凝固点降低法测定物质摩尔质量实验的改进

通过实验试剂的选择和引进凝固点测定软件对凝固点降低法测定物质摩尔质量的实验进行改进。选用水作溶剂测定尿素的摩尔质量,解决了环保问题;使用凝固点测定软件,使实验过程通过电脑绘制步冷曲线,降低了人为误差,实验结果的精确度明显提高。     

第5届全国大学生化学实验邀请赛(试卷C1)实验C1 凝固点降低法测定未知物的摩尔质量

一、实验目的 (1)掌握凝固点降低法测定物质的摩尔质量的基本原理与实验技术. (2)测定水的凝固点降低值,计算未知物的摩尔质量.     

凝固点降低测定物质摩尔质量实验装置的改进

介绍一种改进的凝固点降低法测定物质摩尔质量的实验装置,通过调节合适的阻凝温度与散热补偿电流,对样品凝固点的测定精度可以达到±0.003℃,对样品摩尔质量的测定误差可控制在0.5%左右。     

凝固点降低法测定摩尔质量实验装置的改进

对凝固点降低法测定摩尔质量的实验装置进行了改进。改进后操作简单,所得结果准确。     

介绍一个绿色物理化学实验——凝固点降低法测定葡萄糖的摩尔质量

以葡萄糖-水为体系对传统的凝固点降低法测定摩尔质量实验进行了改进,以低温小钢珠代替晶种,建立了一种控制过冷深度的有效方法;利用干燥的方法解决了葡萄糖样品中结晶水不确定的问题。     

凝固点降低法测定摩尔质量实验方法改进

以差示扫描量热法（DSC）测定环己烷溶液的凝固点降低值。在降温速率1℃·min^-1、氮气气氛下,测定了叔丁醇和甘油的环己烷溶液的凝固点降低值,计算了两种物质的摩尔质量,误差在10％之内。     

凝固点降低法测定摩尔质量实验改进

用改进的凝固点测量管 ,在 - 5℃和 - 1℃双温冷却剂中测量葡萄糖等物质的摩尔质量 ,比其他方法操作简便 ,所测的表观摩尔质量值更接近实际值     

“凝固点降低法测定分子量”实验的改进

“凝固点降低法测定分子量”实验是基础物理化学实验中的一个经典实验.而以往的体系是:以苯作溶剂,以萘作溶质.此体系有以下几个缺点:(1)、苯易挥发,其蒸气对人体有害;(2)、废液不便回收利用,若排出又会造成环境污染;(3)、实验费用较高.     

双差示法测定溶液凝固点下降

提出一种测定溶液凝固点下降的新方法。将溶液和纯溶剂同时置于冷浴中，用半导体制冷块降温。用温度探头分别感应纯溶剂（Ｒ）、溶液（Ｓ）和冷浴（Ｗ）的温度：ＴＲ、ＴＳ和ＴＷ，并组成两个惠斯登电桥指示温差。当（ＴＲ－ＴＳ）－（ＴＳ－ＴＷ）出现最大值时，（ＴＲ－ＴＳ）为溶液凝固点下降值。本方法需要搅拌，降温速率以０８—３０Ｋ／ｍｉｎ为宜。测定了萘苯溶液的凝固点下降值，苯中萘浓度２０—７００ｍｍｏｌ／Ｌ时线性良好。     

步冷曲线法——对凝固点降低测定摩尔质量的改进

要测量溶剂和溶液的凝固点之差,对于纯溶剂如图1(a)所示,凝固点是在一定时间内固定不变。但对于溶液,除温度外还有溶液浓度的影响。当晶体生成,放出的凝固热使体系温度回升,由于不断析出溶剂晶体,溶液的浓度逐渐增大,凝固点会逐渐降低。因此,凝固点不是一个恒定值。以前通常把回升到最高点的温度作为凝固点,由于这时已有溶剂晶体析出,所以溶液浓度已不是起始浓度,该凝固点也已不是原浓度的凝固点。由图1(b)可以看出,这时的凝固点比实际凝固点要低,以此数值计算出的ΔTf要大于真值,最后计算出的摩尔质量要小于真值。建议测出步冷曲线,按图1(…     

Novel Sampling for the Determination of Naphthalene in Air by Gas Chromatography–Mass Spectrometry

Here are reported two new sampling method approaches for the determination of naphthalene in ambient air for concentrations from 0.25 to 18.7?µg/L. The first method used for gas phase naphthalene analysis produced an average recovery of 88.8% and the second method using headspace sampling produced an average recovery of 93.8%. The second method showed better recovery than the former, so it was used for subsequent comparative gas-phase determination of naphthalene. The second method was validated at various naphthalene concentrations and humidity using a naphthalene gas generator to produce various naphthalene standards and a naphthalene-monitoring instrument. The naphthalene concentrations generated using the gas generator and determined second sampling method with gas chromatography–mass spectrometry (GC–MS) were compared to the sensor measurements and were in good agreement. In summary, the sampling methods presented provided reliable gas-phase naphthalene determination when coupled with GC–MS.     

Preconcentration and determination of naphthalene in air and water using activated carbon adsorption,carbon disulfide extraction and gas chromatography

A new method for the determination of naphthalene in air and water has been developed. The naphthalene was preconcentrated using activated carbon adsorption with carbon disulfide extraction and determined by gas chromatography with flame ionization detection. The chromatographic peak of naphthalene was separated well from the potential interferents turpentine, terpenene, isoborneol, camphor and isobornyl acetate. The detection limit was 0.52 g/ml of CS₂, equivalent to 2.6 g/m³ of air or 0.05 g/ml in 50 ml of water. The precision for 10 g/ml naphthalene was 1.7%. The adsorption capacity, sampling efficiency and desorption efficiency of 100 mg of activated carbon for naphthalene in air were 8.8 mg, 98.8% and 95.2%, respectively. The extraction efficiency of 5 ml of carbon disulfide for naphthalene in water was 97.6%. The method was successfully applied to the determination of naphthalene in air and water from an industrial plant.     

凝胶点前氯乙烯－邻苯二甲酸二烯丙基酯共聚物表征，支化度模型及悬挂双键活性

根据单烯－二烯自由基共聚合反应特点，提出一种新的支化点对分子量的分布模型，讨论了用凝胶色谱－特性粘数法表征文化聚合物时，文化点对分子量分布和式［η］０，ｂ／［η］０．１＝ｇ０中的指数ｃ对结果的影响．建立了氯乙烯－二烯类单体悬浮聚合凝胶点前的平均支化度模型．用凝胶点前平均文化度和平均分子量模型拟合实验结果发现：ａ．新的支化分布模型更合理，且ｃ＝０．７２；ｂ．悬挂双键活性下降一个数量级；ｃ．对本文样品，特性粘数和分了量仍符合Ｍａｒｋ－Ｈｏｕｗｉｎｋ方程，［η］＝０．２３５７Ｍ￣０．５２７．     

Predictions of molecular geometries and electronic spectra of complex unsaturated molecules from MC-LCAO-MO method with particular reference to triplet-triplet transitions of naphthalene

An MC-LCAO-MO approach which has been proposed for open-shell systems of unsaturated hydrocarbons having degenerate MO's is applied to naphthalene, calculating its molecular geometry and electronic spectrum. The results are compared with those obtained by the usual semi-empirical SCF-CI method and with experiment. As for benzene, anthracene, phenanthrene and triphenylene, the bond lengths and the -electron energies in their ground states are calculated in the same manner. Most of the calculated bond lengths are in fairly good agreement with experiment. The total -electron energies of the ground states obtained by the MC-LCAO-MO and SCF-CI methods agree within about 0.01 eV when CI is included and within about 0.1 eV when CI is not invoked. It is found that the electronic spectrum of naphthalene obtained by the present method is in good agreement with that derived from the SCF-CI method and also explains most part of experiments. A detailed discussion is given on the calculated triplet-triplet absorption spectrum and its intensity distribution of naphthalene.     

Matrix-assisted laser desorption ionization time-of-flight mass spectrometry for the analysis of polydienes

An analytical method based on matrix-assisted laser desorption ionization (MALDI) time-of-flight mass spectrometry has been developed to provide information on oligomer structure, average molecular weight, and molecular weight distributions of polydienes (e.g., polybutadiene and polyisoprene), an important class of industrial polymers. This MALDI method involves the use of all-trans-retinoic acid as the matrix, copper (II) nitrate as the cationization reagent, and tetrahydrofuran as the solvent. The incorporation of this copper salt generates Cu⁺ adducts with the polymer chains. It also improves the signal strength and extends the upper mass range when used with all-trans-retinoic acid, as compared to silver nitrate. With this formulation, it is demonstrated that polybutadienes of narrow polydispersity with masses up to 300,000 u and polyisoprenes of narrow polydispersity with masses up to 150,000 u can be analyzed. The upper molecular weight limit is set by the requirement of using higher matrix-to-polymer ratios with increasing polymer molecular weight, to the point where the instrument can no longer detect the small quantity of polymer present in the matrix host. It is also shown that this sample preparation generates previously unreported adduction behavior. The practical implications of this adduction behavior on polymer structural analysis, accuracy of molecular weight determination, and the upper molecular weight limit of oligomer resolution are discussed. It is illustrated that, in a linear time-lag focusing MALDI instrument, oligomer resolution can be obtained for polydienes with molecular weights up to 24,000, providing structural confirmation of the end-groups and the repeat unit. The average molecular weights of a number of polydienes of narrow polydispersity determined by MALDI are compared to those obtained by gel permeation chromatography, and discrepancies are noted.     

Weight loss and isotopic shifts for water drops frozen on a liquid nitrogen surface

A liquid nitrogen freezing method was used to collect raindrops for the determination of isotope-size distribution. Water drops that fall onto a surface of liquid nitrogen stay suspended for 10 to 20 s, until their temperature reaches the Leidenfrost point (126 K). As their temperature falls to the freezing point, they release their heat by thermal conduction. At the freezing point, latent heat of fusion is released, along with a significant loss of water. After freezing completely, the ice droplets stay suspended, cooling by thermal conduction until they reach the Leidenfrost point. They then lose buoyancy and start sinking. Consistent isotopic changes of 1.5 +/- 0.4 and 0.33 +/- 0.05 per thousand for hydrogen and oxygen, respectively, were found for droplets with radii between 1.0 and 1.5 mm. Isotope fractionation appeared to occur at the same time as water loss, as the droplets were freezing, in what was probably a kinetic effect.     

用MALDI-TOF-MS法快速测定天花粉蛋白分子量

采用ＭＡＬＤＩ－ＴＯＦ－ＭＳ法快速测定了天花粉蛋白的分子量,并讨论和对比了三种不同基质对其影响,认为用基质芥子酸是最佳适宜条件。实验结果表明本方法优于其它传统的测定生物大分子分子量方法。     

Negative temperature programming in SFC with packed capillary colums

Summary A simple method to produce negative, asymptotic temperature programming was developed by modifying a GC temperature programmer, which allowed to control the density of a supercritical fluid near its critical point. When a packing material with relatively large particles (40m) was used, the flow rate was maintained constant during the temperature programming. This method was applied to the determination of molecular weight distribution of polystyrene oligomers.     

水溶性聚合物和两性聚合物——Ⅰ.环氧乙烷-苯乙烯-环氧乙烷三嵌段聚合物(PEO—PSt—PEO)的合成和表征

用萘钠为引发剂的相继阴离子聚合合成了环氧乙烷-苯乙烯-环氧乙烷三嵌段聚合物(PEO-PSt-PEO),对经纯制的嵌段聚合物和母体聚苯乙烯用粘度法、GPC、¹H-NMR、折光指数增量(dn/dc)和溶解性测定等方法进行了表征。发现:1.在高引发剂浓度下,聚苯乙烯的[η]和M反而随[M]/[I]的减小而增加,说明存在引发剂的自抑制效应;2.嵌段聚合物在三种不同溶剂中的dn/dc与其组成有良好的线性关系,因此,dn/dc测定可作为确定嵌段聚合物组成的一个可靠方法;3.PEO-PSt-PEO三嵌段聚合物在THF中GPC谱图的峰值分子量与母体聚苯乙烯相似;4.聚苯乙烯含量较低的嵌段聚合物在THF中的溶解性较差。     

正十六烷体系凝固过程的分子动力学模拟

采用分子动力学模拟的方法,根据体系热容和自扩散系数的突变,计算了正十六烷体系以及正十六烷和降凝剂α-辛基萘、α-十二烷基萘及α-十六烷基萘等α-烷基萘混合体系的凝点,凝点降低结果与实验值相一致.用径向分布函数及末端距离分布对凝固温度附近体系的微观结构变化进行了研究.结果表明,凝固过程中正十六烷分子倾向于转变成为全反式的构象,以利于分子间平行有序的排列,这和熵减小的原理相一致.结合正十六烷的构象变化,探讨了烷基萘降凝的机理.