Chapter 16 Water : A Precious Resource Class

Transcription

1 Chapter 16 Water : A Precious Resource 1. Water is 70 per cent of Earth s surface 2. All Water on Earth is called Hydrosphere ALL WATER In the Earth s Atmosphere On surface of the Earth Under the ground Water Vapour = 0.001% Is very important for life 2.15% as ice sheets in the North and South Poles; % in Rivers and Lakes 97.2% in Oceans Difficult to estimate 10x10learning.com 16 An Ocean is the great body of water on Earth s surface 71 % is Ocean on Earth 29% is land on Earth 61% is Ocean in Northern 39% is Land In Northern Southern is called Ocean 81% is Ocean in Southern 19 % is land in Southern Northern is called Land 10x10learning.com x10 Learning TM Page 1

2 1. A colourless, tasteless, odourless liquid : 70% of human body and 70% of surface of Earth.H2O is the formula and chemical name is Di-hydrogen oxide, molecular mass is 18 amu. It can exist in all the three states of matter as water, water vapour, and ice. Water 2. It is a homogeneous chemical compound. Its elements can be separated only by chemical methods, such as electrolysis of acidified water. Heat is evolved when Hydrogen combines with Oxygen to form water. Water is a universal solvent. 3. The density of water is gcm -3 at 4 degree centigrade. An unusual quality of water is that, when cooled, it first contracts in volume, but at 4 degree C, it starts to expand and continues to expand till it reaches zero degrees. Its boiling point at sea level, with an atmospheric pressure of 760mm Hg is 100 degree C. Increase in atmospheric pressure raises the boiling point and decrease in atmospheric pressure lowers it. 4. Vegetables and fruits and vegetation matter contains 60 to 70 % water It is present as water of crystallisation in many salts, such as CuSO4,.5H2O, MgCl2,.6H2O, ZnSO4,.7H2O, 10x10learning.com 5. The pleasant taste of water is due to dissolved matter, like air, carbon dioxide, minerals. Distilled water has no taste, and Pure Water does not conduct electricity. It is a good conductor only due to the presence of dissolved minerals. It is a stable compound and does not decompose on heating 2 Chemical composition of Water Chemical composition of water depends upon whether the water is fresh or salty. Fresh water is needed for living beings, and for agriculture. It is found in lakes, rivers, and under the ground. Brooks, and geysers are natural sources of underground water. Man extracts underground water through wells and pumps. In last 50 years this has resulted in overuse of underground water. 10x10learning.com 19 Exercises 10 x10 Learning TM Page 2

3 1. Mark T if the statement is true and F if it is false: 1.1 The freshwater stored in the ground is much more than that present in the rivers and lakes of the world. True 1.2 Water shortage is a problem faced only by people living in rural areas. False 1.3 Water from rivers is the only source for irrigation in the fields. False. 1.4 Rain is the ultimate source of water. True 2. Explain how groundwater is recharged? Answer. Ground water can be recharged through water harvesting. Many of the smaller rivers that carry water only during the rainy season, are used for this purpose. Check dams are built across these rivers. This prevents the rain water from flowing away into the sea. It is made to stay within the rivers for a longer duration, and recharge the ground water. In addition rain water harvesting structures are built where ever possible, on roof tops of houses, along hills and hillocks where it is easy to collect the rain water flowing down the hills, in a canal like structure at the bottom. The collected water is useful for irrigation and for animals. Rainwater harvesting has enabled many of the dry rivers to be revived. Construction of new bawris that is a age old way to conserve rain water to make it last for a year is another method. Many old bawaris have also been cleaned and re filled during rains. Many ponds have been cleaned out and recharged. In some places traditional and historical water reservoirs systems, that had fallen into disuse, have been revived. 3. There are ten tube wells in a lane of fifty houses. What could be the long term impact on the water table? Answer. The long term impact would be a severe depletion of underground water table. Tube wells tend to draw out more water than is needed due to the high water pressure they build up. This overuse of ground water depletes the water table very quickly. The rains are not sufficient to recharge all the excess water that has been drawn out. In contrast, the traditional wells or a hand pump in each house are better as there is no overuse or wastage of water. 10 x10 Learning TM Page 3

4 The underground water that could last an entire year, if there were only wells and hand pumps, would get exhausted in five to six months due to tube wells. As such, the long term impact of tube wells is adverse. 4. You have been asked to maintain a garden. How will you minimise the use of water? Answer. Water use in a garden can be minimised through a sprinkler that is placed at a central point to cover the entire garden. If drip irrigation method is used, it would economise the use of water even further. 5. Explain the factors responsible for the depletion of water table. Answer. Excessive use of tube wells for irrigation, neglect of rain water harvesting, unused traditional methods such as bawalis and tanks. Irregular rainfall is another cause as the amount of rainfall in many regions has been reducing over the years. 6. Fill in the blanks with the appropriate answers: 6.1 People obtain groundwater through wells and tube wells. 6.2 Three forms of water are water vapour, ice and liquid water. 6.3 The water bearing layer of the earth is Lithosphere. 6.4 The process of water seepage into the ground is called recharging of ground water table. 7. Which one of the following is not responsible for water shortage? (i) Rapid growth of industries (ii) Increasing population (iii) Heavy rainfall (iv) Mismanagement of water resources 8. Choose the correct option. The total water (i) in the lakes and rivers of the world remains constant. (ii) under the ground remains constant. (iii) in the seas and oceans of the world remains constant. (iv) of the world remains constant. 10 x10 Learning TM Page 4

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