9. Define the functions of the Participles. Translate the sentences

1. Units referred to as basic are elements. 2. Elements are referred to as basic units of matter. 3. Substances composed of two or more elements are called compounds. 4. Substances are composed of some elements combined chemically. 5. Combined together the two different substances are referred to by chemists as a compound. 6. Different substances not combined chemically are called mixtures.7. Chemical substances worked at can be divided into three classes. 8. Mixtures experimented upon are of great importance.

10. Translate into Russian The Laboratory Preparation of Oxygen

Oxygen may be easily prepared in the laboratory if potassium chlorate is heated. The reaction mentioned above takes place quickly if some manganese dioxide is mixed with the potassium chlorate, however, as a result of the reaction, the manganese dioxide is not changed. As is known oxygen forms compounds with all the elements but the inert gases. The compounds formed have been called oxides. Examples are hydrogen oxide, aluminium oxide, ferrous oxide, ferric oxide, sulphur dioxide. Most: of the elementary substanсes combine so strongly with oxygen that they burn either spontaneously (phosphorus) or after ignition (sulphur, hydrogen, magnesium, aluminium, iron, etc.).

A few, such as mercury, for example, form oxides slowly, even when heated; and others, such as iridium, cannot react directly with oxygen, although their oxides can be made by indirect methods. Oxygen can also be prepared from solutions.

11. Practice the following dialogue.

- May oxygen be easily prepared in the laboratory?

- Oxygen may be easily prepared in the laboratory if potassium chlorate is heated.

- Does the reaction take place quickly?

- The reaction takes place quickly if some manganese dioxide is mixed with the potassium chlorate.

- Is manganese changed in a result of the reaction?

- No, it is not

- Does oxygen form compounds with all the elements?

-.No, it doesn’t. It does not form compounds with inert gases.

12. Point out the verbs in the Passive Voice, state their form.

1. At present many experiments are being made. 2. The components of a solution have been determined. 3. The students of our group have been given the new textbooks. 4. Our students are being shown new samples. 5. The substance has been broken down into two simpler chemical substances. 6. Substances which cannot he-broken down into simpler chemical substances by chemical means-are called elements.

13. Translate into Russian. Pay attention to "either... Or"

1. This problem may be solved either experimentally or theoretically. 2. The theoretical questions can be answered either in written or oral form. 3. Hydrogen can be got either by the electrolysis of water or by steam iron process. 4. The substances may be weighed either before the experiment or after it. 5. The changes in the state or composition of substances may be either physical or chemical.

UNIT IV ^{Injurious Substances and Human Body}

Grammar: Passive Voice(Continuation)

Text: Air Pollution