AJKOER
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Amazing Cleaning By Vinegar/Bicarbonate of Metal Sink, But How?
I was asked to really clean up a stainless steel sink.
I decided to apply Baking Soda to the wet sink that I just cleaned with common dishwashing liquid (still not appealing). I proceeded to scrub with the
dry NaHCO3 using a sponge. I then added some vinegar to the sponge and repeated the operation followed by rinsing.
I was actually surprised by the results per this simple green protocol (the sink looked restored!).
As to how this was effective, here is an explanation from commentary at https://www.livescience.com/why-baking-soda-vinegar-clean.ht... to quote:
"As a base, baking soda dissolves organic compounds like dirt, grease and other sticky ickies. In addition, the mineral structure of each baking soda
particle provides a gentle abrasive to clean without leaving scratches behind. As an acid, vinegar breaks down minerals that form from hard tap water,
forming unsightly stains on sinks, tubs and counters."
This explanation, I suspect, is a bit off as I do not have hard water and the sink was effectively cleaned by the dishwashing liquid of 'dirt, grease
and other sticky ickies'. However, I do accept that Baking Soda particles may have provided a good gentle abrasive effect. But is that completely the
answer?
Perhaps the answer is simply devoided of some more advanced chemistry and, to that extent, I present the following possibilities for consideration.
First, my sink is essentially stainless steel composed of iron containing at least 10.5% chromium, less than 1.2% carbon and other alloying elements.
The presence of iron and chrome metals with air exposure may feed a galvanic cell, a source of solvated electrons, leading to superoxide (O2 + e- =
•O2-) and the very acidic •HO2 radical (H+ + •O2- = •HO2).
Or, the galvanic cell may accelerate the action of acetic acid (a galvanic synthesis, see comments here http://www.sciencemadness.org/talk/viewthread.php?tid=152560...) creating iron acetate thereby assisting in stripping the metal surface.
Also, as the cleaning action occurred in the presence of air/oxygen and an acid, some Fenton-generated hydroxyl radicals (•OH) activity. The latter
with bicarbonate is a path to the longer-lived carbonate radical anion:
•OH + HCO3- = H2O + •CO3-
capable of breaking down organics (as in stain removal).
Further, the self-reaction of the carbonate radical is a path to the oxalate ion:
•CO3- + •CO3- -> C2O4(2-) + O2
where iron oxalate is a known stain remover.
Also, per this work, 'Photocatalytic oxidation activity enhanced by iron-oxalate chelates for Fenton-like oxidation of As(III) in oxalate systems' at
https://www.sciencedirect.com/science/article/abs/pii/S22133... , suggesting the presence of light could be further beneficial.
In total, likely too complex, but is there some answer, or not, between these alternatives?
[Edited on 29-9-2022 by AJKOER]
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Lionel Spanner
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For an initial experiment I'd suggest cleaning it with vinegar and a different solid base of a similar strength, e.g. sodium acetate, ground to a
similar fineness as the baking soda, and see if it cleans as effectively.
Also, for what it's worth, steel is passivated by many acids, including acetic: it forms a very thin metal oxide layer that protects the metal
underneath and (presumably) acts to prevent organic matter from sticking to it.
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AJKOER
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One source (see https://chemistrycachet.com/the-truth-about-cleaning-with-ba...) claims it is the chemical reaction itself that is responsible!
Now, that reaction just creates sodium acetate and CO2, but, on further thought, in the presence of a galvanic cell with solvated electrons, a
possible reaction I have not yet proposed is:
CO2 + e- = •CO2-
where the carbon dioxide radical anion is a powerful reducing radical, as per a source at https://pubs.acs.org/doi/10.1021/jacs.1c04427, "Radical Chain Reduction via Carbon Dioxide Radical Anion (CO2•–)", which notes, to quote:
"The carbon dioxide radical anion (CO2•–) is a highly reactive intermediate that is routinely accessed through electrochemical reduction of CO2."
But, in the current context, there may be a possible, albeit limited, galvanic cell version of its creation occurring.
[Edited on 29-9-2022 by AJKOER]
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AJKOER
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I found an interesting work on the impact of CO2 on the corrosion of steel, "Electrochemistry of CO2 corrosion of mild steel: Effect of CO2 on iron
dissolution reaction " here http://www.icmt.ohio.edu/documents/Journals2017/Electrochemi... . To quote from the abstract:
"The kinetics of the iron dissolution reaction was investigated in CO2-saturated acidic sodium chloride solutions. While the effect of CO2 on the iron
dissolution reaction during corrosion process has received little attention in the existing literature, the experimental polarization curves obtained
in the present study on X65 mild steel suggest that CO2 and/or its related carbonate species are directly involved in the metal dissolution reaction.
The presence of CO2 was found to significantly influence the kinetics and the mechanism of the iron dissolution reaction at partial pressures as low
as 1 bar. The higher corrosion rates observed in CO2-saturated brines as compared to strong acid solutions at the same pH could possibly be explained
by the effect of CO2 on the kinetics of the anodic reaction."
In the current case, no NaCl but an electrolyte of NaHCO3, but still I would expect some electrochemically assisted impact on the corrosion at the
steel surface.
Further, with alkaline Baking Soda, I would expect speciation of the Fe around the hydroxide anion (OH-) and perhaps carbonate anion, as well.
Upon a subsequent addition of chelating acid source (like Acetic acid), a speciation disruption and associated reactions, ultimately leading to a
fresh iron surface.
Supporting reference, for example, "Importance of Iron Complexation for Fenton-Mediated Hydroxyl Radical Production at Circumneutral pH" at https://www.frontiersin.org/articles/10.3389/fmars.2016.0013... , to quote:
"Quantitative HO• production also appears likely for L = citrate, although uncertainties with the speciation of Fe(II)-citrate complexes as well as
difficulties in modeling the oxidation kinetics of these complexes has prevented a definitive conclusion."
And, even more advanced chemistry may arise from possible interfacial reactions occurring at the Fe surface with gases, see, for example, this 2013
work, "Fenton chemistry at aqueous interfaces" at https://www.pnas.org/doi/10.1073/pnas.1314885111 where I am not expressly suggesting a major role for Fenton chemistry per se, but likely aspects
of some advanced and complex chemistry.
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teodor
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Your sink is dirty not because of corrosion, but because you have a deposit of Ca2+ and Mg2+ salts.
Many acids can perfectly do the job.
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Herr Haber
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Well... I would have loved an understandable answer as to why people like to clean stuff with vinegar and baking soda.
I dont see any cleaning effect from the sodium acetate formed and as I could have forseen, I cant understand most of what Ajkoer is saying.
The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
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Tsjerk
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Someone here can probably explain the chemistry perfectly, I can't, but have you ever tried holding a dirty oxidized copper coin in NaCl/vinegar?
Either the sink was dirty with carbonate salts as teodor suggests and vinegar alone would have worked or the dissolved sodium ions together with
vinegar did the trick as it does for copper oxide.
Spoiler: it doesn't involve radicals and it works with NaCl instead of baking soda.
[Edited on 29-9-2022 by Tsjerk]
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Bedlasky
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I used to clean coins in citric acid. CuO dissolve in acids very easily.
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Lionel Spanner
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Indeed: early advertising for the cleaner Cillit Bang (containing a lot of phosphoric acid) used its effect on coins as part of their advertising
("look what it did to a penny!")
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Rainwater
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Theory....
1) NaHCO3 + CH3COOH = CH3COONa + H2CO3
2) 2H2CO3 + Ca+ = Ca(HCO3)2 + H2
3) H2CO3 = H2O + CO2
So could be carbonic acid is an intermediate.
Converts calcium insoluble compounds into soluble bicarbonates, then
A blast of co2 from the back.
Got a good test for hydrogen gas?
Also, vinegar eats stainless steel, so by dissolving the thin oxide layer(substrate) the dirt cant stick.
It will also dissolve lime stone
"You can't do that" - challenge accepted
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AJKOER
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Apparently, I should also note the possible formation of the highly acidic •HO2 radical from the metal auto-oxidation (see https://www.sciencedirect.com/topics/engineering/auto-oxidat... ) of Fe metal introducing the superoxide radical anion •O2- that, in air or pH
<4.88, exists as the cited hydroperoxyl radical.
Interestingly, •HO2 is a precursor to, and a reactive substitute for, H2O2 which is known to react directly with CO2 creating the
peroxymonocarbonate anion (CO4-), see this 2021 reference "Kinetics and Mechanism of Peroxymonocarbonate Formation" at https://pubs.acs.org/doi/abs/10.1021/ic1007389 . The latter is a targeted intermediate in percarbonate-based oxygen bleaches.
[EDIT] There is 2016 reported research in this area, see "Potential Energy Surfaces for the Reactions of HO2 Radical with CH2O and HO2 in CO2
Environment" at https://pubs.acs.org/doi/abs/10.1021/acs.jpca.6b07257 , to quote:
"We report on potential energies for the transition state, reactant, and product complexes along the reaction pathways for hydrogen transfer reactions
to hydroperoxyl radical from formaldehyde H2CO + HO2 → HCO + H2O2 and another hydroperoxyl radical 2HO2 → H2O2 + O2 in the presence of one carbon
dioxide molecule...The van der Waals complexation with carbon dioxide does not affect hydrogen transfer from formaldehyde, but it lowers the barrier
for hydroperoxyl self-reaction by nearly 3 kcal/mol. This indicates that CO2 environment is likely to have catalytic effect on HO2 self-reaction"
Also, work by Richardson in 2002, "The oxidative destruction of chemical warfare agents (CWA) and biological ... by Peroxymonocarbonate," at https://apps.dtic.mil/sti/pdfs/ADA406835.pdf where the army was engaged in a project to improve the efficiency of bicarbonate-activated hydrogen
peroxide for CWA and BWA destruction. Also cited therein, the work: "Catalytic Oxidation of Biomolecules by Peroxymonocarbonate: A Reactive Oxygen
Species in Biochemistry?". As such, in my opinion, a possible induced presence of peroxymonocarbonate should not be discounted here.
More interesting to me, is given the previously cited reference around the anodic corrosion of steel as accelerated by CO2 and the chromium content of
steel, some Cr-based reactions are possible. In particular, per this 2021 work "Valence State Modulation of Chromium in Selective Hydrogen Peroxide
Production Electrocatalysts" at https://pubs.acs.org/doi/abs/10.1021/acsaem.1c02024 where, however, here we have a galvanic cell situation (not electrolysis), but I would not
role out a catalytic role for Cr ions.
Clearly, with oxygen, acid, and iron, some Fenton (see https://www.sciencedirect.com/topics/earth-and-planetary-sci... ) chemistry-based oxidation-reduction reactions with associated creation of
reactive active oxygen species may be likely. Further advanced chemistry from the presence of a galvanic cell fostering Fenton with so-called
Galvano-Fenton (see this 2021 research: "The Galvano-Fenton process: Experimental insights and numerical mechanistic investigation applied to the
degradation of acid orange 7" at https://www.sciencedirect.com/science/article/abs/pii/S00134... ).
Clearly, the chemistry around steel, bicarbonate, and acetic acid can be made to be simple, with seemingly green benign intermediates, or far more
complex from more recent work extending into several domains, where CO2 and even chromium ion presence may be viewed as catalytic agents.
[Edited on 1-10-2022 by AJKOER]
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teodor
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You started the story with: "I was asked to really clean up a stainless steel sink". And then you proceed citing: "The oxidative destruction of
chemical warfare agents etc". Now I am waiting for the next story.
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Bedlasky
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AJKOER, don't get me wrong, but you really overcomplicate things. Not everything involve radicals.
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Tsjerk
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Haha  you will get it and I dare it will involve radicals.
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teodor
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But seriously, AJKOER, if your theory of galvanic action and Cr ions is correct, would it be the case that a 1.5-volt battery plugged between the sink
and the tap water would keep one's sink perfectly clean? If so, I have only one question: what should be the polarity?
[Edited on 2-10-2022 by teodor]
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violet sin
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Sodium ions clean grease well in my sink cleaning experience. Wether from trisodium phosphate, caustic lye, borax or table salt with some lime
juice... TSP and sodium hydroxide cleaned the grease mess from albacore tuna, black cod and salmon very well. Otherwise it just squished the grimy
dirt in circles.. the mess would offer a large amount of drag while wiping, but nearly nothing would come off ON the towel.
You can get spoilt milk smell from baby bottles/nipples with warm water and either baking soda or borax.. no problem. Nothing else added incase
you're wondering. Life observation, not a chemistry lesson.
@ Bedlasky one post down
The sodium being easily lost and making alkaline solutions I thought was obvious, and the point. Of course sodium could be replaced by potassium and
others and the effects similar. The sodium variety is cheap, commonly available and in all the compounds I mentioned. It works great on stainless
and not commonly seen as magic.
[Edited on 3-10-2022 by violet sin]
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Bedlasky
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Sodium hydroxide, phosphate and borax form alkaline solutions. Base + fat leads to saponification. Sodium ions really don't effect this.
Alkaline salts in general are good for transforming organic matter to soluble form. I use sodium carbonate for cleaning pots with burned food.
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Neal
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The smell of smelly coins is more from the sweat from our hands/skin. That chemical is 1-octen-3-one (octenone). And ways to remove that from coins is
acetone, isopropanol, or and ethyl acetate.
[Edited on 5-10-2022 by Neal]
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Bedlasky
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Coins don't look dirty because of octenone. Yeah, it is responsible for smell, but not for ugly look.
[Edited on 5-10-2022 by Bedlasky]
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Texium
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Quote: Originally posted by Rainwater  | Theory....
1) NaHCO3 + CH3COOH = CH3COONa + H2CO3
2) 2H2CO3 + Ca+ = Ca(HCO3)2 + H2
3) H2CO3 = H2O + CO2
So could be carbonic acid is an intermediate.
Converts calcium insoluble compounds into soluble bicarbonates, then
A blast of co2 from the back.
Got a good test for hydrogen gas? |
Ack! No. First off, you have Ca+ written, which is effectively
nonexistent, then you have it being oxidized by carbonic acid, which I guess would probably happen IF you actually had calcium(I) somehow, but you
don’t. Your “calcium insoluble compounds” are going to be predominantly calcium carbonate: CaCO3, a typical calcium(II) compound.
Which acetic acid dissolves. There is no redox going on here, and definitely no hydrogen gas being produced.
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Lionel Spanner
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This thread reminds me a lot of working with recent chemistry graduates (including myself, when I was new to the world of work) who attempt to
interpret largely physical phenomena purely in chemical terms, and as a result, get themselves into a serious intellectual twist.
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draculic acid69
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Just the other day I was cleaning a massive amount of what one would think was limescale off a a ss hot water urn. I tried vinegar (minimal rxn, maybe
cleaned 1%) tried heat(hot water_no rxn)
tried the boiling in bicarbonate and vinegar (no rxn) and can effectively say in this case of trying to remove a thick baked on clay/egg shell looking
crust over one hour that vinegar, baking soda, individually or together did nothing to remove any of this crust at all. We do have hard water here
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