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Author: Subject: Reaction between aluminum and chlorides in weakly acidic meidum
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[*] posted on 11-7-2019 at 01:37
Reaction between aluminum and chlorides in weakly acidic meidum

at the end of a dinner with coworkers, we were collecting all the trash and stuffing things together. Among these, there was a plastic cup containing some aluminum foil, some paper imbued with lemon juice, a slice of lemon, and presumably some salt.

At some point this cup started getting hot and fuming.

I assumed that the salt was NaCl, but was still wondering what the hell happened there.

In pure HCl solutions, you have H+ and Cl- ions dissolved in water. In citric acid + NaCl solution, you have the majority of citric acid undissociated, but then you would have a small concentration of citrate ion, H+, Na+ and Cl-, which could be assimilated to a dilute solution of HCl.

This led me to think that what happened was the corrosion of aluminum with HCl: Al + 3HCl -> AlCl3 + 3/2H2. However, it went too fast and I didn't get such results even with 10% HCl (of course the 37% will just eat through it instantly. Talking about the household grade of HCl here), so I was wondering what else could have catalysed the reaction.

Could an excess of chloride ion and the formation of AlCl4- complex play a role in this? Perhaps sequestering the Al3+ ion from the half reaction of Al and driving the equilibrium towards the generation of more H2? Or maybe I didn't notice the presence of some other "item" inside the cup and I made some electrochemical cell with aluminum - paper imbued with lemon juice - other metal?

[Edited on 11-7-2019 by Metallus]
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[*] posted on 11-7-2019 at 04:53


OK, will have a very electropositive metal Al (as aluminum foil here which could be annealed or even have an acrylic coating to make it appear passive, where the foil may be an Al alloy, say Al/Fe, as I recall Reynold's Extra strength foil adds iron), oxygen from air, H+ (lemon juice a source of both ascorbic and citric acid) and NaCl (a good electrolyte and also capable of piercing the protective Al2O3 coating) and perhaps even a role for sunlight (see below).

The answer, in my opinion, is more likely (than a simple reaction of water/lemon juice on freshly exposed aluminum metal), an electrochemical cell with the Al alloy being attacked with accompanying heat, as battery cells do, at times, get hot! Also, the role of the paper (you found resting in the cup) is perhaps crucial as a gas/water interface. Then, oxygen and solvated electrons could lead to the creation of the superoxide radical anion, capable of reducing Fe3+ back to Fe2+, thereby promoting cyclic activity in the reaction system:

O2 + e- = •O2-

where in a surface chemistry reaction with water vapor exists as the perhydroxyl radical, •HO2, at pH < 4.88 (thanks to the lemon juice). Some reactions:

•O2- + Fe3+ = O2 + Fe2+ (a reversible reaction)

Fe2+ + H+ + •HO2 = Fe3+ + H2O2

An interesting transport reaction between superoxide and Al3+, extending the reactive half-life of the superoxide I would image, which engages in the following reactions:

Al(lll) + •O2- = [Al.•O2](2+)

[Al.•O2](2+) + Fe3+ + 2 H+ = Fe2+ + Al3+ + H2O2

Then, some possible fenton and fenton-like chemistry with any formed hydrogen peroxide:

Fe2+ = Fe3+ + e-

Al = Al3+ + 3 e-

H2O2 + e- = •H + HO2- = •OH + OH-

Below is more detail with references per a prior thread ( ):

Quote: Originally posted by AJKOER  

.......related goal is to use the recycling ability of the aluminum ion with respect to transition metals to their lower valence states as a means to foster chemical decomposition reactions.

The first alluded to article is ‘Oxidative Stress Gated by Fenton and Haber Weiss Reactions and Its Association with Alzheimer’s Disease’ by Tushar Kanti Das, et al, published in Archives of Neuroscience, July 2014 2(3): e20078, DOI: 10.5812/archneurosci.20078.

The authors cite, in Figure 4, “ Formation of Aluminum Superoxide Semi reduced Radical Ion and Aluminum Superoxide Complex (43)”, with described reactions proceeding as follows (also adopting notation and water complexing from the second article):

[Al(H2O)4](3+) + O2•− <-> [Al(O2•−)(H2O)4](2+)

[Al(O2•−)(H2O)4](2+) + Fe(3+) --> O2 + [Al(H2O)4](3+) + Fe(2+)

And, in the presence of H+ :

[Al(H2O)4](3+) + O2•− + H+ <-> [Al(O2•−)(H+)H2O)4](3+)

[Al(O2•−)(H+)H2O)4](3+) + [Al(O2•−)(H+)H2O)4](3+) --> 2 [Al(H2O)4](3+) + H2O2 + O2

Note per below, the action of hydrogen peroxide on ferric also leads to ferrous:

H2O2 = H+ + HO2-
Fe(3+) + HO2- --> Fe(2+) + •HO2 ( or, pH> 4.88, H+ + O2•− )

Hydroxyl radical can also be formed via the classic Fenton reaction:

Fe(2+) + H2O2 --> Fe(3+) + •OH + OH-

Another work: ‘Pro-oxidant Activity of Aluminum: Stabilization of the Aluminum Superoxide Radical Ion’ by J. I. Mujika, F. Ruiperez, I. Infante, J. M. Ugalde, C. Exley, and X. Lopez in J., published in Phys. Chem. A 2011, 115, 6717–6723, American Chemical Society, .Link: .

In the Mujika article to quote “In addition, the presence of LMM ligands such as citrate could also have an indirect effect in the oxidation capacity of aluminum by augmenting the bioavailability of Al3+ species, shifting the formation of Al(OH)4- to higher pH’s. However, one should also take into account the effect of citrate chelation itself in the thermodynamic equilibrium of [AlO2•]2+ formation.”

With respect to the chemistry, some more reactions relating to formation of superoxide, solvated electrons electrons and ferric salts per a planned experiment:

•OH + H2O2 = O2•− + H+ + H2O (or HO2• for pH < 4.88)

Al --> Al3+ + 3 e-
Fe2+ + 2 e- --> Fe
Net Electrochemical Cell: Al + Fe2+ --> Al3+ + Fe + e-

e- + n H2O = e-(aq)

e-(aq) + O2 = O2•−

From the added presence of Citric acid crystals,
Fe2+ --> Fe3+ + e-
e- + OH• --> OH-
Fe2+ + OH• --> Fe3+ + OH- (the creation of a basic ferric citrate from a hydroxyl radical attack)

Yet more chemistry from a prior thread (see ):

Quote: Originally posted by AJKOER  
Here is an extract on one of my prior discussion of Fenton-type reactions proceeding from in situ formed H2O2, to quote:

"Well, let's start with some possible Fenton based reactions creating the hydroxyl radicals, .OH and the superoxide anion, .O2- . As a reference, see, for example, "Generation of Hydroxyl Radicals from Dissolved Transition Metals in Surrogate Lung Fluid Solutions" by Edgar Vidrio, et al at . Cited reactions :

Cu(l)/Fe(II) + O2(aq) → Cu(ll)/Fe(III) + .O2-

As an alternate reference for the above reaction (which I have personally performed on Cuprous citrate using an air pump from an old fish tank), see for example,

The reaction chain continues as:

Cu(l)/Fe(II) + .O2- +2 H+ → Cu(ll)/Fe(III) + HOOH

Cu(l)/Fe(II) + HOOH → Cu(ll)/Fe(III) + .OH + OH-

Net of the last three reactions:

3 Cu(l)/Fe(II) + O2(aq) +2 H+ → 3 Cu(ll)/Fe(III) + .OH + OH-

And, in the presence of sunlight (or a reductant like Citric or Ascorbic acid), a cyclic reaction could ensue in the case of sunlight:

Cu(ll)/Fe(lll) (aq) + hv → Cu(l)/Fe(ll) (aq) + HO• + H+ "
[Edited on 11-11-2017 by AJKOER]

An added quote from the Vidrio's work detailing the limited recycling ability of citrate (and ascorbate):

“Similar reactions can occur with Cu, Cr and Ni. Furthermore, biological chelators and reductants can greatly enhance the production of ROS (Burkitt et al., 1991; Engelmann et al., 2003; Wenk et al., 2001). For example, in the presence of ascorbate (Asc), a biological reductant, the oxidized form of the transition metal produced by the Fenton reaction can be reactivated (R2 and R3), thus allowing additional ROS to be produced.

Fe(III) + Ascn → Fe(II) + Ascn+1 (R2)
Cu(II) + Ascn → Cu(I) + Ascn+1 (R3) “
Note reference (43) is “Exley C. The coordination chemistry of aluminium in neurodegenerative disease. Coordina Chmst Rev. 2012;256(19-20):2142–6. Here is the Abstract and Highlights:

“The coordination chemistry of aluminium in neurodegenerative disease, Link:
The coordination chemistry of a metal ion defines its optimal association with a biomolecule such that its binding by specific ligands on that molecule confers function and biological purpose. Aluminium is a non-essential metal with no known biological role which means that its coordination neurochemistry defines aluminium's putative role in a number of neurodegenerative diseases. In examining this chemistry it is found that very little is known about the complexes formed and ligands involved in aluminium's interactions with neurochemically-relevant ligands. Aluminium's action as a pro-oxidant as well as an excitotoxin are highlighted while the evidence for its interactions with amyloid beta, tau and DNA are discussed and it is concluded that it is too early to discount these ligands as targets for the neurotoxicity of aluminium.
► There are few quantitative data describing the coordination chemistry of aluminium in neurodegenerative disease. ► One compelling line of evidence relates to the putative aluminium superoxide semi-reduced radical ion (AlO22+) and its powerful action as a pro-oxidant. ► Another important candidate is aluminium's complex with ATP and its potential to disrupt neuronal signalling and induce excitotoxicity. ► Though there are no quantitative data to describe aluminium's interactions with amyloid beta this does not preclude their association in the brain. ► The biological reactivity of aluminium supports myriad as yet unidentified interactions with biomolecules associated with brain function in health and disease.”

[Edited on 7-10-2018 by AJKOER]

[Edited on 11-7-2019 by AJKOER]
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