The temperature at which a liquid boils, is dependent not only upon the nature of the liquid itself, but also upon the pressure prevailing at the time the boiling point is determined. An increase in the atmospheric pressure causcs a rise in the boiling point of a liquid; a dccrcasc results in a lowering of the boiling point.
Each individual substancc capable of existing in the liquid state has its own definite boiling point. Consequently, this property is used for identifying or characterizing a substancc in the same way that density and other physical properties arc employed.
Inasmuch as the boiling point of a substancc is affcctcd by changes in pressure, it has been found ncccssary to set up a standard pressure at which all boiling points can be compared. A pressure of 760 mm Hg has been selcctcd as the standard. Thus, if the boiling point of water is given as 100° C, the measurement is understood to have been made at a pressure
of 760 mm Hg. Nevertheless, it is quite true to say that the boiling temperature of water is 70°C at a pressure of 233.8 mm Hg; it is also correct to say that carbon tetrachloride boils at a temperature of 70°C, but in this ease the pressure is 620 mm Hg. Boiling temperature should not therefore be used for distinguishing one substancc from another unless the values used have been determined at the same pressure. Unless otherwise stated[8], a boiling point value is understood to be the temperature at which a substancc boils under a pressure of 760 mm Hg.
One atmosphere (standard atmospheric pressure) is equal to 101.325 kNnr2. It is not an approved SI (International System) unit of pressure, but it is especially important in chcmistry bccausc many properties of substanccs have been measured and recorded at 1-atm pressure. An approved SI unit of pressure is the pascal (1 Pa = 1 H/m2).
Another unit of pressure that has been much used in the past is the torr, which is the height in millimetres of a column of mercury that balances the pressure. The symbol mmHg is sometimes used for torr. The name of the unit is taken from the name of the Italian physicist Evangclista Torricelli (1609-1647), known for having invented the mercury barometer. One atmosphere is equal to 760 torr.
Words and Word-Combinations to Be Memorized
approve, balance, boiling point, capable, consequently, decrease, be dependent upon, employ, height, invent, lower, otherwise, record, select, set up, therefore, at the time, unless
Ex. 5. Give the Russian equivalents for the following:
be dependent on (upon), determine the boiling point, exist in the liquid state, consequently, in the same way, be affcctcd by, set up, nevertheless, distinguish one substancc from another, unless, be equal to, unit of pressure, be recorded at 1-atm pressure, invent a barometer
Ex. 6. Give the English equivalents for the following:
воздействовать на, природа самой жидкости, вызвать повышение точки кипения, приводить к, каждое отдельное вещество, иметь свою собственную точку кипения, сравнивать, выбрать в качестве стандарта, выполнить измерения, совершенно справедливо, атмосферное давление, итальянский физик, ртутный барометр
Ex. 7. Fill in the blanks with prepositions where necessary.
1. The boiling point... a liquid is dependent... the nature of the liquid itself and the pressure. 2. A changc... the atmospheric pressure results... a changing ... the boiling point. 3. There was a need ... set... a standard
pressure. 4. Usually measurements are made... 1-atm pressure. 5. Standard pressure is taken to be ... a pressure ... 760 mm. 6. Boiling points should be used ... distinguishing one substance ... another only ... the same pressure. 7. Another unit ... pressure is the torn 8. One atmosphere is equal... 760 mm.
Ex. 8. Translate the sentences into Russian, paying attention to the constructions to do and to have something done.
1. The student translated an English articlc. 2. The student had an English articlc translated. 3. The student had translated an English articlc yesterday by S o'clock. 4. She sent the letter to her mother. 5. She had her letter sent two days ago. 6. She typed the paper. 7. She had the paper typed for her. 8. Each chcmical element has been given its own name. 9. Each chemical clement has its own name given to it. 10. Each chcmical clement has its own name.
Ex. 9. Translate the sentences into Russian.
1. He likes reading. 2. He avoids making complex calculations. 3. There is no need doing it at once. 4. The teacher suggested going on an excursion. 5. Don't use this apparatus, it wants repairing. 6. Excuse my being late. 7. Now I am very careful in the laboratory, I can't forget my having burnt my left hand with an acid. 8. They were sorry for having missed the last lecture. 9. The student denied the laboratory assistant having helped him with the experiment. 10.1 don't mind my sister's taking my notes. 11. Under ordinary conditions the precipitate may fail to begin forming. 12. It is necessaiy to practise identifying the constituent elements of a sample. 13. The fundamental chemical laws are worth studying. 14. The confcrcncc is going to be very interesting, we cannot help going there. 15. Mendclcycv's wide interests in various sciences did not prevent him from taking part in social life. 16. Alkali metals are capable of reacting with a number of the non- metals, forming binary products, c. g., chlorides, bromides, etc. 17. Before working in the laboratory, students must learn what measures should be taken against being poisoned by chemicals. 18. Everybody knows of D. I. Mcndeleycv's having organized the Chamber of Weights and Measures in Russia. 19. Alchemists succccdcd in both preparing a number of new elements and inventing useful picccs of apparatus. 20. S. V. Lcbcdcv succeeded in making the first synthetic rubber in the world.
Ex. 10. Translate the sentences into English.
1. Есть необходимость знать факторы, которые оказывают влияние на точку кипения вещества. 2. Главными из таких факторов являются: природа самого вещества, температура и давление. 3. Повышение атмосферного давления, как известно, приводит к повышению точки кнпенм жидкости. 4. Для получения сравнимых результатов следует проводить измерения при одинаковом давлении. 5. Давление в 760 мм ртутного столба принято как стандартное давление в 1 ат- мосфсру. 6. Другой единицей давления, которой часто пользовались в прошлом, а иногда пользуются и сейчас, является торр. 7. 1 торр равен V76o атмосферы, название происходит от имени итальянского физика Э. Торричелли.
Ex. 11. Answer the following questions:
1. What factors is the boiling point of a liquid dependent on? 2. How docs the atmospheric pressure affect the boiling point? 3. What was the need of setting up a standard pressure? 4. What pressure was selected as a standard? 5. In what way can the boiling point be used in comparing the substanccs? 6. What do wc mean if the pressure is not pointed out in the description of an experiment? 7. What other units of pressure do you know?
Section II
Упр. 1. Назовите значения следующих интернациональных слов:
scalc, object, contact, thermal, energy, ordinarily, thermometer, astronomy, philosopher, alcohol, normal, human, calibrate, convcrt, absolute, engineer
Упр. 2. Определите значення выделенных слов по контексту.
1. Не had lived in Leningrad before 1990 and then settled in Moscow. 2. It's rather warm today, what temperature is it? — 16 degrees. 3. The analysis is easier to make by means of a microscopc. 4. Wc have devised a pcrfcct plan of doing the work.
Слова к тексту:
quality — качество; tube — трубка; centigrade scale — стоградусная шкала; Swedish—швсдский; choice—выбор; perhaps—возможно; fever — жар, лихорадка; saturate — насыщать