Thread: Bleaching action

How does sodium hypochlorite/calcium hypochlorite perform bleaching action on colored matters? What is the components of these chemicals which really cause the bleaching?

The components are any oxidizing agents present i.e. sodium hypochlorite, hydrogen peroxide etc. Reducing bleahes also exist i.e Sodium dithionite although although they are less common. These bleaches work by breaking down or changing parts of molecules present in the fabric called chromophores which are responsible for colour. As the chromophores are broken down or altered to only absorb non visible spectrums, the colour of the substance is removed.

Originally Posted by Lucky

The components are any oxidizing agents present i.e. sodium hypochlorite, hydrogen peroxide etc. Reducing bleahes also exist i.e Sodium dithionite although although they are less common. These bleaches work by breaking down or changing parts of molecules present in the fabric called chromophores which are responsible for colour. As the chromophores are broken down or altered to only absorb non visible spectrums, the colour of the substance is removed.

that makes sense, but does that mean that the substance is still there, but you just can't see it? and what causes certain things to 'stick' to things so well so they won't come out?

http://www.answerbag.com/q_view/58505

May answer the original question for you.

Another member originally posted the entire text here without acknowledgement. Which is contrary to the practice we prefer.

Originally Posted by Chemboy

Originally Posted by Lucky

The components are any oxidizing agents present i.e. sodium hypochlorite, hydrogen peroxide etc. Reducing bleahes also exist i.e Sodium dithionite although although they are less common. These bleaches work by breaking down or changing parts of molecules present in the fabric called chromophores which are responsible for colour. As the chromophores are broken down or altered to only absorb non visible spectrums, the colour of the substance is removed.

that makes sense, but does that mean that the substance is still there, but you just can't see it? and what causes certain things to 'stick' to things so well so they won't come out?

If you get a red stain on a jumper (as I did a few minutes ago) it appears red because the substance (or specifically chromophores) will reflect red light into your eyes and abosrb all other visible wavelengths. If the chromophores are altered to only absorb non visible wavelengths of light i.e. UV, all visible wavelengths will be reflected and the substance will appear white, loosing its colour

As for non removable stains I would imagine they must have stable chromophores which cannot be broken down by oxidation, aswell as acting like a dye and containing suitable functional groups to bond to the fibres.

But what I want to know is, in the process of bleaching action between the colored component and sodium hypochlorite, chlorite ion or hypochlorite ion really accepts the electrons during oxidation. I want to know the reactions in detail.....

It will do yes. As this is a redox reaction, while the chromophore loses electrons to be oxidised the hypochlorate will also gain electrons to be reduced to a chloride ion and water. You can see this in the half equation .....

ClO- (aq) + 2 H+ (aq) + 2 e- ---> Cl- (aq) + H2O (l)