Текст 9 b

The Action of Chlorine on Other Elements

At ordinary temperatures chlorine is a pale green gas, with normal boiling and freezing points of -35° and -102°, respectively. It occurs in nature mainly as sodium chloride. Chlorine is prepared in very large quantities industrially. It is moderately¹ soluble in water. Dry chlorine is somewhat inert chemically and it has no appreciable action upon bright metallic sodium, copper, etc. Moist chlorine is very active. It does not combine with oxygen directly, although several compounds of chlorine and oxygen can be obtained indirectly. In sunlight, equal volumes of hydrogen and chlorine combine with explosion, whereas in the dark hydrogen does not appear to combine with chlorine with appreciable velocity. Chlorine oxides are highly reactive and unstable, they are likely to explode under various conditions. Probably the best characterized is chlorine monoxide Cl₂O. It is a yellowish red gas at room temperature, the liquid boiling at 2°C. It explodes rather easily on heating. It is known to dissolve in water forming an orange-yellow solution. Chlorine dioxide is also highly reactive and likely to explode very violently.

Примечание к тексту

1. moderately – умеренно

VIII. Изложите содержание текста на английском языке.

LESSON 10

Грамматика. Инфинитив в функции подлежащего и обстоятельства (цели и следствия).

Предтекстовые упражнения

I. Обратите внимание на функцию инфинитива в следующих предложениях и переведите предложения на русский язык:

1. To separate air into its components requires the use of fractional distillation of liquid air. 2. To separate air into its components one must use fractional distillation of liquid air. 3. In order to purify water it should be either thoroughly filtered or boiled. 4. The solution prepared was sufficiently saturated to be used in this case. 5. The amount of the material was too small to be studied by the method in question. 6. The experiment was repeated so as to obtain more accurate results. 7. The analysis of the compounds of silicon and those of carbon has been made in order to establish the difference between them. 8. Crystalline silicon is hard enough to scratch glass. 9. The particles were so fine as to be invisible. 10. The work was such as to require a special equipment. 11. The substance was so volatile as to be collected only with great difficulty. 12. Mary Curie together with her husband Pierre Curie investigated pitchblende to discover an element of greater radioactivity than uranium itself. 13. Selenium and tellurium burn in air to form dioxides. 14. To produce penetrating rays from uranium compounds by any artificial means is not possible. 15. To produce artificial diamonds from carbon high pressure and high temperature are required.

II. Прочитайте и переведите следующие слова без словаря:

lithium /lm/, rubidium /ru:bdm/, periodic /prdk/, calcium /klsm/, caesium /si:zjm/, amalgam /mlgm/, hydrolyze /hadrlaz/

III. Запомните чтение следующих слов:

toward /tw:d/, usually /ju:l/, develop /dvelp/, slaked /slekt/, benzene /benzi:n/, benzine /benzi:n/

Text 10 A

Alkali Metals

The elements of the Periodic Group I A, lithium, sodium, potassium, rubidium and caesium are called the alkali metals. These are alike in having a single electron in the outermost shell; since this electron is far removed from the rest of the atom, it is easily lost. Therefore, from the chemical point of view, these elements are the most active metals known. As we progress from lithium toward caesium, a striking increase in radius of the atom is to be observed.

Properties. Alkali metals have relatively low melting points and boiling points. They are soft enough to be easily cut with a knife, the softest being caesium. The latter is soft enough to be moulded¹ between fingers. They are also very light, the lightest being lithium, sodium and potassium. They are so light as to float on water.

The untarnished² surfaces of these metals may be seen to have a silvery lustre, but they rapidly tarnish and lose their lustre. The metals are usually stored in oil so as to exclude air. When stored in this way, they usually do not have a metallic appearance because of a surface coating.

The alkali metals are too active to be found free in nature. They are known to react with a number of non-metals, forming binary products, e. g. with chlorine to form chlorides, with bromine to form bromides and with sulphur to form sulphides.

The alkali metals are such active metals as to displace hydrogen from water, producing gaseous hydrogen and the hydroxide of the metal in solution. Potassium, rubidium and caesium develop enough heat in this reaction to ignite the liberated hydrogen.

2 Na + 2 H₂O = H₂ + 2 NaOH

They also displace hydrogen from acids, but the reaction is too violent to be of importance.

Reacting with oxygen, lithium yields the simple oxide, sodium, on the other hand, yields the peroxide unless the temperature is kept relatively low. When heated in air sodium and potassium readily take fire, each metal forming a mixture of oxides. The ordinary temperature is sufficient to ignite rubidium and caesium.

To prepare sodium hydroxide, a solution of sodium carbonate is added to slaked lime, calcium hydroxide, suspended in water. When exposed to air sodium hydroxide absorbs moisture and carbon dioxide, so it is used to remove both moisture and carbon dioxide from the air.