III. Speaking

1. Express the law of Conservation of mass in your own words.

2. Explain why the concept of conservation of matter is considered a scientific law.

IV. Reading

1. Read the text and check the new words in the dictionary.

Text B

Antoine Lavoisier

Known as 'The Father of Modern Chemistry', Antoine Lavoisier (1743-1794) made many important contributions to science. Many scientists of that day were studying combustion, and the mechanisms of this process. Lavoisier, too, was fascinated by combustion and disagreed with the phlogiston theory, which he set out to disprove. He did this by carefully weighing the reacting materials and the products that were made in a chemical reaction. This was a very important step in the development of chemistry, and is now known as quantitative chemistry, that is, chemistry that involves accurate measuring. In order to accurately measure changes in mass that happened during his experiments, Lavoisier developed a balance that could weigh to 0.0005g. Measurement was important because Lavoisier strongly believed that matter was conserved through any reaction and this belief led to the development of the Law of Conservation of Mass.

He examined his idea of the conservation of mass by studying the combustion of phosphorous and sulphur. Through this, he discovered that it did not support the phlogiston theory because after burning, the mass of the material was greater than it had been at the start. If the elements had really contained phlogiston and lost it during the reaction, they should have weighed less, not more. Further experiments were required to find out what was happening in these reactions, and Lavoisier discovered that air was absorbed as these elements burnt. He realized that something (later identified as oxygen) was taken in during combustion rather than being given out (the phlogiston theory).

Thus it appeared that oxygen was one of the most important elements. One of these was that respiration was caused by chemical reactions with oxygen in the air.

By carefully composing and decomposing water, he discovered that it is made up of oxygen and hydrogen. He gave names to elements which reflected their functions. For example, he came up with the name oxygen because it means acid-former, and that is what oxygen does. This system of chemical nomenclature is still largely in use today.

2. Put the events into chronological order according to the text.

1. Scientists use the system of chemical nomenclature.

2. Lavoisier developed a very accurate balance.

3. He named elements according to their functions.

4. Combustion had been studied by many scientists.

5. He disagreed with other scientists.

6. Lavoisier was fascinated by combustion.

7. Further experiments showed that air is absorbed while burning.

8. Lavoisier studied the combustion of phosphorous and sulphur.

3. Find the synonyms to the words in bold from the text.

d. Find out the derivatives of the following words. Then complete the sentences with an appropriate derivative.

↑ ↑ ↑

← discovery → ← measurement → ← reaction →

1. The drug is not a new…………

2. Accurate……….. is essential.

3. There are many important industrial processes that use electrophilic ……….

4. The sulphur in the coal ……….. with the limestone during combustion.

5. She helped to……… out the ingredients.

6. A hitherto unknown worm that survives without oxygen was also……… by a scientific team.

7. Objectives should be………. and achievable.

8. When bonds are broken in a chemical reaction, the …….. involved are colliding with enough kinetic energy to break the atoms apart.

9. Uranus was only recently……….., by means of the telescope—a hundred and twenty years ago.