MadSci Network: Chemistry

Re: does bleach dissolved in water have acid and base coexisting?

Date: Wed Jul 1 20:17:13 2009
Posted By: Jerry Franzen, Chemistry Teacher
Area of science: Chemistry
ID: 1239030796.Ch

The acive agent in the so-called "chlorine" bleach is NaOCl, sodium 
hypochlorite.  It is one of the products produced when Cl2 reacts with a 
solution of NaOH, a very strong base.  To the extent that any acid, either 
HOCl, hypochlorous aicd, or HCl, hydrochloric acid, is formed in the 
reaction, that acid would be neutralized by the NaOH solution.  In fact, 
there is undoubtedly an excess of NaOH present in the bleach solution.  
So, I would say that a solution of "chlorine" bleach does have base 
coexisting with it, but not a significant amount of acid.  It can't be 
both acidic and basic at the same time.

The "chlorine" bleach solution will test positive for base using a variety 
of test papers and indicators(although some of these may not function 
properly because of the strong oxidizing power of the solution) and in a 
determination of its pH.  The Ph is well above 7.0.  The solution is also 
very slippery to the touch, another characteristic of solutions that are 
basic.  The reaction between Cl2 and NaOH is reversible, and thus one can 
detect the odor of Cl2 above such solutions.

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