The main compound in chlorine bleach is “sodium hypochlorite (NaOCl)”. This compound becomes hypochlorous acid (HOCl) by hydrolysis:
NaOCl + H2O ↔ HOCl + Na+ + OH-
Actually the chlorine in the bleach exists as hypochlorous acid. This compound is so oxidative that it has a property of bleaching and sterilization. Gaseous chlorine is generated when hypochlorous acid is mixed with hydrochloric acid. Hydrochloric acid is used in toilet cleaner.
HOCl + HCl ↔ H2O + Cl2 ↑
Gaseous chlorine decays the skin and eyes. Furthermore, there is even risk of death at high concentrations. Please be careful when using these cleaners.
Hypochlorous acid also generates gaseous chlorine in the presence of not only hydrochloric acid but also other acids, such as acetic acid (CH3COOH, vinegar).
2HOCl + 2HAc ↔ Cl2↑ + 2H2O + 2Ac- (Ac : CH3COO)
In general, there is following equilibrium between chloric species (Cl2, HClO, ClO-).
Cl2 + H2O ↔ HCl + HOCl
HOCl ↔ H+ + OCl-
The ratio of the chloric species depends on pH, water temperature and coexistent compounds. pH especially influences the ratio. The ratio of Cl2 gas is increased as pH is decreased, and the ratio of OCl- is increased as pH is increased. (The ratio of HOCl is almost 100% at pH 5, but 60% for HOCl and 40% for Cl2 at pH 2. The ratios of both HOCl and ClO- are 50% at pH 8.)
As for hypochlorite ion (ClO-), it is less oxidative than HOCl. It is reported that the antiseptic property of ClO- is around 1/80 as much as HOCl. The higher the pH, the more ClO-, therefore bleaching and antiseptic effects are decreased when alkaline is added, even though gaseous chlorine is not generated at high pH.