscosity of approximately 0.4 mPa·sec, after which the rate constants begin to decrease. The drop in rate constant with increasing fluidity of the medium may be related to a nonequilibrium character of the elementary act in the interaction of the reactants in the solvent cage. In viscous media such as isopropyl alcohol, isobutyl alcohol, and isoamyl alcohol, the reaction radius is greater than the sum of the radii of the reacting particles. The long-range character of these processes is due to the relatively weak dependence of the quenching probability on distance.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 2, pp. 161–167, March–April, 1989.     

Dichroism of absorption and polarization of phosphorescence of molecules of the closed form of nitrobenzospirothiopyran

The spectral-polarization characteristics of absorption and phosphorescence of molecules of the initial form of nitro-substituted indolinospirobenzothiopyran were studied in oriented polyethylene films and in solutions with different polarity. An oscillator model of the electron transitions responsible for the formation of absorption and luminescence spectra was suggested. It was established that the principal differences in the spectral and photophysical properties of the compound studied and its oxygen-containing analog are associated with the fact that the electronegativity of the S atom is lower than that of the O atom. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1143–1146, June, 1997.     

Determination of heats of detonation and influence of components of composite explosives on heats of detonation of high explosives

The heats of detonation of 20 simple high explosives and explosive mixtures were determined by means of an adiabatic detonation calorimeter designed by the authors. The results indicated that the performance of the instrument was reliable and the experimental data were very accurate. For explosive mixtures, there was a linear accumulative relationship between the heats of detonation of the explosive mixture and its components. Accordingly, the heats of detonation of explosive mixtures could be calculated directly from the heats of detonation of simple explosives and the characteristic heats of other components. The experiments showed that the gold or brass shell of the cylindrical charge could be substituted by a thick-walled porcelain shell, which had the advantage of cheapness.

     

物质分配系数的测定实验改进

实验教学目的是从解决实际问题出发,以实验技术训练和实验设计思想培养为目标。介绍了将单一的物质分配系数测定实验改进为综合实验,提高了实验效果及实验资源利用率。     

Neutral diterpenoids of oleoresins of five species of conifers of Transcarpathia

The compositions of the neutral diterpenoids of the oleoresins of five species of conifers growing in the Transcarpathia have been studied. It has been found that the oleoresins ofAbies alba M.,Larix decidua M., andPicea excelsa L. contain more than 50% of neutral diterpenoids. The group and qualitative compositions of the oxygen-containing diterpenoids have been determined. In the oleoresins ofAbies alba,Picea excelsa, andPicea abies tertiary alcohols — cis-abienol and isocembrol — predominate, while inLarix decidua the main component is the hydroxy ester larixyl acetate. Primary alcohols related to the resin acids have been found in all the oleoresins investigated. Features of the distribution of diterpenoids according to the species of conifers have been revealed. The results obtained are necessary for the chemotaxonomy of conifers of the family Pinceae.Novosibirsk Institute of Organic Chemistry, Siberian Branch, Academy of Sciences of the USSR. Translated from Khimiya Prirodynkh Soedinenii, No. 6, pp. 812–816, November–December, 1988.     

Calculation of enthalpies of hydrogenation of hydrocarbons

Sets of hydrogen molecule equivalents have been developed which permit the calculation of hydrogenation of different types of carbon-carbon bonds from ab initio total energies (3-21G and 6-31G* basis sets, and, to a more limited extent, for MP2/6-31G* data) of reactants and products. The calculated enthalpies of hydrogenation are in good agreement with experiment for unstrained molecules, with average errors on the order of 2 kcal/mol. The 6-31G* equivalents allow the enthalpies for strained molecules to be calculated accurately, but the 3-21G equivalents do not. The equivalents for both basis sets have been tested by calculating the enthalpies of hydrogenation of carbon-carbon bonds in nitrogen- and oxygen-containing organic molecules, free radicals, and classical carbocations. The results are in good agreement with experiment in most cases.