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How to detect residual chlorine in water by iodometric method

by:BOQU     2023-03-19
Residual chlorine in water is commonly used as a disinfectant, usually in liquid chlorine. After liquid chlorine reacts with microorganisms, bacteria or reducing substances in water, the amount of chlorine remaining in water is called residual chlorine, including free available chlorine and Combined available chlorine. Appropriate residual chlorine for drinking water can inhibit the growth of bacteria, but excessive residual chlorine will have an impact on human health. Therefore, the country has strict requirements on the residual chlorine content in the outlet water of water plants and the terminal water of residents' pipe networks. Today, I will talk about how to use the iodometric method to detect residual chlorine in water. 1. Classification of residual chlorine in water Free available chlorine includes hypochlorous acid (HOCL) and hypochlorite (OCL-). In the process of water disinfection, these two substances will be produced rapidly after chlorine is dissolved in water. Combined available chlorine is a complex mixture of inorganic chloramines (NHCL) and organic chloramines (RNCL). If the raw water contains NH3·H2O, chloramines will be formed after adding chlorine. At this time, free available chlorine and combined available chlorine exist in the water at the same time, so the determination of residual chlorine in water quality should include free chlorine and combined chlorine. my country requires that for drinking water chlorinated and disinfected, the content of free chlorine should not be lower than 0.3mg/L after 30 minutes of contact between chlorine and water, and the terminal water of the pipe network should not be lower than 0.05mg/L. Chlorine disinfection of miscellaneous water in cities requires greater than 1.0mg/L after 30 minutes of contact, and the content at the end of the pipe network must be greater than 0.2mg/L. 2. Detection of residual chlorine in water quality In an acidic solution, residual chlorine in water reacts with KI to release a stoichiometric amount of I2. At this time, starch solution is used as an indicator and titrated with Na2S2O3 standard titration solution until the blue color of the solution disappears. Calculate the residual chlorine content in water from the consumed Na2S2O3 standard titration solution. The calculation formula is as follows: cV1*35.45*1000/V water If the water sample contains a lot of NO2, Fe, Mn, it will cause certain interference, we can use acetic acid buffer solution to buffer the water sample to pH3.5-4.2 to eliminate These distractions.
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