What happens to the pH of water when chlorine gas is added?

When chlorine gas is added to water, it forms hydrochloric acid and hypochlorous acid, leading to a decrease in pH. This occurs because the formation of these acids introduces more hydrogen ions (H+) into the water, which lowers the pH level. As a result, chlorine addition makes the solution more acidic.

Understanding the chemistry involved is key here; chlorine reacts with water through a hydrolysis process. The reaction produces acids that shift the balance of hydrogen and hydroxide ions, ultimately resulting in a more acidic environment and therefore a decreased pH. This is an important consideration in water treatment since maintaining appropriate pH levels is crucial for effective disinfection and the overall quality of the water being treated.