Tieng anh nganh hoa

UNIT 3 :
WATER
Water is one of the most important of all chemical substances. It is the chief constituent of living
matter. Its physical properties are strikingly different from those of other substances.
Ordinary water is impure, it usually contains dissolved salts and dissolved gases, and sometimes
organic matter. For chemical work water is purified by distillation. Pure tin vessels and pipes are often
used for storing and transporting distilled water. Glass vessels are not satisfactory, because the alkaline
constituents of glass slowly dissolve in water. Distilling apparatus and vessels made of fused silica are
used in making very pure water. The impurity, which is hardest to keep out of water, is carbon dioxide,
which dissolves readily from the air.
The physical properties of water. Water is a clear, transparent liquid, colorless in thin layers. Thick
layers of water have a bluish-green color. Pure water freezes at 0 o C, and boils at 100 o C. These
temperatures are means of identifying water, for no other substance has these freezing and boiling points.
The physical properties of water are used to define many physical constants and units. The unit of
mass in the metric system is chosen so that 1 cm 3 of water at 4 o C/ the temperature of its maximum
density/ weighs 1.00000 gram. A similar relation holds in the English system: 1 cu. Ft. of water weighs
approximately 1,000 ounces.
Steam and ice
Steam is water in the gaseous state. A cubic inch of water gives about a cubic foot of steam.
When gaseous water is mixed with other gases, as in the air, we speak of it as water vapor; when
unmixed, we call it steam. Water may exist as steam at temperature lower than 100 o C, provided the
pressure is less than the usual atmospheric pressure of 15 pounds per square inch.
If water is cooled sufficiently, it solidifies at 0 0 C to ice. There is considerable expansion during
the solidification, and consequently ice is lighter than an equal volume of water.
If we apply heat to ice, it melts. The water that runs off the melting ice is at a temperature of 0 0 C,
the same temperature as the ice.
EXERCISES
A. Read and translate into Vietnamese
constituent, properties, strikingly, ordinary, impure, contain, purified, distillation, pure, vessel, pipe,
distilled, alkaline, apparatus, fused, silica, impurity, carbon dioxide, air, transparent, bluish-green,
identify, temperature, define, unit, weigh, approximately, ounce, gaseous, cubic, inch, pressure,
atmospheric, square, sufficiently, equal, volume, ice, steam.
B. Answer the following questions
1. Why is water important to a human beings?
2. What are the characteristic properties of water?
3. Are glass vessels satisfactory for storing and transporting distilled water?
4. Where does carbon dioxide readily dissolve from?
5. What is the color of water?
6. How is the unit of mass in the metric system chosen?
7. What is steam?
8. What is the difference between steam and vapor?
9. What is ice?
C. Translate into English
1. Nc bình thng là mt cht không tinh khit, bao gm các hp cht khác nhau, vì vy nó c
tinh ch bng chng ct.
2. im sôi và im óng bng là nhng tính cht c trng ca nc, và c s dng xác nh
nó.
3. Nc óng bng c gi là nc á.
4. Nu chúng ta em un sôi nc lên trên 100 0 C, nó bin thành hi.
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