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从过去所积累的材料来看,我们可以说周期表上几乎所有的金属元素,在不同程度上都具有形成络合物的能力。由于大部分的化学反应是在溶液中进行的,而且根据现代的见解溶液中所有的金属阳离子和一部分阴离子(无机的或有机的)或中性分子几乎都是以络离子形式存在的。因此了解离子在溶液中存在的状况是一个很重要的化学问题。近二三十年来化学家们的注意力均集中于研究在溶液中(水溶液及含水的混合溶剂)所形成络离子的组成及其稳定性,而后者是以稳定常数来表示。测定溶液中络离子逐级稳定常数的实验方法常用的有下列几种:1)电位法(包括 pH 法);2)极谱法;3)分光光度法;4)溶解度法;5)溶剂萃取法;6)离子交换法等。根据我们所研究体系的特性而选择不同的实验方法。例如要测定金属离子与某些可溶性的酸或硷(无机的或有机的)的络合作用,那么以选择 pH 法最适宜;如果所研究的体系包括有微溶盐,那么以选择溶解度法为最适宜;如果所研究的体系有不溶于水的螯合物(内络盐)生成,则以用溶剂萃取法为最适宜等等。虽然在这些不同实验方法中所测得的物理量不同(例如在电位法中测得的是电动势或溶液的 pH 值,极谱法中测得的是半波电势及扩散电流,分光光度法测得的
From the material accumulated in the past, we can say that almost all of the metal elements in the periodic table, to varying degrees, have the ability to form complexes. Since most of the chemical reactions are carried out in solution, and according to modern insight almost all of the metal cations and a part of the anions (inorganic or organic) or neutrals in the solution exist as complex ions. Therefore, understanding the presence of ions in solution is a very important chemical issue. In the last two or three decades, chemists have focused their attention on the composition and stability of complex ions formed in solution (aqueous and aqueous mixed solvents), which is expressed as a constant of stability. The experimental methods used to determine the step-by-step stability constant of complex ions in solution are as follows: 1) Potential method (including pH method); 2) Polarography; 3) Spectrophotometry; 4) Solubility method; Method; 6) ion exchange method. Choose different experimental methods according to the characteristics of the system we studied. For example, to determine the complexation of a metal ion with some soluble acid or base (inorganic or organic), pH is the most appropriate choice; if the system under investigation includes sparingly soluble salts, Most suitable; if the system studied is insoluble in water chelate (internal complex salt) is generated, then the solvent extraction method is the most suitable and so on. Although the physical quantities measured in these various experimental methods differ (eg, the potential of the electromotive force or the solution is measured in the potentiometry, the half-wave potential and the diffusion current are measured in the polarography, and the spectrophotometric measurement of