7. Answer the following questions to the text using the dictionary.

1. How is it usually possible to change matter from one state to the other?

2. Can all kinds of matter be obtained in each of the three states?

3. What do solids have?

4. What characterizes gases?

5. Why should a chemist know the states of matter?

6. What other substances besides water can be obtained in the three states?

Lesson IV

Why is water so important?

Lead-in

What comes to your mind if you see or hear the word “water”?

Complete the following chart with your ideas and share the information with your fellow students.

Vocabulary

1) steam	- пар
2) surface	- поверхность
3) ice	- лед
4) change of state	- изменение состояния
5) heating	- нагревание
6) point of view	- точка зрения
7) chemical reaction	- химическая реакция
8) decomposition	- разложение, распад, деструкция
9) fundamental	- основной, базисный
10) importance	- важность, значение
11) physical change	- изменение физических свойств
12) compound	- соединение
13) electric current	- электрический ток
14) hydrogen	- водород
15) oxygen	- кислород

1. Pay attention to the pronunciation of the following words.

[i:] steam, heating, teacher, easy

[Λ] substance, fundamental, current

2. Pay attention to the stress in the following words. Pronounce them.

´compound	re´action
´hydrogen	ex´periment

3. Read and translate the following words both as nouns and verbs.

change	state	water	mark	influence	increase
experiment	experience	comment	matter	heat	decrease

4. Read the text and fulfil the exercises.

The most common material on earth

Three-quarters of the Earth’s surface is covered by water. This makes water the most common material on Earth. Like other substances, water can exist as a liquid, gas or solid. Water in the form of gas (water vapour) is commonly called steam. Solid water is ice. We can change one form into another by simply changing the conditions, for example, by heating it up or cooling it down. The change from one form to another is usually called a change of state. Changes of state are examples of a physical change. They don’t involve making new substances.

Single substances are either compounds or elements. What about water? From the chemical point of view water has many points of interest, because it enters into chemical reactions which are of fundamental importance. Water not only reacts with many substances but it also has a marked influence upon many chemical reactions.

Water can be decomposed. So, it can be an element, can’t it? Decomposition of water can be made by electric current. In this way two volumes of hydrogen and one volume of oxygen are obtained. So, we can say that water is a compound of hydrogen and oxygen. The chemical name for water is hydrogen oxide. Is it possible to make water from its elements? The answer is – yes! In fact, it is quite easy to do (but rather dangerous).

Hydrogen is the water former. When it is burnt in air, water is formed. The “artificial water” formed in this way is exactly the same as “natural water”. The experiment can be made in the laboratory, but only by the teacher, and with strict safety precautions.