English for chemists

Lesson 30
ГРАММАТИКА: Инфишгтв и инфинитивный оборот в функции обстоя­ тельства. Придаточные обстоятельственные предложения.
Section I
Ex. 1. Practise your reading.
It is a matter of common experience that the capacity of a solvent to dissolve in a given solute is often limited.

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Ex. 2. State what parts оГ spccch the following words belong to:
mix, mixture, mixing, mixer, mixed, mixablc, misciblc, miscibility
Ex. 3. Define the meanings of the word case in the following sentences:
1. Wc shall first limit ourselves to the case of ideal solutions. 2. In case a solute and its solution rcach equilibrium, a saturated solution may result. 3. A homogeneous material has the same properties throughout, it is far from the case with heterogeneous materials. 4. According to their properties the halogens should be very reactive, and this is really the case. 5. Reacting with oxygen, an element forms an oxide in which case the process is known as oxidation. 6. Phosphorus is very active chemically, but this is not the case with nitrogen. 7. During oxidation, heat and light arc often liberated, in this case the process is callcd combustion. 8. It was supposed that oxidation of copper could be prevented under low temperatures, and such was the case. 9. One cannot cxpcct that gas molcculcs would always behave in the same way as is the case with liquid molcculcs. 10. If there arc several ways of doing something, one should know all of them so that he could choose anyone, as the case may be.
Ex. 4. Analyse the following sentence:
There arc many pairs of substanccs which can be mixed in any proportions to form homogeneous solutions.
Text 30 A
Solubility
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 placed in contact with an excess of solute attains and maintains a constant concentration of solute, the solute and solution arc at equilibrium, and the solution is said to be saturated. The solubility of a substancc 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 the 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 chemicals, and is the controlling factor in a variety of geological and other natural phenomena. The solubility of a substancc 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 ease of ideal solutions.

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The liquids (hai form an ideal solution arc always misciblc in any proportions and, thus, have infinite solubility in cach other. The reason for this is easy to see if wc rccall two facts. First, limited solubility and a saturated solution result only when a solute and its solution reach equilibrium. Second, the equilibrium state is a compromise between a natural tcndcncy toward minimum energy and maximum molccular chaos. Now, the mixing of two ideal liquids is always accompanied 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 locate one solute molcculc in solution, wc could not predict what the identity of its nearest neighbours was, as wc could, if the molcculc were in the pure solute phase. Consequently, the solution has a higher entropy than the pure solvent and solute, and the tcndcncy toward maximum molccular chaos favours the mixing of the two liquids. Moreover, the fact that there is no energy changc in the mixing proccss means that the tcndcncy toward minimum energy docs not restrict the solution proccss. Consequently, the two liquid components of an ideal

solution can mix in any proportion.

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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 ease, it is not the case with, such is the ease, a chemical, 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 chemicals, 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 close packcd, moreover, restrict the proccss, emphasize the importance
Ex. 6. Give the English equivalents for the following:
общеизвестно по опыту, что.. ограниченная способность, избы­ ток растворимого вещества, быть в равновесии, в насыщенном ра­ створе при данной температуре и давлении, другими словами, значе­ ние концепции растворимости для химии, во множестве природных явлений, ограничиться случаем, идеальный раствор, достигать рав­ новесия, сопровождаться увеличением температуры, а не..., даже если, нет изменения энергии

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Ex. 7. Fill in (he blanks with articles where ncccssary.

1. Substanccs like ...		water and ...		ethyl alcohol can be mixed in any
proportions. 2. ... capacity o f ...			solvent to dissolve ...				given solute is
often limited. 3 ....	solubility o f...		substancc in ...