The pH of chlorine bleach is 13, which indicates that it is quite basic. This indicates that the H+ concentration in a solution of chlorine bleach is approximately one millionth of the H+ concentration in pure water.
Because chlorine bleach is so basic, it is safe to use. When chlorine is combined with water, the hypochlorite ion and chlorine gas are in equilibrium. However, if the pH is decreased, such as when bleach is mixed with an acid, the hydrogen and oxygen atoms in the hypochlorite ion combine with the additional hydrogen ions to form water molecules. As a result, chlorine gas is produced, which is hazardous to people.