Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: skatebiker on May 24, 2008, 03:33:16 AM
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I want to do copper etching using this compound.
I think about electrolyzing muriatic acid with an iron/steel anode.
My idea is that the folllowing happens:
A: 2Fe + 6e -> 2Fe3+ (yellowish brown)
C: 6H2O + 6e -> 3H2 + 6OH- (reacts with the available H+ to H2O).
Any practical experiences ?
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First, iron will simply dissolve in hydrochloric acid (giving - at first) Fe2+. Then Fe2+ should be oxidized further. Google etchant regeneration or something like that.
In fact aeration can be enough, search forums, this thing was discussed several times.
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Basically, one can dissolve Fe in even dilute HClO (Hypochlorous Acid) to make FeCl3, a safe reaction.
HClO can be prepared by adding a weak acid (Boric, Acetic, Ascorbic or a very dilute mineral acid) to NaClO. Then distilled half off of the solution to capture 5/6s of the total available HClO vapors and the gaseous anhydride, Cl2O.
HClO can also be prepared by more directly by combing HCl and H2O2. Avoid excess H2O2, as this decomposes HClO to HCl liberating oxygen.
CAUTION: As can be seen on YouTube, the reaction of Iron and HCl/H2O2 can proceed quite vigorously with the generation of Cl2.
If anyone is interested in the reaction chain via the HClO route, here is my best guess:
Fe + HClO --> FeO + HCl
HCl + HClO <--> Cl2 + H20
Hence, the observed chlorine creation. Continuing:
2 FeO + HClO + 3 H2O --> HCl + 2 Fe(OH)3
This is the oxidation of Ferrous Oxide mentioned in the extract (see below) from Mellor. Continuing with a hypothetical (but temporary) creation of Iron Hypochlorite:
Fe(OH)3 + 3 HClO --> Fe(OCl)3 + 3 H20
And, a possible an immediate reaction is that the Fe(OCl)3 oxides more iron and decomposes:
Fe(OCl)3 + 2 Fe --> Fe2O3 + FeCl3
Normally (per Mellor), the reaction of HClO on a metal oxide is a suggested path to creating the metal hypochlorite. Apparently, however, Iron hypochlorite either does not exist or immediately decomposes (as I have proposed above with further oxidation). Interestingly, my speculated behavior parallels the properties of Aluminum Hypochlorite (albeit a slightly more stable compound) which upon contact with a fabric, for example, bleaches and then immediately decomposes with deposits of Al2O3 into the fabric itself.
Note, as the solution clearly becomes reddish brown, it is FeCl3 that forms and not FeCl2 which is yellow in aqueous solutions.
REFERENCE: "A comprehensive treatise on inorganic and theoretical chemistry, Volume 2 By Joseph William Mellor
EXTRACT
"Iron filings immediately decompose hypochlorous acid with a brisk effervescence produced by the evolution of chlorine; the iron is partly oxidized and in part dissolved as chloride without the formation of any chlorate. A. J. Balard commented on this: "The greater number of other metallic substances do not decompose hypochlorous acid, and I am yet entirely ignorant of the cause of the peculiar behaviour of iron." P. Grouvelle passed chlorine through water with iron hydroxidelin suspension and a bleaching liquid along with ferric chloride was produced, and he found the liquid retained its bleaching properties after boiling for a quarter of an hour; but A. J. Balard failed to confirm this statement; he could not make ferric hypochlorite either (i) by the action of hypochlorous acid on iron hydroxide, for hypochlorous acid does not dissolve ferric oxide; or (ii) by the action of calcium hypochlorite on ferric sulphate, for calcium sulphate and ferric oxide are produced. Hence, adds A. J. Balard, "ferric hypochlorite cannot exist;" the results by P. Grouvelle are due to the formation of ferric chloride and hypochlorous acid in dil. soln.; when the mixture was heated, a portion of the acid distilled off, and the reaction which occurred with the cold soln. was reversed, for ferric oxide and chlorine were formed. Ferrous oxide is oxidized to ferric oxide by hypochlorous acid."
A free google book. Link:
http://books.google.com/books?pg=PA275&lpg=PA275&dq=ferric+hypochlorite&sig=zHHdZcLpiC-8m8HCOj-kix87YZ4&ei=11P7TcXXMdHTgQepiZneCw&ct=result&sqi=2&id=7XoGAQAAIAAJ&ots=R0bAIgamIM#v=onepage&q=ferric%20hypochlorite&f=false
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