中学化学教学中平衡常数的价值和意义的分析

高中《化学反应原理》新增设了化学平衡常数、电离常数、盐的水解常数、溶度积常数4项内容。通过分析得出,化学中的平衡常数是经过长期实验、推演得出的综合数值,它不但蕴含着化学平衡的知识内容、科学的实验方法,同时包含着丰富的人文精神。基于此提出平衡常数的教学可以增强学生的科学本质观,培养学生的科学方法观以及人文精神,利于提高学生的科学素养。     

《化学反应原理》中与化学平衡常数有关的几个问题

论证了中学教材为什么要引入化学平衡常数,讨论了中学教材中的化学平衡常数是经验平衡常数还是标准平衡常数,指出了应用平衡常数表达式进行计算时须遵循的规则。重现了人教版、鲁科版和苏教版《化学反应原理》教材中与化学平衡常数有关的几道例题及其解题过程,分析了解题过程中存在的问题,并提出了解决问题的策略。     

从科学概念本体和发展史视角对化学平衡相关问题的分析

中学化学教学中关于化学平衡的认识存在多种误区,本文先从科学概念本体的视角系统考察了化学平衡的相关概念,对各种认识误区进行了分析,明确了原有分析化学平衡问题的视角的缺陷;再从科学概念发展史的视角探讨了化学平衡问题的分析方法,确立了符合热力学基本规律的更科学、更实用的化学平衡问题的分析工具——平衡常数;最后明确了基于平衡常数的化学平衡的相关认识及其基于平衡常数的平衡观构建的重要价值,可促进教师更加科学地认识化学平衡问题,关注并在教学中落实化学平衡常数的教学价值,为中学化学中四大平衡的教学提供借鉴和参考。     

关于化学实验平衡常数和化学标准平衡常数

大学化学中化学平衡常数是一个涉及知识面很广又经常使用的重要常数。由于平衡常数的获得方法不同,造成平衡常数的名称不同,概念不同,适用范围不同,甚至有时数值也不尽相同。     

勒夏特列原理和化学平衡常数学习现状的调查分析和教学反思

1问题的提出化学平衡是化学反应原理的一个重要课题,新课程更不例外,但新教材引入了平衡常数,课程标准要求学生知道平衡常数的含义。那么现在学生在解决化学平衡问题时是更习惯用传统的勒夏特列原理还是新引入的平衡常数呢?平衡常数的引入能否     

凸显“定性与定量相结合”化学思想方法的教学设计——以“化学平衡常数”为例

将"定性与定量相结合"的思想方法运用于化学平衡常数的教学,利用经典实验和简单反应,以已有定性认知为基础,突出定量探究,彰显平衡常数定性和定量的双重特征,关注定性分析和定量分析的差异性和统一性,突出化学平衡常数的应用价值。     

运用溶度积计算平衡常数解答疑难问题

运用溶度积计算出与氢氧化镁沉淀相关的反应、与硫化铜沉淀相关的反应、与碳酸钙沉淀相关的反应的平衡常数。通过以上的计算与分析,让学生熟练掌握了运用溶度积计算化学平衡常数,从而判断反应能否发生。     

发挥核心概念“平衡常数”教学功能的化学平衡复习教学的研究

结合化学平衡复习课的教学现状,分析了化学平衡复习教学的定位和学生的已有认识,阐明了平衡常数是化学平衡复习教学中的核心概念,具有促进平衡知识结构化和解决分析平衡问题思路方法的功能。还进行了发挥核心概念"平衡常数"教学功能的化学平衡复习的教学设计和实践研究,取得了较好的教学效果,探讨了有效的教学策略。     

平衡常数计算中的单位问题

化学平衡常数是基础化学中一个重要的概念。学习时常有人提出:平衡常数有没有单位?一般教材中是不标明单位的,但在计算中又为什么特别强调所用量的单位?在推行国际单位制后,对化学平衡常数的计算带来什么影响?关于第一个问题已有多篇文章阐明,这里不再赘述。本文就后两个     

化学平衡解题通用方法探讨*

对于复杂的化学平衡,平衡时刻浓度、分压、物质的量、转化率之间存在错综复杂的关系,给解题带来了很大难度。提出了“列表-设未知数-计算分压-计算平衡常数-求解”的5步解题通用方法,并利用该方法,结合CASIO计算器独特的解题特色,对近几年化学竞赛中出现的2道化学平衡试题进行了剖析。     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.