Pict. 2. Distribution of Earth’s Water
The Earth is often called the "blue planet" because it appears blue from space. This blue colour is caused by reflection from the oceans which cover about 70% of the area of the Earth. Water is one of the five elements that make up this planet, along with fire, earth, air, and metal. Because of its prominence, water has long played an important religious and philosophical role in human history. The belief that water was a fun- damental substance existed for more than 2,000 years until experiments
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in the second half of the 18th century showed that water is a compound made up of the elements hydrogen and oxygen. Civilization has histori- cally developed and flourished around rivers and major waterways. As the Earth's population grows and the demand for fresh water increases, water purification and recycling become increasingly important.
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Decide whether the following statements are true or false accord- ing to the text.
1. Water is composed of the chemical compounds hydrogen and oxy- gen.
2. Solid, liquid, and gas are the three physical states in which water ex- ists on the Earth.
3. Water is a colourful, tasteful and odourless liquid at room tempera- ture.
4. Water has the ability to solve any substance easily.
5. Water takes part in all processes that occur in plants and animals.
6. The formula of a water molecule seems complex in structure, but the physical and chemical properties of the compound are simple.
7. Water in its solid state is denser than water in its liquid state.
8. Water is valueless for transportation, for recreation, and as a habitat for a myriad of plants and animals.
9. The “water cycle” is a synonym for the “hydrologic cycle”.
10. There are three classes of characteristics of water: physical, chemical, and biological.
11. The chemical characteristics of water include its acidity, alkalinity, pH, turbidity, and hardness.
12. Salt water constitutes about 3% of all the Earth’s water supply.
13. Both groundwater and surface water are fresh water.
14. Today water purification and recycling are increasingly important be- cause of the Earth’s population growth.
Answer the following questions.
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1. What is water?
2. In what physical states does water exist on the Earth?
3. Is water a solvent for all other substances?
4. What do living organisms use aqueous solutions for?
5. What are the examples of unusual and complex properties of water?
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6. What are three classes of water characteristics?
7. What do the physical, chemical and biological characteristics of water include?
8. Is 97% of all water on the Earth salt or fresh water?
9. Ground water is fresh water, isn’t it?
10. Is fresh surface water contained in rivers, lakes and seas?
11. Why is the Earth often called the “blue planet”?
12. Where has civilization developed historically?
13. Why do water purification and recycling become increasingly im- portant?
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