Of the total global water, the oceans and inland saline water bodies hold 97.3% and the fresh water amounts to only 2.7%.
Water constitutes about 65% of our body and is an essential element for its growth.
- The density of ice is less than that of water and hence ice floats over water.
- Water has maximum density (1 g) at 4°C.
- M.P. is 273.2 K and B.P. is 373.2 K
- Chemically heavy water is deuterium oxide (D2O).
- It was discovered by Urey in 1932.
- It is colourless, odourless and tasteless liquid.
- It has been finding use in nuclear reactors as a moderator because it slows the fast moving neutrons.
- Its MP is 276.8 K and BP is 374.4 K.
Properties of water
The freezing point, boiling point, heat of fusion and heat of vaporisation of water are higher as compared to the hydrides of the other members of same group of oxygen.
Hard and Soft Water
Water which produces lather with soap solution readily is called soft water, e.g., Rain – water, dematerialized water.
Water which does not produce lather with soap solution readily is called hard water. e.g.. Sea – water, river water, well water, tap – water.
Cause of Hardness of Water
The hardness of water is due to presence of the bicarbonates, chlorides and sulphates of calcium and magnesium (Ca++ and Mg++).
Types of Hardness of Water
(A) Temporary Hardness
This type of hardness in water is due to the presence of bicarbonates of calcium and magnesium. It can be removed by boiling.
(B) Permanent Hardness
This type of hardness is due to presence of bicarbonates of calcium and magnesium, it can be removed by boiling but some chlorides and sulphates of calcium and magnesium are also present with it which can not be removed by boiling.
Softening of Water
The process of removal of hardness from water is called softening of water.
- Water is treated with a calculated amount of washing soda (Na2CO3) which converts the chlorides and sulphates of calcium and magnesium into their respective carbonates.
- Iron Exchange Method : This method can be classified into two parts :
(A) Inorganic cation Exchanges : This method is also known as “Permutit Method”.
These are complex inorganic salts like “hydrated sodium – aluminium silicate” (Na2Al2Si2O8 . xH2O) which have interesting property of exchanging cations such as calcium and magnesium ions in hard water with sodium salt ions.
These complex salts are known as “Zeolites”.
(B) Organic ion Exchanges : These are complex organic molecules having giant hydrogen frame work attached to acidic or basic groups.
These are called ion exchange resins.
These are superior to zeolites because they can remove all types of cations as well as anions present in water. The resulting water is known as deionised water or dematerialized water.
Note : Mass of 1 mole of D2O and T2O are 20 gm and 22 gm respectively.