Jose
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Help me predict this reaction...
I am doing an experiment consisting of the galvanic reaction between aluminum and copper in a solution containing dilute zinc acetate with a balloon
containing 78% N2 and the rest O2 (filled it with an air pump).
In solution we have the anions OH- and CH3COO-. For the cations we have Zn+2 and H+
For the anode reaction Al is oxidized to Al+3. For the cathode O2 is reduced to OH- and combines with Al+3 to become Al(OH)3?
I have observed bubbles coming out of the Aluminum foil. Could they be acetate ions becoming ethane or hydroxide ions being oxidized to O2?
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Metacelsus
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What's the pH of the solution? It could be hydrogen gas.
Is the copper present as the metal, or in an ionic form?
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Jose
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Copper metal attached to aluminum foil. If there is some unreacted acetic acid that may be the case. There could be some aluminum displacing zinc from
solution.
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zed
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Yes, we have no Bananas!
Gotta test it!
Normally, the reduction of carboxylic acids to hydrocarbons, is quite difficult.
But, I'm hearing noises that suggest electricity is involved here, in which case, it isn't entirely impossible.
If your testing facilities are crude, I Suppose you could capture a quantity of the gas, combust it with Oxygen, and bubble the resulting product
through a Barium Hydroxide solution. The CO2 in the ethane residue, would create a precipitate of Barium Carbonate.
The combustion product of Hydrogen, would show no reaction.
So, what kind of instrumentation do you have access to?
Can you maybe collect gas via a hypodermic needle, and inject it into an instrument that can tell you what is what?
[Edited on 17-6-2018 by zed]
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Jose
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Electricity is not being used to make the products. Its a galvanic reaction involving two metals in a solution of zinc acetate with some unreacted
acetic acid.
I checked yesterday night the solution and the bubbling at the anode stopped, suggesting that whatever reactant was producing the gas is already
consumed; probably some chlorine from tap water. If this is the case then it means that the only elements or compounds that discharge at either
electrode must be below hydrogen in the electrochemical series such as oxidation of chlorine at the anode and reduction of oxygen at the cathode.
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AJKOER
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More interesting variation for a more likely obvious reactions forming Al(OH)3, breakdown of the H2O2 and a possible attack of the acetate anion, add
a polyphosphate. The action of the latter with O2 can form the superoxide radical anion and the hydroxyl radical. The latter acts on H2O2 forming HO2
(or H+ and more superoxide at pH > 4.88). The superoxide and H2O2 in the presence of transition metals (like Cu) also forms hydroxyl radicals and
at more neutral to basic pH, perhaps small amounts of singlet oxygen.
A source on the effects of polyphosphates (or PolyP, see https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4380828/) to quote:
"Reaction of H2O2 or HOCl with redox-active metal ions like Fe2+ or Cu2+ generates the highly reactive and toxic hydroxyl radical (OH•) via the
Fenton reaction [3]. At least two distinct mechanisms explain how polyP might reduce the cytotoxic effects of the Fenton reaction. In vitro studies
have been shown that PolyP dramatically reduces the OH• yield of the Fenton reaction (Figure 2C) [22], despite the fact that chelation of Fe2+ by
polyP accelerates the rate of the Fenton reaction by several orders of magnitude [23]. The explanation for this apparent contradiction appears to lie
in the ability of polyP to stabilize the Fe3+ intermediate, thereby inhibiting the regeneration of Fe2+, which is necessary for additional cycles of
OH• generation [23]. However, additional work is needed to validate this model in vivo."
Also, another approach, try adding some sea salt and briefly heating in a microwave (without the balloon) and then connecting the balloon may jump
start a reaction as well.
[Edited on 19-6-2018 by AJKOER]
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Jose
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Where are you getting the H2O2 and polyphosphate from?
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AJKOER
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A proposed new variation of your experiment is to add PolyP. My research suggests heating dry ammonium phosphate produces ammonium polyphosphate,
where the starting required ammonium phosphate could (I have yet to test) be created in solution from aqueous trisodium phosphate acting on ammonium
sulfate and freezing out the sodium sulfate hydrate.
The presence of O2 leads to reactive oxygen species (ROS includes H2O2 in acidic environments). Hydrogen peroxide can apparently be formed, in situ,
from created superoxide arising from the action of solvated electrons (promoted by PolyP) acting on O2 plus 2 H+. Electrons in water (or in other
mediums, arising from anodic metals including in the current context, Al, Zn and Cu) can be partially solvated.
A couple of studies, but see, for example, Li Wang, Feng Wang, Pengna Li, Lizhi Zhang64, DOI : 10.1016/j.seppur.2013.10.002 , link: https://www.researchgate.net/publication/259159308_Ferrous-t... . To quote part of the abstract:
"In this study, we demonstrate that ferrous–tetrapolyphosphate complex could activate dioxygen to produce reactive oxygen species for highly
efficient aerobic degradation of toxic organic pollutants at room temperature and pressure. Cyclic voltammogram study revealed the chelation of
ferrous ions with tetrapolyphosphate could significantly reduce the redox potential of Fe 3+ /Fe 2+ to efficiently activate molecular oxygen in air.
The dioxygen activation ability of ferrous–tetrapolyphosphate complex was found to be related to its concentration and pH value in the solution. The
mechanism of dioxygen activation induced by ferrous–tetrapolyphosphate complex and the degradation pathway of sodium pentachlorophenol were studied
in detail."
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Note, if the source of Al is aluminum foil, you may wish to heat it (even to redness) to remove any plastic coating and breakdown the annealing that
was performed to reduce its reactivity (like to food acids).
[Edited on 19-6-2018 by AJKOER]
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