borontrichloride
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Copper(II) Lactate Synthesis
My 2nd attempt at amateur chemistry.
Copper wire placed in jar within a solution of 2.020% w/w lactic acid and 1.300% w/v sodium hypochlorite at a 1:1 stoichiometry.
Initially the solution didn't mix, resembling a liquid-liquid extraction. Some shaking immediately showed mixing and produced a very strong smell of
Cl₂.
The equation seems to only balance if it is postulated that various gases form alongside the sodium lactate:
2 Na⁺ ⁻OCl + 2 CH₃COHCOOH → Cl₂ + H₂ + O₂ + 2 CH₃COHCOO⁻ ⁺Na
Within 10 minutes the copper wire was showing blue residues, suggestive of the 2⁺ oxidation state.
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DraconicAcid
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With any generic acid HA, bleach gives chlorine gas, not hydrogen. Lactic acid, however, can be oxidized by bleach because it has an alcohol group.
You'd be better off oxidizing the copper with bleach with a different acid, such as hydrochloric or acetic, precipitating the copper as copper(II)
carbonate, and then reacting that with lactic acid.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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borontrichloride
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That makes perfect sense. I initially suspected it formed Cl₂ and water but couldn't balance the equation and suggested that equation instead.
2 Na⁺ ⁻OCl + 2 CH₃COHCOOH → Cl₂ + H₂O + 2 CH₃COHCOO⁻ ⁺Na
I am missing one oxygen on the right.
My first experiment involved the solution going completely black as the reaction proceeded. I initially suspected it was dirt but I forgot to consider
that, which I now realise it was, the formation of copper(II) oxide which is black.
So the sodium hypochlorite alone seems to be able to oxidise the copper wire well enough because adding in the carbonate after that formed the aqua
green colour suggestive of CuCO₃.
So now I think to add some acetic acid to the lactate solution, re-form my lactic acid, then wait for a colour change. If nothing then simply bin the
solution, rinse the copper wire, then research how to make copper(I) oxide which is apparently a beautiful red.
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DraconicAcid
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If you're suing a regular solution of bleach, there will be chloride ions present, so the reaction is:
OCl- + Cl- + 2H+ --> H2O + Cl2
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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borontrichloride
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Thanks. I have since thrown out the solution.
Fortunately I have found that Oust kettle descaler is pure lactic acid granules so I will get some tomorrow and add it into one of my vials of copper
being oxidise by sodium hypochlorite and hopefully form copper lactate.
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DraconicAcid
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Make sure there is no hypochlorite left in the vial before adding the lactic acid.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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borontrichloride
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So you'd suggest heating the vial to evaporate the hypochlorite? I only ask because the black copper oxide is in solution. I thought I could just add
in the ligand because when I add in carbonate it immediately turns blue so hopefully adding in the lactic acid can provide the same effect.
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borontrichloride
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A little background reading - apparently removing the lid and exposing it to the atmosphere will evaporate Cl₂ from it. I did add some water because
the bleach I used was very thick. Can't see water evaporating just by being exposed to the atmosphere but I'm happy for water to remain as it is a
solution.
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DraconicAcid
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Copper(II) oxide is insoluble. If your solution is black, it's not copper(II) oxide. Add carbonate to precipitate whatever copper salt you have,
filter out the precipitate, and react that precipitate with lactic acid.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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borontrichloride
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Interesting. So how would you account for the black residue?
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Bryce
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I would definitely make it from the copper (ii) carbonate or hydroxide. You can get a hodgepodge of those by electrolysing an appropriate salt with
copper electrodes, or buy basic copper carbonate from ebay or a pyrotechnics supplier by the pound if that's available to you. The basic copper
carbonate and hydroxide are pretty insoluble.
I've made copper phthalate and benzoate just by using the basic carbonate and the organic acid in solution. Some will precipitate out, making it easy
to separate them by filtering and washing, other copper ii / organic acid salts are more soluble, and you may need to do something more involved to
separate them from the remaining acid. (You'd want in general an excess of the acid if you're dealing with a copper salt that precipitates, otherwise
you will end up with unreacted copper carbonate in your product.) With the copper phthalate, it was actually more soluble than the phthalic acid,
which crystalized out first on evaporation. I even ended up with some large phthalic acid crystals with pure blue crystals of copper phthalate growing
off of them.
[Edited on 14-7-2017 by Bryce]
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