What is Water?

            How long can you survive without water? Without water, we cannot survive for more than a few days. Water is called elixir of life. Without it, life on earth would not be possible. Human beings, plants and animals all need water for their survival. Perhaps that is why nature has covered more than 70% of the earth’s surface with water. About 97% of the total water on earth is in the ocean.

Structure of water molecule

            Water is a compound of hydrogen and oxygen. It contains two parts of hydrogen and one part of oxygen by volume, as shown in figure. Pure water is colorless, odorless, transparent ad tasteless. We get water Form Rivers, lakes, fountains, wells, rains, oceans, etc. water exists in three state—solid, liquid and gas. Normally, it is found in the liquid state, but when it is cooled to 0 degree centigrade, it freezes into ice. When it is heated to 100 degree centigrade, it turns into steam.

            Water obtained form nature is not pure, but contains many slats and minerals dissolved in it. Due to these impurities, it develops a taste slightly different than pure water. Some of the impurities make water hard. Hard water does not form lather with soap. The hardness of water is of two types- temporary and permanent. Temporary hardness is due to the presence of bicarbonates of calcium and magnesium. It is removed by boiling the water. The presence of chlorides and sulphates of calcium and magnesium in water cause permanent hardness. This hardness can be removed by mixing sodium carbonate with the water.

            Water has many fascinating properties. For example, ice is lighter than water. That is why ice and big icebergs float on the surface of seas. Water has the maximum density at 4 degree centigrade. Due to this property, during winters, only the upper surface of water in lakes and ponds freezes but the lower portion remains liquid. Hence marine life can easily survive in such lakes and ponds.

            The structure of water is such that most substances dissolve in it. Hence, water is regarded as a universal solvent. Seawater is saline because many minerals remain dissolved in it. Air dissolves itself in water enabling aquatic animals to breathe. Water is a liquid which does not evaporate easily. That is why soil retains moisture for a long period; this benefits trees and plants.

            Water content in different living organism varies. Trees and plants have 60% to 80% water, fresh fruits 85% to 95% and plants living in water contain 98% water. Human body contains 65% water.

            A civilized man on an average used 35 gallons of water every day for drinking bathing and washing. One should be careful about drinking water. Often, water contains germs of dangerous diseases like typhoid, cholera, diarrhoes, dysentery, etc. boiled water is, therefore, hygienic. Water can be made free from germs by filtering, boiling and mixing potassium permanganate or chlorine tablets in it.

How is Oxygen Useful to Us?

            Oxygen is the most important gas in the atmosphere. Without oxygen, there would be no life on the earth. No living being, plants or animals, can survive without it. Do you know what it is, and why is it absolutely essential for us?

            Oxygen is a gaseous element. Two scientists discovered oxygen independently. Carl Scheele, a Swedish Chemist, discovered oxygen in 1772 and Joseph Priestley from England in 1774. It is a colorless, tasteless and odorless gas. The atmosphere around us contains 21% oxygen, 78% nitrogen and other gases about 1%.

            On the earth’s crust, oxygen is found in the forms of oxides of metals. Oxygen can be liquefied at -182.9 degree centigrade under a certain pressure. In the liquid state, it becomes light blue in color. At -218.4 degree centigrade, it is converted into solid state.

            In the laboratory, oxygen is obtained by heating a mixture of potassium chlorate and manganese dioxide. Fro the atmosphere, it is obtained by the fractional distillation of air. The air is compressed to tow hundred times the normal atmospheric pressure and passed through a narrow hole into a chamber. When the pressure is suddenly dropped, the air gets liquefied and is collected in the chamber.

            Nitrogen gas is separated form this by special method ad oxygen is obtained in the liquid state.

            All living beings need oxygen for breathing. Plants also breathe oxygen. They absorb oxygen during the light. During the day, they give off oxygen by the process of photosynthesis.

            Burning oxygen gas along with acetylene gas produces a flame of high temperature called oxyacetylene flame. This flame is used for welding and cutting metals. Liquid oxygen is also used as a fuel in space vehicles.

            Oxygen cylinders are used by patients in hospitals having breathing problems and also by mountaineers and divers in the sea. Oxygen helps in the oxidation of food in our body, which ultimately give us energy. Fuels can burn due to oxygen in the atmosphere.

            We cannot breathe in pure oxygen, as it is harmful for our body cells. Fresh air in essential for us because it contains oxygen and other gases it he correct proportion. It is for this reason that we should keep the doors and windows of our rooms open to let in fresh air.

Sea-divers take oxygen cylinders with them to breathe while in the sea

            This is the reason why one should not cover one’s face while sleeping, as it would prevent him from breathing in fresh air. During winters, one should not close the doors and window and light a fire of coal inside the room to keep warm, because during this process, oxygen is used up and carbon dioxide is released, which is very harmful.