III. Read and translate the text. There are three big classes of chemical compounds: acids, bases and salts

CHEMICAL COMPOUNDS

There are three big classes of chemical compounds: acids, bases and salts. What are acids? In Latin, the word meaning "sharp" is acidits. Think of the acute mouth sensation that the mention of rhubarb, lemon juice and vinegar produces and you will understand the derivation of the word. These substances are "sharp" or sour.

Acetic acid is present in vinegar; ants' stings and stinging nettles contain formic acid; citric acid is one of the substances found in citrus fruits such as lemon; grape juice includes tartaric acid; sour milk pres­ents us lactic acid; green apples are rich with malic acid; sour taste of rhubarb and spinach is stipulated by oxalic acid. Finally, in our stom­ach, hydrochloric acid provides digestion.

In the laboratory you can find the following acids: hydrochloric acid, nitric acid, sulphuric acid, phosphorous acid, carbonic acid.

Some acids, such as citric, boric and tartaric, are solids, butyric acid is a liquid. Many acids arc water solutions of gases. In most cases, however, the significant acid properties do not become evident until the substance has been dissolved.

Chemically, the action of acids is due to the presence of hydrogen ions, H+, that determines its chemical properties. An acid is a sub­stance whose water solution yields hydrogen ions. Acids turn litmus from blue to red and conduct electricity,

What are bases? Bases are substances whose properties are chemi­cally opposed to those of acids. While acids are sour, bases are usu­ally bitter, if you rub some sodium hydroxide solution between your fingers, you will note that it feels slippery. All solutions of strong bases feel the same way because they react with the oil of your skin to actually make soap.

All bases contain the hydroxyl radical, OH-, determining chemical properties of bases. Thus, a base is any substance whose water solution yields hydroxyl ions.

As chemically opposed to acids, bases have opposite properties. To summarize, bases often taste bitter, feel slippery, turn red litmus blue, turn colorless phenolphtalein red, contain one or more of the hy­droxyl groups, neutralize acids and finally conduct an electric current in water solutions. Among the most important are sodium hydroxide, potassium hydroxide and so on.

Neutralization is the action between an acid and a base to form a salt and water. The hydrogen ion (H+) of acids combines with the hydroxyl ion (OH) of the base to form water. These ions are charged particles that make all special properties of acid and base vanish.

The metal of the base is now free to join with the nonmetal, or radical of the acid to form salt. Thus, a salt is the product other then water, obtained by neutralizing an acid with a base.

IV. Language development.

Find the odd word in each row.

1. Liquid, solid, water, gas.

2. Sweet, sharp, sour, bitter.

3. Act, neutralize, yield, dilute.

4. Acid, ion, base, alkali.

Complete the sentences.

1. There are 3 classes of chemical compounds:...

2. The Latin word acidus means....

3. There are such acids:....

4. You can meet such acids in the laboratory:....

5. Bases are substances....

6. Bases react with acids....

7. Neutralization is....

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