Siddy - 3-7-2008 at 20:34
Hi,
Ive got a simple question, not really related to anything in particular.
How is hydrogen peroxide concentration calculated? eg, food grade is "35%" Is that w/w, w/v or molarity or what?
Im just interested in know the grams per L of h2o2, but unsure what the percentage is referring to, iv searched a few MSDS's and they only refer to
percentages and not mass or volume.
12AX7 - 3-7-2008 at 20:41
It doesn't make much difference, as the density isn't far off. If you need more accuracy than that, then I don't know.
Tim
Ozone - 3-7-2008 at 21:20
I depends upon who you buy it from. For example, Aldrich material may be 35% m/m whilst Hach material is 50 % w/v. I have not seen H2O2 sold on mole
%. If it is the least bit old (which much of what you get will be) it is never the disclosed concentration. Elsewhere on this site I have outlined a
titration which can be used to assay your material (which should be done every day if you plan to be quantitative).
If stored in the dark and refrigerated, the material stores quite well (the more concentrated the better). My 30 % assayed at 23.1 % m/m and it is at
least three years old.
H2O2 density not linear. It is anomalous; hydrogen bonding, etc. increases with concentration then decreases as water is excluded (so far as I know).
Cheers,
O3
[Edited on 3-7-2008 by Ozone]
chemoleo - 4-7-2008 at 18:53
Only mass percent makes sense - 35 g pure H2O2 and 65 g pure H2O, so w/w. Reagents are rarely delivered any other way these days (thank god), and I've
never seen anything but this on a reagent bottle.
Think of the confusion that otherwise results (having to take account of density, dilution effects etc)! Suppliers would be stupid to not do it this
way!
leu - 4-7-2008 at 20:51
The standard laboratory analytical procedure:
http://www.h2o2.com/intro/highrange.html
This website is familiar to many of the members but the URL for the procedure has been changed. This page from the site answers your question as far
as various concentration conventions:
http://www.h2o2.com/intro/properties/physical1.html
Siddy - 9-7-2008 at 17:57
Thanks guys, ill take the percentages as w/w now!
I wanted this information for no specific reason. if i used H2O2 i would assay the molarity before use (id dig up my first year prac manual it was one
of my first experiments).
[Edited on 9-7-2008 by Siddy]