What is the chemical behavior of chlorine in water?

Chlorine in water undergoes a series of chemical reactions that result in the formation of hypochlorous acid.

When chlorine is added to water, it reacts with the water molecules to form hypochlorous acid (HOCl) and hydrochloric acid (HCl). This reaction is known as hydrolysis and is the first step in the disinfection process. Hypochlorous acid is a strong oxidizing agent that can react with and destroy microorganisms such as bacteria and viruses.

The effectiveness of chlorine as a disinfectant depends on the pH of the water. At a pH of 7.5, approximately 80% of the chlorine is present as hypochlorous acid, which is the most effective form for disinfection. As the pH increases, the proportion of hypochlorous acid decreases, and the effectiveness of the chlorine as a disinfectant decreases.

Chlorine can also react with organic matter in the water to form disinfection byproducts (DBPs), such as trihalomethanes (THMs) and haloacetic acids (HAAs). These DBPs are a concern because some of them have been linked to adverse health effects, such as cancer and reproductive problems.

Overall, the chemical behavior of chlorine in water is complex and depends on a variety of factors, including pH, temperature, and the presence of organic matter. While chlorine is an effective disinfectant, it is important to monitor and control its use to minimize the formation of DBPs and ensure safe drinking water.