It is difficult to give a definition which tells clcarly and briefly how <r solutions differ from mixtures and compounds, in spite of the fact that solutions arc among the most familiar substances to be found in nature. However, it is often true that the most common concepts wc use are the most difficult to define precisely. A solution is a homogeneous substancc that has, over ccrtain limits, a continuously variable composition. The word "homogeneous" sets a true solution apart from a mcchanical mixture, for mixtures have macroscopic regions which have distinct and different composition and properties. The properties and composition of a solution arc uniform, as long as the solution is not examined at the molecular level. There arc substanccs, however, not to be clcarly classified as solutions or
mixtures. A solution of soap in water has a cloudy appcarancc due to particles which consist of many soap molcculcs collected together. Such a substancc has properties and composition which might be described as cither inhomogcncous or homogeneous depending on the experiment to be done. Therefore, there is no sharp dividing line between mixtures and solutions.
The requirement that solutions have continuously variable composition distinguishes them from most compounds. However, many solid materials wc commonly think of as compounds actually show variable composition. Cuprous sulphide and ferrous oxide arc examples of compounds which might also be thought of as solutions. No matter how carefully wc made our definitions of solution, mixture, and compound, wc must expect to find ccrtain substanccs not to be uniquely classified as one of these. There is no reason to expect nature to be cooperative and producc only substanccs which arc easily classified, and sincc this is the case, the most useful definitions are often the shortest, rather than the most exhaustive.
Words and Word-Combinations to Be Memorized
actually, appcarancc, brief, briefly, this is the case, certain, classify, clearly, continuously, depending on, distinct, examine, familiar, ferrous, for, homogeneous, level, as long as, mechanical, no matter, precisely, requirement, to set, uniform, variable
Ex. 5. Give the Russian equivalents for the following:
to give a definition, to tell clearly and briefly, in spite of the fact, it is often true, the most common concepts, over ccrtain limits, as long as, a cloudy appcarancc, the experiment to be done, a sharp dividing line, no matter how carcfully, sincc this is the case
Ex. 6. Give the English equivalents for the following:
отличаться от, свойства растворов, вещества, которые можно найти в природе, точно определить, гомогенное вещество, переменный состав, нсслсдовать на молекулярном уровне, четко классифицировать, в зависимости от эксперимента, нет оснований ожидать
Ex. 7. Fill in the blanks with articles where necessary.
1. It is rather difficult to give ... definition of... solution. 2.... word "homogeneous0 sets ... true solution from ... mechanical mixture. 3.... ferrous oxide is... example of... compounds wc may consider as ... solution. 4. ... most useful definitions arc often ... shortest. 5. At ... molccular level... properties of... solutions are not examined well enough.
Ex. 8. Give synonyms for the following:
precisely, distinct, different, examine, however, due to, consist of, many, do, material, commonly, actually, show, also, sincc
Ex. 9. Give antonyms for the following:
difficult, familiar, often, apart, different, short, most, certain, variable
Ex. 10. Translate the sentences into Russian.
1. Professor N was the first to prepare this kind of glass electrodes in our laboratory. 2. They stayed at the laboratory till 8 in the evening, bccausc they had a lot of work to do. 3. There arc two points to discuss. 4. This is the condition for everybody to observe. 5. There arc some rules never to be forgotten. 6. Students who study chcmistry must learn to do experiments. 7. Here is the room where chcmicals arc stored. 8. The need often arises in chcmical research to measure die concentration of a solution widi a high degree of precision. 9. A student about to begin an experiment must get his supervisor's permission. 10. The substancc to be dissolved is callcd die solute. 11. There arc a lot of problems for chemists to solve. 12. Acids arc chcmicals to be used carcfully. 13. Not die least of D. I. Mcndclcycv's services to chemistry was his publication of the first text-book of chcmistry to be based throughout on the periodic system of classification. 14. Jolm Dalton was by no means the first to speculate about an atomic theory. 1S. Lavoisier was the first to realize the importance of the balance for chcmical investigation. 16. D. I. Mcndclcycv was the first Russian chcmist to rcccivc widespread recognition in (he West during his lifetime. 17. The first clement of the series of noble gases to be discovered was argon. 18. Oxygen is frequently chosen as one of the first elements to be studied in chcmistry. 19. The rise of temperature gives more opportunity for the molecules to react. 20. There is usually a limit to how much solute a given volume of solvent can hold at a given temperature. 21. Compounds have properties that differ from those of the constituent elements. 22. Wc arc living at a time when chcmistry is used almost everywhere. 23. The periodic law D. I. Mcndclcycv discovered created a new era in the history of chcmistry. 24. The question whether a particular gas is lighter or heavier than air can be easily solved. 25. The state of a g substancc depends usually on die temperature and pressure it is subjected to. 26. The elements water is composed of arc hydrogen and oxygen. 27. The first clement wc shall study in detail is oxygen. 28. It is rccommcndcd that water wc use for drinking should be boiled. 29. It often happens that the neccssary condition for the reaction to begin is die presence of a catalyst. 30. It is the usual laboratory practicc that the potassium chloratc oxygen is to be produced from is placed in a vessel and heated.
Ex. 11 .Translate the sentences into English without using a dictionary.
1. На вопрос о том, чем растворы отличаются от смесей, не всегда легко ответить. 2. Среди веществ, которые можно найти в природе, немало растворов. 3. Свойство гомогенности позволяет отличить истинный раствор от механической смеси. 4. Некоторые свойства растворов можно объяснить только на молекулярном уровне. S. Нет оснований полагать, что вещества, которые мы находим в природе, всегда легко классифицировать.
Ex. 12. Answer the following questions:
1. Why is it difficult to give a definition of a solution? 2. Solutions arc among the least known substanccs, aren't they? 3. What is usually considered as the main property of solutions? 4. In what way can you characterize a solution of soap in water? S. Can one easily classify substances to be found in nature? 6. What definitions arc the most useful?
Scction II
Упр. 1. Назовите значения следующих интернациональных слов:
type, component, ethyl alcohol, zinc, metal, palladium, composition, really, contain, specify
Упр. 2. Проверьте, помните лн вы значения следующих слов; если нет, обратитесь к словарю:
just as, relationship, list, satisfy, treat, respectively