buffer preparation

[Han]

bertrutten from gmail.com wrote in news:56cfe663-ccb7-4da3-a7ce-2a25962e06e5
@i12g2000prf.googlegroups.com:

> Hello,
> 
> How do i work this out?
>:
> 
> I need 2mM H2O2 from a stock solution H2O2 of 30%, density 1.11 gr/ml,
> M.W. 34
> 
> 
> anybody?
> thanks upfront
> 
> b
> 
There is 3 problems here: Lack of understanding, lack of math knowledge 
and false precision.

What is a 2 mM solution?
Answer:  A solution that contains 0.002 moles of the substance per liter.  
Or 2*34/1000 g H2O2 per liter.
How much H2O2 is in a 30% solution with density 1.11?
Answer: 30 g per 100 gram solution.
Answer 2:  volume of 100 gram solution with density 1.11:  100/1.11 ml 
(close enough).

The rest of the math is up to the reader.

False precision:  30% H2O2 does not stay like that forever.  There is an 
expiration date.  In addition, the 30% may always have been +/- 1-3%.

2 mM seems like a fairly low concentration to do much, but I'm not a 
redox maven.  Please make sure you generate such solution freshly and 
with scrupulously clean glassware.  Very small amounts of oxidizable 
contaminants will reduce the H2O2 content drastically.




-- 
Best regards
Han 
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