石蕊溶液与苯混合后现象的探究

为了研究苯能否从石蕊溶液中萃取出石蕊,通过用相机记录实验现象的方法,对用不同方法配制的3种石蕊溶液与苯混合振荡后经历不同时间后的现象进行研究,发现苯层不能呈现石蕊的颜色,从而得出苯不能从水中萃取出石蕊的结论。     

化学指示剂石蕊漫谈

石蕊试剂是化学和生物等实验中普遍使用的,用来检测溶液酸碱性的指示剂。本文介绍了石蕊试剂的变色机理,并从生物学角度阐述了石蕊试剂的制取,同时用翔实的资料陈述了科学家波意耳开始发现及推广使用石蕊这一化学指示剂的来龙去脉,以及石蕊地衣植物的广阔用途。     

硝酸与石蕊试液反应本质的质疑

硝酸与石蕊试液的反应曾经是高中化学教材中硝酸的性质实验之一,此内容也多次在高中生近年来的化学试题中出现,而硝酸与石蕊试液的作用情况比较复杂,其一是石蕊试液与稀硝酸和浓硝酸的反应现象不相同;其二是在不同温度下石蕊试液与浓硝酸反应的现象也不完全相同。室温下将紫色石蕊试液滴人稀硝酸中,溶液立即变为红色,微热之,无明显变化发生;而室温下将紫色石蕊试液滴人浓硝酸中,溶液的颜色会由红色变为橙色,最后变为黄绿色,并伴随有大量红棕色气体产生。对此实验现象,有的教师解释为浓硝酸具有强氧化性,石蕊试液与浓硝酸作用时发生了氧化还原反应,逸出的红棕色气体是浓硝酸的还原产物二氧化氮。而稀硝酸的氧化性弱于浓硝酸,在此仅表现出酸性,因而只能使紫色石蕊试液变红。浓硝酸与石蕊试液作用是否主要发生的是氧化还原反应？黄绿色产物是什么物质？针对上述疑问,我们进行了反复研究,大量实验事实说明,浓硝酸与石蕊试液在发生酸色反应后,主要发生的是硝化反应,同时伴随有硝酸的分解反应,二者发生氧化还原反应的可能性很小。     

怎样配制紫色石蕊试液?

用蒸馏水配制好的石蕊溶液滴入酸性溶液中,呈明显的红色,但滴入中性溶液和碱性溶液时,两者的区别往往不明显,都有一定程度的蓝中略带紫色。因此,这样配制的石蕊溶液用于演示实验往往失败。     

初中化学恒沸现象探析——以加热通有二氧化碳的石蕊溶液未能恢复紫色为例

根据加热通有二氧化碳的石蕊溶液未能恢复至紫色，揭示氯化氢与水形成恒沸溶液的本质，得到不能通过对溶液加热煮沸的方法除去氯化氢杂质的结论。     

苯酚水溶液与石蕊试剂反应显色的研究

在大、中学有机化学的教学中,讲到“酚的化学性质”时,经常听到有些老师讲：“苯酚的酸性极弱,弱到不能使紫色石蕊试液变色。”一些较有影响的化学书刊,在讲到同样的问题时也这样认为。也有人认为苯酚能使石蕊变红,用蒸馏水做对照实验效果很好。苯酚水溶液与石蕊试剂反应显色情况到底如何呢?笔者做了如下的探讨。     

品红能否检验SO2

1课题引入教科书在介绍浓硫酸与铜反应时有这样的叙述:浓硫酸与铜在加热时能发生反应,放出能使紫色石蕊试液变红或使品红溶液褪色的气体。从对实验现象的分析中,我们可以得出这样一个结论:浓硫酸与铜反应生成的气体并不是氢气。实验证明,反应生成的气体是二氧化硫[1]。这段话虽     

对《硝酸与石蕊试液反应本质的质疑》的实证探索

通过一系列实验证明,浓硝酸对石蕊显色反应后的褪色现象,就其反应本质而言仍然是一种氧化还原反应。至于浓硝酸对石蕊发生硝化反应的说法,至今还缺少确凿的事实依据和有公信力的理论支撑。     

基于思维可视化的盐类水解教学实验设计

针对教材中“影响盐类水解平衡的主要因素”部分的实验进行改进。确定室温下滴加了石蕊的酸性溶液在pH=5.0时发生颜色突变,根据此条件下水、氨水的电离平衡常数,定量计算并配制0.09 mol·L^-1的硫酸铵溶液,添加石蕊后初始颜色为紫色,通过对比加热、降温时溶液的显色变化,将铵根离子水解平衡移动的过程可视化。通过在“颜色溶液”中加入强碱弱酸盐探究双水解反应的本质,进一步验证温度、浓度对盐类水解造成的影响。实验简便快捷、效果明显,以可视化的思维过程助益学生建构完整的认知模型。     

高灵敏共振瑞利散射法对痕量药物奥曲肽的测定

采用共振瑞利散射法测定多肽药物奥曲肽.在pH 4.1的B-R缓冲溶液中,奥曲肽和石蕊相互作用后,共振瑞利散射显著增强,在285 ～367 nm范围内呈现高的散射强度,且以310 nm处的ΔIRRS最强.奥曲肽的质量浓度在0.007 3 ～0.45 mg/L范围内与ΔIRRS成正比,检出限(3σ)为2.2 μg/L.该法用于奥曲肽合成样品和注射液中奥曲肽含量的测定,结果满意,实现了以廉价试剂、简便方法快速测定痕量贵重药品的目的.     

Investigation of the sorption of water vapor on cation-substituted vermiculite. 2. Thermodynamic description of sorption equilibria

The changes in the thermodynamic functions of the sorbents were calculated for the first time from measurements of the deformations of vermiculite during the sorption of water vapor and adsorption-calorimetric data.Institute of Physical Chemistry, Russian Academy of Sciences, 117915 Moscow. Institute of Colloid Chemistry and the Chemistry of Water, Academy of Sciences of the Ukraine, 252180 Kiev. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 6, pp. 1270–1275, June, 1992.     

Thermodynamics of ionization of water over wide ranges of temperature and pressure

We have summarized results of many experimental investigations of the thermodynamics of ionization of H₂O(liq.) from 0–300°C and from 1.0 atm to nearly 8000 atm. Results of these investigations (equilibrium constants, enthalpies of ionization, heat capacities, partial molal volumes, and compressibilities) have been used for a number of thermodynamic calculations. It is particularly noteworthy that it is possible to use thermal data from 0–145°C with an equilibrium constant for 25°C in calculating reasonably accurate equilibrium constants for temperatures as high as 300°C. Similarly, it is possible to use volumetric data that refer to 1.0 atm in calculating useful equilibrium constants that apply for pressures as high as 2000 atm.Much of the work reported here was done while the author was on leave at the University of Lethbridge.     

Thermochemistry of aqueous solutions of alkylated nucleic acid bases. VIII. Enthalpies of hydration of 6-alkyluracils

Enthalpies of solution in water H _sol ^o and enthalpies of sublimation H _sub ^o were determined for a number of crystalline derivatives of uracil: 1,6-dimethyluracil (m ₂ ^1,6 Ura), 1,3,6-trimethyluracil (m ₃ ^1,3,6 Ura), 6-ethyl-1,3-dimethyluracil (e⁶m ₂ ^1,3 Ura), 6-propyl-1,3-dimethyluracil (pr⁶m ₂ ^1,3 Ura) and 6-butyl-1,3-dimethyluracil (but⁶m ₂ ^1,3 Ura). Standard enthalpies of hydration H _hydr ^o and standard enthalpies of interaction H _int ^o of the solutes with their hydration shells were calculated. The data obtained show that dependence of H _int ^o on the number of-CH₂- groups of n-alkyl chain added upon substitution of diketopyrimidine ring is nonlinear. This finding is discussed in connection with results of X-ray diffraction structure determinations for the crystalline compounds.     

STUDIES ON THE REACTIVITY PATTERNS OF HETEROCYCLICS IN AQUEOUS DMSO‐INTERACTION BETWEEN POSITIVE END OF SULFOXIDE DIPOLE AND LONE PAIR ON RING NITROGEN IN PYRIDINE DERIVATIVES

Abstract

The signals for the α, β, and γ protons of pyridine exhibit a downfield shift in DMSO-d₆, compared to CCl₄ as solvent, the order being γ > β > α. This is attributed to an interaction between the positive end of the DMSO dipole and the lone pair of electrons on the ring nitrogen. This effect is also reflected in the faster rate of alkaline hydrolysis of ethyl isonicotinate over ethyl nicotinate and ethyl picolinate in aqueous DMSO relative to aqueous ethanol. Similar solvent effects are also observed in the pmr spectrum of pyrazine.     

Protonation of leucoemeraldine in the solid state and in solution

The protonation of leucoemeraldine in power form and in N-methylpyrrolidinone (NMP) solution by HCIO₄ and HBF₄ has been studied by x-ray photoelectron spectroscopy (XPS), infrared (IR), and ultraviolet (UV)-visible absorption spectroscopy. In powder form, less than 25% of the amine nitrogens can be protonated in the absence of oxygen. The effects of oxygen on the degree of protonation and the distribution of amine and imine units upon deprotonation of the salt are investigated. The degree of protonation in leuccemeraldine can be increased to about 50% with 3 M HCIO₄, similar to that achievable with emeraldine base in powder form. In NMP solution, leucoemeraldine is easily oxidized by dissolved oxygen. Protonation of both leucoemeraldine and emeraldine base in NMP solutions results in metastable species which gradually undergo deprotonation. The resulting products are affected by the O₂ content of the solutions. © 1993 John Wiley & Sons, Inc.     

Thermodynamics of lonization of aqueous lodic acid,an “almost-strong” electrolyte

We have made calorimetric measurements of enthalpies of dilution of aqueous iodic acid and have used these results for evaluation of the standard enthalpy of ionization of HIO₃(aq.). We have also made calorimetric measurements of enthalpies of addition of perchloric acid solution to aqueous solutions of KIO₃, KNO₃, NaIO₃, and NaNO₃ and have used these results to obtain further values for the standard enthalpy of ionization of HIO₃(aq.). On the basis of all these results, we have selected H^o=–660±125 cal-mole^–1 as the best available standard enthalpy of ionization of HIO₃(aq.) at 298.15°K, compared to the previously accepted –2400 cal-mole^–1. Using the best available K=0.157 for ionization, we also obtain G^o=1097 cal-mole^–1 and S^o=–5.9 cal-^oK^–1-mole^–1 for ionization of HIO₃(aq) at 298.15°K.On study leave from Department of Inorganic and Analytical Chemistry, LaTrobe University, Bundoora, Victoria, 3083, Australia, to University of Lethbridge.On study leave from Department of Chemistry, University of Wollongong, Wollongong, N.S.W. 2500, Australia, to University of Lethbridge.     

Thermochemical study of aliphatic and phenyl-substituted geminal diacetates

The standard enthalpies of combustion _c H ^o of aliphatic diacetates1 and aromatic diacetates2 were measured calorimetrically. The enthalpies of vaporization _vap H ^o or sublimation _sub H ^o of1 and2 were obtained from the temperature function of the vapor pressure measured in a flow system. From _f H ^o(g) of1 and2 new values of group increments for the estimation of standard enthalpies of formation of these classes of compounds were derived. The geminal interaction energy between the geminal acyloxy groups shows no anomeric stabilization.Geminal Substituent Effects, Part 12, for part 11 see Ref. 7.     

Relation between characteristic adsorption energy and internal pressure in the theory of volume filling of micropores

An equation for the internal pressure acting on an adsorbate in micropores was obtained on the basis of the assumption that the chemical potential of an adsorbate in micropores is equal to that in an equilibrium gas phase and using the Dubinin-Radushkevich equation. The empirical relation between the characteristic adsorption energy and the half width of pores was expressed in terms of internal pressure and diameter of adsorbate molecules. The two-dimensional pressure was calculated for micropores with plane-parallel walls, where the width of a micropore coincides with the diameter of an adsorbate molecule. The results obtained were compared with the two-dimensional pressure of a monolayer on a free planar surface for an adsorbate and adsorbent of the same nature.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1928–1930, October, 1995.     

钾明矾溶液水解度计算公式

根据盐类水解关系式和水的离子积计算公式,建立了计算盐类水解度和水解产物离解常数的完全方程式。计算值同实验值比较,钾明矾溶液水解度平均偏差为0.6％,离解常数pK_b=11.6±0.1,水的离子积pK_w平均偏差小于0.06,从而改进了苏联的计算公式。