Прочтите текст про себя (контрольное время чтения—3,5 минуты). Ionic Theories
About the mid-1880's, Arrhcnius postulated in his ionization theory that (1) electrolytes arc completely dissociated into their constituent ions in the limit of infinite dilution, (2) the equivalent conductancc of the free ions is independent of concentration, (3) the equilibrium between the ions and the undissociatcd molcculcs conforms to the law of mass action. Thus, in the second postulate Arrhcnius assumed that the decrease in conductivity with increasing concentration is due to the association of free ions to form neutral molcculcs. Wc now know that the original postulate is invalid since the mobility of the free ions decrease with increasing concentration owing to interaction between ions of opposite charge. In 1920, Bronstcd's theory of specific ion interaction was based on the approximation that chemical interaction is limited to that between ions of opposite sign. By the reasoning given, it was shown that ions of the opposite chargc arc more likely to approach close to one another than arc ions of the like charge, and this basic conccpt led to die considerable advances made by Bronstcd in his own studies of mixed electrolyte solutions.
The first statistical theory of electrolyte solutions, the intcrionic attraction theory, was developed by Dcbyc and Huckcl in 1923 and its application has been remarkably successful in interpreting the behaviour of very dilute solutions. The ions arc regarded as unpolarizablc point charges distributed in a continuum possessing a diclcctric constant identical with that of the pure solvent, and it is also recognized that ions group themselves a little closer around an ion of the opposite chargc than they do around ions of the like chargc. This leads to an ion atmosphere surrounding cach ion in solution. From the theory, it is sought to calculate the average potential energy of a given ion in solution due to all the other ions, assuming the medium to have the diclcctric constant of the pure solvent. In the argument strong electrolytes are assumed to be completely
dissociated into ions, and observed deviations from this ideal behaviour arc then ascribcd to electrical interactions between the ions.
Упр. 3. Передайте основное содержание текста в нескольких предложениях.
Упр. 4. Какие слова в тексте означают «закон действия масс»?
Упр. 5. Найдите в тексте ответы на следующие вопросы:
1. Каковы основные положения теории ионизации? 2. Чем, по мнению Аррсннуса, объяснялось уменьшение проводимости при увеличении концентрации? 3. Какое допущение послужило основанием для теории Брснстсда? 4. Какая теория наиболее успешно объясняла поведение разбавленных растворов? 5. Как объясняется поведение ионов в растворе на основе теории Дсбая и Хюкксля?
Упр. б. Закончите следующие предложения:
1. The original postulate suggested by Arrhcnius is invalid because... 2. Bronstcd made considerable advances in... 3. The first statistical theory of clcctrolytc solutions was... 4. According to the theory developed by Dcbyc and Hiickcl, an ion atmosphere surrounding each ion in solution is due to... 5. Using the theory by Dcbyc and Hiickcl one can calculate...
Section III
Ex. 1. Make up short dialogues according to the example. Example:
— I don't quite catch the difference between these theories.
— Look here, it's veiy simple. The main point is the difference in the behaviour of ions.
— Oh, now I sec. Thanks a lot.
Ex. 2. Respond to the following statements:
1. A great deal of work has been done on the problem of interactions in clcctrolytc solutions. 2. Theories of solutions arc in some respects similar to theories of gases. 3. The problem of electrolysis has interested chemists for almost two centuries.
Ex. 3. Give detailed answers to the questions.
1. What do the properties of clcctrolytc solutions depend on? 2. Whose contribution to the development of the theory of clcctrolytc solutions was of considerable importance? 3. What fundamental ideas have been developed at the department of the theory of solutions of the University of St. Petersburg?
Ex. 4. Discuss (he following topics:
1. The Behaviour of Electrolyte Solutions.
2. The Development of Ideas concerning Electrolyte Solutions.
3. Generally Accepted Principles Concerning Electrolyte Solutions.