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Author Topic: Bleach and sodium hydroxide  (Read 13289 times)

Offline mattmckee

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Bleach and sodium hydroxide
« on: 29/03/2011 13:24:17 »
Our technicians use bleach to make chlorine gas when needed for school experiments, e.g. chlorine water to show displacement of the halogens. It was producing a cloudy white chlorine water - not as expected.   We realised it must be because the bleach had sodium hydroxide in  - so two questions
1) why put that in bleach?  To help it unblock drains?
2) what did it make then - that made it look cloudy?

It did this each time it was tried..

Thanks

Matt ???


 

Offline lightarrow

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Bleach and sodium hydroxide
« Reply #1 on: 29/03/2011 18:37:43 »
Our technicians use bleach to make chlorine gas when needed for school experiments, e.g. chlorine water to show displacement of the halogens. It was producing a cloudy white chlorine water - not as expected.   We realised it must be because the bleach had sodium hydroxide in  - so two questions
1) why put that in bleach?  To help it unblock drains?
2) what did it make then - that made it look cloudy?

It did this each time it was tried..
Ok, but *how* did they make chlorine from bleach?

About NaOH, it's quite necessary to make bleach:

Cl2 + 2OH- → ClO- +  Cl- + H2O

without a strong base as NaOH the solution's pH wouldn't be high enough to make those concentrations of ClO- (bleaching agent).
 

Offline mattmckee

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Bleach and sodium hydroxide
« Reply #2 on: 29/03/2011 23:38:48 »
 :-\thanks - so do all bleaches contain some NaOH, the techs got some 'less lidl' bleach which didn't contain NaOH and it made chlorine water no problem which went and worked as it should on displacement of halogens.

is it used in manufacturing bleach or is it used as it sounded in your reply in making the pH suitable for lots of ClO-.

Is it that more expensive bleaches have a way to get lots of ClO- without using the NaOH?

Cheers

Matt
 

Offline lightarrow

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Bleach and sodium hydroxide
« Reply #3 on: 30/03/2011 12:15:44 »
NaOH is used as a cheap way to increase pH, of course you could use everything else strongly basic and which doesn't react with chlorine.
 

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Bleach and sodium hydroxide
« Reply #3 on: 30/03/2011 12:15:44 »

 

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