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Solution theory

Chemical terminology

People's early understanding of solution has a long history of human application of solution. Water, animal and plant body fluids, vinegar, and wine all belong to solution. It is recorded that in the 4th and 5th centuries, the Greek alchemist Synesios made a hydrometer to measure wine, vinegar milk , honey and other aqueous solutions. During the period of medicinal chemistry, many people engaged in the research of mineral water, which promoted the analysis of solutions

Chinese name: Solution theory
Foreign name: theories for electrolyte solution

Partial ionization theory: dissociation and ionization
Crystal structure theory: crystalline structure
Ionic binding theory: conjugation theory

catalog

five Areus
six Ionization theory
seven Ostwal
eight Kisgakov

brief introduction

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Development of theories for electrolyte solution 1886: Vat Horff: colligative property of matter

1887: Arrhenius: partial ionization theory

1918: Ghosh: crystal structure

1923: Debye-H ü ckel theory

1926: Bjerrum ion binding theory

1927: Onsager: Debye-H ü ckel-Onsager theory

1948: Robinson and Stokes: solvation theory

Infiltration phenomenon

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In ancient times, people had noticed the solution, and carried out various researches and guesses on it, but the fruitful research was as late as 1748. In this year, Knoller discovered the phenomenon of infiltration. In the experiment, Knoller sealed the container filled with alcohol with an animal bladder. After putting it into water, he found that the water passed through the bladder membrane into the container. After a period of time, the bladder membrane was almost broken by the incoming water. Later, many scientists did similar experiments until Dutroxia reached a conclusion in 1827. He called this phenomenon infiltration, and believed that under similar circumstances, the pressure is proportional to the depth of the solution.

Semipermeable membrane

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After Duteroxia, Traube and other scientists have been looking for a membrane that can only allow water to pass through. Vantehoff later called it a semipermeable membrane. After many hardships, Traube obtained several semipermeable membranes in 1867. He and other scientists successfully measured the maximum pressure using these semipermeable membranes. The most effective one is a semi permeable membrane formed by depositing copper thiocyanate on a porous magnetic cylinder, which was modified by German Pfeiffer to make an instrument for measuring osmotic pressure. With this instrument, he did a lot of measurement work. All kinds of data proved that the osmotic pressure depends on the concentration of solution and increases with the increase of temperature.

Vant Hoff

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Van terhoff is a versatile chemist, whose research scope is extremely wide. He has pointed out to chemists for a long time how to apply thermodynamics to chemistry, especially how to combine thermodynamics with the concept of affinity. Vantehoff found several Thermodynamic law His research object is mainly ideal gas. After Pfeiffer's research results came out, he pointed out that Osmotic pressure law It's the same thing as the gas law for dilute solutions. He believes that the formula PV=iRT is also applicable to solutions, where I value is close to 1, depending on the nature of the dissolved substance. He came to the conclusion that osmotic pressure method can be used to determine the attraction of solvent to solution. The paper on this discovery was first published in 1885.

As early as 1778, Blaig discovered the fact that the freezing point of liquid containing solute was reduced. In 1882, French Raoult further pointed out that the decrease of freezing point was proportional to the molecular concentration of solute. Five years later, it not only provides an important new method for determining molecular weight, but also shows that the formation of these phenomena depends on the permeability of solution, thus confirming the conclusion of van terhoff.

Areus

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At that time, people had found that although Vantehoff's osmotic pressure formula could be applied to the solution with organic solute, it could not be applied to the solution with acid, alkali and salt solute. Raoult certainly did not ignore this fact in his work. Later, he realized that the permeation effect depends on the number of particles in the solution, just as the pressure of gas is attributed to the number of all molecules in a certain volume. It has been measured in experiments that the number of particles in acid, alkali and salt solutions has increased. This means that these solute molecules have dissociated in the aqueous solution, and the solution has conductivity. These facts prove that there is a certain connection between dissociated particles and charged particles. It was the young Swedish chemist Aleus who first made it clear.

Ionization theory

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Arrenius put forward this ionization theory in 1883 during his doctoral defense. Before that, he had made more accurate measurements of the conductivity of many salt aqueous solutions. The main argument of Arenius' ionization theory is that the electrolyte will dissociate immediately after dissolution, and there will always be ions in the solution regardless of whether there is current passing through. When this argument not only makes Hitov's electrolytic solution conductive Ion migration number The additivity of ion conduction with Kollausch has been explained, and the seepage anomaly observed by Thor and Van Hoff has also been well explained. Arenius believes that, Weak electrolyte Only a part of it is electrolyzed, so the solution of these substances can be used Law of mass action 。 Aleus wrote such an excellent paper at such a young age, which should be awarded the highest award according to common sense. However, the school only reluctantly passed it with a reserved attitude, and he himself was dismissed as a "ridiculous pupil".

Arrenius, who was extremely distressed, could not get support at home, so he wrote to many famous foreign scholars to seek confidants, including Mayer, Mendeleev, etc. However, it is hard to find a bosom friend. What we get is a cold answer, even when we are in the sea, there is no echo. At this time, only one person, Ostwald in Riga, went to Uppsala in person to meet Arenius with more courtesy than Arenius expected. Prior to this, Ostwald was observing the strength of acid and alkali, and doing research on the heat release from neutralization of acid and alkali. He encountered many problems, and when puzzled, he received a letter from Arenius, which made him enlightened. Ostwald and Arenius became friends at first sight and established a strong friendship.

At first, the reason why people refused to accept Arenius's ionization theory was that the ions with opposite charges that had existed for a long time could not exist independently in the solution. Moreover, the conditions for correctly distinguishing atoms and ions were not available at that time. However, Ostwald and Vantehoff gave enthusiastic support to Arenius' ionization theory. With the vigorous promotion of the two of them, the ionization theory has finally become famous. In addition to the value of the theory itself, people have almost completely accepted this theory. Facts have proved that this treatment is well deserved by the ionization theory.

Arenius is famous in the scientific community for this reason, but he refused to be hired by many foreign universities and insisted on returning to Stockholm to be a lecturer. Later, he served as a professor, president of the university and director of the Nobel Institute. His research scope is extensive. In 1889, he played the concept of activating molecules when explaining gas reactions, and proposed a famous formula to express the relationship between the number of activated molecules in chemical changes.

Ostwal

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Ostwal made positive contributions to the application and promotion of ionization theory. In 1885, he put forward the famous dilution law according to ionization theory, which greatly supported ionization theory. In 1894, Ostwald proposed that the reaction in analytical chemistry should be regarded as an ionic reaction, and explained the color of solution with the special color of ions. In addition, Ostwald also studied catalysis and trained many scientists in his laboratory, such as Beckman, Nernst, etc.

Kisgakov

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In Russia, Kisgakov is Ionization theory He criticized the opponents of ionization theory in his paper Analysis of Objections to Ionization Theory. Kablukov actively supports the ionization theory. As early as he worked in the Ostwald laboratory, he had completed the study of the conductivity of hydrogen chloride in various solvents, and found the abnormal phenomenon of the dilution curve of its molecular conductivity in organic solvents. In 1891, he put forward the theory of ion hydration in solution in his doctoral thesis "Modern Solution Theory from the Perspective of Chemical Equilibrium Theory".

Just like the golden rags, some serious defects of the ionization theory were exposed to people soon after its appearance. Arenius regarded the solution as similar to the gas mixture, in which the molecules are distributed in an disordered state and in thermal motion. In fact, electrolyte solution Due to the existence of mutual attraction, the ions in are orderly distributed in the solution to a certain extent, especially in strong electrolytes.

Theory of electrode potential

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In 1889, the theory of electrode potential was developed by Nernst on the basis of van der Hoff and Arrhenius solutions. The theory has mechanical properties and is based on the model of crystal dissolution and solution precipitation crystallization. Before him, many scientists had tried many times to clarify the internal cause of the current generated on the electrode, and Nernst expounded his own view on this. He believes that the current is generated at the interface between metal and solution, based on two competing forces at the interface: one is the pressure of metal dissolution, which is the reason why metal atoms in solution become ions; The other is the osmotic pressure opposite to the pressure of metal dissolution, which depends on the concentration of ions in the solution.

Ionization theory

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According to Nernst's theory, in a galvanic cell composed of two metals immersed in solution, only the metal whose dissolution pressure is greater than its ion osmotic pressure can be dissolved. At the moment, the cations of another metal are completely separated on another electrode, because the relationship between its dissolution pressure and osmotic pressure is just opposite. Nernst's theory can only be applied to ideal solutions. Later, the improvement of Gibbs promoted the research of batteries.

At this time, Vantehoff's solution theory and Ashley's ionization theory rapidly increased the experimental data, providing a theoretical and experimental basis for people to further study solutions.

Classification of solutions

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Saturated solution: A solution in which the solute cannot be dissolved in a certain amount of solvent at a certain temperature. Unsaturated solution : A solution in which the solute can continue to be dissolved in a certain amount of solvent at a certain temperature. Mutual conversion of saturated and unsaturated solutions: unsaturated solutions can be converted into saturated solutions by increasing the solute (applicable to all solutions) or reducing the temperature (applicable to most solutes whose solubility increases with temperature, otherwise the temperature must be increased, such as lime water), evaporating solvent (when the solvent is liquid). Saturated solution can be converted into unsaturated solution by increasing solvent (applicable to all solutions) or increasing temperature (applicable to most solutes whose solubility increases with temperature, and vice versa, reducing temperature, such as lime water). Regular solution: 1929 J H. Hildebrand proposed the regular solution model, and defined the regular solution as: the heat of formation (mixing) is not zero, and the mixing entropy is the mixing entropy of the ideal solution, that is, △ H ^ M ≠ 0 △ S ^ M=△ S ideal mixing=- R ∑ xi lnxi Regular solution is a solution that is closer to the actual solution. Its formation is consistent with that of ideal solution except that the entropy of mixing is not equal to zero. Thermodynamic laws derived from regular solutions are widely used in non electrolyte solution Especially for many alloy solutions. Therefore, for metallurgy and metal material science, Regular solution theory It is very important.

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