2. Consult the dictionary and write down all the meanings of the following words, define the part of speech they belong to. Make up sentences using some of these words.

To treat, indeed, upper, inner, proper, through, except, originally, followed by.

III. Read and translate the text from English into Russian, say what its main points are.

EXPERIMENTS IN THE LABORATORY

The dictionary treats the word “experiment” as “a scientific test done in order to learn something or prove the truth of an idea”. The term “experiment” is often associated with chemistry and chemistry laboratories. Indeed, it is difficult to study a substance or an element, to give any theoretical conclusion in chemistry without conducting the proper experiments. Many experiments can be carried out in the laboratory. Here are some of them.

PREPARATION OF HYDROGEN CHLORIDE

To obtain hydrogen chloride (HCl), which is often referred to as a hydrochloric acid gas, it is necessary to pour some sulphuric acid through a tube over the crystals of sodium chloride in a flask. The flask is to be heated. On warming the flask, the hydrogen chloride is expelled as a colourless gas with a suffocating odour. It produces heavy clouds of white fumes when it comes in contact with the moist air of the room.

It is soluble and it cannot be collected over the water as are oxygen and hydrogen. It is much heavier than the air and may be passed through a glass tube to the bottom of a bottle. If we dissolve some of the gas in water the solution has a sour taste, reddens blue litmus, reacts with zinc etc. – it is a hydrochloric acid. When all the sodium chloride originally present in the flask has been transformed, the reaction is complete. The flask then contains a salt called sodium acid sulphate (NaHSO4) together with unchanged excess of sulphuric acid.

OBTAINING HYDROGEN BY MEANS OF KIPP’S APPARATUS

In order to obtain hydrogen Kipp gas generator (Kipp’s apparatus) may be used.

Kipp gas generator consists of two parts. The lower part of the generator has two compartments – the middle bulb and the lowest compartment with a tap; and the other part is a spherical funnel with a long stem leading into the lower part of the Kipp’s apparatus.

The upper spherical funnel of the apparatus contains the solution of hydrochloric acid. Iron or zinc is placed in the middle bulb of the generator. When the tap is turned on the acid flows down from the funnel and interacts with the metal. When the tap is turned off the hydrogen formed displaces the acid into the lower part of the gas generator. Then, the acid passes up the inner tube into the spherical funnel. Hydrogen comes out through the outlet.

PREPARATION OF SALTS

The word “salt” denotes a number of important chemical compounds. All these compounds are solids at room temperature. They can all be crystallized, and as it is known crystals vary in colour and form.

To get salts it is necessary to know some methods of their preparation. Salts can be prepared either by the interaction of an acid with a base or by the reaction of an acid with a metal. There are other laboratory and commercial methods by which salts may be prepared. Except those cases in which a salt is produced through the reaction of a metal with an acid most methods to make salts involve double replacement reactions. Here are a few equations representing reactions in which salts are produced.

1. The reaction of zinc with hydrochloric acid results in the replacement of hydrogen atoms in the acid by zinc. Thus, a salt called zinc chloride is formed.

Zn + 2HCl ––– H2 + ZnCl2 (replacement)

metal acid salt

2) The interaction of calcium carbonate and hydrochloric acid gives double replacement followed by decomposition into water, carbon dioxide and salt – calcium chloride.

CaCO3 + 2HCl ––– H2O + CO2 + CaCl2

carbonate acid salt

(double replacement followed by decomposition)

So, salts are produced by several types of chemical reactions. The number of possible kinds of salts that can be formed is practically limitless.