Fill in the gaps with the verbs given below. Transform them into the appropriate form.

1. The woman …a new phenomenon is their lecturer. 2. …this paragraph you should take notes. 3. Give this sample to the analyst … at the bench. 4. … a good specialist, our teacher can explain to us difficult problems. 5. … many books in organics my friend must know much about organic substances. 6. … a new phenomenon, specialists can put down new data.

to observe, to be, to have, to explain, to read, to experiment, to analyse

Read and translate the text. Write out the words which possibly could help you to characterize any other gas.

CHLORINE

Chlorine is an element with atomic number 17, atomic weight 35.5 (thirty-five point five). It is a gas at ordinary temperatures and is never found free in nature. It is found in nature only combined with other elements. At normal temperatures, chlorine is a diatomic gas (CL₂), greenish-yellow in colour and about 2 ½ (two and a half) times as heavy as air. It liquefies at atmospheric pressure at-34.1 C⁰ (minus thirty-four point one degrees Centigrade) to a yellowish liquid approximately 1 ½ (one and a half) times as heavy as water. The liquid freezes at-100.98C⁰ (minus one hundred point nine eight degrees Centigrade).

Chlorine is soluble in water and indirectly exerts bleaching and bactericidal action by reacting with water to form hypochlorous acid.

Cl₂ + H₂O HCl + HCLO HCL+ (O).

The hypochlorous acid is unstable. It gives up oxygen to form more HCl. The oxygen attacks and destroys bacteria. It also oxidizes coloured organic substances, forming colourless or less-coloured components.

Chlorine is one of the most active elements. It ranks in reactivity about with oxygen. Chlorine combines directly and readily with hydrogen and most non-metals except nitrogen, carbon and oxygen. It also unites with all the familiar metals except gold and platinum.

Participating in a number of important organic reactions, in some cases chlorine appears in the final product, as in insecticides (DDT) or in the plastic polyvinil chloride.

Chlorine is generally produced by electrolysis of water solutions of sodium chloride in electrolytic calls. When sodium chloride or potassium chloride solutions are subjected to electrolysis, there are there products: caustic soda or caustic potash, chlorine and hydrogen. If fused sodium chlorine is used, there are two products: chlorine and metallic sodium.

Notes to the text:

ordinary – обычный
to liquefy – переходить в жидкое состояние
approximately – приблизительно
soluble – растворимый
to exert – оказывать
hypochloorous acid – хлорноватистая кислота
unstable – неустойчивый
to oxidize– окислять, оксидировать
caustic potach – едкий калий
fused = molten – расплавленный
ranks in reactivity about with – по своей реактивности почти не уступает кислороду
insecticide – инсектицид
polyvinil chloride – поливинилхлорид
sodium chloride – поваренная соль, хлористый натрий
caustic soda – едкий натрий

15. Answer the questions:

1.What state is chlorine found in nature in?

2.What temperature does chlorine liquefy at?

3.Is chlorine easily soluble in water?

4.What is the reactivity of chlorine?

5.What method is chlorine generally produced by?

6.What action does chlorine exert in water?

7.What products are obtained when sodium chloride or potassium chloride solutions are subjected to electrolysis?

8.What products are produced if fused sodium chloride is used?

16. Find the pairs of antonyms:

easily, impure, final, indirectly, abundant, stable, heavy, with difficulty, inactive, rare, original, light, directly, unstable, active, pure.

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