Testing and evaluation of bleaching agents

The relationship between °Tw and strength of bleaching powder solution is shown in Table 16.7. These methods of expressing strengths of solutions, however are far from accurate and hence quantitative estimation by titration for practical control of bleaching operation is preferable. 

5 g sample is made up to 500 ml in a volumetric flask. 50 ml of this solution is pipetted out to a 250 ml conical flask and 25 ml of distilled water is added followed by 20 ml of KI solution (10%) and 10 ml of glacial acetic acid. The liberated iodine is titrated against N/10 sodium thiosulphate solution using starch solution as indicator towards the end point when the blue colour will be discharged. 

The estimation by above method expresses chlorates as well as hypochlorites as available chlorine. The errors due to chlorates can be avoided by titration with an N/10 solution of sodium arsenite (Na HAsOj) 

2 g sample is made up to 500 ml in a volumetric flask. 25 ml of solution is pipetted out and then 25 ml of 10% KI solution and of 10% H SO are added. The content is titrated against O.IN Na S O solution using starch as an indicator till blue colour disappears completely. 

10 ml of sample solution is diluted to 1000 ml with distilled water. 10 ml of this solution is pipetted out into a conical flask and 10 ml of 10% H,SO is added to it. This solution is then titrated against O.IN KMnO till pink colour of permanganate solution persist. 

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