氮化镁的制取及其性质实验

镁条在空气中燃烧可以生成MgO 和Mg3N2,MgO是一种白色的固体物质,这是大家都熟悉的结论.Mg3N2是一种什么样的物质呢?由于镁条在空气中燃烧生成的产物中所含Mg3N2的量极低,所以我们很难据此实验说明Mg3N2的性质,<无机化学>教材中也没有说明Mg3N2的制取方法和性质.为了说明此问题,笔者经反复研究[1],确定了在中学化学实验室中简易可行的制取氮化镁及证明氮化镁性质的实验方案.     

对氮化镁制备及性质的再探讨

通过探究实验,结合文献资料,对镁在空气中燃烧是否有氮化镁生成和为何难以观察或检验的原因提出个人看法.     

铝热反应实验的改进

1 问题的提出 笔者认为教材[1～3]中铝热反应实验存在如下问题:(1)镁条不易点燃;(2)镁条燃烧产生的强光对眼睛有害;(3)反应过程中产生大量的烟.针对上述问题,我们进行了如下改进.     

镁条表面“灰黑色外衣”的探究

金属表面锈蚀物的成分比较复杂。镁是一种活泼金属,在空气中也容易生锈。但在空气中久置的镁条表面的"灰黑色物质"到底含有哪些物质?着重研究镁条表面的锈蚀物的形成过程及镁锈的主要成分。     

谈初中化学基本概念的教学

遵循认识事物的规律,依据学生的知识水平和智力水平,从以下几个方面入手教授化学基本概念。一、从实验事实引出概念课堂演示实验可以很好地集中学生的注意力,由教师对演示实验的现象分析、引导学生正确地推理,来形成化学基本概念。例如,在讲授化学变化与物理变化两个概念时,除了演示镁条燃烧和加热碳酸氢铵分解两个实验外,还可以补充一个对比实验,即用剪刀将纸剪碎和将纸点燃的两个小实验。     

污水污泥的燃烧特性

通过对几种污泥样品进行热重分析,研究了污泥的燃烧特性,根据燃烧实验所得的热失重曲线,对几种污泥的燃烧过程进行了分析,对实验数据进行处理,采用Ｐｈａｄｎｉｓ法微分法相结合的方法确定了燃烧反应机理并求出了反应动力学常数Ａ和Ｅ。在燃烧的不同阶段,总反应速度控制因素不同。     

酚酞遇碱褪色又一说

通过实验的方法,探究镁条与沸水反应的实验中酚酞在稀碱溶液里褪色的原因,以及温度对一些常用酸碱指示剂的变色范围的影响。     

围绕教育功能进行实验改进和教学——以“燃烧的条件”实验为例

以初中化学"燃烧的条件"实验为例,首先从科学方法、科学知识、转变学生认识等3个方面分析其教育功能,然后在此基础上从对比实验和认识逻辑2个角度对人教版《义务教育教科书化学(九年级上册)》"燃烧的条件"实验进行了分析,进而提出对该实验的改进意见和教学建议。     

三硝基均苯三酚金属(Li,Na, K,Mg)化合物的快速热分解

利用温度快速跃升傅立叶变换红外(T-jump/FTIR)原位分析技术对三硝基均苯三酚(TNPG, 2,4,6-三硝基-1,3,5-苯三酚)的锂、钠、钾、镁金属盐的快速热分解反应过程进行了系统研究. 确定了三硝基均苯三酚系列化合物快速热分解过程产生的可挥发金属化合物的类型, 得到了快速热分解过程主要红外活性气体产物的种类、分布及浓度随时间的变化关系曲线, 提出了其快速热分解方程式. 利用计算机模拟方法, 采用REAL程序对三硝基均苯三酚系列化合物的燃烧性能(燃烧产物和燃烧温度等参数)进行了计算, 与T-jump/FTIR分析技术得到的实验结果进行比较分析和讨论.     

煤燃烧过程中表面形态变化规律的研究

以分形几何为理论工具,采用低温氮气吸附法,对四种煤在低温燃烧过程中表面形态变化作了考察。通过对原煤及燃烧过程中煤焦表面分维的测定,结合实验中所测得的比表面积,分析得到了煤燃烧过程中表面结构的变化历程,揭示出此种气因多相瓜在具有分形动力学的行为特征。     

Di­methyl­phenyl­sulfonium tri­fluoro­methane­sulfonate and methyl­di­phenyl­sulfonium tri­fluoro­methane­sulfonate

The bonding geometry of sulfur in the cations of the title compounds, C₈H₁₁S⁺·CF₃SO₃^? and C₁₃H₁₃S⁺·CF₃SO₃^?, respectively, is similar and is independent of the ratio of the Me/Ph substituents. As expected, in both cations, the S—Ph bonds are somewhat shorter than the S—Me bonds. In both crystal structures, the interaction between cations and anions is similar.     

2,4‐Di­nitro­phenyl­hydrazones of 2,4‐di­hydroxy­benz­aldehyde, 2,4‐di­hydroxy­aceto­phenone and 2,4‐di­hydroxy­benzo­phenone

In 2,4‐di­hydroxy­benz­aldehyde 2,4‐di­nitro­phenyl­hydrazone N,N‐di­methyl­form­amide solvate {or 4‐[(2,4‐di­nitro­phenyl)­hydrazono­methyl]­benzene‐1,3‐diol N,N‐di­methyl­form­amide solvate}, C₁₃H₁₀N₄O₆·C₃H₇NO, (X), 2,4‐di­hydroxy­aceto­phenone 2,4‐di­nitro­phenyl­hydrazone N,N‐di­methyl­form­am­ide solvate (or 4‐{1‐[(2,4‐di­nitro­phenyl)hydrazono]ethyl}benzene‐1,3‐diol N,N‐di­methyl­form­amide solvate), C₁₄H₁₂N₄O₆·C₃H₇NO, (XI), and 2,4‐di­hydroxy­benzo­phenone 2,4‐di­nitro­phenyl­hydrazone N,N‐di­methyl­acet­amide solvate (or 4‐­{[(2,4‐di­nitro­phenyl)hydrazono]phenyl­methyl}benzene‐1,3‐diol N,N‐di­methyl­acet­amide solvate), C₁₉H₁₄N₄O₆·C₄H₉NO, (XII), the molecules all lack a center of symmetry, crystallize in centrosymmetric space groups and have been observed to exhibit non‐linear optical activity. In each case, the hydrazone skeleton is fairly planar, facilitated by the presence of two intramolecular hydrogen bonds and some partial N—N double‐bond character. Each molecule is hydrogen bonded to one solvent mol­ecule.     

Bis(μ‐hexa­methyl­enetetr­amine)­bis(aqua­di­bromo­cadmium)­di­aqua­di­bromo­cadmium dihydrate

The title compound, poly­[[di­aqua­di­bromo­cadmium‐μ‐(1,3,5,7‐tetra­aza­tri­cyclo[3.3.1.1^3,7]decane‐N¹:N⁵)‐aqua­cad­mium‐di‐μ‐bromo‐aqua­cadmium‐μ‐(1,3,5,7‐tetra­aza­tri­cyclo[3.3.1.1^3,7]decane‐N¹:N⁵)‐di‐μ‐bromo] dihydrate], [Cd₃­Br₆­(C₆­H₁₂­N₄)₂­(H₂O)₄]·­2H₂O, is made up of two‐dimensional neutral rectangular coordination layers. Each rectangular subunit is enclosed by a pair of Cd₃(μ₂‐Br)₆(H₂O)₃ fragments and a pair of (μ₂‐hmt)Cd(H₂O)₂Br₂(μ₂‐hmt) fragments as sides (hmt is hexa­methyl­enetetr­amine). The unique Cd^II atom in the Cd₂Br₂ ring in the Cd₃(μ₂‐Br)₆(H₂O)₃ fragment is in a slightly distorted octahedral CdNOBr₄ geometry, surrounded by one hmt ligand [2.433 (5) Å], one aqua ligand [2.273 (4) Å] and four Br atoms [2.6409 (11)–3.0270 (14) Å]. The Cd^II atom in the (μ₂‐hmt)Cd(H₂O)₂Br₂(μ₂‐hmt) fragment lies on an inversion center and is in a highly distorted octahedral CdN₂O₂Br₂ geometry, surrounded by two trans‐related N atoms of two hmt ligands [2.479 (5) Å], two trans‐related aqua ligands [2.294 (4) Å] and two trans‐related Br atoms [2.6755 (12) Å]. Adjacent two‐dimensional coordination sheets are connected into a three‐dimensional network by hydrogen bonds involving lattice water mol­ecules, and the aqua, bromo and hmt ligands belonging to different layers.     

Tetra­phenyl­phos­phonium 4‐hydroxy‐2,2,6,6‐tetra­methyl­piperidinyl­oxy‐4‐sulfonate

The title compound, C₂₄H₂₀P⁺·C₉H₁₇NO₅S⁻, consists of an organic monovalent cation and an organic monovalent anion, the latter being derived from the TEMPO radical (TEMPO is 2,2,6,6‐tetra­methyl­piperidin‐1‐oxyl). Two inversion‐related anions interact via two –O—H⃛O—S– hydrogen bonds, forming a dimer in which there are no short contacts between the spin centres (–N—O) of the TEMPO(OH)SO₃⁻ anions. Furthermore, no significant magnetic interaction is observed between the dimers because the dimer is surrounded by cations. These results are consistent with the paramagnetic behaviour of the title salt.     

9,10‐Di­phenyl‐9,10‐epi­dioxy­anthra­cene and 9,10‐di­hydro‐10,10‐di­methoxy‐9‐phenyl­anthracen‐9‐ol

9,10‐Di­phenyl‐9,10‐epi­dioxy­anthracene, C₂₆H₁₈O₂, (I), was accidentally used in a photo­oxy­genation reaction that produced 9,10‐di­hydro‐10,10‐di­methoxy‐9‐phenyl­anthracen‐9‐ol, C₂₂H₂₀O₃, (II). In both compounds, the phenyl rings are approximately orthogonal to the anthracene moiety. The conformation of the anthracene moiety differs as a result of substitution. Intramolecular C—H⃛O interactions in (I) form two approximately planar S(5) rings in each of the two crystallographically independent mol­ecules. The packing of (I) and (II) consists of molecular dimers stabilized by C—H⃛O interactions and of molecular chains stabilized by O—H⃛O interactions, respectively.     

Methyl­tri­phenyl­stibonium tetra­fluoro­borate

In the title compound, [Sb(CH₃)(C₆H₅)₃]BF₄, there are four independent cations and anions in the asymmetric unit. The geometry around the Sb atom is distorted tetrahedral, with Sb—C distances in the range 2.077 (4)–2.099 (10) Å and angles at the Sb atom in the range 103.3 (3)–119.0 (4)°.     

2,4,6‐Tri­chloro­phenyl­iso­nitrile and 2,4,6‐tri­chloro­benzo­nitrile

The molecular structures of the title compounds, 2,4,6‐tri­chloro­phenyl­iso­nitrile (IUPAC name: 2,4,6‐tri­chloro­phenyl isocyanide), C₇H₂Cl₃N, and 2,4,6‐tri­chloro­benzo­nitrile, C₇H₂Cl₃N, are normal. The two structures are not isomorphous, but do contain similar two‐dimensional layers in which pairs of mol­ecules are held together by pairs of Cl?CN [3.245 (3) Å] or Cl?NC [3.153 (2) Å] interactions. The two‐dimensional isomorphism is lost through different layer‐stacking modes.     

{[(N‐Methyl‐p‐toluidino)­di­phenyl­phospho­ranyl­idene]­methyl}(N‐methyl‐p‐toluidino)­di­phenyl­phospho­nium iodide

The cationic part of the homodifunctional amino­phospho­ranyl ligand, C₄₁H₄₁N₂P₂⁺·I^?, shows interesting features associated with the N—P—C—P—N skeleton. The P—C(H) bond distances [1.696 (3) and 1.697 (3) Å] possess partial double‐bond characteristics. The nature of the P—C(H) and P—N bonds suggests that the positive charge is only distributed around the P—C—P atoms. The structure has near twofold symmetry through the central methyl­ide‐C atom.     

Specific heat on Sr<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>7</Subscript> and Sr<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>7</Subscript>

Summary Specific heats on the single crystals of Sr₂Nb₂O₇, Sr₂Ta₂O₇ and (Sr_1-xBa_x)₂Nb₂O₇ were measured in a wide temperature range of 2-600 K. Heat anomalies of a λ-type were observed at the incommensurate phase transition of T_INC (=495 K) on Sr₂Nb₂O₇ and at the super-lattice phase transition of T_SL (=443 K) on Sr₂Ta₂O₇; the transition enthalpies and the transition entropies were estimated. Furthermore, a small heat anomaly was observed at the low temperature ferroelectric phase transition of T_LOW (=95 K) on Sr₂Nb₂O₇. The transition temperature T_LOW decreases with increasing Ba content x and it vanishes for samples of x>2%.     

Glass formation in the CaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> and SrO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> systems

A physicochemical study of glasses based on the MO-Bi₂O₃-B₂O₃ and SrO-Bi₂O₃-B₂O₃ systems was performed. Glass formation regions were found. The structural and optical properties, as well as the thermal behavior of the glasses, were studied.