The most important chemical substance

Water is hydrogen oxide, a compound of hydrogen and oxygen. It can be made if hydrogen or hydrogen containing substances are burnt in air or oxygen. Most of the world’s water is liquid but an important fraction is solid, as ice or snow. Many mineral substances contain water of crystallization (e.g. copper sulfate) and in the atmosphere there are millions of tons of water vapour.

Fresh water which is accumulated on the earth's surface is known as surface water. Lakes, rivers, reservoirs, streams, swamps and any other natural storage basin contain surface water. Not all surface water areas are natural as there are many man-made lakes and reservoirs. On the other hand, fresh water (from rain, melting snow or ice) which soaks into the soil is known as ground water.

Clouds consist of minute droplets of water or crystals of ice. Water dissolves a very large number of substances and it is the most important solvent. It does not dissolve greasy, fatty substances or most plastics. It was established that ordinary water is impure, it contains dissolved salts and gases and sometimes organic matter. For chemical work water is to be purified by distillation. Pure water is colourless, tasteless, and odourless. Rain water is nearly pure water, containing only small proportions of dust and dissolved gases.

When the chemists had examined the properties of water, they found that physical properties of water could be used in many physical constants and units. The freezing point of water (saturated with air at 1 atm pressure) is taken as 0 °C and the boiling point is of water at 1 atm is taken at 100 °C. The unit of volume in metric system is chosen so that 1 ml of water at 3.98 °C (the temperature of its maximum density) weighs 1.0000 g/cm³.

So water is one of the most important of all chemical substances. It is a main constituent of living matter and of the environment in which we live.

3. Divide the text into some logical parts and entitle them.

4. Translate the following sentences into English using lexical material of the text:

1. Вода является основным растворителем большого количества веществ.

2. Обычная вода содержит примеси.

3. Вода может быть очищена методом дистилляции.

4. Дождевая вода практически очищена.

5. Вода – главная составляющая всех живых веществ.

Text C

1. Pay attention to the following words and word combinations:

сonsumption – потребление

annually – ежегодно

vessel – сосуд

to satisfy the demands – удовлетворять потребности

fuel – топливо

vary – изменяться

2. Read the text and be ready to say if the following statements are true or false. Use the following phrases:

I think it’s right.

It seems to be wrong.

I can’t agree with it.

As far as I know …

To my mind

On the contrary

1. Natural forms of water are always pure.

2. Consumption of water increases greatly.

3. There isn´t any water problem nowadays.

4. Sea water contains many solids.

5. Distillation of sea water gives pure water. This operation demands little fuel.

6. Water purification by using the Sun as the source of heat is economically proved.