What is Reaction of calcium hypochlorite and water?

Answer 1

Bleaching power is a mixture of Calcium Hypochlorite(Ca(ClO)2), Calcium Chloride(CaCl2) and Ca(OH)2. Adding water containing CO2 forms HClO:

Ca(ClO)2 (s) + H2CO3 (aq) --> 2 HClO (aq) + CaCO3 (s)

With sunlight, HClO can decompose releasing nascent oxygen and forming HCl:

HClO (aq) --uv rays--> 0 (g) + HCl (aq)

It is well known that Chlorine (Cl2) in water is in equilibrium with Hydrochloric (HCl) and Hydrochlorous (HClO) acids with the side of the equation representing the current state affected by pH, temperature and the respective concentration of the reactants:

HCl (aq) + HClO (aq) <---> Cl2 (g) + H2O (l)

Increasing HCl ( per the UV ray decomposition reaction) in the presence of HClO, will drive the reaction above to the right producing Cl2.

It is also possible in the case of solid bleaching powder exposed to moist air containing CO2, that HClO will be produced. However, the evaporation of the HClO may release the Hypochlorous acid gaseous anyhydride, namely DiChlorine Mono-oxide, Cl2O which has a pungent smell similar to Cl2. Another possible path way for Cl2O formation is by the action of any Cl2 produced acting on the moist CaCO3, which was formed by the action of CO2 on either Ca(OH)2 or Ca(OCl)2:

2 Cl2(g) + CaCO3 (s) --> CaCl2 (s) + CO2 (g) + Cl2O (g)

Noted, if one passes Cl2 through a fresh precipitate of CaCO3 in solution, instead of Cl2O, one produces HClO (this is one cited method for the preparation of HClO). To be complete, there is also a cited reaction between CaCl2 and Cl2O, that produces Ca(OCl)2 and Chlorine gas (Cl2):

2 Cl2O(g) + CaCl2 (s) --> Ca(OCl)2 (s) + 2 Cl2 (g)

Note, this path producing Chlorine is true for Ca, Sr and Li, but not apparently for Sodium (Na) where a different path is followed. This also implies that by adding moisture, one can replace Cl2O with HClO and liberate Cl2. Note the following reaction from http://en.wikipedia.org/wiki/Calcium_hypochlorite

2 Ca(ClO)2 + 2 CO2 → 2 CaCO3 + 2 Cl2 + O2

which also claims the production of Chlorine by the action of CO2 on the Calcium salt, which is not observed when ones adds CO2 to NaClO.