In ancient times water was considered as an element, but in 1781 Henry cavendish clearly proved that water is a compound of hydrogen and oxygen, because
In water, hydrogen and oxygen always remain in a fixed ratio (2: 1).
The properties of water are completely different from those of hydrogen and oxygen.
The components of water (Hydrogen and Oxygen) cannot be separated by physical methods.
For these reasons it is clear that water is not a homogeneous or heterogeneous mixture, but a compound. For the first time in 1842, Duma found the ratio of hydrogen and oxygen present in water by weight. after which chemists found the mass and volumetric composition of water and told that its molecular formula is H2O.
So we can say that water is the monoxide of hydrogen.
Occurrence: Water is a natural substance, about 75% of the earth is water. It is the main component of the animal and plant world. About 70% water is found in the human body. The water which is found in the main state in nature is called natural water.
Sources of water in nature:
In nature, water is found in three states – solid, liquid and gas. Water is mainly obtained from the following sources –
Rain water: – This is the purest natural water. It is obtained by evaporation and liquefaction of water of river, sea etc. In addition to gases like ammonia (NH3), carbon dioxide (CO2), nitrogen dioxide (NO2), 0005 % solid impurities are also found.
Rain water being pure, it is used for making medicines and in place of distilled water in the laboratory.
River or Spring water: River water comes due to rain and melted snow on the mountains, this water is also pure near the mountains, but due to continuous flowing on the ground, some solid impurities dissolve in it and insoluble impurities arise. The water of the river becomes muddy due to impurities like soil etc.
Sea water: – This is the most impure water. Usually 3 – 5% solid impurities are dissolved in it. Which about 26% common salt (NaCl) is dissolved.
Apart from this magnesium salt, potassium chloride, bromide and iodide salt etc. are also found in abundance.
Mineral Water: – Due to seepage into the porous surface of the earth, almost all the impurities dissolved in rain water get separated. When this water collects in such places, from where it cannot go down, sometimes it starts coming out of the earth in the form of a waterfall.
It contains dissolved salts of various solid impurities – sodium, potassium and calcium etc. Some of these also have medicinal properties. Such water of springs is called mineral water and it is used as water for medicine.
Well Water: Some part of the rain water is filtered through the sandy pebble layers of the land and collects below. In this water insoluble substances are less, but soluble substances are in more quantity. The properties of this water depend on the chemical composition of the land.
In some places this water is obtained by digging deep wells.
The water used for drinking is called potable water or potable water. Natural water is not good for drinking, because in addition to many soluble and insoluble substances, it contains microscopic bacteria and germs. Due to which various diseases such as cholera, intermittent fever, dysentery etc. occur, so the drinking water should be absolutely pure.
The following properties should be present in drinking water –
It should be transparent, colorless and odorless.
Let it be clean.
It does not contain germs and germs.
It does not contain harmful solute substances: – such as nitrate, nitrite, ammonium salt etc.
It is very important to have some essential minerals salt and air dissolved in drinking water. This makes it tasty and healthy.
Purification of Drinking Water :
The following 5 steps are used for the purification of drinking water –
Insoluble impurities are removed by decantation or filtration.
Water is made colorless and odorless by filtering it with coal.
Water is made free from harmful micro-organisms by mixing air, ozone, chlorine, potassium parmagnate, tutia, bleaching poweder etc.
Alum is added to the impure water, due to which the suspended impurities coagulate and settle down, then the water is carried away to other ponds.
Drained water is filtered from sand, bricks, pebbles etc.
Drinking water treatment in cities
Industrial method: – The system of purifying water in cities is different. For this, water works are constructed in cities.
In which the following methods of water purification are used.
Aggregation and coagulation – First of all, the water of river, pond and lake is filled in big pucca tanks, in which there are layers of pebbles, sand, fine sand and coal. These tanks are also called setting tanks.
In these, many suspended substances settle down, those suspended substances are in collide state, for them, alum is added to the water. Due to this the collide impurities precipitate and settle down.
Some germs also get destroyed by the use of alum and sit down. The remaining germs are destroyed by sunlight. This type of precipitation of collide substances is called coagulation.
Filtration: After the stabilization tanks, the water is taken to the big filtrate tanks. These tanks have thick layers of sand, gravel, pebbles and charcoal.
This method is similar to the method of four pots. Water is slowly filtered from these layers and is fed into the tanks through the taps installed in the tanks.
Sterilization of water: After filtering the water, the germs and bacteria present in it are destroyed by the following methods –
By boiling – By boiling the filtered water, the germs present in it are destroyed. This method is mostly used in homes.
Chlorination: Chlorine is a bactericidal substance. An appropriate amount of liquid chlorine bleaching powder is used to destroy the bacteria in the water.
Ozonization: – Ozone is also a bactericidal gas. If ozonization makes oxygen flow into water, then the germs present in it are destroyed.
By Ultra Violet rays: Ultra violet rays are also a good means of killing bacteria. These rays are received from Mercury lamp and flowed on the stream of water. This kills the bacteria in a very short time and no inappropriate odor or taste is produced in the water.
By aeration: Under this method, water is thrown into the air in the form of a fountain, due to which it is affected by the ultraviolet rays of the sun and the bacteria are destroyed.
By potassium permanganate: – In order to destroy the germs from the well water, potassium permanganate is added to it.
Distilled water: Distilled water is required for various experiments in the laboratory. Natural water is taken in a copper vessel and heated in a furnace. Distilled water is the liquid formed from the condenser of the water vapor produced by it, which is collected in the receptacle vessel. This water is soft.
Chemically Pure Water :
First the water is distilled, but some impurities remain in the impure water and it is necessary to separate these impurities to obtain chemically pure water. To separate these impurities chlorine is passed into the water and then the water is boiled to separate them.
After this the water is distilled by adding alkaline potassium permanganate solution. On condenser for the second time, chemically pure water is obtained.
Water is a compound not a mixture :
Hydrogen and oxygen combine chemically in the mass ratio of 1 : 8 or in the volumetric ratio of 2 : 1 to form water. Water is a pure substance, which has its own special properties. The properties of water are completely different from the properties of its constituents.
Water has a certain proportion of its components. In a water molecule, one oxygen atom is combined with two hydrogen atoms, so water is a compound. It is not a mixture of oxygen and hydrogen.
Hydrogen + Oxygen → Water
Water → Hydrogen + Oxygen
Volumetric composition of water: There are two main methods to find the volumetric composition of water –
Method of analysis: Electrolysis of water – This is the method of separating the components of water by passing an electric current through the water. The pot in which electrolysis is done is called Voltameter.
Voltameter: – Voltameter consists of three tubes of lead, which are related to each other. By filling in the middle tube, it reaches the side drains. Both the side tubes are of the shape of a burette, in which there is a barrier at the top and the house centimeter sign is made on both the tubes. The mouths of both the tubes are closed by cork. Through the cork, a platinum wire, on which the platinum letter is attached, is entered inside both the tubes. These letters are called electrodes.
Method :- Taking a boltameter, fill some water in it, in which a small amount of sulfuric acid is mixed. Now close the barriers of both the side tubes.
After this, the platinum wires in both the tubes are connected separately to both the poles of the battery. As soon as the electric current flows, gases start collecting in the tubes on both sides and the water level in the tubes starts falling.
After a while the volume of gas collected in both the tubes is read. We see that the volume of the gas collected at the cathode is twice the volume of the gas collected at the anode.
The gases collected in both the tubes are tested by taking a burning straw in them. In the gas whose volume is less, the straw burns faster and in the gas whose volume is more, the straw gets extinguished. The first gas is oxygen and the second hydrogen.
Conclusion :- This experiment proves that water is a compound of hydrogen and oxygen. The ratio of hydrogen and oxygen in water in terms of volume is 2 : 1.
Identification of Water: Heat a few crystals of blue copper sulfate in a test tube. After some time the color of the crystals turns white. Now taking these white crystals in a porcelain cup, pour a little liquid on them. If the color of the cristals again turns blue, then the given liquid is water.
The water reacts with the bud and generates heat.
Water turns the dry blue crstals of cobalt chloride red.
The freezing point of pure water at normal pressure is 0 C and the boiling point is 100 C.
Water reacts with sodium to produce hydrogen gas and becomes alkaline. This alkaline water turns red litmus blue.
Properties of Water :
Physical properties :
Pure water is clear, colourless, odorless, free and transparent.
Its freezing point is 0°C and boiling point is 100°C.
It is found in all three states – solid, liquid and gas.
It is a bad conductor of heat and electricity. It can be made a good conductor of electricity by adding a few drops of acid to it.
Water remains in the form of crystal water in crystal substances and maintains their colour, shape and luster etc.
Example: copper sulfate and zinc sulfate
Water is a universal solvent.
The density of water is 1 gram/cubic cm at ordinary temperature about 20 C, which is maximum
To convert water from solid state to liquid state, 80 c of heat is required per gram. This is called the latent heat of ice. 536 calories of heat are required to convert water into liquid state. This is called the latent heat of vapor.