[solipse]

I'm currently studying the decomposition of bleach for a project, and I have read so many contradictory things my head is simply spinning right now. Well, this is what I think I know - please correct me where I'm wrong.

Bleach is composed of an aqueous solution of NaOCl.
Since it is an ionic compound in an aqueous solution, it will disassociate into free Na⁺ and OCl^- ions.
The OCl^- ions will then go on to oxidize other substances, but it is unstable, and decomposes over time. Its decomposition is also affected by the pH of the solution.

On the article for 'Bleach', Wikipedia states that:

Hypochlorite and chlorine are in equilibrium in water; the position of the equilibrium is pH dependent and low pH (acidic) favors chlorine.

Cl₂ + H₂O H⁺ + Cl^- + HClO

So, why does it say HClO? Does the OCl^- combine with the hydrogen in water? If so, are both HClO and ClO^- called hypochlorite? AND, why do the manufacturers state that the bleach contains NaOCl if it unavoidably decomposes to form different products?

However, this document from a chemical manufacturing company says that the main decomposition pathway of OCl^- is to chlorate and chlorine, and does not mention a pH equilibrium as far as I can tell.

3OCl^-  ClO₃^- + 2Cl^-

I guess I'm asking if a kind soul could please make an understandable outline for me how NaOCl behaves in an aqueous solution, and how the decomposition of its constituent ions is affected by pH?

[Borek]

HClO is a weak acid, ClO^- is its conjugate base.

[solipse]

Alright, good to know. Still, that doesn't exactly help me grasp the big picture of this.

[Enthalpy]

Ionization is very partial.

[AndersHoveland]

Bleach consists of roughly equal parts NaCl and NaOCl dissolved in water.

The hypochlorite ion can combine with a hydrogen ion to form hypochlorous acid HOCl. After a long period of time, or when the solution is boiled or exposed to prolonged sunlight, the hypochlorite will disproportionate into chlorate and chloride.

Adding acid to hypochlorite salts (such as NaOCl ) changes the equilibrium,
and chlorine is given off. Bubbling this chlorine back into a base (that contains hydroxide ions) will turn the chlorine gas back into hypochlorite and chloride salts.

If acid is added to a solution of calcium hypochlorite which does not contain any chloride ions, then some calcium perchlorate will form and some unstable chlorine dioxide ClO2 will be produced.


hypobromite, however, decomposes after about only 20 minutes at room temperature, but solutions can be stored much longer at 0degC.

[ajkoer]

 
The product of the decomposition of NaClO in a PH range of 5 to 9 is actually a two stage decomposition into NaClO2 and then NaClO3 with a PH of 6.9 providing the max yield of chlorate. The equations are:

                                                        2 NaClO --> NaClO2 + NaCl

                                             NaClO2 + NaClO --> NaClO3 + NaCl

 This accounts for 95% of the reaction. Note, the literature at times cites only the production of NaClO2 with exposure to   sunlight, just NaClO3, or more correctly, a decomposition mixture of both chlorite and chlorate.

 The other 5% of the reaction mixture produces O2 in this PH range of 5 to 9. The equation is as follows:

                                                      2 NaClO --> O2 + 2 NaCl

 The literature again sometimes misleadingly asserts this as the only reaction.

 In PH of 5 or less, Chlorine is the main product, as strong acids decompose NaClO. For example, with HCl:

                                              NaClO + 2 HCl --> Cl2 + NaCl + H2O

 Reference: Handbook of Detergents: Production Volume 142, pages 445 to 446 by Uri Zoller and Paul Sosis. This is a Google book and these pages can be viewed online.