Санкт-петербургского государственного университета высшее профессиональное образование т. А. Степанова, И. Ю. Ступина
жүктеу/скачать 5,96 Mb. Pdf көрінісі
|
1stepanova t a english for chemists
| Scction II
Упр. 1. Назовите значения следующих интернациональных слов: postulate, ionization, dissociate, equivalent, association, neutral, opposite, specific, base, conccpt, statistical, attraction, interpret, polarize, identical, potential, dielectric, deviation, ideal, mobility, approximation Упр. 2. Проверьте, помните ли вы значения следующих слов; если ист, обратитесь к словарю: infinite, dilution, conform, assume, decrease, increase, valid, owing to, remarkably, distribute, seek (+ инфинитив), ascribe Text 28 В Прочтите текст про себя (контрольное время чтения— 3,5 минуты). Ionic Theories About the mid-1880’s, Arrhenius postulated in his ionization theory that (1) electrolytes are completely dissociated into their constituent ions in the limit of infinite dilution, (2) the equivalent conductance 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 Arrhenius 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 sincc the mobility of the free ions decrease with increasing concentration owing to interaction between ions o f 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 chaigc arc more likely to approach close to one another than arc ions of the like charge, and this basic conccpt led to the considerable advances made by Brdnstcd in his own studies o f mixed electrolyte solutions. The first statistical theory o f clcctrolytc 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 chaigcs distributed in a continuum possessing a dielectric constant identical with that of the pure solvent, and it is also recognized that ions group themselves a little eloser around an ion of the opposite chargc than they do around ions of the like chargc. This leads to an ion atmosphere surrounding each 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 dielectric constant of the pure solvent. In the argument strong electrolytes arc assumed to be completely 188 dissociated into ions, and observed deviations from this ideal behaviour arc then ascribed to electrical interactions between the ions. Упр. 3. Передайте основное содержание текста в нескольких пред ложениях. 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 Аррениуса, объяснялось уменьшение проводимости при уве личении концентрации? 3. Какое допущение послужило основанием для теории Брснсгсда? 4. Какая теория наиболее успешно объясняла поведение разбавленных растворов? 5. Как объясняется поведение ионов в растворе на основе теории Дебая и Хюкксля? Упр. б. Закончите следующие предложения: 1. The original postulate suggested by Arrhenius is invalid bccausc... 2. Bronstcd made considerable advances in... 3. The first statistical theory o f cicctrolytc solutions was... 4. According to the theory developed by Debye and Hiickcl, an ion atmosphere surrounding each ion in solution is due to... 5. Using the theory by Debye and Hiickcl one can calculate... жүктеу/скачать 5,96 Mb. Достарыңызбен бөлісу:
|