While there arc many pairs of substanccs which, like water and tfthyl alcohol, can be mixed in any proportions to form homogeneous solutions, it is a matter of common experience that the capacity of a solvent to dissolve a given solute is often limited. When a solvent placcd in contact with an cxccss of solute attains and maintains a constant concentration of solute, the solute and solution are at equilibrium, and the solution is said to be saturated. The solubility of a substance in a particular solvent at a given temperature is the concentration of the solute in the saturated solution. In other words, the solubility of a solute is the dissolved concentration characteristic of the state of equilibrium between die solute and the solution. It is difficult to overemphasize the importance of the conccpt of solubility to chcmistry; it is the basis of innumerable laboratory and industrial processes that prepare, separate, and purify chcmicals, and is the controlling factor in a variety of geological and other natural phenomena. The solubility of a substance in a particular solvent is controlled principally by the nature of the solvent and solute themselves, but also by the conditions of temperature and pressure. To analyse these factors, wc shall first limit ourselves to the case of ideal solutions.
The liquids thai form an ideal solution arc always miscible in any proportions and, thus, have infinite solubility in cach other. The reason for this is easy to sec if wc recall two facts. First, limited solubility and a saturated solution result only when a solute and its solution reach equilibrium. Sccond, the equilibrium state is a compromise between a natural tendency toward minimum energy and maximum molccular chaos. Now, the mixing of two ideal liquids is always accompanicd by an increase in entropy or molccular chaos, bccausc in the solution, the solute molcculcs arc spread randomly throughout the solvent, rather than being nearly closest packed as they arc in the pure solute. That is, even if wc could loeate one solute molcculc in solution, wc could not prcdict what the identity of its nearest neighbours was, as wc could, if the molecule were in the pure solute phase. Consequently, the solution has a higher entropy than the pure solvent and solute, and the tendency toward maximum molccular chaos favours the mixing of the two liquids. Moreover, the fact that there is no energy change in the mixing proccss means that the tendency toward minimum energy docs not restrict the solution proccss. Consequently, the two liquid components of an ideal solution can mix in any proportion.
Words and Word-Combinations to Be Memorized
as is the case with, as the case may be, in case, in which case, it is far from the case, it is not the ease with, such is the case, a chcmical, contact, emphasize, excess, experience, be a matter of common experience, favour, ideal, identity, maintain, maximum, natural, purify, result, saturate, saturated, solubility, spread, themselves, toward(s), a variety of
Ex. 5. Give the Russian equivalents for the following:
mix in any proportions, the capacity to dissolve a solute, placc in contact with, the solubility in a particular solvent, purify chcmicals, be a controlling factor, a variety of phenomena, be controlled by the nature of the solvent and solute, be misciblc in any proportions, be spread randomly throughout the solvent, be closc packcd, moreover, restrict the process, emphasize the importance
Ex. 6. Give the English equivalents for the following:
общеизвестно по опыту, что...; ограниченная способность, избыток растворимого вещества, быть в равновесии, в насыщенном растворе при данной температуре и давлении, другими словами, значение концепции растворимости для химии, во множестве природных явлений, ограничиться случаем, идеальный раствор, достигать равновесия, сопровождаться увеличением температуры, а не..., даже если, нет изменения энергии
Ex. 7. Fill in the blanks with articles where ncccssary.
1. Substanccs like ... water and ... ethyl alcohol can be mixed in any proportions. 2. ... capacity of... solvent to dissolve ... given solute is often limited. 3. ... solubility of... substancc in ... particular solvent at ... given temperature is its concentration in ... saturated solution. 4. It is difficult to overemphasize... importance of... conccpt of... solubility to ... chcmistry. 5. Wc shall first analyse ... ease of... ideal solution.
Ex. 8. Give synonyms for the following:
capacity, limit, placc, principally, be accompanied by, because, toward, consequently
Ex. 9. Give antonyms for the following:
constant, saturated, at first, always, easy, dccrcasc, near, minimum, seldom, limited
Ex. 10. Translate the sentences into Russian.
1. The capacity of a solvent to dissolve a given solute is often limited though there are many pairs of substanccs which can be mixed in any proportions. 2. In order to control our environment, the first puipose of science must be to study and understand it. 3. To answer the question "What are the uses of sulphuric acid?" fully, one would need to write a book. 4. The alkali metals arc usually stored in oil so as to cxcludc air. 5. In order for two molcculcs to react with cach other, they must, first of all, be in the presence of cach other. 6. For hydrogen to be obtained from water, electrolysis may be used. 7. Sodium is a white metal soft enough to be easily cut with a knife and light enough to float on water. 8. The minerals in which aluminium occurs, arc too numerous to recite. 9. The vapour pressure of many pure liquids or solids is very low, in fact, so low as to be immeasurable by dircct means. 10. The catalytic substance can be recovered unchanged after the reaction is completed. 11. As the temperature is raised, the rate of evaporation increases. 12. Once die validity of a hypothesis has been tested by all possible experiments and is found to be in harmony with all the facts, it assumes the status of a theory. 13. Whenever a chemical reaction occurs, an energy changc takes placc. 14. Liquid bromine should be kept in well-stopped bottles, as this element is poisonous. 15. The discovery of silicon was an important event in chcmistry, for the properties of the element were found to be very closc to those predicted by D. I. Mendeleyev on the basis of his periodic law. 16. Where the currcnt enters or leaves the liquid, there are cvidcnccs of chcmical action having taken placc. 17. If sulphur trioxidc is thrown into water, it will dissolve with the evolution of much heat. 18. If there were no order in the way in which atoms of different elements combine to form the molcculcs and crystals of compounds, it would be ncccssary for us to memorize one by one the formulas of thousands of substanccs. 19. If wc had chosen the second oxide, the valcnce of sulphur and, therefore, its equivalent weight
would have been different. 20. With a few exceptions the molten metals arc completely soluble in one another, so that it is possible to make solutions of all concentrations. 21. True salts arc always ionic, whether they arc in solution or in their crystalline forms. 22. Fluorine and hydrogen combinc violently even in the dark, provided a tracc of moisture is present.
23. Strange as it may seem, the reaction may procccd both ways.
24. Important as the problem of solubility may be, wc shall not consider it now. 25. Let us consider any factors lest anything may be omitted. 26. Unless the electron microscopc had been used, it would not have been possible to obtain these results. 27. Were the parameters maintained, the reaction would go to completion. 28. Physics and chcmistry are so closely related that textbooks of these two subjects contain much in common.
29. Many oxides arc found to combinc with acids to form salts and water.
30. Carbon monoxide cannot properly be described as either a basic or an acidic oxide, inasmuch as it docs not react with water.
Ex. 11. Translate the sentences into English without using a dictionary.
1. Различные вещества обладают различной способностью растворяться в данном растворителе. 2. Растворимость всщсства — это его концентрация, характерная для состояния равновесия между растворимым веществом и раствором. 3. Понятие растворимости представляет собой основу для многочисленных лабораторных и промышленных процессов. 4. Растворимость зависит как от природы самих растворителя и растворяемого всщсства, так н от условий процесса. 5. Два жидких компонента идеального раствора могут смешиваться в любой пропорции.
Ex. 12. Answer the following questions:
1. In what way can the capacity of a solvent to dissolve a given solute be characterized? 2. What state is regarded as equilibrium between the solute and solution? 3. What is usually callcd the solubility of a substancc in a particular solvent? 4. What is the importance of the conccpt of solubility? S. What is an ideal solution?
Scction II
Упр. 1. Назовите значения следующих интернациональных слов:
convert, hypothetical, contract, absorption, mole, entropy, compromise, dcducc, argument, energetically, chaos, generalization, rationalize, accompany, anticipate
Упр. 2. Проверьте, помните ли вы значения следующих слов; если нет, обратитесь к словарю:
melt, in turn, stage, involve, represent, extend, evolution, infinitely, likewise, markedly, subtle