TCEQ Class B Surface Water License Practice Test 2025 – The All-In-One Guide to Exam Success!

Free chlorine is considered to be more powerful than combined chlorine due to its higher oxidation potential. In water treatment, free chlorine, which includes forms such as hypochlorous acid (HOCl) and hypochlorite ion (OCl-), is highly effective at inactivating bacteria and viruses. This is because free chlorine exists in an active state that readily reacts with and destroys pathogens.

Combined chlorine, on the other hand, refers to chlorine that has already reacted with ammonia and organic nitrogen compounds to form chloramines. While combined chlorine can also provide some disinfection, it typically has a lower effectiveness against microorganisms and is less potent due to the chemical bond it forms with nitrogen. As a result, free chlorine is preferred for immediate disinfection needs, particularly in swimming pools and treatment facilities designed to maintain water quality.

Additionally, combined chlorine tends to have a longer lasting residual in water compared to free chlorine, but this residual is less effective in sanitization, further confirming why free chlorine's strength is essential for effective treatment.