242
10. What form of water is called water vapor?
Exercise 5.
Listen to the text about water and decide if you would agree
with the following statements. Write “Yes” or “No” in the box next to each
statement and be ready to explain your answers.
Tapescript
Three-quarters of the Earth is covered in water. This makes water the
most common substance on Earth . Like other substances water can exist
as a liquid, as a gas, or as a solid. Water in the form of a gas (water
vapour) is commonly called steam. Solid water is ice. We can change one
form into another form 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 the
physical change. They do not 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. Well, water can be decomposed.
So it can’t be an element, can 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 of water is hydrogen oxide. Right? Is it
possible to make water from its elements? The answer is – yes! In fact, it
is quite easy to do (but dangerous). Hydrogen’s the water former,
remember? 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 by the teacher, and with strict safety
precautions.
Keys:
1. Water is the most abundant substance on the Earth. Yes
2. We can not change one form of water into another by simply changing
the conditions.No
3. The three forms of water are all the same chemical substances. Yes
4. A change of state involves making new substances.No
5. Water can be decomposed into its elements by electrolysis. Yes
6. Water vapour is usually defined as steam. Yes
7. Water’s chemical symbol is H2O.Yes
8. Water can be synthesized by burning hydrogen in the air.Yes