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प्रश्न
Discuss the treatment of water using bleaching powder
उत्तर
In small water-works, about 1 kg of bleaching powder per 1,000 kilolitres of water is mixed and water is allowed to stand undisturbed for several hours the chemical action
produces hypochlorous acid
`Ca0Cl_2 + H_2 0 → Ca(OH)_2 + Cl_2`
`Cl_2 + H_2 0 → HCl + HOCl`
germs + HOCl → germs are killed
The disinfecting action of bleaching powder is due to the chlorine made available by it.
Drawbacks:
1. Bleaching powder introduces calcium in water, thereby making it more hard.
2. Bleaching powder deteriorates, due to its continuous decomposition during storage. So whenever it is added, it has to be analysed for its effective chlorine content.
3. Only a calculated quantity of bleaching powder should be used, since an excess of it gives a bad taste and smell to treated-water.
