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A kinetic spectrophotometric method for determination of trace nitrite in two dynamic ranges (2–100 and 100–500 ng/mL) based on its catalytic effect on the reaction between methylthymol blue and potassium bromate in acidic (sulfuric acid) media is described. The reaction was monitored spectrophotometrically by measuring the decreasing color of methylthymol blue at 437 nm by the fixed‐time method of 4.0 min at 30°C. The detection limit is 0.6 ng/mL, and the relative standard deviations for 50.0 and 250.0 ng/mL nitrite are 1.6% and 1.3%, respectively. The method was used for the determination of nitrite in water samples. 相似文献
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以明矾的净水作用蕴含的化学反应原理为例,着重分析高中“化学1”模块内的7处教学衔接,进而简要论述高中选修模块“化学与生活”“化学反应原理”中的教学衔接。运用思维导图、模型图、概念图、流程图等图示思维教学方式,进行模块内和模块间的知识衔接教学,有利于强化学科理解能力,培养学生的化学核心素养。 相似文献
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Highly regioselective homocoupling of N,N-dialkylanilines can be achieved in water with cerium reagents, in which various N,N,N′,N′-tetraalkylbenzidines are obtained from N,N-dialkylanilines either by direct oxidation by cerium(Ⅳ)reagents or by cerium(Ⅲ) reagents in the presence of hydroperoxide. 相似文献
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We have determined the activation parameters logA and E for the Arrhenius equations for the kinetic isotope effect (c-C6H12/c-C6D12) and the 5/6 effect (c-C5H10/c-C6H12) in reactions of the C—H bonds of cycloalkanes with HOCl in aqueous solutions in the interval 30-90 °C. The data obtained are consistent with a chlorination mechanism including a pre-activation step with formation of an HO· ... Cl· pair, linear abstraction of the H atom by the OH group and angular attack by the Cl atom "at a distance" on the carbon atom. 相似文献
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Justyna Wiktorowicz 《Phosphorus, sulfur, and silicon and the related elements》2014,189(7-8):1144-1148
Abstract13C kinetic isotope effect (KIE) was determined by means of 13C NMR for the carbonyl atom in 2-nitrobenzaldehyde in its reaction with 2H-2-oxo-5,5-dimethyl-4-phenyl-1,3,2-dioxaphosphorinane in acetonitrile at 25°C. The observed isotope effect k12/k13 = 1.0238 ± 0.0031 evidences that the formation of the P?C bond in the Pudovik reaction catalyzed by triethylamine is less advanced than the π-bond breakage of the aldehyde carbonyl group. 相似文献
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在硫酸介质中,亚硝酸盐对溴酸钾氧化苯胺蓝褪色反应有明显的催化作用,据此提出了测定痕量亚硝酸盐催化分光光度方法。优化的试验条件如下:1 1.0mol·L-1硫酸溶液的用量为1.8mL;2 3×10-4 mol·L-1苯胺蓝溶液用量为1.5mL;3 0.02mol·L-1溴酸钾溶液用量为1.1mL;4反应温度为30℃。该方法的线性范围分别为0.01~0.2mg·L-1和0.2~1.0mg·L-1,检出限(3s/k)为4.6×10-6g·L-1。方法用于水样的分析,回收率在96.0%~104%之间,测定值的相对标准偏差(n=6)在1.6%~2.3%之间。 相似文献
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铁与水蒸气的反应除生成Fe3O4外,是否还有其他铁的氧化物生成呢?该反应为何要用酒精喷灯加强热?如果用酒精灯加热,铁粉能否被氧化?实验时有氢气生成,则铁能被氧化,那么其氧化产物又是什么呢?就这些问题,在查阅了资料的基础上做以下分析说明。1对课本上铁与水蒸气反应的研究该反 相似文献
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The hydrogen isotope separation factor decreases with increasing overvoltage on mercury-like electrodes in acid solutions. This dependence qualitatively differs from that for the ratio between hydrogen evolution rates in light and heavy water, which increases with polarization. The reason for the difference is that the isotope separation factor depends on the kinetic isotopic effect (KIE) in two reaction stages: discharge and electrochemical desorption. Experimental data show that a decrease in KIE with potential in the latter stage outweighs the increase in KIE in the former. The KIE decreases in the desorption reaction because this process is activationless; therefore, there is no potential dependence of the relative contribution made by vibrationally excited states of the product in this case, i.e. no dependence that is responsible for the increase in KIE at the discharge stage. The same factor has no effect on KIE for a barrierless discharge, which also decreases with increasing overvoltage. Thus, all experimentally observed dependences of KIE on potential are explained in the framework of a unified approach. 相似文献
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铝与硫酸铜溶液反应置换出铜的效果极差,但铝在有卤离子存在的铜盐溶液中反应置换出铜的效果极好。通过一系列实验对其原因进行研究,并对课堂教学中用铝与铜盐溶液反应的实验探究提出建议。 相似文献
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水中的碘酸根、亚氯酸根和溴酸根是重要的消毒副产物,主要通过大体积浓缩后直接电导检测,或通过柱前或柱后化学反应将目标物转化成容易检测的物质后检测。本方法采用大体积进样柱后衍生紫外检测的分析方法,通过条件优化获得了较高的灵敏度和信噪比。利用一套自动分析系统,可以满足饮用水中痕量碘酸根、亚氯酸根、溴酸根的同时监测。碘酸根、亚氯酸根和溴酸根的检出限分别为0.5,0.4,0.1 μg/L。对于不同的加标样品,碘酸根、亚氯酸根和溴酸根的回收率分别为70.8%~98.0%,92.4%~100%和93.2%~104.1%。该方法应用于北京市场上的瓶装饮用水分析,结果显示瓶装纯净水中的碘酸根、亚氯酸根、溴酸根浓度均低于检出限,而瓶装矿泉水中碘酸根、溴酸根的最高含量分别达到9.4 μg/L和78.4 μg/L。 相似文献
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《Analytical letters》2012,45(11):2015-2023
Abstract A flow injection kinetic method has been developed for the determination of nitrite, based on its catalytic effect on bromate oxidation of chlorophosphonazo-pN in H2SO4 medium. The reaction is followed spectrophotometrically by measuring the decrease in the absorbance at 551 nm. The sampling frequency was 83 h?1. The calibration curve was linear between 0.050 and 1.00 μg/ml, and the detection limit was 0.018 μg/ml. The proposed method was applied to the determination of nitrite in waters and soil with satisfactory results. 相似文献
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A sensitive flow injection method is proposed for the determination of formaldehyde based on its catalytic action upon the redox reaction between crystal violet and potassium bromate in phosphoric acid medium. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of crystal violet injected at the maximum absorption wavelength of 600nm. A calibration graph from 0.018 to 1.400µgmL–1 is obtained, and the detection limit is 0.007µgmL–1 in a sample volume of 30µL. Up to 15 samples can be analyzed per hour with a relative standard deviation of 1.2 and 2.3%, respectively, for the determination of 1.0 and 0.1µgmL–1 of formaldehyde. The method is free from most interference. This method has been applied to the determination of formaldehyde in air, decoration boards and paints, and the results compare well with those provided by iodimetry. 相似文献
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1.问题的提出
过氧化钠与水反应的实验是中学化学课堂重点演示实验,从目前情况看该实验的研究还有许多亟待解决的问题.特别是过氧化钠与水反应生成氧气质量的理论计算和实验结果的矛盾[1]、过氧化钠与水反应后溶液具有漂白性的原因[2-3]、双线桥标出过氧化钠与水反应过程中电子的得失[4]等疑难问题更为突出,所以从实验和理论上对上述疑难问题加以认真的研究是非常必要的. 相似文献
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从铝的电极电势可知,理论上铝能和水反应产生氢气;同时,汞齐化的铝片在潮湿的空气中可与氧气发生反应。基于以上原理,笔者改进并设计了铝和水反应的连续实验。 相似文献
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基于BrO3-与I-在酸性介质中发生氧化还原反应形成具有紫外吸收的I3-的性质,采用了紫外分光光度法测定水体中微量溴酸盐含量,方法加标回收率在98%~102%之间,相对标准偏差RSD为1.7%,线性相关系数为0.9991,检测限为4.0μg/L,能满足现有标准的检测要求。 相似文献
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建立一种检测饮用水中痕量溴酸盐的离子色谱方法。利用On GuardⅡAg柱过滤去除水中氯离子,直接进样,电导检测器检测。该方法避免了氯离子对溴酸盐的干扰,测定水质溴酸盐的灵敏度和准确度均有很大提高。溴酸盐的检出限为0.005 mg/L,测定结果的相对标准偏差为7.56%(n=7),加标回收率为92.0%~110.0%。该方法操作简便快速、准确度高,适合于饮用水中痕量溴酸盐的测定。 相似文献