Name the methods of removing permanent hardness from water
Answers
(a) By the use of soda:
Soda removes both temporary and permanent hardness. It is also inexpensive and easy to use. This makes it the ideal substance for softening water in the home.
(b) Other softening agents in the home:
It is difficult for the housewife to be very precise in the use of soda and the water softened by soda may often contain an excess of it, which even if it is slight, may damage certain fabrics. Hence, other softening agents could be used. They are:
(i) Soap:
Soap is used as a softening agent. However, the use of soap as a softening agent is extravagant on account of its high cost compared with soda.
(ii) Caustic soda:
t removes temporary hardness but reduces permanent hardness only when the lather is very slight.
(iii) Solution of Ammonia:
It may be used for softening water, when the fabrics to be treated would be harmed by soda. If used in excess, ammonia may destroy the Iustre of rayon's, discolour and injure animal fabrics and loosen the dyes of coloured articles. Since, it is not possible to be very certain of the quantity to be used; this is not practicable for softening water.
(iv) Borax:
It is useful for softening water containing over 20% of hardness. Borax is usually used to reduce the alkalinity of soap solution rather than to soften water.
(c) Removal of Permanent Hardness by the Base-Exchange Process:
Base exchange process' is a chemical method by which, softening of permanent hardness in water can be done on a large scale or for household purposes. It is the most popular and effective means of softening hard water. It was discovered by Dr. Robert Gans, who found out the natural minerals called 'Zeolites', which is very effective in softening water,
The Base-Exchange Process includes the following procedures:
The water passes through specially prepared zeolite- a sodium compound, called base-exchange compound. it is has the property of being able to exchange its sodium base for another. When hard water passes through the zeolite, the hardening compounds of calcium and magnesium are caught up by the zeolite and become compounds of sodium. Since sodium salts in water do not precipitate out on heating or form soap curds the water is called 'soft'.
When a given quantity of water, determined by the size of the appliance, has been softened, the zeolite becomes depleted; having parted with all its sodium, but this can be remedied, as the substance has the property of being able to exchange its base again and to take back sodium in place of calcium and magnesium. This process is called 'regeneration'.Zeolite water softeners made for domestic use are either connected with the men water-supply or fixed on to a water tap.
Temporary hardness is caused by dissolved calcium hydrogencarbonate (which is removed by boiling). Permanent hardness is caused by dissolved calcium sulfate (which is not removed by boiling). Water can be softened using washing soda or an ion-exchange resin.