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PHYSICAL AND CHEMICAL PROPERTIES

The behaviour of one material with another and its behaviour under special conditions are called chemical properties. Wood burns when it is heated in air. If a current of electricity from a battery or a dynamo is passed through water, the water is split into two gasas, hydrogen and oxygen. Also, if yeast is added to a solution of sugar in water, the sugar is converted to alcohol and carbon dioxide. These effects are chemical properties of wood, water and sugar, respectively.

The physical properties are usually enough to distinguish one substance from

another, and the chemist uses them for that purpose. When iron rusts, the ruts is a brown powder, very different from the iron. This alone tells the chemist that the iron has changed to another substance. Ashes are very different from wood and coal. Alcohol is a liquid and Sugar is a solid and taste is very different. Alcohol has an odour and sugar is odourless. These examples show how helpful physical properties are in distinguishing between substances.

Sometimes it is not easy to tell one substance from another and then chemist must use chemical properties or measure some of the physical properties quantitatively. For example, wood alcohol and grain alcohol are both colourless liquids. They have similar odours and both mix with water in all proportions, but wood alcohol boils at 65ºC and grain alcohol at 78ºC. Consequently, the boiling temperature of the liquid tells the chemist which liquid it is. Likewise, chloroform and carbon tetraphloride are both colourless liquids that smell much alike, but chloroform boils at 61ºC and has the specific gravity 1.489, whereas carbon tetrachloride boils at 77ºC and has the specific gravity 1.595. Obviously, the careful measurement of either of these physical properties is a way to tell these liquids apart. The measurement of these properties can distinguish one of these liquids from all others, for no two substances are likely to have the same quantitative values for two physical properties.

Examination of the chemical properties is often the easiest way to tell one substance from another. For example, grain alcohol burns, but carbon tetrachloride does not – a simpler test is hard to imagine. If a chemist has the problem of identifying an entirely unknown substance, he must decide which properties are most likely to be useful. Experience helps him to make the selection and also tells him what properties are the most easily and quickly determined.

Questions

1. What colour is chloroform? 2. Does sugar have an odour? 3. What physical properties can be helpful in distinguishing one substance from another? Give examples.

KEYS

1. 2. 3. 4. 5. 6. 7. 8.

б) – – – + – + + –

а) – + + – – + – –

в) + – – – + + – +

1 (+) 2, 4, 5, 6, 7, 9, 11 2 (–) 1, 3, 8, 10, 12

(+) 1, 5, 6, 7, 9, 10, 11 (–) 2, 3, 4, 8, 12

1. This discussion is very useful. 2. He is not unskillfull. 3. It was a successful attempt. 4. It is not useless to make experiments. 5. He is a very skillful chemist. 6. It is harmful to drink much coffee. 7. You must be very careful with this gas. 8. Slow heating destroys harmful organisms.

1. This is a very powerful engine. 2. Oxygen is a colourless gas. 3. The operation was very painful. 4. His answer was quite unsuccessful. 5. This work is not useless. 6. The results of his work were very useful. 7. The number of elements is not limitless. 8. He is a very helpful man.

Speaker 1) careless 2) harmful 3) useful 4) skillful 5) helpless 6) painless 7) tasteful 8) meaningless

1) – 2) – 3) + 4) + 5) – 6) + 7) + 8) –

1. – 2. –

3. + 4. +

5. + 6. –

7. + 8. –

9. + 10. –

11. + 12. –

13. – 14. –

15. + 16. +

1. colouless, 2. faultless, 3. airless, 4. powerful, 5. careful, harmful, 6. starless, 7. harmful, 8. useless

2, 5, 6, 7, 10, 12

Speaker 1) quite useless – absolutely useless 1) + 2) not very harmless – harmful 2) + 3) absolutely doubtless – doubtful 3) – 4) quite unlimited – limitless 4) + 5) not very skillful – quite skillful 5) – 6) rather meaningless – not very meaningful 6) + 7) absolutely tactless – tactful 7) – 8) quite helpless – helpful 8) – 9) not quite uneventful – eventless 9) – 10) distasteful – very tasty 10) –

1. The author means it is harmful. 2. The author means they are doubtful. 3. The author means it will be painful. 4. The author means it was fruitless. 5. The author means he is skillful. 6. The author means it was unsuccessful. 7. The author means they were tactless.

1. Oh, no, half a century ago operations were more painful than now. 2. + 3. Oh, no, bananas are tasteful. 4. Oh, no, freezing is harmless for meat products. 5. + 6. Oh, no, drinking water is tasteless. 7. Oh, no, phosphorus is a harmful substance.

A – 3, B – 1, C – 2, D – 3, E – 1, F – 1, G – 2

1) water, 2) sugar, 3) wood and grain gases, 4) the inert gases, 5) butter-milk, 6) bacteria

1 – 2, 2 – 1, 3 – 1, 4 – 1, 5 – 2, 6 – 2

КОМПЛЕКС 8 УЗНАВАНИЕ И ПОНИМАНИЕ СЛОВ, ИМЕЮЩИХ