m1tanker78
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How to approximate H2O2 concentration??
I searched the forum as well as the web and came up empty-handed.
My wife and I use h2o2 quite a bit in place of harsh chemicals for things like treating greens (especially leafy ones like lettuce), laundry, oral and
topical antiseptic. I even use it to etch printed circuit boards. I've been buying the regular 3% solution and concentrating part of it for a while
now. The concentrated h2o2 is perfect to keep in first aid kits and to have during camping/hunting. The thing is, I have no idea what concentration it
is (as a percentage).
All I can say is that it is considerably more viscous than plain water and it will bleach skin if applied undiluted and left for a few minutes. I'm
not talking about the whiteness that typically develops - besides that, it literally bleaches the pigment out of the skin. As I type, I have a sample
of dark hair soaking in a few drops of it to see if it will bleach hair as well. I've read that ~30% h2o2 is used to lighten hair color in some
salons, etc.
Sooo, do any of you know of a way to roughly quantify the concentration of h2o2? I've toyed with the idea of using copper ions dissolved in HCl as
well as some type of pigment. These tests really wouldn't quantify the concentration, though.
Tom
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Cuauhtemoc
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Titration?
If you just want a very rough estimate, you don't even need a burette, just see how much KMnO4 you need with a graduate cylinder or something.
Prepare a solution of H2O2 and H2SO4, and add a solution of KMnO4(known concentration) until the solution turns pink.
I'm sure google can get you the right stoichiometry.
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condennnsa
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pure H2O2 has a density of 1.463 so you can measure your concentration pretty close with a graduate cylinder and a scale. nothing fancy. Here is a
chart http://www.h2o2.com/technical-library/physical-chemical-prop...
[Edited on 14-1-2011 by condennnsa]
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m1tanker78
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The density test is an excellent idea! Now let me kick myself for not having a sensitive enough scale. Mine measures grams in steps of 5. I only have
about 5 mL of the h2o2 in question. Even then, the scale isn't sensitive enough to accurately weigh 5 mL. I guess I'll have to wait until I get my
hands on a jeweler's scale or similar.
Thanks for the tip and the link condennnsa,
Tom
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DougTheMapper
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Use MnO2 or a similar catalyst to decompose a 1-10mL sample of the peroxide to H2O and O2. Collect the O2 produced with an inverted graduated cylinder
or buret (filled with water). Volume of O2 produced can be used to determine concentration. Be sure to note temperature of gas before volume is taken
to ensure accuracy. Also be aware that even 3% will give off about 10 times the liquid volume in gas.
Victor Grignard is a methylated spirit.
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ScienceSquirrel
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It depends where you live but you can buy 30 -35% off the shelf in most jurisdictions.
A litre is about £10 where I live
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m1tanker78
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@Doug: Thanks for the tip. I like that idea because I can use almost any quantity I want - even a couple of drops. The down side is that I don't think
I have any MnO2 on hand. Unless that's the same stuff they put in batteries (with impurities, no doubt)?
@Science Squirrel: Must be nice  'Round here, 35% can be procured at some
pharmacies with a Dr.'s prescription. I can get the prescription without a problem. What I refuse to do is pay $117.xx last I checked (USD) for 500 mL
(!!)
Bottom line is I need to get around to buying/making a few chemicals that should be standard in an amateur lab setting. KMnO4 comes to mind. Best I
have at the moment is a whole bunch of red cabbage pH indicator paper I made.
I also may end up making a simple balanced scale to see how much water it takes to balance 1mL of my H2O2 in question. May even be a fun project for
my 5 y.o. son to get in on.
I'll check back in if there's any progress,
Tom
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m1tanker78
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Is there anything else that will decompose H2O2 in a few hours? I can put together the aparatus to collect the oxygen.
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The WiZard is In
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Attachment: Chem H2O2 Strength-volume.doc (20kB)
This file has been downloaded 668 times
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m1tanker78
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Thanks Wiz. Looks like I'll be tearing some alkaline batteries apart later today
I still plan to build a simple balanced scale in order to see how much DH2O it takes to balance 1mL of H2O2 (and just for fun).
Tom
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Formatik
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There is also another way to attack this. Another method to use is mass loss. Measure the mass of the involved compounds and mixing container. Dilute
the H2O2 with H2O to a weak dilute concentration. The water dilution is a must here, because if you are working with higher strengths where reaction
is violent, the steam released makes this all entirely useless. Then add tared KMnO4 or MnO2, etc. and let it decompose to completion. Measure the
mass for how much oxygen was released.
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m1tanker78
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@Formatik: I don't intend to be a pest; I have a couple of questions...
Assuming I have 60% H2O2 and I use 2mL of it to make a 50mL solution. (All of these numbers are arbitrary):
1. Would the change in mass still be tiny? The biggest obstacle I have to overcome is the fact that I don't have an adequate scale.
2. Do you have a ballpark figure as to how long the reaction would take based on the above scenario?
3. Do I need to constantly stir the solution as it's reacting?
I'm going to try and test a few reactions between some dirty MnO2 and different concentrations of my unknown oxy water.
I appreciate the suggestion,
Tom
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m1tanker78
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What about reacting a specific mass of MnO2 with a specific volume of the unknown H2O2 and measuring temperature change???
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ScienceSquirrel
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You are going to struggle to get a reasonable assay of the concentration of your peroxide without a decent scale and some glass.
The easiest way is to measure the oxygen evolved from a known mass using a burette, after that volumetric methods could be quite accurate. Measuring
mass loss or heat evolved on a small scale are very tough propositions without some serious gear.
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m1tanker78
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I have a crude setup which will allow me to measure a quantity of water displaced by a gas. I'm sure you all would cringe if you could see it...
My question is in what proportion should I combine the MnO2 and H2O2? Should I try to make it to where there is an excess of MnO2 at the end of the
reaction? I tried a few tests with 3% h2o2 as well as my unknown in very small quantities. The "3%" reacted readily and my concentrated h2o2 steamed
off before it could even finish reacting. It's pretty clear that I'm going to have to dilute my unknown considerably so that it doesn't skew the test
like Formatik mentioned above.
To sum it up:
1. What proportion?
2. Do I need to stir/swirl the solution while it's reacting?
3. Just to be sure, I need to weigh the MnO2 before reacting and take note of the volumes of my unknown H2O2 and water. Is this correct?
Please let me know if I'm missing anything,
Tom
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m1tanker78
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I've been reading up on this and it seems MnO2 is merely a catalyst in the decomposition of H2O2. If that's the case, the quantity of MnO2 I use
shouldn't matter too much. In the end, the ammount I use should only affect the decomposition RATE. I hope that's correct. Trial and error...
Tom
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m1tanker78
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Ok, I measured the water displacement for 2 different samples of H2O2:
First Sample:
30mL of commercial 3% displaced 202.32 cubic cm. 202.32/30=6.744 cubic cm per mL so approximately 2.5% H2O2. A fair ammount of heat
and some steam was evolved.
Second Sample:
29mL of distilled H2O + 1mL of my unknown concentration H2O2 displaced 49.3 cubic cm. This works out to approximately 15% H2O2.
Minimum heat/steam evolved.
One problem I ran into was that even after rinsing the reaction container well, there was still some MnO2 residue impregnated on the inner walls. As
soon as I poured the 2nd sample, it began to fizzle before I could even replace the lid. In both tests there was inevitably a few mL worth of water in
the gas tube at the beginning. I'm going to switch to a glass reaction container in hopes that most of the residue can be rinsed clean.
I'll post the results of the second set of tests once I get around to doing them in glass...
Tom
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Formatik
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I would just invest in a scale, small glass 10mL graduated cylinder, etc. They are not expensive and worth it.
Density measurement is the least complicated. You start to test density of known liquids like 3%, 35% H2O2, etc, then when you start to get the same
values you know you are on the right track.
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unionised
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I just wondered about this "My wife and I use h2o2 quite a bit in place of harsh chemicals "
What were you using that was more harsh than H2O2?
http://www.youtube.com/watch?v=3D_Z13dLnUw
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m1tanker78
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@Formatik: No doubt, I need to invest in some basic gear.
@unionised:
| Quote: | | What were you using that was more harsh than H2O2? |
Physically harsh:
Chlorine bleach, Lysol toilet bowl cleaner, Soft Scrub shower cleaner, some Lysol aerosols, ammonia for floors, dilute bleach to soak veggies and
greens, etc, etc...
Harsh on the wallet ($$$):
Most mouth wash products, anti-fungal creams and sprays.
The H2O2 rocket link you provided:
" The exhaust products are steam and oxygen." I doubt they're getting that kind of thrust with anything less than 98% H2O2  The strongest H2O2 in my house is 15-20%
That's not to say H2O2 isn't harsh in any way. Care must be taken - especially with anything over 3%.
Tom
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The WiZard is In
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You need a more powerful computer.....
Qualitative chemical analysis: a guide in qualitative work, with data for ...
By Albert Benjamin Prescott, Otis Coe Johnson
P. 288
http://tinyurl.com/6x9qect
<>. Estimation. (c) By decomposition of KI in presence of an excess of dilute H2SO4 and titration of the liberated iodine with standard Na2S2O2.
Exercises in elementary quantitative chemical analysis for students of ...
By Azariah Thomas Lincoln, James Henri Walton
P. 84
http://tinyurl.com/5wpaxtr
EXERCISE XXX
Determination of the Strength of Hydrogen Peroxide
Procedure. — Dilute 10 c.c. of the hydrogen peroxide solution to 250 c.c., mix thoroughly. Introduce 25 c.c. of this solution into an Erlenmeyer
flask in which one gram of potassium iodide dissolved in a little water and 30 c.c. of dilute sulphuric acid have been placed. After five minutes
dilute to 100 c.c. and titrate with the standard thiosulphate in the usual manner. Repeat, and from the data calculate the percentage of hydrogen
peroxide in the sample, assuming the specific gravity to be one. Calculate the number of grams of available oxygen in each cubic centimeter of the
original peroxide solution.
Note. — The stated order of adding the reagents must be followed, as potassium iodide when added to a neutral solution of hydrogen peroxide
decomposes it catalytically, with the evolution of oxygen.
A text-book of volumetric analysis: with special reference to the volumetric ... By Henry William Schimpf
http://tinyurl.com/4szelte
&c., &c., &c.
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m1tanker78
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| Quote: | | You need a more powerful computer..... |
Wiz, thanks for the links! Unfortunately, I don't have any iodine to prepare KI but the links to the texts are excellent reading.
Tom
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franklyn
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1. Potassium Permanganate titration already described above
http://www.h2o2.com/technical-library/analytical-methods/def...
2. Direct measure of density with a hydrometer
or just accurately weigh a measured volume.
( Density ( ρ ) is weight divided by volume )
3. Observe temperature when boiling commences
4. Direct reading with a refractometer
Scales and range calibration vary depending on intended use. This one spans 2 ranges Brix scale
http://cgi.ebay.com/NEW-0-80-Heavy-Duty-Brix-Refractometer-S...
Refractive index nD to Brix scale conversion chart => http://www.2spi.com/catalog/ltmic/brix.html
Attachment: Refractive Index nD to Brix scale.rtf (16kB)
This file has been downloaded 586 times
This one ranges from 1.3330nD to 1.3848nD , which spans the available concentrations of H2O2
http://cgi.ebay.com/Oil-Refractometer-oil-testing-low-Refrac...
Serologic type will span Refractive index 1.33 to 1.36
http://cgi.ebay.com/Clinical-Refractometer-/320640716344
.
[Edited on 16-1-2011 by franklyn]
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The WiZard is In
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Quote: Originally posted by m1tanker78  |
Wiz, thanks for the links! Unfortunately, I don't have any iodine to prepare KI but the links to the texts are excellent reading.
Tom |
KI is not hard to find OTC... people were stocking up a few years
back, memory does not supply - in the event we were Nuked or the
local Nuke plants core headed toward China.
http://tinyurl.com/4qngrhf
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