Microwave Concentration of Hydrogen Peroxide Lab

[YayItGoBoom!]

I decided to come up with my lab (this is my first one whoopdie do) to see just what people such as I, who are lacking in certain precursors, could make do with the chemicals that they have. There is not much in the way of procedure for concentrating H2O2. The first batch of AP I tried failed miserably, using Megalomaniac’s recipe, replacing 30 mL 30% H2O2 with 300 mL 3%. The acetone was Klean Strip and the acid was 6M HCl. There was almost no yield after three days. I don’t have any other H2O2 available, and 3% is pretty cheap, so I wanted to find out what I could do to make the reaction yield more.

Procedure:
Place 400 mL (300 mL would be the correct moles, but I wanted to take into account some H2O2 would be lost through microwave) in a Pyrex beaker. Microwave in 2 minute intervals until the solution is 50 mL. Let this cool to 3° C.

Cool 50 mL acetone in glass vessel (I used a Mason jar), and add the cooled H202. Stir and place in ice bath. Add X mL of 36% HCl (I am not sure how much is sufficient, I used 8 mL to be generous) drop by drop, while stirring. Let the solution sit in the ice bath for 24 hours.

I set this up about four hours ago, and the jar has a good amount of precipitate, some on the bottom, the rest is forming a crystal skin on the top of the precipitate. This surprised me because I expected a lot of the H2O2 to boil away. Its not overflowing with AP by any means, but its certainly a nice first yield.


I also have a question about the “skin” of crystals forming on the surface of the solution. This is my first batch, and I don’t want it to be an infamous one. I have heard stories and seen videos of AP being very stress tolerant as far as primaries go, but I am still concerned for good reason. Would it be alright to swirl the jar just to get the crystals to break up enough to fit through the jar (the neck tapers slightly)? It is a noobish question I know, I am just concerned about my fingers.

I put this in the water cooler because its just kind of a half-assed lab, and I'm semi-new and don't need the flaming. If it does find interest, it would be appreciated if a mod moved it to the Other Explosives board.

[Hang-Man]

My last batch had such a high yield AP mushroomed out of the beaker. You can do pretty much whatever you want with AP so long as its even a little wet. I never though of useing a microwave to concentrate chems...

[megalomania]

Does anyone remember the chemical test to determine the concentration of hydrogen peroxide? I think you react it with potassium permanganate to release the oxygen or something... I quite forget. Anyway a certain quantity of H2O2 will react with a known amount of the reactant and you can determine how much H2O2 you have.

Hmm, yes, you titrate the H2O2 (acidified I believe) with potassium permanganate solution. You would do this with the original volume of 4% (400 mL) and then titrate afterwards (50 mL) and see how much H2O2 you lose. No indicators needed either, the permanganate will color the soln when the endpoint is reached. All one needs is an accurate way to weigh the KMnO4.

EDIT: here we go...visit http://www.ic.sunysb.edu/Class/che133/lectures/calc035.html or read what I have reproduced below.

1. Standardization of Potassium Permanganate, KMnO4
1.1 Preliminaries

Potassium permangante is standardized by its reaction with sodium oxalate, Na2C2O4
The stoichiometric relationship between them would be given by the overall equation:

5 Na2C2O4 + 2 KMnO4 + 8 H2SO4 = 2 MnSO4 + K2SO4 + 5 Na2SO4 + 10 CO2+ 8 H2O

As usual, considering only the net ionic equation for this reaction simplifies it considerably.

5 C2O42- + 2 MnO4- + 16 H+ = 2 Mn+2 + 10 CO2+ 8 H2O

We see that 2 moles of permanganate ion, MnO4- react with 5 moles of oxalate ion, C2O42-
Therefore, 1 mole of permanganate ion reacts with 5/2 = 2.500 moles of oxalate ion, or

1 mmole of permanganate ion reacts with 5/2 = 2.500 mmoles of oxalate ion, and

1 mmole of oxalate ion reacts with 2/5 = 0.4000 mmoles of permanganate

[Keep in mind that the coefficients 5, 2, 16, 10 and 8 in the chemical equation are integers and have, basically, an infinite number of significant figures.]

The nominal concentration of the potassium permanganate solution is 0.025 M (The objective of the standardization is to find the exact value of this concentration.)

We wish to use about 30 mL of this solution in a titration in order to use the buret to its maximum precision.

30 mL of the solution will contain 30 mL X 0.025 mmoles / mL = 0.75 mmoles
Recalling that
1 mmole of permanganate ion reacts with 5/2 = 2.500 mmoles of oxalate ion
0.75 mmole of permanganate ion reacts with 5/2 X 0.75 mmoles of oxalate ion = 1.9mmoles

The molar mass of sodium oxalate is 134.0 Therefore, 1.9mmoles of sodium oxalate will weigh 1.9 mmole X 134 mg / mmole = 250 mg
In order to consume 30 mL of 0.025 M potassium permanganate, we will need approximately 250 mg of sodium oxalate.

Having established this, the standardization procedure will require us to weigh out samples of sodium oxalate weighing approximately 250 mg.

1.2 Calculations for the standardization

Suppose we actually weigh out a sample of sodium oxalate weighing 224.7 mg and that it requires 31.73 mL of a potassium permanganate solution that we wish to standardize. What concentration do we calculate for the potassium permanganate solution?

The sample of sodium oxalate contains 224.7 mg / (134.0 mg / mmole) = 1.677 mmole

Recalling that
1 mmole of oxalate ion reacts with 2/5 = 0.400 mmoles of permanganate

1.677 mmole of oxalate ion reacts with 2/5 X 1.677= 0.6707 mmoles of permanganate

That number of mmoles of permanganate ( 0.6707 mmoles ) were contained in a sample of a solution whose volume was 31.73 mL

Therefore, the concentration of the permanganate is 0.6707 mmoles / 31.73 mL = 0.02114 M

2.0 Titration of hydrogen peroxide
2.1 Preliminaries

The equation for the reaction between potassium permanganate and hydrogen peroxide is similar to that with sodium oxalate.

5 H2O2 + 2 KMnO4 + 3 H2SO4 = 2 MnSO4 + K2SO4 + 5 O2+ 8 H2O

Again, the net ionic equation is simpler,

5 H2O2 + 2 MnO4- + 6 H+ = 2 Mn+2 + 5 O2+ 8 H2O

We see that 2 moles of permanganate ion, MnO4- react with 5 moles of hydrogen peroxide, H2O2
Therefore, 1 mole of permanganate ion reacts with 5/2 = 2.500 moles of hydrogen peroxide, or

1 mmole of permanganate ion reacts with 5/2 = 2.500 mmoles of hydrogen peroxide, and

1 mmole of hydrogen peroxide reacts with 2/5 = 0.4000 mmoles of permanganate


2.2 Dilution of the Hydrogen Peroxide (See also the Web pages dealing with dilution.)

Most commercial hydrogen peroxide is sold at a concentration of 3% by weight (i.e., 30 g of H2O2 in 1000 g of solution). Assuming a density of near 1 g / mL, this would correspond to about 30 g / (34 g / mol ) = 0.88 mole per liter, or 0.88 M.

A 25 mL sample of this hydrogen peroxide solution would contain 25 X .88 = 22 mmoles of hydrogen peroxide and would require 8.8 mmoles of potassium permanganate. At a concentration of 0.025, such as we use in this exercise, this would consume 350 mL of the permanganate reagent - i.e., seven 50 mL burets full.

For that reason, we dilute the hydrogen peroxide for purposes of the titration. We must perform this dilution with precision so as to be able to convert the result on the dilute solution back to the original commercial hydrogen peroxide.

We choose a dilution by a factor of 1 / 10.00. This is accomplished by diluting a 25 mL sample of the commercial material to 250.0 mL in a volumetric flask. The original solution will have a concentration exactly 10.00 times as large as the concentration we determine from the titration.

2.2. Determination of the concentration of the diluted solution of hydrogen peroxide

The sample we titrate is a 25.00 mL sample of the diluted hydrogen peroxide delivered using a transfer pipet.

Suppose the 25.00 mL sample requires 28.64 mL of the potassium permanganate that we standardized in Section 1.2 which has a concentration of 0.02114 M.

28.64 mL of 0.02114 M potassium permanganate contains 28.64 mL X 0.02114 mmole / mL = 0.6054 mmoles of potassium permanganate

1 mmole of permanganate ion reacts with 5/2 = 2.500 mmoles of hydrogen peroxide

0.6064 mmoles of permanganate ion reacts with 5/2 X 0.6054 = 1.514 mmoles of hydrogen peroxde

This number of mmoles was contained in 25.00 mL of diluted hydrogen peroxide.

Therefore the concentration of the diluted hydrogen peroxide was 1.514 mmoles / 25.00 mL = 0.06054 mmoles / mL


2.3. Determination of the concentration of the original, commercial solution of hydrogen peroxide

The concentration of the original hydrogen peroxide is 10.00 times as large as what we have just found.

Therefore, the concentration of the original hydrogen peroxide solution is 10.00 X 0.06054 = 0.6054 M


2.4. Determination of the percent by weight of the original, commercial solution of hydrogen peroxide

HOWEVER, the exercise requires reporting the hydrogen peroxide concentration not as molarity, but, as percent by weight.

To perform this conversion, we need to know the density of the hydrogen peroxide. We are told to assume that the density of dilute solutions of hydrogen peroxide are the same as that of pure water (1.000 g/mL at room temperature).

Our solution has a concentration of 0.6054 M. Therefore, 1.000 liter of the solution will contain 0.6054 moles of hydrogen peroxide.

0.6054 moles of hydrogen peroxide weighs 0.6054 moles X 34.02 g / mole = 20.60 g

From the density, 1.000 L = 1000. mL of the solution weighs 1.000 g / mL X 1000. mL = 1000. g.

The weight percent of hydrogen peroxide in the original commercial solution is 20.60 / 1000. = 2.060 %

[YayItGoBoom!]

Interesting, thanks for the link Mega. I will have to read that once I am done cramming in 4 AP chem chapters by the end of the quarter this Friday. I would also love to test how well concentrating with heat works, as soon as I can get some permanganate.

Anyways, microwaving is kind of an interesting way of purification. I like it better than boiling on the stove because a) you don't get the maternal "WHAT THE HELL ARE YOU DOING WITH YOUR SCIENCE EXPERIMENTS ON MY COOKTOP!" b) you can use glass instead of metal with microwave, metal....ugh it just inerferes with everything. Plus with glass I can monitor just how much solvent is left.

The batch is progressing nicely, about half of the 100 mL is filled with crystals. I would take a stab and say 20-30 g. Later this week, probably Thursday, I'm going to add 300 mL of water to wash and then filter, dry, and test by Saturday.

[T_Pyro]

I've used the microwave before to concentrate solutions like CuCl2 and SrCl2, but the process with hydrogren peroxide is new to me. I'd guessed that the peroxide bonds would start breaking up in the presence of high-energy radiations... However, if it works, I'd love to try that, too!

A slightly simplified method that I'd use to find the volume strength of H2O2 would be to directly react a known volume of H2O2 solution with MnO2 and measure the volume of oxygen gas liberated by the downward displacement of water in a graduated cylinder. At STP, vol. of gas liberated divided by volume of solution taken= volume strength of the solution.
To calculate strength in w/w:

v=volume of O2
T=absolute temperature
P=atmospheric pressure
mass of solution taken=m

Therefore no. of moles of O2 = P*V/(R*T) ( = n)
Therefore no. of moles of H2O2= 2*n
Therfore w/w strength of H2O2 solution = (2*n*34)/m

[atlas#11]

I usualy just use the stove on a low setting to minimise decomp., it is effective but it takes about 4 hr. for a quart to get down to around 1/10 volume, but I usualy only go down to about an eighth of original volume to avoid runaways with my HMTD. I never thought of using a microwave either, You say you got a decient yeild? I would think that the radiation would cause more decomposition than just heating it but if it's all ya got then use it.

I vowed never to make AP again as long as I live. Of course in a life or death situation I wouldn't hesitate but for recreational purposes HMTD is as unstable as I'm going to get. I know it's not much better than AP but it's more stable and that's enough for me. Next time I get some nitrate I'll whip up some TNP and make potassium picrate or DDNP or anything more stable than peroxides. Their just too damn unstable for me.

[YayItGoBoom!]

Yea, its 100 mL of solution, and when shook up, it has about the consistency of pea soup. I got a rather comical idea earlier thinking about it, have you ever heard of Farina? Its this nasty cream of wheat gunk that old people eat, its thick white goupy stuff. It reminded me of that, and I laughed to myself at the idea of breakfast blowing up in someone's face and blasting them with that gunk.

I wouldn't use the microwave for larger batches because of just that, I believe a lot of H2O2 is lost in the process, and its much better to buy higher concentrations of it.

While we're having such a jolly exchange, does anyone know if NaOH could be used as a catalyst instead of an acid? I've heard of one reaction to form H2O2 is Na2O2 + 2H20 -> NaOH + H2O2. If lye works, you could whip up batches of AP like its nobody's business, that is if you could get your hands on sodium peroxide.

[Marvin]

Neither hydrogen peroxide or acetone are compatable with strong alkali.

[SimplisticNick]

Concentrating Hydrogen Peroxide with a microwave truly does confuse my logical thinking..
I'm not a chemist, but I know H2O2 is a strong oxidizer. When the microwaves strike the H2O2 molecules, isn't that enough power to break off one O atom leaving useless H2O?

[The Anarch]

I'm sure that happens to a significant amount of the H2O2, but I tried YayItGoBoom's microwave method and it worked very well. Using a whole pint of 3% H2O2 I could only get maybe a gram or two of AP, while only a cup concentrated in the microwave got me upwards of 20 grams. For those confined to using 3% H2O2, the microwave is the way to go.

[SimplisticNick]

Will do - Ill try this tonight!
My first synth. of AP gave off very little yeilds, although I tried with 2,000 mL of 3% H2O2.

[xyz]

YayItGoBoom, the "skin" of AP on top means that there's some excess acetone in your synth (nothing to worry about, most procedures cause this) which is dissolving a small amount of the AP. As the acetone evaporates from the top of the mixture, a "skin" of recrystallized AP is formed.

So long as it's still wet, you can gently break it up with a thermometer or other blunt object, if it's thick enough to be out of the water then wait until all the AP has formed, then pour in enough water to cover the AP before gently breaking it up.

[FUTI]

H2O2 decompose exposed to heat. Microwave isn't same as hotplate but it is only heating through radiation...this could change the process to some point but as writen above H2O2 still decompose but apparently to a smaller extent (but IIRC it does decompose slower in dilute solutions anyway).

So I have a question does anyone know is this concentrating process result of microwave or not? In other words can we use hotplate of magnetic stirrer instead? If it is microwave that are crucial for a process (which I can believe) what is the explanation for it doesn't degrade H2O2 thermaly (maybe H2O different dipole moment or something?)?