Прочтите текст про себя (контрольное время чтения — 5 минут).
Hydrogen Production
Hydrogen is a very widely distributed element. It is found in most of the substanccs that constitute living matter, and in many inorganic substanccs. There arc more compounds of hydrogen known than of any other element.
Free hydrogen, H2, is a colourless, odourless, and tasteless gas. It is the lightest of all gases, its density is about one-fourteenth that of air. Its melting point (-259°C or 14K) and boiling point (-252.7°C) arc very low, only those of helium arc lower. Liquid hydrogen, with density 0.070 gfcnr3, is the lightest of all liquids. Crystalline hydrogen, with density 0.088 g/cm~3, is also the lightest of all crystalline substances. Hydrogen is very slightly soluble in water, 1 litre of water at 0°C dissolves only 21.5 ml of hydrogen gas under 1-atm pressure. The solubility decreases with increasing temperature, and increases with the increase in the pressure of the gas.
In the laboratory, hydrogen is easily made by the reaction of an acid such as sulphuric acid, H2S04, with a metal such as zinc. The equation for the reaction is:
H2S04(aq) + Zn(c) ZnS04(aq) + H2(g).
Sometimes hydrogen is prepared by the reaction of some metals with water or steam. Sodium and the other alkali metals react very vigorously with water, so vigorously as to generate enough heat to ignite the liberated hydrogen. An alloy of lead and sodium, which reacts less vigorously, is sometimes used for the preparation of hydrogen.
Much of the hydrogen that is used in industry is produced by the reaction of iron with steam. The steam from a boiler is passed over iron filings heated to a temperature of about 600°C. The reaction that occurs is
3Fc(c) + 4H20(g) Fc,04(c) + 4H2(g).
After a mass of iron has been used in this way for some time, it is largely converted into iron oxide, Fcj04. The iron can then be regenerated by passing carbon monoxide, CO, over the heated oxide:
Fcj04(c) + 4CO(g) 3Fc(c) + 4C02(g).
There is, of coursc, nothing special about sodium and iron, except their low cost and availability, that is the reason why they arc used for the preparation of hydrogen. Other metals with electronegativity about the same as that of sodium (x=0.9) react with water as vigorously as sodium, and metals with electronegativity about the same as that of iron (x=1.8) react with steam in about the same way as iron.
