硅酸及其盐的研究 ⅩⅪ.三甲基硅烷化-气相色谱法测定单硅酸的离解常数

由于硅酸的聚合性质,单硅酸易发生聚合,溶液中硅酸总量不能代表单硅酸的含量,因而其离解常数不易测准,各家所得数据不一.本文用三甲基硅烷化-气相色谱法测得硅酸溶液中单硅酸含量以求得不同时间下单硅酸的最快聚合点的pH,并以时间外推法求得单硅酸的标准离解常数.本文还用离子强度外推法,求得了单硅酸热力学离解常数。这些常数和公认值一致.     

硅酸及其盐的研究 ⅩⅪ. 三甲基硅烷化-气相色谱法测定单硅酸的离解常数

由于硅酸的聚合性质,单硅酸易发生聚合,溶液中硅酸总量不能代表单硅酸的含量,因而其离解常数不易测准,各家所得数据不一.本文用三甲基硅烷化-气相色谱法测得硅酸溶液中单硅酸含量以求得不同时间下单硅酸的最快聚合点的pH,并以时间外推法求得单硅酸的标准离解常数.本文还用离子强度外推法,求得了单硅酸热力学离解常数.这些常数和公认值一致.     

硅酸及其盐的研究——ⅩⅢ.单硅酸胶凝作用中的离解常数

硅酸的离解常数是表征硅酸基本性质的重要数据,前人已有不少工作,但由于测定的方法和条件不同,所得数据很不一致.本工作用“N”曲线法测求了硅酸的各级离解常数.     

硅酸及其盐的研究 ⅩⅩⅠ.三甲基硅烷化-气相色谱法测定单硅酸的离解常数

单硅酸的离解常数是表征其基本性质的重要数据,前人已有不少工作,但由于测定的方法和实验条件不同,所得数据很不一致。     

硅酸及其盐的研究——Ⅹ.单硅酸聚合反应动力学

本文用一方程逼近钼硅黄显色的消光-时间曲线,求得了双硅酸的显色速度常数,从而建立了一个在多种聚合度的硅酸水溶液体系中测定单硅酸的方法.利用这个方法,确定单硅酸聚合反应的初速度对其自身浓度是二级反应.根据本实验室提出的硅酸聚合理论,计算了速度常数和相应的活化能,进一步证明了以前所提机制的正确性.     

硅酸及其盐的研究(ⅩⅥ)——硅酸胶凝作用中的离解常数

以HOAc和H₂SO₄为酸化剂,研究了不同SiO₂/Na₂O摩尔比的硅酸钠在酸化后胶凝时间和pH的关系.从“N”曲线的结构求得了硅酸在胶凝作用中的各级离解常数.     

硅酸及其盐的研究(Ⅻ)—氟离子与硅酸的反应及其平衡常数

在酸性范围内,在不同F/SiO_2值及不同硅酸浓度的溶液中,用氟电极法测得氟和硅酸的结合量,并求得反应式: Si(OH)_4+HF(?)[Si(OH)_3F]+H_2O 其平衡常数β_1=1.7×10~2。从而验证了在酸性含氟硅酸溶液中主要存在着这种初始反应。同时求算了六氟硅酸的总形成常数β_6=2×10~(12)。     

渐进因子分析－pH－分光法测定多元酸的离解常数

根据多元酸平衡体系中型体具有先出现先消失的特点,提出了用渐进因子分析与化学平衡结合迭代,从pH-分光矩阵中求解多元酸离解常数的新方法。用该法测定了多元酸茜素S和铬天青S的离解常数,并讨论了确定型体存在区域的经验式。结果表明该方法稳定、可靠、算法收敛快,所测得的离解常数与文献值吻合。     

均三溴氯磺酚离解与质子化作用的研究

本文报道测钪新试剂均三溴氯磺酚在水溶液中的离解与质子化作用，用电位法和光度法测得了它的逐级离解常数与质子化常数，以及热力学参数，并由分布函数获得试剂主要存在形式和ｐＨ值的关系。     

硅酸及其盐的研究(ⅪⅩ)——CNDO/2法研究单-、双-和三硅酸的酸强度

本文用CNDO/2的量化计算方法估计了单硅酸、双硅酸和三硅酸分子中氢氧键的强度,并以此解释实验发现的这几种硅酸溶液的酸强度:单硅酸>双硅酸<三硅酸。     

Étude d'équilibres en solution à l'aide des échangeurs d'ions : I Dissociation du perchlorate d'argent et de l'acide nitrique dans les mélanges eau—acide acétique—acide perchlorique ou acide nitrique

A theoretical relationship postulated between the distribution coefficient of a monovalent element and the parameters upon which it depends (acid concentration in solution, dissociation constants of the acid and the salt, selectivity coefficient of exchanged ions) has been verified for the dissociation of silver perchlorate in water—acetic acid—perchloric acid mixtures. The dissociation constants found have been compared with the experimental values obtained by potentiometric measurements. The relationship established has been employed for the determination of nitric acid dissociation constants in water—acetic acid-nitric acid mixtures containing less than 25 % by weight of water. From the results the pK value for nitric acid in pure acetic acid has been evaluated by extrapolation. The theoretical relationship might be used to determine an acid dissociation constant when the dissociation constant of a salt is known and vice versa.     

邻苯二甲酸在异丙醇-水混合溶剂中电离热力学性质的研究

有机酸在混合溶剂中电离热力学性质的研究,无论在化学还是在生物领域中都有十分重要的意义。长期以来,人们对其进行了大量的研究,但对芳香族酸在混合溶液中的电离热力学性质的研究还只限于单取代苯甲酸在乙醇-水等少数几种混合溶剂中的热力学性质。为此,我们在278.15—318.15K范围内测定了无液接电池:     

On the acid behaviour of the alcoholic group of serine

The behaviour of l-serine in strongly alkaline solution was studied at 25 degrees C and in 3.00 mol/l NaClO(4), as a constant ionic medium, to obtain quantitative information about the eventual dissociation of its alcoholic group. A spectrophotometric method was employed to measure the free concentration of hydrogen ions. Two indicators, methyl thymol blue and eriochrome blue type R, were used. Their values as protonation constants and absorbance coefficients were determined in advance. The method here proposed has been validated beforehand by applying it to d-mannite and glycerine and by comparing results so obtained with those previously provided by literature. The investigation showed weak acid properties of the -OH of serine and its dissociation constant was determined. Polynuclear species or further dissociation were not observed.     

Acids in dimethylformamide. III. Ionic equilibria of dicarboxylic acids

Dissociation and homoconjugation constants of succinic, malonic, and dimethylmalonic acids have been determined potentiometrically at 25°C. Conductometric studies on the tetraethylammonium salts of the acids permitted the evaluation of the corresponding dissociation constants, which allowed a better fit of calculated curves with experimental data. Homoconjugation of two monovalent anions with a divalent anion was pointed out in all cases. No appreciable homoconjugation of the monovalent anion with the diprotic acids was found. In order to standardize the glass electrode at high paH values, the dissociation constant of diethylbarbituric acid has also been determined.     

Dissociation constant of aqueous trifluoroacetic acid by cryoscopy and conductivity

The dissociation constant of trifluoroacetic acid in aqueous solution has been determined at 25°C by electrical conductivity (0.65 mol-l^–1) and at 0°C by cryoscopy (1.05 mol-l^–1) and electrical conductivity (0.98 mol-l^–1). The good agreement between the values of the constant determined by cryoscopy and conductivity at 0°C lends confidence to the value at 25°C determined by electrical conductivity. The constant determined at 25°C is in reasonable agreement with values determined by differential refractometry (0.92 mol-l^–1) and from acidity function data (0.80 mol-l^–1) reported by other workers. This work renews confidence in the electrical conductivity method for determining dissociation constants of moderately strong acids.     

ASCORBIC ACID AS A PHOTOOXIDATION INHIBITOR

Abstract— The rate constant for total quenching of singlet oxygen by ascorbic acid has been determined using the inhibition of the bleaching of 9, 10-dimethylanthracene by AA in pyridine. The rate constant was 8.4 × 10^-6 M ^-1 s^-1, as determined photochemically, and 1.06 10^-7 M ^-1 s^-1 as determined in a dark reaction.     

The effects of high concentrations of aqueous tetramethylammonium chloride and other salts on the dissociation of phenylphosphonic acid and on the enolization of acetone

The dissociation constants of benzoic acid and phenylphosphonic acid have been determined in aqueous solutions containing tetramethylammonium chloride at concentrations up to 15 and 13 molal, respectively. The second dissociation constant of phenylphosphonic acid has also been determined in concentrated solutions of alkali halides. Whereas the organic electrolyte increases the observed pK values of the acids, the inorganic electrolyte idecrease them. The rate of enolization of acetone, catalyzed by phenylphosphonate dianion is increased by the presence of tetramethylammonium chloride, but is decreased by the presence of inorganic salts, in accordance with the changes in the apparent acidity constants of phenylphosphonate monoanion that the two different kinds of electrolyte bring about. The slope of the Brónsted plot for the inorganic salts is 0.76; that for the organic electrolyte is 0.46. Non-quaternary ammonium salts also increase the rate of the phenylphosphonate dianion catalyzed enolization of acetone, but this appears to be due to a considerable extent to the formation of reactive iminium ion intermediates.