Ontario Operator-in-Training (OIT) Practice Exam

What compounds are formed when chlorine reacts with ammonia in water?

1. Free chlorine

2. Chlorine demand

3. Combined chlorine

4. Aqueous chlorine

The correct answer is: Combined chlorine

When chlorine reacts with ammonia in water, it forms combined chlorine. This process involves the interaction of chlorine with the nitrogen and hydrogen in ammonia, resulting in chloramines, which are a group of compounds including mono-, di-, and tri-chloramines. These chloramines have disinfecting properties and are less reactive than free chlorine. This reaction is significant in water treatment as it helps control the formation of disinfection byproducts that can occur when chlorine reacts with organic matter. Combined chlorine is often monitored in water supplies because it is an indicator of the efficacy of chlorine disinfection, and it also affects the overall water quality. The formation of combined chlorine contrasts with free chlorine, which is the form of chlorine that has not reacted with ammonia or other substances and is still available for disinfection. Understanding this distinction is crucial for water treatment operators to effectively manage disinfection processes and ensure safe drinking water.