Determination of Percentage of Available Chlorine in Bleaching Powder Iodometric Titration

Bleaching powder is Calcium hypochlorite [Ca(OCl)2] which combines with water liberating hypochlorite ion (OCl-), which further forms hypochlorous acid (HOCl) and acts as disinfectant. Percentage of chlorine in bleaching powder can be determined by iodometric method or by Orthotoulidine method. This experiment is useful to assess the quality of bleaching powder and also useful to estimate the amount of bleaching powder required for effective disinfection of water.
Chlorine liberates free iodine from potassium iodide solution in acidic medium. The liberated iodine is titrated with standard sodium thiosulphate solution using starch as the indicator. The amount of thiosulphate consumed is directly proportional to the chlorine content in bleaching powder.