М. М. Кутепова The World of Chemistry Мир

Make up a dialogue out of the statements above and act it in front of your fellow students. You are given a few situations where such a dialogue could take place:

1. 
   At the seminar you’ve just attended one of the students has made a report on water. In your opinion his/her report deserves attention. You’re telling him/her this and you are discussing some details you’ve become interested in.
   
2. 
   Two students are speaking about new information on water they’ve found in Nature.
   
3. 
   A journalist is interviewing a famous scientist who has just presented a very interesting communication on water.
   

si

4. 
   You’ve just watched a scientific programme on TV about different uses of water and some chemical explanations of the material. Criticize the programme.
   
5. 
   You were given an assignment to test water from a tap. You offer a few solutions to the problem speaking with your lab instructor.
   

15. 
    Read another text on water. What ideas correspond to those expressed in ex. 2 and ex. 11 and what are different?
    

The abundance of water in liquid, solid and gaseous state is a matter of common observation. Water is not only the most abundant compound, but it is also very important for life. To be sure life would be impossible without water. For many purposes water must be pure. The purest natural water is rain. But we can’t say that it is really pure. The same can be said about ground water. It contains a great deal of impurities which fail to settle. Dissolved substances do not settle and don’t evaporate with water, and this makes their removal difficult. One of the most important problems is to obtain water sufficiently pure to meet our needs. The choice what process is to be used for purification of water depends upon the uses for which it is intended as well as the impurities it contains. Water used for steam boilers should be free from substances that cause corrosion and scale formation. Water for washing should not contain substances that react with soap. When water is to be used for drinking, it is necessary to kill the microbes it may contain. To achieve this, water which is to be purified is thoroughly filtered. Another way to purify water is to boil it. None of these methods is fit for producing pure water in the chemical sense, because most of the soluble salts are unaffected by the treatment. To remove these and to prepare chemically pure water suitable for scientific use, we take advantage of the fact that water is usually changed to steam while most of the dissolved substances as have already been mentioned are not volatile. If we condense the steam, we are thus able to remove all the impurities except volatile ones. This process is called distillation. Distilled water has many uses, both in the laboratory and in industry, when even a small quantities of impurities are undesirable,

16.