Sciencemadness Discussion Board

A new riddle

woelen - 22-1-2012 at 06:34

This is a very simple experiment and easy to obtain common chemicals are involved, but still this experiment puzzles me. When S2O8(2-), peroxodisulfate, and hydroxide ion are mixed, then a yellow compound is formed.

This compound only appears at very high concentrations of hydroxide. I made a little web page about this.

http://woelen.homescience.net/science/chem/riddles/persulfat...


[Edited on 22-1-12 by woelen]

plante1999 - 22-1-2012 at 07:25

I suspect the yellow compound to be en intermediat in peroxodisulfate reduction to O2 and Na2SO4.

unionised - 22-1-2012 at 12:25

I can't think of a mechanism off hand but superoxide ions are the right colour and have the right elements present.
http://en.wikipedia.org/wiki/Superoxide
They are also unstable so that fits too.
Do you have an ESR spectrometer handy?

[Edited on 22-1-12 by unionised]

Huk40 - 22-1-2012 at 14:24

I had similar experience with sulfur compounds.Onto a little pile of Resorcinol i added dropwise H2SO3.A compound with a yellow color formed.After addition of water da yellow color dissapeared.

PS:If it would be any help.

kotze - 22-1-2012 at 14:45

This could be sodium ozonide. It has been prepared from solid NaOH and ozone and is relatively stable at room temperature; it is described as a yellow to red compound. You could try treating dry NaOH with ozone and see if the resulting compound has similar properties.

unionised - 22-1-2012 at 14:50

Ozone is a known by-product of the decomposition of hydrogen peroxide so that's possible.

AndersHoveland - 23-1-2012 at 10:51

The yellow color is probably due to the transient formation of radicals, either superoxide ions, ozonide, or possibly sulfate radicals.
Quote:

A mechanism for the base activation of persulfate [involves] the base-catalyzed hydrolysis of persulfate to hydroperoxide anion and sulfate followed by the reduction of another persulfate molecule by hydroperoxide. Reduction by hydroperoxide decomposes persulfate into sulfate radical and sulfate anion, and hydroperoxide is oxidized to superoxide. Stoichiometric analyses confirmed that hydroperoxide reacts with persulfate in a 1:1 molar ratio. Addition of hydroperoxide to basic persulfate systems resulted in rapid decomposition of the hydroperoxide and persulfate and decomposition of the superoxide probe hexachloroethane. The presence of superoxide was confirmed with scavenging by Cu(II). Electron spin resonance spectroscopy confirmed the generation of sulfate radical, hydroxyl radical, and superoxide.

Mechanism of base activation of persulfate. O.S. Furman, A.L. Teel, R. J. Watts, Department of Civil and Environmental Engineering, Washington State University, Pullman, Washington, USA.



Decomposition of peroxide compounds in a wide variety of reactions are known to produce several different reactive radicals. Ozone is a known byproduct of the decomposition of persulfate.
Quote:

Formation of Ozone from Peroxides
28 grams of ozone per cubic metre of oxygen evolved, by gently heating small quantities of powdered barium peroxide in eight times its volume of concentrated sulphuric acid. Hydrogen peroxide is likewise formed in small quantities under these conditions. The same investigator showed that similar results were obtained with other peroxides, notably those of magnesium, zinc, sodium, and potassium.

Formation of Ozone from Persulfate
By the thermal decomposition of the persulphates, small
quantities of ozone are likewise disengaged, Malaquin (" J.
Pharm. Chem.," VII, 3, 329, 1911) gives the following details
for the preparation of ozonised oxygen by this means.
Twenty gms. of dry and freshly prepared ammonium persul-
phate are mixed with 15 gms. of nitric acid in a small flask;
the air is subsequently displaced by carbon dioxide, and the
mixture cautiously raised to 65° to 70° C. The reaction,
which is strongly exothermic, proceeds somewhat vigorously
when once started, and the resulting oxygen, after removal
of the carbon dioxide, contains 3 to 5 per cent, of ozone and
small quantities of nitrogen.
Quote: Originally posted by unionised  
Ozone is a known by-product of the decomposition of hydrogen peroxide.


I have never read this anywhere. Do you have a reference?

[Edited on 23-1-2012 by AndersHoveland]

unionised - 23-1-2012 at 11:18

It was in a very old text book of my dad's.

woelen - 23-1-2012 at 13:59

In the meantime I did some experiments with peroxodisulfate. One thing which I conclude from these experiments is that no hydrogen peroxide or peroxide is formed from peroxodisulfate. Some experiments which lead to that conclusion:

1) Peroxodisulfate does not lead to formation of dark blue complexes based on CrO(O2)2 with dichromate in acidic solution, nor to formation of red/brown peroxo complexes based on Cr(O2)4(3-) in alkaline solution. You get simply orange dichromate or yellow chromate.

2) A strongly alkaline solution of Na2MoO4 turns deep yellow when dilute hydrogen peroxide is added and this becomes very dark red/brown when the concentration of hydrogen peroxide rises above a few percents. With peroxodisulfate the solution remains colorless, regardless of concentration.

3) Alkaline peroxodisulfate is capable of instantaneously oxidizing of light green Ni(OH)2 to a black solid, probably hydrous NiO2 or hydrous Ni2O3. When hydrogen peroxide is added to Ni(OH)2, suspended in a solution of NaOH, then nothing happens. On the other hand, when peroxide is added to a suspension of the black material in alkaine solution, then it immediately looses its color and becomes light green again, so peroxide and the black nickel compound cannot coexist.

Based on experiments (1) and (2) one can conclude that peroxodisulfate does not decompose to hydrogen peroxide and sulfate or bisulfate, not in alkaline solution, nor in acidic solution, otherwise I would see peroxo complex of chromium or molybdenum.

Based on experiment (3) I come to the conclusion that peroxodisulfate gives an amazingly strongly oxidizing species in alkaline solution of sufficient high pH. This species must be an even stronger oxidizer than peroxodisulfate itself, because peroxodisulfate in acidic or neutral solution is not capable of oxidizing nickel(II) to an higher oxidation state.

The yellow species as mentioned in my first post might be the strongly oxidizing species I found in experiment (3). I have looked up some information and ozonide might be a candidate. This ion is unstable, but it can exist for some time, also in contact with water. Superoxide does not seem to be a candidate to me. Superoxide decomposes in water immediately and gives hydrogen peroxide as one of the decomposition products. I would have noticed that with the dichromate and molybdate experiments and this also would not lead to the formation of the black compound with nickel(II).



[Edited on 23-1-12 by woelen]

AndersHoveland - 23-1-2012 at 14:05

Quote: Originally posted by woelen  
no hydrogen peroxide or peroxide is formed from peroxodisulfate.


The decomposition of peroxydisulfate under alkaline or acidic conditions only leads to formation of oxygen, but hydrogen peroxide can be formed if concentrated sulfuric acid is used.

AndersHoveland - 23-1-2012 at 14:06

Quote: Originally posted by woelen  
no hydrogen peroxide or peroxide is formed from peroxodisulfate.


The decomposition of peroxydisulfate under alkaline or acidic conditions only leads to formation of oxygen, although hydrogen peroxide can be formed if concentrated sulfuric acid is used.

kmno4 - 23-1-2012 at 16:51

Your yellow something is surely Na2O2. Its hydrate (x8H2O, colourless) can be prepared from 30% H2O2 and NaOH(aq) + ethanol (see Inorg. Synth.)
Again, I would suggest giving amounts in "mg" or "g", because "spatula" means nothing.
One must remember that reduction of S2O8(2-) gives HSO4(-) and it cause self-propagating, exothermic reaction with NaOH (releasing O2) in concentrated solutions.
I would try experiments with mixing cold, concentrated (~20-30%) solutions, with additional ice bath during addition of NaOH to Na2S2O8 (or vice versa).

woelen - 24-1-2012 at 01:09

I do not agree with you that it surely must be Na2O2. I have some reagent grade anhydrous Na2O2 and its color is much lighter than what I observe. See wikipedia for a picture of a sample of my Na2O2.

And also have a look at the experiments I did with dichromate, molybdate and nickel(II). I described these in my previous post. All these experiments evidently show that no peroxide is formed. The color must really be due to some other compound.

kotze - 24-1-2012 at 13:44

This is certainly sodium ozonide. "The inorganic ozonides" by Petrocelli and Chiarenzelli sheds some light on these fascinating compounds. Alkali ozonides (or "ozonates") are known to be formed from cold alkali hydroxide solutions and ozone, the color ranging from yellow to red-brown. Even cooled ammonia solution shows dark red coloration when treated with O3. Solid ozonides have been prepared from moist(!) alkali hydroxides and ozone gas at room temperature. There're conflicting reports on the stability of sodium ozonide, ranging from full decomposition within a few days to showing now signs of decomposition after 18 month of storage @RT. The presence of moisture is deemd to be essential to the formation of ozonide, and in the case of tetramethylammonium ozonide, the presence of impurities actually increased(!) its stability. Solid ammonium ozonide (one scary fellow for sure!) is stable only at -126°C.
It is known that persulfate thermally decomposes yielding ozone gas, and it is quite possible that this is through some ozonide, O3- intermediate. Even "ozonic acid", HO3, seems to exists, as cold water treated with ozone colours blue litmus red and increases electrical conductivity.

AndersHoveland - 24-1-2012 at 14:35

http://pubs.acs.org/doi/abs/10.1021/ja01151a024

The question is whether the decomposition of persulfate under alkaline conditions liberates any ozone.

Panache - 24-1-2012 at 19:43

Quote: Originally posted by kotze  

It is known that persulfate thermally decomposes yielding ozone gas.


Do you have reference for this or if not was the result through infernence or actual collection or direct reaction of the ozone. In otherwords can it be used as a convienent ozone source as i have a couple kilos of the persulfate sitting around bored in the dark and i am quite sick of it emailing me constantly asking for something to do.