- Q. NO. Explain the methods of removing permanent hardness.
Answer. Permanent hardness can only be removed by using chemicals. Calcium (Ca2+) and magnesium (Mg2+) are removed as insoluble salts by adding washing soda (Na2CO3) or sodium zeolite.
- By using washing soda: The addition of washing soda removes the calcium and magnesium ions as the insoluble calcium and magnesium carbonates, respectively.
Na2CO3(aq) + CaSO4(aq) CaCO3(s) + Na2SO4(aq)
Na2CO3(aq) + MgSO4(aq) MgCO3(s) + Na2SO4(aq)
Using Sodium Zeolite: Sodium zeolite is a naturally occurring resin of sodium aluminum silicate NaAl (SiO3)2, which can also be prepared artificially. It is used for softening of water at domestic as well as on industrial scale. When water is passed through resin sodium ions of the resin are exchanged with the unwanted calcium and magnesium ions of the hard water as shown in figure.
Na2 zeolite + CaSO4(aq) Ca zeolite + Na2SO4(aq)
When resin is fully used up it can be regenerated by flushing it with concentrated solution of NaCl. The reverse process takes place because of high concentration of sodium ions.
Ca zeolite + 2NaCl Na2 zeolite + CaCl2
- No.3. Explain the water pollution because of industrial waste.
Answer. Industrial units are installed to produce the desired substances (chemicals, cloth, leather goods, paper, plastic items, petrochemicals and rubber items) on commercial scale to meet the needs of the society. But unfortunately all the industrial units discharge their wastes (chemicals and solid materials) either to open ground or to water channels. This is called industrial effluent. The industrial effluent may be highly toxic organic chemicals, inorganic salts, heavy metals, mineral acids, oils and greases, etc. On the other hand, water used as cleaning agent in industries is directly discharged out. This water contains all kinds of toxic chemicals and detergents.
When these effluents or used water enter lakes, streams, rivers or oceans, they either get dissolved or float suspended in water. Even they get deposited on the bed. This results in the pollution of water, i.e.
(i) They deteriorate the quality of water.
(ii) They reduce the quantity of dissolved oxygen, ultimately affects aquatic life arid ecosystem.
(iii) They can also seep down and affect the ground water deposits. They contaminate the water deposits. When this water is used by human beings it causes serious diseases like cancer .and gastro. This polluted water damages soil, crops, plants and animals.
(iv) Heavy metals like cadmium, lead and mercury are toxic and health hazards for human beings. Acute cadmium poisoning causes high blood pressure, kidney damage and destruction of red blood cells. Acute lead poisoning causes disfunction of kidney, liver, brain, central nervous system and reproductive system. Mercury poisoning causes neurological damage.