Sciencemadness Discussion Board

Revealing Reactions that are Potentially More Complex

AJKOER - 9-12-2018 at 06:18

This thread is to present example of reactions where, most likely, the underlying mechanism, is more complex than one may, at first, think.

1> First example, the reaction of the stable radical .NO2 with water. If you believe it to be:

2 .NO2 + H2O = HNO2 + HNO3

not exactly, as there is not here a direct action of a radical with water, but of a radical with a radical and then with water, more precisely:

.NO2 + .NO2 = N2O4

N2O4 + H2O = HNO2 + HNO3

Source: See Table l at https://books.google.com/books?id=mckVFtJ7YecC&pg=PA30&a...

2> Based on this 2001 US Patent 7,067,099 (see https://patents.google.com/patent/US7067099 ), which relates to “A method for preparing aluminum sulfate which comprises subjecting sulfuric acid and aluminum hydroxide to reaction, wherein the reaction is advanced in the presence of at least one member selected from the group consisting of nitric acid and a peroxide", so why does H2O2 assist in the attack of Aluminum metal with an acid? Now, SO2 and H2O2 may create weak H2SO4, but how does that help? My take, perhaps, is the formation of acidic radicals, see my thread at http://www.sciencemadness.org/talk/viewthread.php?tid=94166#... .

3> The action of HOCl on Iron metal. The literature is more or less ignoring this reaction to avoid presenting a likely inaccurate explanation on this one. Given the electropositive nature of Fe, an oxygen source (HOCl), and H+ (from decomposition of HOCl, or reported Cl2 creation), some electrochemistry likely at work also creating electrons introducing radicals, like for example:

e-(aq) + HOCl = .ClOH-

with this only recently recognized radical anion whose decomposition into either .OH + Cl- occurs at pH > 5 and at pH < 5 forms OH- + .Cl . This is not an elementary reaction system for sure!

Some sources: See Table S1 referenced at http://www.sciencemadness.org/talk/viewthread.php?tid=98989#... and http://www.sciencemadness.org/talk/viewthread.php?tid=86070#... and Table 1.2a on p. 13 at https://www.bnl.gov/isd/documents/92710.pdf and finally https://aip.scitation.org/doi/abs/10.1063/1.470852?journalCo... .

4> The reaction of .NO and O2 takes more than a minute before any .NO2 is apparently created. Is there more going on? Not that it is frequently commented on in textbooks, but here is some commentary from Atomistry (http://nitrogen.atomistry.com/nitric_oxide.html) on NO, to quote:

"The general explanation of the formation of ruddy fumes when nitric oxide is brought into contact with air or oxygen is that nitrogen peroxide is produced:
2NO + O2 = 2NO2.
There seems to be little doubt that nitrogen peroxide is the final product, but it is by no means decided whether the above equation truly represents the mechanism of the oxidation.
In the first place, it would seem that nitrogen trioxide is the sole product when the oxidation is carried out below - 110°, even with excess of oxygen:
4NO + O2 = 2N2O3,
and the production of nitrogen tetroxide only occurs above -100°: 2N2O3 + O2 = 2N2O4.
Raschig maintains that at ordinary temperatures a similar intermediate formation of the trioxide occurs, the second oxidation to the peroxide taking a much longer time. According to Lunge, however, the primary product of oxidation is the peroxide, the reaction being of the third order.
Further evidence in favour of nitrogen trioxide being the first oxidation product of nitric oxide, is the instantaneous formation of N2O3 when nitric oxide and oxygen are mixed in the ratio of 4 to 1 at ordinary temperatures, the product remaining stable. When the proportions of nitric oxide and oxygen are as 2:1, the N2O3 stage is reached very rapidly, then further oxidation to N2O4 occurs, 34 per cent, in 20 seconds, and completely in 100 seconds. "

4> This one may be speculative as my observations is that flame heated water to boiling releases a somewhat steady stream of steam in dry air conditions, but upon termination of the heating, for a few minutes, it appears that more steam is actually being released from the once boiling solution. If anyone agrees with this observation, is there a simple explanation? If the implied goal is to make steam (to increase humidity), could it be more efficiently performed by periodic, and not constant, heating!?

Now is the opportunity for others to contribute.
-----------------------------------------------------------

Note, the purpose for this thread in to enlighten many as to the science that surrounds us constantly, but not often mentioned.

It is not intended to provide embarrassing questions to your underpaid, over worked, little appreciated, and perhaps not highly trained/educated science teacher!

[Edited on 9-12-2018 by AJKOER]

woelen - 10-12-2018 at 00:36

The reaction between NO and O2 is much faster than what you suggest. I have done this reaction quite a few times and on my website there even is an experiment about this with a movie, showing the reaction.:

http://woelen.homescience.net/science/chem/exps/NO_O2/index....

Formation of brown NO2 is almost immediately and not a matter of minutes.

--------------------------------------------------------------------------------------------

The fifth observation I also know. You can see it in the kitchen when preparing food. When the heat source (e.g. a gas flame) is turned off, then the pan, filled with hot water, seems to give off more steam. But this only is what it seems to be.
When the gas flame is still present, then you get more water vapor, but the hot air from the flame, which goes around the pan, does not allow the water vapor to condense into visible droplets. When the flame is taken away, then the flow of hot air around the pan stops at once and then the water vapor, still coming from the hot water, easily condenses into small droplets, giving more visible water.
So, you don't get more water vapor when heating is interrupted, you only get more visible water vapor, but the total amount still is lower.

Ubya - 10-12-2018 at 03:21

Quote: Originally posted by AJKOER  

.
In the first place, it would seem that nitrogen trioxide is the sole product when the oxidation is carried out below - 110°, even with excess of oxygen:
4NO + O2 = 2N2O3,
and the production of nitrogen tetroxide only occurs above -100°: 2N2O3 + O2 = 2N2O4.
Raschig maintains that at ordinary temperatures a similar intermediate formation of the trioxide occurs, the second oxidation to the peroxide taking a much longer time. According to Lunge, however, the primary product of oxidation is the peroxide, the reaction being of the third order.
Further evidence in favour of nitrogen trioxide being the first oxidation product of nitric oxide, is the instantaneous formation of N2O3 when nitric oxide and oxygen are mixed in the ratio of 4 to 1 at ordinary temperatures, the product remaining stable. When the proportions of nitric oxide and oxygen are as 2:1, the N2O3 stage is reached very rapidly, then further oxidation to N2O4 occurs, 34 per cent, in 20 seconds, and completely in 100 seconds. "

[Edited on 9-12-2018 by AJKOER]


Have you ever made some NO2? N2O3 stable at ordinary temperature for many seconds??? Where? I bet you are still referring to - 100 °C where probably it's stable but not at room temperature.

Sulaiman - 10-12-2018 at 04:52

Based on only a few observations, I think that NO -> NO2 conversion rate may be humidity dependant.
Maybe dry NO + O2 would be a lot slower ?

+1 on the removal of heat (plume) causing more VISIBLE condensation idea.

I suspect that your equation "N2O4 + H2O = HNO2 + HNO3" is also unlikely to be so simple,
there must be intermediates ?

AJKOER - 11-12-2018 at 11:45

Actually found an updated published work available for free download (search on 'Formation of nitrogen oxides via NO + O2 gas–solid reaction on cold surfaces', by M. Minissale et al., in Chemical Physics Letters 565 (2013), p. 52–55). To quote:

"We explain the presence of these species through the reaction scheme shown below:

.NO + O2 = .NO3 R1

.NO + .NO3 = 2 NO2 R2

together with the following reactions:

.NO + .NO = (NO)2 R3

.NO2 + .NO2 = (NO2)2 R4

.NO + .NO2 = N2O3 R5 "

with the reaction R1 (the creation of the nitrate radical!) is occurring with NO contact onto oxygen layers on very cold surfaces (especially 10 K to 30 K), which is certainly more complex than I expected.

A note on the observed reaction time, apparently it refers to the time required for the completion of the reaction, that is: 2 NO + O2 = 2 NO2, which may be hard to visually assess together with the fact that colorless NO gives no information on its concentration at a point in time. I would also guess that the presence of water droplets containing dissolved oxygen could behave chemically different with NO than would dry air/oxygen (see https://www.ncbi.nlm.nih.gov/pmc/articles/PMC47296/).


[Edited on 12-12-2018 by AJKOER]

Sigmatropic - 11-12-2018 at 13:58

They almost certainly mean the peroxynitrite radical, not the nitrate radical.
Then this acts as an oxidant in eq. 2.
Nothing really complex if you ask me. Eq 3-5 are equilibria distracting from where the actual productive chemistry is going on which is in eq 1 and eq. 2.

AJKOER - 11-12-2018 at 15:24

Quote: Originally posted by Sigmatropic  
They almost certainly mean the peroxynitrite radical, not the nitrate radical.
Then this acts as an oxidant in eq. 2.
Nothing really complex if you ask me. Eq 3-5 are equilibria distracting from where the actual productive chemistry is going on which is in eq 1 and eq. 2.


No, read the text available for download, a small file.

Now, I would agree if there were any solvated electron creation (from transition metal impurities undergoing an auto-oxidation reaction with oxygen,..), then possibly the formation of the superoxide radical anion:

Fe(ll) --> Fe(lll) + e-

e- + O2 = .O2-

which can quickly react with .NO radical, creating the peroxynitrite ion, see, for example: http://www.jbc.org/content/early/2001/05/23/jbc.M102341200.f... .

.NO + .O2- --> ONOO-

[EDIT] Correction, while that source paper says the nitrate radical, another source states the action of .NO on O2 forms the peroxynitrite radical, .O=NOO, as you claimed. See p. 31 of reference below.
-----------------------------------------------------

I claim complexity because the formation of the .NO3 radical implies to me the potential formation of various NxOy species, for example:

.NO3 + .NO3 = N2O6 (See Eq (29) at https://books.google.com/books?id=mckVFtJ7YecC&pg=PA30&a... )

[Edited on 12-12-2018 by AJKOER]