Terminus_Est
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NaCl + H2O2 + Aluminum: What are the products?
Ok so a while ago today I was wondering what would happen if ordinary table salt is mixed with 3% hydrogen peroxide and aluminum so I decided to try
it. I poured some salt into a small empty plastic container so that it would only cover the bottom and then filled the container 2/3rds of the way
with peroxide and capped it and shook the container until all the salt was dissolved. Then I opened the container and added a small wad of aluminum
foil and watched for anything.
There was a reaction taking place after all. There was alot of fizzing going on in the solution and around the foil and the container was getting a
bit warm as well. Then after waiting a while and when there was little to no fizzing going on, there was a whitish precipitate at the bottom. And what
about the sodium and chloride ions? Did any of them react with the aluminum?
[Edited on 20-11-2012 by Terminus_Est]
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weiming1998
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Quote: Originally posted by Terminus_Est  | Ok so a while ago today I was wondering what would happen if ordinary table salt is mixed with 3% hydrogen peroxide and aluminum so I decided to try
it. I poured some salt into a small empty plastic container so that it would only cover the bottom and then filled the container 2/3rds of the way
with peroxide and capped it and shook the container until all the salt was dissolved. Then I opened the container and added a small wad of aluminum
foil and watched for anything.
There was a reaction taking place after all. There was alot of fizzing going on in the solution and around the foil and the container was getting a
bit warm as well. Then after waiting a while and when there was little to no fizzing going on, there was a whitish precipitate at the bottom. And what
about the sodium and chloride ions? Did any of them react with the aluminum?
[Edited on 20-11-2012 by Terminus_Est] |
Aluminium is slowly attacked by water itself in the presence of sodium chloride as a catalyst. Usually, aluminium is not attacked by water due to a
passivating layer of oxide that surrounds the metal. Adding a source of chloride ions removes/inactivates the coating partially, allowing water to
slowly react with the metal.
What happened is that the water reacted with the aluminium, forming aluminium hydroxide. The acidic stabilisers and the H2O2 itself could also react
with the aluminium. In both cases, the precipitate is mainly aluminium hydroxide, with a bit of other aluminium salts if the H2O2 you used had acidic
stabilisers. In both cases, your observations are consistent with the formation of aluminium hydroxide.
Edit: The sodium chloride isn't consumed during the reaction; it merely acts as a catalyst.
[Edited on 20-11-2012 by weiming1998]
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Avi
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Is the h2o2 required
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Velzee
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No, as it only makes the reaction occur faster.
Check out the ScienceMadness Wiki: http://www.sciencemadness.org/smwiki/index.php/Main_Page
"All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident."
—Arthur Schopenhauer
"¡Vivá Cristo Rey!"
—Saint José Sánchez del Río |
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PHILOU Zrealone
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Also to take into account apart from the H2O2 stabilisers...
-the anti clogging material into the salt (often potassium iron hexacyano ferrate).
-the unpure Al from the foil so other metals/metaloids are present that may react with the H2O2.
So reaction can be quite complexer.
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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AJKOER
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Per this source: Alok D. Bokare and Wonyong Choi, "Review of iron-free Fenton-like systems for activating H2O2 in advanced oxidation processes",
published in Journal of Hazardous Materials, May2014. Link: https://www.google.com/url?sa=t&source=web&rct=j&...
To quote from the article, page 126:
"The use of bare ZVAl (without surface modification or pre-treatment) as Fenton-type catalyst to generate HO• was first demonstrated by Bokare and
Choi [86]. In the presence of O2, in situ generation of H2O2 and the subsequent decomposition into HO• was achieved by electron transfer from
commercial ZVAl samples under acidic condition (Fig. 2b). After the dissolution of the native surface oxide (Al2O3) layer on ZVAl at acidic pH(pH ≤
4) to expose the bare Al metal surface, the sequential generation of H2O2 and HO• was utilized for the oxidative mineralization of organic
pollutants (4-chlorophenol, phenol, nitrobenzene and sodium dichloroacetate) [86]."
where ZVAl stands for zero valent aluminum.
Apparently, in addition to Al(OH)3, there are created some reactive oxygen species (ROS), including the superoxide radical anion, which in the
presence of an acid forms H2O2, in situ. This can then drive a Fenton-like reaction with Aluminum going from a valent state of zero to +3, along with
the creation of hydroxyl radicals, HO•, capable of mineralizing organic pollutants. My take on a possible radical pathway:
2 Al + 6 O2 = 2 Al(3+) + 6 O2•-
6 O2•- + 6 H+ → 3 H2O2 + 3 O2 (See, for example, https://books.google.com/books?id=PQ3OBQAAQBAJ&pg=PA491&... )
Al + 3 H2O2 → Al(3+) + 3 HO• + 3 OH-
Al(3+) + 3 OH- → Al(OH)3 (s)
The hydroxyl radical can further react with H2O2 creating the HO2• radical, depending on pH, via:
HO• + H2O2 → H2O + HO2•
while the presence of particular ROS has been observed, the reluctant of the authors to cite a reaction chain is understandable as the precise
reaction path (including non-radical pathways) have yet to be been confirmed.
[Edit] If any added H2O2 contains H3PO4, then in addition to Aluminum hydroxide and transient ROS, some Aluminum phosphate could be recovered. I would
also suspect that aeration and adding acid would increase the rate of the dissolution of the Aluminum. I view the role of NaCl as an electrolyte for
essentially an electrochemical based corrosion reaction in the presence of acid and oxygen.
[Edited on 3-8-2016 by AJKOER]
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