Question

What are the major biocidal species of chlorine in water?

1) Hypochlorous acid (HOCl) and hypochlorite ion (OCl-)
2) Chlorine gas (Cl₂) and chloramine (NH₂Cl)
3) Chlorine dioxide (ClO₂) and chlorite ion (ClO₂-)
4) Chlorate ion (ClO₃-) and perchlorate ion (ClO₄-)

Answer 1

The major biocidal species of chlorine in water are hypochlorous acid (HOCl) and the hypochlorite ion (OCl-), which form when chlorine gas (Cl2) dissolves in water and contributes to the disinfecting power of chlorine in water treatment.

Step-by-step explanation:

The major biocidal species of chlorine in water are hypochlorous acid (HOCl) and the hypochlorite ion (OCl-). When chlorine gas (Cl₂) is dissolved in water, it undergoes a chemical reaction to form hypochlorous acid (HOCl) and hypochlorite ions (OCl-), as well as hydrochloric acid (HCl). This process can be represented by the equation Cl₂ (aq) + 2H₂O(l) → HOCl(aq) + H3O+ (aq) + Cl⁻ (aq). Hypochlorous acid is a strong oxidant and is more effective as a disinfectant compared to the hypochlorite ion, but both contribute to the free chlorine residual, which is responsible for the disinfection of water.